I have been trying to diagnosis a rough running engine for about 3 years now!!! Basically the car shakes like it’s missing. Well I have done the usual stuff like a full tune-up and checked to make sure there is no arching from the wires in the dark. I replaced the dizzy with a new GMPP unit. I have also checked for vacuum leaks buy plugging all vacuum lines...no change but replaced all vacuum lines to be sure. I also checked around the intake manifold for leaks with a propane torch and carb cleaner but nothing was found. I checked to make sure the electrical grounds were clean and tight. I also shot the header primary tubes with a digital pyrometer and all tubes were around 800 degrees while at idle. Everything looks fine. I have also tried a new intake gasket 3 times along with a new manifold. I had the heads redone with new seals and a valve job along with a port and polish. I ran a compression test that came back all within 5%-10% of each other. I swapped cams, replaced the timing chain, roller rockers, pushrods and ran the valves a number of times but still no luck. I have gone through about 500 chips just for the idle....running it rich, lean...and timing from 10 all the way to 35 at idle and no luck.

Well now I am thinking that the junkyard ECM I am running is not good??? I tried doing a cylinder balance test, unplugged the IAC valve and EST and started pulling injector plugs. Well I started on the passenger side and pulled one off....it made a very little difference but a difference...continued pulling and replacing injectors on the passenger side one at a time with the same results... Moved to the driver side and did the same but this time when I pulled them off and let it run the car started to die after about 10 seconds. I did this to all of them on the driver side and all responded the same way. This was very different than what the passenger side did.... So I went to recheck the pass side and pulled off 2 plugs at once and the car responded slightly worse than when one was pulled but it still was running....pulled 3 off and the car was still running.... Tried this on the driver side and the car died when I pulled 2 off.

So what does this mean??? Is there a problem with the ECM, injectors, fuel rails, injector harness???? I am out of ideas here!!!

 

Are those the original injectors? maybe they're leaking/ dirty. Mine were leaking so bad that I could hear them 'hissing' through the throttle body after I shut the engine off.

 

They are 3 year old SVO red tops. 30lb/hr set at 30 in the prom.

 

I would get a scan tool on it before going too much further. You should be able to get a reading as to what your computer/ecm is reading and what youre actually getting. If there is an ecm issue, like something faulty inside, this could happen. I would check it first on a scanner before dropping any more money and just buying another ecm. Im sure youve had enough of that already from the grocery list of parts you mentioned earlier...

 

I would guess that there is another problem. Something is wrong with the injector firing on that side of the motor, or there is still a vacuum leak somewhere. Hmmmmm.... This is beginning to sound a little like my split BLM problem where the pass side of my motor is always rich. I would check and clean the ECM grounds on the back of the heads before doing anything else (that's where the ECM gets its grounds). That is my next step as well as checking the compression in every cylinder (you've already done that). So I'm trying to catch up with you there. I believe the injectors have power all the time, just like most of the sensors on our motors. It is my understanding they are fired when the ECM wants them to be by the ECM supplying the ground to the injector circuit. If that ground is faulty, I don't think they will not fire correctly. So I'm going for grounds cleaning in my case, you might want to check that as well.

If that doesn't solve my problem, I'm pulling my SuperRam intake all the way to the intake manifold and looking for leaks. If I don't see anything, I plan to pull the intake as well. Something has to be leakng if the grounds are all okay. Last resort in my mind is a head gasket, but I really shudder to think of going that deep.

Since you can pull injectors on one side and not see much difference in the way it runs, it has to be something in the fuel/air supply to those cylinders. Since the compression is okay, then it almost seems to me like it has to be a grounding/electrical issue to those injectors, or extra fuel or air is getting in there somewhere.

I've been fighting this same problem for many months myself. It's been so frustrating for me that I'm about to pull the motor and put something else in. It has just about soured me on this setup, and I hate to admit that. Hopefully you can find your problem w/o getting as "down" as I'm getting about it all.

 

They are leaking if the motor still ran. With no fuel it should have stalled like the other side.
While you have the intake apart to reseal it, send those injectors off to be checked/cleaned. I think they will show a problem.

 

SLP headers have the O2 sensor on the drivers bank.

RBob.

 

If that was directed at me - You're right up to a point. SLP put one bung in the driver's bank, which is where my NB sensor is that controls the ECM. However, I added two more bungs, one in each bank, which is where I have the 2 WB sensors.....

 

It was just an FYI to where the O2 sensor is located and why the difference when pulling driver side injector plugs vs. passenger side injector plugs.

Need to also disconnect the O2 sensor to prevent closed loop fueling corrections.

RBob.

 

Gotcha, didn't think it could run with them completly unplugged though.
Having normal fuel on the "controlled" cyls would keep it running?
Didn't seem to indicate by the post that it ran really bad with the three unplugged that's why I was thinking there was still fuel present.
Kinda had to remember my younger days when removing all plugs from one side to watch a V8 run and sound like a VW.

 

Ok did some more checking yesterday. I hooked up the fuel feed and return lines line Holley recomends but it didnt make any difference. See this post: https://www.thirdgen.org/forums/alternative-port-efi-intakes/354201-does-matter-how-fuel.html

Now since I had the fuel rails off I flipped them over with the injectors in them and used tie wire to hold them in the rails while I pressurized the rails. I then had someone crank the motor over while I watched them spray...all of them sprayed the same and with a good patteren and none were leaking.

I also ran the valves again with no change.

I am starting to believe that what I am seeing is not a miss...Something is causing the motor to idle ruff. At higher rpms and during a brake torque the motor seems smoother. I am lost.......

I am running a base timing of 8 degrees with the computer advanceing it to 25 degrees at idle. Idle MAP is in the 50-60kPa range and desired idle speed is 850rpm. Any sugestions?

 

May be worth checking this post:

https://www.thirdgen.org/forums/tech-general-engine/339080-these-springs-causing-my.html

It has to do with the same type of issue with it being caused by the lifters.

RBob.

 

RBob..what is the resolution to the problem? I have used stock replacements and Comp R that I have in there right now. I put that red assembly lube in the cup and on the pushrod for start up portestion on both sets...could this cause them to get stuck? Also can I just tighten all lifters untill they bottom out and then rotate the engine over by hand to bleed them all teh way down...I really dont wanna pull the intake a 5th time.......

 

To prove the issue they backed off the rockers to 0 lash (or a hair of lash). And ran the engine.

RBob.

 

Why are you running 8 degrees base timing? I believe stock timing is 6...shouldnt make a huge difference but thought Id throw it out there just in case.

 

It idled best at 8 degrees...anyway its set int he chip as base timing and the car isnt exactly stock.

The lifters are not the problem...I backed them all off till they all made noise and the car still idled the same. Also when I loosened them I seen the lifter push the push rod back up when the spring pressure was removed.

Another question for guys with similar setups.....on the WBO2 what AFRs are you guys seeing at idle. I have to idle at about 800-950rpms in order for it to run ok. My timing is at 25 and I am using the stock idle O2 constraints so the computer is trying to see a 14.7:1 AFR at idle.....Which way should I go with the idle O2 constants to see if it will prove.

 

Try running a piece of wire from one cylinder head to another and to the -battery terminal, and see what happens. ULTM8Z did something like that and it fixed his 4 year struggle with a rough idle. Give it a good connection, to be fair, but you can do just a test with some scrap wire to see if things improve.

 

FWIW - cleaning both head grounds, running a tie wire between the heads, tying the passenger's head to a starter bolt, and tying the drivers head to the battery didn't solve my problem. Guess I'll start pulling the SR tonight and looking for vac leaks. Hope your doing better than I am!

 

You may have already tried this... I like to put the inductive coupler for my timing light on each spark plug wire and then watch the strobe light flash for a couple of minutes. If there is a misfire at the spark plug you will see the flash pattern skip/stumble.

 

I tried grounding the heads to the battery with jumper cables and also tried using the timing light on every plug and nothing seems to be exposing the problem...

 

I know the feeling. I finished my SR pull and re-seal last night and it didn't solve my problem either. I'm about to give up on it and do something else. Trying a post in Alternative Intakes one more time first....