Fuel Distributor Issues

[TonyDi]

After dealing with 3126 for a long time now I feel closer to the underlying problem.

After reactivating the lambada circuit I now found that the injectors fire indefinitely once the plate is moved. Once they start they don't stop even though the adjustment screw is hand tight in the counter clockwise direction.

Has anyone had a similar problem or is this a problem? Any help would be greatly appreciated.

[Delorean Industries]

After dealing with 3126 for a long time now I feel closer to the underlying problem.

After reactivating the lambada circuit I now found that the injectors fire indefinitely once the plate is moved. Once they start they don't stop even though the adjustment screw is hand tight in the counter clockwise direction.

Has anyone had a similar problem or is this a problem? Any help would be greatly appreciated.

Hi Tony. This is how K Jet works. When the air metering plate is deflected fuel in continuously injected. Only in the rest position will you see the injectors stop flowing.

The CO adjustment screw which you have turned all the way counter clock wise does not control the flow of fuel off idle. Once the plate is deflected the position of the distributor piston is changed allowing fuel to flow at a metered rate.

Any more information on your fuel system issues? You definitely need to flow test your injectors and check the spray pattern to determine the fuel distributor and injectors condition.

[Ron]

The CO adjustment screw which you have turned all the way counter clock wise does not control the flow of fuel off idle.Not that it is his problem, but if you turn the screw to where it raises the plunger at idle, the plunger will be higher throughout the arms travel...???

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At this point, I would pull a few injectors, put them a jar and turn the screw clockwise (being careful not to push the plate down) until they just started to spray and back it off until they just quit. Then put it all back together and set the CO with a dwell meter per manual.

[Delorean Industries]

Not that it is his problem, but if you turn the screw to where it raises the plunger at idle, the plunger will be higher throughout the arms travel...???

======

At this point, I would pull a few injectors, put them a jar and turn the screw clockwise (being careful not to push the plate down) until they just started to spray and back it off until they just quit. Then put it all back together and set the CO with a dwell meter per manual.

Nope. You can't manipulate the fuel curve of K jet like that.

[DMCTek]

At this point, I would pull a few injectors, put them a jar and turn the screw clockwise (being careful not to push the plate down) until they just started to spray and back it off until they just quit. Then put it all back together and set the CO with a dwell meter per manual.

+1

As mentioned you should also make sure injectors flow is even on all 6.

[Delorean Industries]

If you run into an injector with a flow issue switch the lines on the distributor with another port. This will rule out the injectors, distributor or both. Even rebuilt units have had issues in the past. Nothing iodine safe and everything should be subject. You need to replace nothing to diag k jet. Do not throw parts at the problem.

[Ron]

Nope. You can't manipulate the fuel curve of K jet like that.Are we on the same page here... are you saying that if I hold the plate steady anywhere but at the idle position then turn the CO screw in, the plunger will not rise???

[Delorean Industries]

Are we on the same page here... are you saying that if I hold the plate steady anywhere but at the idle position then turn the CO screw in, the plunger will not rise???

Yes, That is correct when fuel pressure is on the system. The Co adjustment is attached via a piece of spring steel. The adjustment only effects idle. You can not manipulate the fuel curve of K jet by this screw. That is why boost applications require a hobbs switch, shimming the line pressure or adjusting the control pressure screw in the warm up regulator.

[TonyDi]

So even if the plate returns to rest the injectors should fire?

The spray pattern is not ideal but I'm just trying to get it respectable it was getting somewhere around 10mpg.

Under "Waking a Sleeping Delorean" they said to leanit out until it stopped then tap the plate & enrich it until the injectors fire again. Is that incorrect?

[Ron]

Yes, That is correct when fuel pressure is on the system. The Co adjustment is attached via a piece of spring steel. The adjustment only effects idle. You can not manipulate the fuel curve of K jet by this screw. That is why boost applications require a hobbs switch, shimming the line pressure or adjusting the control pressure screw in the warm up regulator.

I see where I missed "Idle Circuit", but exactly where is the spring steel? I can't find it in several diagrams... Looks like two solid arms sharing a pivot here to me...
7435
THX
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So even if the plate returns to rest the injectors should fire?Only when it is running...the air flow will pull the plate (back) down.



Under "Waking a Sleeping Delorean" they said to leanit out until it stopped then tap the plate & enrich it until the injectors fire again. Is that incorrect?I think you missed where he said "...with the pressure plate slightly pushed down..." This and the above method is just to rough it in...the final adjustment is touchy so you need to set it with a dwell or duty-cycle meter.

In case you don't have one- http://dmctalk.org/showthread.php?102-Workshop-Manual

[Elvis]

Yes, That is correct when fuel pressure is on the system. The Co adjustment is attached via a piece of spring steel. The adjustment only effects idle. You can not manipulate the fuel curve of K jet by this screw. ...


Sorry Josh, I can't believe that.

I can't find a real picture of that screw and the parts around it,
but I found this as a nice overview:

7436

Does somebody have pictures he could post here to prove and clear this situation ?

[Ron]

The only spring I can find around there in the 'Bosch K-Jetronic, Technical Instruction' manual is (#7 below), "A leaf spring ensures the correct zero position in the switched-off phase", but it is on an Updraft unit (Not DeLorean!)
7437

I knew I shouldn't have sold that spare unit I had :rant:

[Delorean Industries]

Cranking the adjust screw richer will not cause a richer mixture across the entire rpm band. Just at idle. The engine only needs so much air throughout the rpm band only moving the metering plate so far. After you are off idle the adjustment screw has no control. Everything is then based on the position of the air metering plate.

I know in theory it sounds like this screw would change everything but it doesn't. If that was the case and adjusting the fuel mixture across an entire rpm band was so simple I'm pretty sure everyone would be doing this in the last forty years compared to the other ways to manipulate the curve.

attached is the spring steel piece inside the metering housing.

[Delorean Industries]

If you really want me to I can attach a wide band to a car here. Cranking it rich and then move it through the rpm band and post a video of it.

[Elvis]

of course you have to disable the Lambda-System to do it.

I am pretty sure we measured it at idle and at higher rpms last time
I had it smog checked.

Any chance you can take a/some more detailed picture(s) ?

Thanks.

[Ron]

If you really want me to I can attach a wide band to a car here. Cranking it rich and then move it through the rpm band and post a video of it.
With all of the other fuel controls overlaying it, I don't see how that would help...

Speaking of the downdraft type, the manual says. "A counterweight compensates for the weight of the sensor plate and lever system (this is carried out by an extension spring on the downdraft airflow sensor)...."
If you would be kind enough to label the two springs in your pic, I would greatly appreciate it.

[Bitsyncmaster]

I would think the adjustment screw would affect the whole RPM range since it moves the air plate position. But of course you need to disconnect the Lambda from compensating for that adjustment. I seem to remember checking the FV duty cycle above idle speed and the adjust did change that.

[Delorean Industries]

You can not set the idle mixture to compensate for a need for more fuel at a higher RPM and vice versa. The Lambda system will compensate at different engine loads though.This has nothing to do with the mechanical base setting. Mechanically though it is not possible. with just the screw. Proving this is also difficult because if you jack it hard rich the car will not even make it into higher rpms off idle and will foul the plugs etc.

[Delorean Industries]

I'm trying to think of a good way to put this:

Once the air flow plate starts to move due to air flow any setting of that screw does matter and no longer effects the air fuel mixture.

[Ron]

I've been following you on that since your first replies...partially why I mentioned the overlying controls. What I don't get is the simple mechanics which you say would allow moving the screw and it not affecting the plunger height throughout the arms travel. I can see it would not be the same amount because the pivot is not centered WRT the contact points, but I can't see how it not be higher throughout (the original question).
If you would label the two springs, I can clear it all up in my thick head...

[Bitsyncmaster]

You can not set the idle mixture to compensate for a need for more fuel at a higher RPM and vice versa. The Lambda system will compensate at different engine loads though.This has nothing to do with the mechanical base setting. Mechanically though it is not possible. with just the screw. Proving this is also difficult because if you jack it hard rich the car will not even make it into higher rpms off idle and will foul the plugs etc.

Yes the working lambda system will keep the mixture set to 14.7 AFR within it's range of control. But if you disconnect the lambda (run open loop), I'm pretty sure the mixture adjustment will give you full mixture control at any engine speed. I could put my tailpipe LM-2 system on to check this but that's how people run open loop and adjust the mixture.

[DMCMW Dave]

Let's try something else.

The fuel distributor is a calibrated mechanical valve. The plunger is the valve. A certain deflection of the metering plate which pushes up on the plunger will meter a fixed amount of fuel to the injectors. That's all it does. The injectors don't "fire" per se. The injectors spray whatever is sent to them once the pressure is high enough to open them. Regardless of any other parameter (other than plugged injectors).

The warmup regulator and the frequency valve affect the resistance to air flow of the plate by adjusting the fuel pressure on either side of the plunger (i.e. the plunger is easier or harder to move). This in turn modifies the relationship between air flow and deflection of the plate, but not the relationship between the deflection of the plate and fuel flow.

The range of the ability of the frequency valve to change the mixture, and therefore the lambda system, is very limited. The early turbo control sytems that ground the O2 sensor during boost are simply cranking the frequency valve to go as rich as possible without any attempt at reacting to load, knock, temperature etc.

So - back to the adjusting screw. The problem is that the adjustment screw action is non-linear with fuel flow - it simply sets the position of the metering flap relative to the plunger on the fuel distributor. Visualize graphing fuel flow relative to the flap position - it's a linear relationship with a fixed slope. As you adjust the screw, it does NOT change the slope of the line, only the point where it crosses zero. Therefore a large adjustment at idle (when the fuel distributor is very nearly closed, i.e. fuel flow off) is a tiny, inconsequential adjustment at, say 3000RPM under load.

If you adjust the screw to richen the mixture very much at load, it will foul the plugs at idle - if it will even run at all. Another analogy for the EFI people - picture an EFI map where you can only raise and lower the whole map, and not differently at different air flow rates/temperatures/RPM. You can't change the slope.

The range of the warmup regulator is fixed and only changes when cold to richen it up during idle. It is also has a somewhat limited range. There are aftermarket versions of the warmup regulator that can be electronically controlled to change the mixture based on other parameters, but it's much more complicated than a screw adjustment.

The only other way to modify the slope on a K-Jet (without re-inventing the regulator and/or lambda systems) would be to redesign the fuel distributor internally, which is why there are dozens of Bosch part numbers for what appears to be the same fuel distributor.

[Bitsyncmaster]

The FD holds a pretty good mixture adjustment for our engine even without the lambda. You can see how good it is by reading the FV duty cycle at different RPM settings.

So what your saying is running open loop, (say 13.0 AFR at idle) the mixture at other RPMs would not be close to 13.0?

[DMCMW Dave]

The FD holds a pretty good mixture adjustment for our engine even without the lambda. You can see how good it is by reading the FV duty cycle at different RPM settings.

So what your saying is running open loop, (say 13.0 AFR at idle) the mixture at other RPMs would not be close to 13.0?

Can't say I've ever tried it, but on a stock engine it might not be terribly far off. The Lambda system is not making gross adjustments, as has often been mentioned it was added to keep the catalytic converter happy. It's more of a fine-tuning than a comprehesive electronic control.

The problem comes in when you mover further from stock and do something to the engine that wants more fuel at a given RPM in the higher ranges, i.e. forced induction, high compression etc. but doesn't need it at idle.

This is all pretty far off the original post now.

[Elvis]

...

So - back to the adjusting screw. The problem is that the adjustment screw action is non-linear with fuel flow - it simply sets the position of the metering flap relative to the plunger on the fuel distributor. Visualize graphing fuel flow relative to the flap position - it's a linear relationship with a fixed slope. As you adjust the screw, it does NOT change the slope of the line, only the point where it crosses zero. Therefore a large adjustment at idle (when the fuel distributor is very nearly closed, i.e. fuel flow off) is a tiny, inconsequential adjustment at, say 3000RPM under load.
...

Dave - thank you for that good explanation.
mathematically spoken: y = a*x+b
the only thing you can change with that screw is "b", not the slope "a".

So there is no spring or whatever that makes it change only at idle.

Thanks, time to grab a beer :-)

[Ron]

...it's a linear relationship with a fixed slope.Thank you very much!

[TonyDi]

Well I have gotten the adjustment to a point where the car will start but then immediately die. The plugs get fouled before the car even warms up to check the dwell. Any ideas?

[Ron]

Try unplugging the cold start valve.

[TonyDi]

Try unplugging the cold start valve.

It won't start at all that way. If I have the pedal down when I hit the ignition it won't start either. When I try to start it it revs for a second then if I am not immediately on the throttle it dies. If I can keep it going response is sluggish & I have to constantly work it to get it to run. I have tried movin the screw a full turn in either direction (in small increments) & it is the same through the whole range except maybe slower stumbling to death. It never matures into a stable idle.

[Elvis]

is the piston in the fuel distributor stuck ?

[TonyDi]

is the piston in the fuel distributor stuck ?

I don't know, how would I test for that?

[Ron]

It won't start at all that way....I was thinking it might be turned on all of the time flooding it (or hung open, which is probably not the case since it don't start with out it).
1. Try unplugging the CSV after it starts.
2. Try manipulating the plate & throttle (independently) by hand and get it to settle down. (If you can, check vacuum leaks, timing, dwell, etc) Dwell last.
3. Like Elvis said, check that the plunger is free!
Needs CSV to start (maybe lean), but fowls the plugs(too rich).....


EDIT: Does the plate have pressure when you press it down and come back up by itself smoothly throughout its travel (right after the fuel pump has ran)? Note: this will dump a lot of fuel into the engine.
To thoroughly check plunger, relieve the fuel pressure. There are 3 screws running straight down through the Fuel Distributor, remove them. If you are lucky, the hoses will allow you to lift it up. The plunger is inserted straight up through the bottom. It should move very freely. So free that it may fall out by its own weight! So be very careful not to let it drop out! It has precision machine work done to it. It can't be scuffed, scared, etc.
Breeze through this link (http://dmctalk.org/attachment.php?attachmentid=971&d=1307763988)to get a look at it. DON'T take your FD apart...or risk extra charges if you have to order one!

[TonyDi]

Timing & vacuum are okay. Both were something I tried prior to this point.

The plate does have pressure but I have not noticed how it returns. I'll check the plunger when I get a chance.

[Elvis]

The plate does have pressure but I have not noticed how it returns. I'll check the plunger when I get a chance.

? what exactly do you mean ?
the plate returns by itself. please explain more detailed what you mean.


did you play with the fuel lines ?

I remember one car I worked on where another guy did swap two hoses.
We compared it to my car and found the mistake. 2 minutes later the car ran again.

[TonyDi]

I gave up & took the car to DMV Do Cal & they found that A) the plunger was sticking & B) most of the ignition system was shot. They said in their 30 years this was one of the most difficult times they've had getting a car running.

[SamHill]

I gave up & took the car to DMV Do Cal & they found that A) the plunger was sticking & B) most of the ignition system was shot. They said in their 30 years this was one of the most difficult times they've had getting a car running.

Please keep us posted. I believe you're far from being out of the woods.