Engine struggles under load

[bytes311]

Hi folks,

Got to drive my DeLorean for the first time yesterday and noticed a few things with it. In idle, it revs up like it has a lot of power, but as soon as I put it in drive, it feels like the engine struggles under load. I also have to feather the gas pedal when accelerating, otherwise the fuel plate on the engine pops. Could that be an indication of an air leak, or bad spark plugs/wires?

[David T]

Hi folks,

Got to drive my DeLorean for the first time yesterday and noticed a few things with it. In idle, it revs up like it has a lot of power, but as soon as I put it in drive, it feels like the engine struggles under load. I also have to feather the gas pedal when accelerating, otherwise the fuel plate on the engine pops. Could that be an indication of an air leak, or bad spark plugs/wires?

Yes, it can be these things and a whole lot more. Typically you would start with leaks because if it is running lean it would have this symptom. The other high probability is the timing is off or the advances (mechanical and vacuum) are not working. The other thing to check is if the frequency valve is buzzing. If it not, that would create a lean condition. If the car has not been tuned up in a long time that is the first thing you should do.

[Jonathan]

Does your car have an automatic transmission? Not sure if you meant put it in drive as opposed to gear, but that sounds like it could also be shift computer governor trouble too. Check the stuff David mentioned though first.

[bytes311]

Yes, it can be these things and a whole lot more. Typically you would start with leaks because if it is running lean it would have this symptom. The other high probability is the timing is off or the advances (mechanical and vacuum) are not working. The other thing to check is if the frequency valve is buzzing. If it not, that would create a lean condition. If the car has not been tuned up in a long time that is the first thing you should do.

Thanks for the quick response, David.

I'll see if I can locate any leaks. The frequency valve does buzz, so I think I can eliminate that as a possible cause. I've messed with the three brass screws just to get it to idle right, which now idles at around 800 RPM, but that's just addressing the symptom of a much deeper problem.

[bytes311]

Does your car have an automatic transmission? Not sure if you meant put it in drive as opposed to gear, but that sounds like it could also be shift computer governor trouble too. Check the stuff David mentioned though first.

It's an auto. <grin>

[David T]

It's an auto. <grin>

The brass screws are supposed to LIGHTLY seated (screwed ALL the way in). The fact that you have to adjust them to get it to idle means something is wrong. Do you have a plug over the mixture screw? Has anyone been messing with it? Since it is an automatic are you sure you are in first gear when starting out?

[bytes311]

The brass screws are supposed to LIGHTLY seated (screwed ALL the way in). The fact that you have to adjust them to get it to idle means something is wrong. Do you have a plug over the mixture screw? Has anyone been messing with it? Since it is an automatic are you sure you are in first gear when starting out?

The plug is missing from the mixture screw, so I've covered it with a piece of duct tape. The three brass screws were slightly opened when I bought the car, so somebody tried tuning it at some point. Would a missing plug cause that much of an issue?

[PJ Grady Inc.]

Is this problem only when the engine's cold? If so those are the symptons of a bad warmup/control pressure regulator.
If it's all the time it could be a lot of things but I would look in the fuel tank for trouble before moving on to vacuum leaks.
Rob Grady


Hi folks,

Got to drive my DeLorean for the first time yesterday and noticed a few things with it. In idle, it revs up like it has a lot of power, but as soon as I put it in drive, it feels like the engine struggles under load. I also have to feather the gas pedal when accelerating, otherwise the fuel plate on the engine pops. Could that be an indication of an air leak, or bad spark plugs/wires?

[David T]

Is this problem only when the engine's cold? If so those are the symptons of a bad warmup/control pressure regulator.
If it's all the time it could be a lot of things but I would look in the fuel tank for trouble before moving on to vacuum leaks.
Rob Grady


The fact that the plug is missing means you had a HUGE vacuum leak and someone probably over-adjusted the mixture screw to compensate. Now you need to check (and if necessary) adjust the mixture screw. Also since the brass screws were messed with you probably need to go over EVERYTHING since if they messed with this who knows what else is not right.

[kings1527]

The plug is missing from the mixture screw, so I've covered it with a piece of duct tape. The three brass screws were slightly opened when I bought the car, so somebody tried tuning it at some point. Would a missing plug cause that much of an issue?

Here's a start:

http://store.delorean.com/p-6399-plug-removeable.aspx

[bytes311]

Here's a start:

http://store.delorean.com/p-6399-plug-removeable.aspx

That was going to be my next question.

Thanks for all the info guys. So far it's been one repair after another, but I'm learning quite a bit.

[PJ Grady Inc.]

Yes a missing CO plug is a big vacuum leak but my point is that very often if a mechanic or DYI'er doesn't know CIS injection they will richen up the mixture to compensate for a bad WUR/CPR (Control Pressure Regulator is the more accurate name). If the problem is primarily cold then that is likely one of the problems but if that's bad the rest of the system is suspect as well. If/when there has been fuel contamination there are often multiple issues.

Now that the CO has been capped it will probably need to be leaned out BTW. The CO plug shown is a repro as Bosch no longer makes them. The problem with that is that the end is now plastic instead of rubber and doesn't seal well. I use a small plastic plug used to cap tubes etc. for a inexpensive/effective plug.
Rob Grady


The fact that the plug is missing means you had a HUGE vacuum leak and someone probably over-adjusted the mixture screw to compensate. Now you need to check (and if necessary) adjust the mixture screw. Also since the brass screws were messed with you probably need to go over EVERYTHING since if they messed with this who knows what else is not right.

[bytes311]

The CO plug is now plugged as it should be, and I leaned out the screw until it idles perfectly, however, i still don't get much power taking off. If I richen it out a little, I have some power, but then it starts to idle hunt. If I lean it out a little, I sacrifice power just to get it to stop idle hunting. Something's still not right. When I accelerate, the motor vibrates pretty rough as it builds up speed. Does that seem normal?

[Bitsyncmaster]

The CO plug is now plugged as it should be, and I leaned out the screw until it idles perfectly, however, i still don't get much power taking off. If I richen it out a little, I have some power, but then it starts to idle hunt. If I lean it out a little, I sacrifice power just to get it to stop idle hunting. Something's still not right. When I accelerate, the motor vibrates pretty rough as it builds up speed. Does that seem normal?

A lot of people set their mixture to get the best idle. What that does is set the mixture rich and shuts down the lambda system (open loop). Running rich will cut your MPG and probably damage your CAT. You really should not adjust mixture without a dwell meter to show you the correct adjustment. Then you can trouble shoot other problems knowing the mixture is correct.

[kings1527]

A lot of people set their mixture to get the best idle. What that does is set the mixture rich and shuts down the lambda system (open loop). Running rich will cut your MPG and probably damage your CAT. You really should not adjust mixture without a dwell meter to show you the correct adjustment. Then you can trouble shoot other problems knowing the mixture is correct.

Great dwell meter at a great price:

http://www.ebay.com/itm/Actron-CP7605-Dwell-Tachometer-Voltmeter-Analyzer-/361225454715?hash=item541ab7047b&item=361225454715&pt=Motors_Automotive_Tools&vxp=mtr

[bytes311]

Great dwell meter at a great price:

http://www.ebay.com/itm/Actron-CP7605-Dwell-Tachometer-Voltmeter-Analyzer-/361225454715?hash=item541ab7047b&item=361225454715&pt=Motors_Automotive_Tools&vxp=mtr

Bid on a dwell meter? :hihi2: I'll look into getting one today. Thanks guys!

[David T]

Bid on a dwell meter? :hihi2: I'll look into getting one today. Thanks guys!

Setting the duty cycle is the LAST thing you do! You have to make sure EVERYTHING ELSE is working as it should before attempting to set the mixture. You DO NOT set the mixture to get best idle.

[PJ Grady Inc.]

A diagnosis would be easier if we knew if your problems were when the engine was cold/hot or all the time.
Rob
Hi folks,

Got to drive my DeLorean for the first time yesterday and noticed a few things with it. In idle, it revs up like it has a lot of power, but as soon as I put it in drive, it feels like the engine struggles under load. I also have to feather the gas pedal when accelerating, otherwise the fuel plate on the engine pops. Could that be an indication of an air leak, or bad spark plugs/wires?

[bytes311]

Setting the duty cycle is the LAST thing you do! You have to make sure EVERYTHING ELSE is working as it should before attempting to set the mixture. You DO NOT set the mixture to get best idle.

Gotcha. So first and foremost I need to get the dwell reading right, and then I should troubleshoot the rest. When I got the car, the three brass screws were opened slightly, so I have no idea what was done before it got to me.

[bytes311]

A diagnosis would be easier if we knew if your problems were when the engine was cold/hot or all the time.
Rob

All the time. Pulled the plugs and the plugs are clean. Cleaned the distributor cap. Cleaned the grounds, and no leaks from what I can see.

Perhaps it would help if I took a video? I don't have a second D, nor do I know anybody with a DeLorean to compare with. I can't really drive it until it's tuned, and I certainly don't want to tow it to the next tech day :hihi2:

[Bitsyncmaster]

Setting the duty cycle is the LAST thing you do! You have to make sure EVERYTHING ELSE is working as it should before attempting to set the mixture. You DO NOT set the mixture to get best idle.

I have to differ with you on this. It takes 60 seconds to hook up the meter and adjust if necessary. Who knows if the PO adjusted it for best idle until you check the adjustment.

[David T]

I have to differ with you on this. It takes 60 seconds to hook up the meter and adjust if necessary. Who knows if the PO adjusted it for best idle until you check the adjustment.

If the motor:

Needs a tune-up
Has vacuum leaks
The linkage is not adjusted properly
The Lambda system is not operating or not operating correctly
The timing, mechanical, and vacuum advance is not working correctly

you can't properly adjust the duty cycle.
If you do adjust the duty cycle and then do ANYTHING else you will just have to adjust the mixture again. If the plug is missing it is a good bet the mixture needs to be set PROPERLY.

[PJ Grady Inc.]

OK that helps a lot. As Dave said it can be many things but for me the keys are "all the time" and the roughness on acceleration which indicates an engine miss. While an ignition problem will cause this (usually a tune up issue as in changing the Dist. cap, rotor, wireset and spark plugs) I'm thinking the car has had fuel contamination issues that were never fully addressed.
First make sure the fuel tank is clean and the pump, boots, and hoses are all in good shape. Many times poeple fix those issues and get the car running and don't go on to fix the resultant fuel injection damage which is very likely your problem. Check the tank before doing anything else if you are a new owner. I/we can give you more info on the CIS system if you decide to go in that direction. I think your main problems will be there. It's very important to check the tank first because if there's trouble there your money for fuel injection repairs will be wasted.
Rob


All the time. Pulled the plugs and the plugs are clean. Cleaned the distributor cap. Cleaned the grounds, and no leaks from what I can see.

Perhaps it would help if I took a video? I don't have a second D, nor do I know anybody with a DeLorean to compare with. I can't really drive it until it's tuned, and I certainly don't want to tow it to the next tech day :hihi2:

[Jonathan]

One additional thought on what Rob just said...

When you mentioned the engine vibrating under load AND you mentioned having the spark plugs/wires out, etc. it reminded me of what the cars do when you get a spark plug cap wet after washing your car and getting too aggressive with the power washer near the engine bay.

I don't think your spark plug wire caps are wet of course, but the symptoms sounded similar enough to think part of your problems could be one or more of those is loose, or maybe even plugged into each cylinder in the wrong order (double check the cylinder numbering against each wire coming from the distributor).

Yes, it does sound like there is potentially more than one thing going on here with your car. I don't have a lot of experience adjusting mixtures or reading dwell measurements, but ensuring the other system components are in place and connected properly is important enough to do before tackling other areas. Compare your vacuum hoses against the routing diagram as well as the electrical connections for each component. And when/if you find something you know not to be right, fix it to make it right before moving on. There are too many little pieces of the engine systems that are intimately connected to skip over a portion you know is not correct assuming there is a bigger problem to be found. Enough small problems can add up to large performance problems.

[PJ Grady Inc.]

BTW you generally shouldn't be cleaning and reinstalling tuneup parts unless they are new AND are of the correct origin for the car. Could you advise as to the cap, rotor, wireset, & spark plug manufacturer part #'s or other markings. Cleaning and reusing incorrect or worn out service parts will just make diagnosing that much harder as you move on to other areas.
Rob


All the time. Pulled the plugs and the plugs are clean. Cleaned the distributor cap. Cleaned the grounds, and no leaks from what I can see.

Perhaps it would help if I took a video? I don't have a second D, nor do I know anybody with a DeLorean to compare with. I can't really drive it until it's tuned, and I certainly don't want to tow it to the next tech day :hihi2:

[dn010]

When my original engine was running rich I had to change my 02 sensor in order to get it tuned properly. I guess the original one got fouled. It is a PITA but it might be another thing to put on your never ending list of things to do.

[David T]

When my original engine was running rich I had to change my 02 sensor in order to get it tuned properly. I guess the original one got fouled. It is a PITA but it might be another thing to put on your never ending list of things to do.

If you are replacing the O2 sensor you should also be doing the valve adjustment (or at least checking them). On any car that has been sitting a long time, running rich, or anywhere near 30,000 miles you should be doing a full tune-up along with the sensor and the valves. Don't forget to rest the Lambda counter.

[kings1527]

Bid on a dwell meter? :hihi2: I'll look into getting one today. Thanks guys!

Something's telling me your competition won't be too stiff on an Actron 7605.

[Farrar]

Checked your transmission fluid?

[PJ Grady Inc.]

Hi Farrar,
This would not cause roughness or a miss on acceleration and could only affect acceleration if the trasmission was slipping due to low fluid. This would be most noticable when cold. Is that what you are thinking here?
Rob

Checked your transmission fluid?

[Farrar]

Hi Farrar,
This would not cause roughness or a miss on acceleration and could only affect acceleration if the trasmission was slipping due to low fluid. This would be most noticable when cold. Is that what you are thinking here?
Rob

No, I was thinking that maybe the previous owner used some "leak fix," resulting in fluid that is too thick. Admittedly, it is a shot in the dark, but I thought I'd ask.

[bytes311]

I ended up taking it to a classic car shop to have it looked over. According to their shop mechanic, the (auto) transmission is stuck in drive, hence the poor performance, and fumes are seeping out from the gas tank where I installed Hervey's fuel pump/sending unit. He also said there's too much carbon coming out of the exhaust. In addition to that, the front right-side caliper is HOT. So several issues are at play here.

[David T]

I ended up taking it to a classic car shop to have it looked over. According to their shop mechanic, the (auto) transmission is stuck in drive, hence the poor performance, and fumes are seeping out from the gas tank where I installed Hervey's fuel pump/sending unit. He also said there's too much carbon coming out of the exhaust. In addition to that, the front right-side caliper is HOT. So several issues are at play here.

That's usually how it goes. Looks like twiddling the mixture ain't gonna do it this time either. Figure on rebuilding the brakes, repairing or replacing the shift computer, a full tune-up, and a lot of other things you will find once you get these issues out of the way.

[bytes311]

That's usually how it goes. Looks like twiddling the mixture ain't gonna do it this time either. Figure on rebuilding the brakes, repairing or replacing the shift computer, a full tune-up, and a lot of other things you will find once you get these issues out of the way.

That's what it's all about, and all I have is time. <grin>

I appreciate everyone's input. You guys are an invaluable resource.

[bytes311]

Well, I figured out why the auto transmission was stuck. Somebody had put the MANUAL transmission connector in the bulkhead. :frantic:

[dn010]

Well, one problem down - more to go. Let us know how the car responds once the connection has been fixed.


Well, I figured out why the auto transmission was stuck. Somebody had put the MANUAL transmission connector in the bulkhead. :frantic:

[bytes311]

Well, one problem down - more to go. Let us know how the car responds once the connection has been fixed.

Haven't driven it yet, but noticed I now have reverse lights. :hihi2: