Attempting to destroy my idle lumpiness

[Trstno1]

Hey guys -

I have been asking questions in other threads attempting to get my engine idle lumpiness gone. Though I think at this point I should start a new thread in order to cover the things I have already tried in order to finally get at the root of this problem once and for all.

Ok, so when I first purchased the car the engine never really ran very good. At first it was a high idle. That led me down the road of getting my lambda system working properly again. I replaced the WUR(which was frozen), FV wiring (which was shoddy at best), the O2 sensor, and the lambda ecu. Now I can state that the lambda system works, and my idle is where it should be at 775 or roundabout. Once the idle was fixed I noticed a lumpiness in the motor that would vibrate the engine and by extension the rest of the car while at idle.

When I posed questions then, the advise I got was that it was probably fuel related. So I conducted a spray pattern test with all injectors in jars and sure enough I had a couple that really were not doing all that great. So I ended up sending them into Hervey for cleaning. I got them back, tested them, they seemed better than before, so I re-installed them. Unfortunately the lumpiness remained. Next people asked if I conducted a compression test on all cylinders, so I did. All of the cylinders were in a nominal state with the exception of cylinder #1 which was just a little lower than the others. When I posted the cylinder readings mostly everyone thought they were acceptable readings and should not be causing the lumpiness(dead cylinder). So I replaced all spark plugs and made sure to identically gap them to a gap setting that was given in another post somewhere here. I also replaced the cap/rotor, spark plug wires, and the coil. The lumpiness remained.

Next I was told that it could be vacuum leaks. I made a fog machine and smoked the motor and found absolutely zero leaks. But just incase, I replaced all vacuum lines and ensured operation of vacuum solenoid, vacuum advance on the distributer, and changed all gaskets around the/under the intake manifold while I was cleaning the VOD. The lumpiness remained.....

So while I have been on another thread attempting to figure out TDC #1 cylinder to ensure that my timing is correct something occurred to me. when I replaced the rotor on the distributer I'm sure that I manually rotated the engine the TDC mark on the crankshaft pulley and also made sure the front of the rotor was facing the correct cylinder (#1), but what I didn't know what that the crankshaft pulley has two notches in it. Is there a chance I lined things up to the #6 cylinder notch on the crankshaft pulley and set the rotor to point at the #1 cylinder? Is that even possible? Would the car even run that way? The only reason I ask is when I was checking my timing with a timing light it showed at about 12 degrees. So I loosened the nut holding the distributer and rotated it until I got 13 degrees but I noticed that the distributer was rotated almost as far counter clockwise as the adjustment would allow. Is this normal or should that adjustment be somewhere in the middle when properly set? Also, how the heck to you tell which notch on the crankshaft pulley is which? #1 or #6 TDC? I guess I am a little confused.

Also, I have not done a valve adjustment. I was planning on tackling that this winter. I just assumed that prior to doing that I should probably make sure that the timing is set correctly first. What am I missing here guys? I am not a mechanic by any means but I have done all the work to my car myself and am learning along the way. I just feel like I'm missing something. I will attach a video to see what you guys think.

https://youtu.be/49za2OAyBuc

As always your help is always appreciated.

Thanks

[DMCMW Dave]

Have you ever compared it to another DeLorean? Are you sure you aren't complaining about odd-fire characteristics?

[Trstno1]

Have you ever compared it to another DeLorean? Are you sure you aren't complaining about odd-fire characteristics?

Thats a great question! Unfortunately I'm in Anchorage, Alaska and haven't seen any other Deloreans running to compare. Man, I would sure love to.

Does your D's engine vibrate the car at idle? Have others that you have seen through the years do so?

I guess I just thought that the stumble/lumpiness was the result of something that needed fixing, not that it could be normal. Is it?

[DMC-Ron]

My car has a "rhythmic" idle; it hunts a bit with the RPM varying +- 25. It runs fine, just not a super smooth idle such as on my Toyota vehicles. Other DeLoreans I saw at the Tech session seemed the same so I assumed it was normal. Since you've looked at all the usual suspects consider that the odd idle might be amplified if you have a loose engine mount. You probably have new ones, but wouldn't hurt to see if they are doing OK. If they're not new, consider doing the crowbar test to check for separation.

Ron

[Trstno1]

My car has a "rhythmic" idle; it hunts a bit with the RPM varying +- 25. It runs fine, just not a super smooth idle such as on my Toyota vehicles. Other DeLoreans I saw at the Tech session seemed the same so I assumed it was normal. Since you've looked at all the usual suspects consider that the odd idle might be amplified if you have a loose engine mount. You probably have new ones, but wouldn't hurt to see if they are doing OK. If they're not new, consider doing the crowbar test to check for separation.

Ron

Good idea. I have not done the crowbar test yet.

[dmruschell]

If you set the distributor 180 degrees out (timed it with #6 instead of #1), the engine would not run. The proper distributor adjustment usually puts it pretty far to one side of the adjustment. The distributor being one tooth off will usually mean it can't be properly adjusted within the given range.

The engine appears to be idling as smooth as can be expected. Both of our DeLoreans have performance cams, so they're jumping all around the engine compartment at idle. Yours seems to be fine.

Do a valve adjustment, since some valve clatter can be heard in the video, but keep in mind some clatter is to be expected by design, so it may be fine. At least then you will have done just about everything to be sure your engine is in great running condition (and it's free, assuming you have feeler gauges).

[Trstno1]

If you set the distributor 180 degrees out (timed it with #6 instead of #1), the engine would not run. The proper distributor adjustment usually puts it pretty far to one side of the adjustment. The distributor being one tooth off will usually mean it can't be properly adjusted within the given range.

The engine appears to be idling as smooth as can be expected. Both of our DeLoreans have performance cams, so they're jumping all around the engine compartment at idle. Yours seems to be fine.

Do a valve adjustment, since some valve clatter can be heard in the video, but keep in mind some clatter is to be expected by design, so it may be fine. At least then you will have done just about everything to be sure your engine is in great running condition (and it's free, assuming you have feeler gauges).

Awesome! Exactly what I wanted to hear. Thanks for clearing that up. I'll just do the valve adjustment and move on to other things.

Thanks!

[David T]

A perfect Delorean will have an idle that hunts. Noticeable because you can hear the frequency valve change pitch. if you do not have the stock cams it will hunt even more. Before touching any valves measure them all paying special notice to cylinder #1.

[Trstno1]

A perfect Delorean will have an idle that hunts. Noticeable because you can hear the frequency valve change pitch. if you do not have the stock cams it will hunt even more. Before touching any valves measure them all paying special notice to cylinder #1.

Will do, thanks for the response. It may be a good time to pull the valve covers to do the valve adjustment and clean up the valve covers.

[David T]

The valves are supposed to be checked every 30,000 miles. No hydraulic lifters in the PRV. At that service you would replace the O2 sensor, tune the car up, check the mixture adjustment and reset the Lambda counter.

[opethmike]

A perfect Delorean will have an idle that hunts.

Simply not true.

[NckT]

Simply not true.

I agree with opethmike, you can easily adjust the idle 'hunting fluctuations out, it's not hard to do either.

[Trstno1]

I agree with opethmike, you can easily adjust the idle 'hunting fluctuations out, it's not hard to do either.

Please tell me how to do it.

[dmruschell]

Simply not true.

Agreed.

Also, a lopey idle is separate from idle hunting. Aftermarket cams can have a lopey idle, and still maintain a fairly steady RPM (not hunting).

[opethmike]

Please tell me how to do it.

No vacuum leaks
Properly functioning lambda system
Proper idle fuel mixture

That's really all there is to it.

[David T]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

[dmruschell]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

I know Mike understands those systems, as do I. Minimizing the situations that need correcting by ensuring there are no vacuum leaks, the lambda system is working properly, and setting the idle fuel mixture correctly will virtually eliminate the overcorrecting that leads to idle hunting.

Both of my DeLoreans have performance camshafts and neither idle hunts when warm (and only one of them sometimes idle hunts when cold). I've fixed the idle hunting issue in a friend's DeLorean by adjusting the fuel mixture with a dwell meter.

A perfect DeLorean /may/ occasionally hunt at idle, but your statement that a perfect DeLorean /will/ hunt at idle is not true.

[opethmike]

Because you have several control systems and none of them synchronize with each other, there is no way to dampen oscillations except in the mechanical system they control. You have to understand control theory to know why this is true. One reason is that the control systems respond to the conditions AFTER they occur, don't correct quickly enough and over correct. That is one reason the idle spec is a plus-minus spec. The goal here is to make the engine run on each cylinder as equally as possible to keep any necessary corrections to a minimum to reduce over correcting. The bigger the correction the control systems must make, the larger the overshoot. Even so there will still be some hunting, especially when the motor is cold. That is why you hear some people say when they disconnect the idle system the engine runs smoother. That is because a control system (the idle control) over corrects. The two main control systems that are active when the motor is warmed up are the idle control and the Lambda system. They operate independently, their only connection is the mechanical system they both control. They both have cycles.

Uh, yeah, but the spec is +/- 50; not anything you are going to notice on either the tachometer, or the feel of the engine.

You should really stop just reading the manuals one of these days and try doing some actual work like those of us who know what we are talking about do. Maybe then someone might be interested in listening to you.

[NckT]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

[cis6409]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT


Have to agree here , nicks advise is spot on ! I've had the pleasure of seeing Nick in action on many occasions on my own car and lots of others .the results speak for themselves .. the idle adjustment he describes works perfectly , it makes the idle so much smoother and throttle response is better to .
No more fluctuating at lights or junctions the needle comes to a stop right on the button no bouncing at all ,cold or hot , it idles like a modern car !
I've gone to lots of tech events in England and organised tech events here for the Irish club and he has come over to help us and done this adjustment on all our cars including a stage 2 hi lift cam spec car from Houston all with the same excellent results

He has shown and helped me understand k jet so much more easier to and has shown me how to rebuild and calibrate CPR and set up fuel pressure In the fuel distributor to optimize and bring it back to spec



Cheers
Shane

[lazabby]

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

Nick, Coming to Houston anytime soon? I'm sure we can put your expertise to good use!

[NckT]

Nick, Coming to Houston anytime soon? I'm sure we can put your expertise to good use!

I've never visited America before, it'll be worth a visit at some point.

[NckT]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

I do apologise about the spelling errors, I'm typing this on my "smart" phone.

In addition, the following:

"Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each."

Should be:

"Unscrew the 2 brass screws nearest the inlet manifold W pipe by 2 full turns each."

Next time I'll use a PC.

Sorry all.

NickT

[Lough Shore Man]

Just another angle on the lumpy idle.. Back in the mid to late 80's ( i know, before a lot of you guys were born ) Mercedes Benz's had the same problem with there cars using the same fuel system at the "D's" mainly there big v8's .. A cure they found was to up grade the steel injector with a brass one.. Lumpy idle cured .. Just a thought.

[David T]

I have experimented with increasing the air bypass similar to what you have described and noticed the idle was smoother. My take is that by reducing the amount of control of the idle motor, the motor was able to dampen itself. I agree, setting things up "by the book" will not give the smoothest idle if that is your goal. I did not do emissions testing but I suspect doing it by the book is the better way for emissions and that is why it is the method offered in the book. The "best" way IMHO is to go ahead and get the motor running the best you can "by the book" and if you then want a smoother idle adjust the air bypass to smooth it out. The only problem I see in your method is that on many cars the heads are broken off of 1 or more of the brass screws. BTW, you are confirming that a "properly set up" PRV "by the book" doesn't run smoothly. I agree, I also agree your method will make it run smoother.

[opethmike]

An in-tune and properly running PRV will run just fine. Put down the books and start actually working with cars, Dave.

[David T]

An in-tune and properly running PRV will run just fine. Put down the books and start actually working with cars, Dave.

I don't now where you came up with the idea I don't work on cars?

[Trstno1]

There are 2 independent systems, and both considered as fixed independent feedback PID control systems with 2 separate Process Variables (PV), fixed Setpoints (SP) fixed Proportional Integral, Derivative values contained within the circuit design.

However, looking at the system with my "Control Engineer" head on, the two Output (OP) are the frequency valve and the Idle control valve.

The main influence of the idle oscillation, other than the odd fire design is the output variable of the idle speed control valve with range 0 to 100% of the valve being 0 to 775 rpm. This control of the Output OP of the Isle control can be influenced such that the output control changed to 725rpm to 775 so full scale deflection of the valve adjusts this small idle range.

This is how I do it, applying experience and experimentation on my own D noting feedback values using oscilloscope to evaluate the feedback etc:

Gently screw all of the 3 brass screws down.
Unscrew the 2 brass screws nearest the throttle plate by 2 full tirns each.
Note the current average idle speed.
Unscrew the brass screw with the slot open until the idle speed is.higher than the previous reading, at this point screw it back in by half a turn.
Re check that the dwell of the idle computer is between 35 to 45 degrees. My preference is that the max.swing of the dwell is about 44
Turn engine off
Fit a metric feeler gauge with "30" in between the lower throttle body screw and its stop.
Adjust the top throttle stop so it just closes the microswitch. This adjustment is important to stop the timing of the idle valve from operating too soon or too late that can cause an off idle oscillation to critically dampen the idle response.

In effect, this adds an air bypass around the throttle plate and the opening of the 2 brass screws by a fixed amount adds the bypass as an air damped effect to critically damped the air flow, effectively changing the Integral of the control to critically dampen the oscillation.

The above assumes everything else is tested and working and that the control pressure and primary fuel pressure is correct and calibrated and that the oxygen sensor oscillates at least by approx 5 hertz at 3000 rpm. It'll also assume that the closing of the throttle is repeatable closed with no mechanical sloppiness.

Although not to "book" it makes the engine run right. I've done this procedure on 40 plus Deloreans at Tech events with oem config catalysed exhausts to performance exhausts with standard k jet to imported (to UK) "Stage 2" (ex Steve Wynnes car I believe) with the performance cams etc with repeatable results.

Feel free to follow the above, I'm happy to share the info to others. Yes, it's not to the 30 plus year old book but I'd rather go with experience and testing, analysis and repeatability of the control function change.

Good luck

NickT

Holy Cow! I just did the adjustments you suggested and my engine is now running better than it has the whole time I've owned it. Kudos sir!! Now, ill let it cool off and see what the adjustments do to my initial cold start up. But when warm holy cow it runs smooth and my engine vibration is 98% gone!

You the man!

Thank you for replying to the thread!!!

[NckT]

You're welcome. I just hope you noted my post 6 posts earlier about my amendment.

I'm glad it worked out for you.

NickT

[MikeWard]

Just to add my 2pence worth, Nick very kindly setup my car using this method a number of years ago and it totally transformed it.

My car hunted a lot, as can be seen in this cold start video I took back in 2012, it was all over the place.
https://youtu.be/oXy4y5Cpa0s

Fast forward to 2013 and here is a video of a cold start after Nicks adjustments, the results speak for themselves.
https://youtu.be/Glh_TaTSP1A

Having seen Nick perform this on multiple other cars over the years, I can say that this method consistently gives repeatable results. Idle is smooth across all engine temps, cold/warm/hot, it always runs smooth. Heed his advice on this setup, ignore the "book".



I did not do emissions testing but I suspect doing it by the book is the better way for emissions and that is why it is the method offered in the book.
My emissions results were better after Nicks adjustments - In the UK emissions are tested yearly as part of the annual vehicle (MOT) test.

[lazabby]

Holy Cow! I just did the adjustments you suggested and my engine is now running better than it has the whole time I've owned it. Kudos sir!! Now, ill let it cool off and see what the adjustments do to my initial cold start up. But when warm holy cow it runs smooth and my engine vibration is 98% gone!

You the man!

Thank you for replying to the thread!!!

Does your car run better now when cold also? Mine hunts when cold so I am thinking about doing this adjustment.

[Trstno1]

Does your car run better now when cold also? Mine hunts when cold so I am thinking about doing this adjustment.

It still searches upon cold startup for 10-15 seconds but then smoothes right out. Certainly worth trying.

[David T]

Does your car run better now when cold also? Mine hunts when cold so I am thinking about doing this adjustment.

Hunting when cold is not a symptom, They All Do That (TADT). It should settle down quickly but it won't get smooth till it warms up a little at least. The CPR (aka warm-up regulator) is like a choke on a carbureated car. It makes the motor run rich and is not very adjustable. How bad it runs and how long it runs bad is a function of the ambient temperature and the calibration of the CPR. If it takes a while it is probably because the heater inside the CPR is burnt up. Very common. That heater speeds up the CPR to shorten the warm-up cycle and reduce emissions.

[NckT]

I'll stick with my non hunting from cold and warm car then :)

[NckT]

It still searches upon cold startup for 10-15 seconds but then smoothes right out. Certainly worth trying.

Does your fuel pump relay operate for a second or 2 when you put your key in to position 2 ?

If not, try linking out the fuel pump relay to operate the fuel pump for a couple of seconds then reinstate the fuel pump relay. If that initial surge you experience goes, I'd recommend you buy the solid state relay that Dave sells.

My own car still uses the original black fuel pump relay and it does operate the fuel pump this way.

Some cars do, some don't, but K jetronic should ideally have this function to prime the fuel system.

Fwiw, I strip down and recalibrate CPR's to oem spec. It's not hard, you just need a fuel pressure gauge, a temperature gauge, a hammer and a drift. As long as the lower diaphragms are in good condition you might as well do it yourself.

[opethmike]

My car was K-Jet for the first five years of my ownership. It never hunted either cold or warm at idle, and I have personally witnessed numerous similar DeLoreans. This idea that they all hunt is bollocks.

[dn010]

I have to agree, back in the K-jet days mine always hunted when it was cold. Yet, I knew another owner whose car never hunted up/down even in the middle of winter. The only way I could get mine to run "ok" was to disconnect the full throttle enrichment switch and put a jumper in the harness side connector.


My car was K-Jet for the first five years of my ownership. It never hunted either cold or warm at idle, and I have personally witnessed numerous similar DeLoreans. This idea that they all hunt is bollocks.

[NckT]

....... bollocks.

As a Brit, the use of this slang word makes me smile, as the main meaning of it over here is not just related to "rubbish" / "wrong" / "incorrect"

https://en.m.wikipedia.org/wiki/Bollocks

And that Sir, is the dogs bollocks ;)

[Bitsyncmaster]

Does your fuel pump relay operate for a second or 2 when you put your key in to position 2 ?

If not, try linking out the fuel pump relay to operate the fuel pump for a couple of seconds then reinstate the fuel pump relay. If that initial surge you experience goes, I'd recommend you buy the solid state relay that Dave sells.

My own car still uses the original black fuel pump relay and it does operate the fuel pump this way.

Some cars do, some don't, but K jetronic should ideally have this function to prime the fuel system.

Fwiw, I strip down and recalibrate CPR's to oem spec. It's not hard, you just need a fuel pressure gauge, a temperature gauge, a hammer and a drift. As long as the lower diaphragms are in good condition you might as well do it yourself.

Yes some cars always prime the system with the key on using the OEM RPM relay. The OEM RPM relay does not have a circuit designed to do that, it just happens to see and ignition pulse when the key is turned on.

My car never hunts. It did when I first bought it. I even have the three brass screws fully closed. I do have a wideband O2 unit so that heated sensor may help reduce hunting problems. But hunting cold the lambda is not even changing mixture.

[NckT]

I think that would be irrelevant as the ecu would only go open loop when the lambda switch would go open circuit once the coolant water temperate goes above 80c.

[Bitsyncmaster]

I think that would be irrelevant as the ecu would only go open loop when the lambda switch would go open circuit once the coolant water temperate goes above 80c.

My car goes closed loop in about 15 seconds from a cold start. I don't have the WOT/temp sensor wire hooked up to the lambda ECU. I have a "power" switch that sets 13 AFR if I want to get more power. But I really never use that power setting.

[NckT]

My car goes closed loop in about 15 seconds from a cold start. I don't have the WOT/temp sensor wire hooked up to the lambda ECU. I have a "power" switch that sets 13 AFR if I want to get more power. But I really never use that power setting.

That makes sense if you've got those disconnected.

[lazabby]

Anyone lately do NickT's suggestion on fix the hunting idle?

[82DMC12]

Anyone lately do NickT's suggestion on fix the hunting idle?

I just read this thread and I'm filing it away for later. I'm almost done with a frame-off restoration and it seems like my idle is a bit more erratic than it was before I started. I am going to have to check all the switches and sensors to make sure they are working, and if they are, I might try something like this. Won't attempt it until I've confirmed everything else though with a smoke machine, timing light, and fuel pressure gauge though.