Ducman82

so new injectors, new plugs, FPR check fine..... wires? exhaust leak? emissions BS (might as well ask)...... maybe try different plugs on that bank? how is the resistant nave from the brain to that bank of injectors?

SeanR

Is the rich side firing on all cylinders?

j.kenzie@sbcglobal.net

I confirmed power to all spark plugs with the inductive pickup lead on my timing light. I think that means they all have spark.
Once again, would one tooth retard on the rich side cam sprocket cause this?
Thanks,
Dave

hacker-pschorr

Possibly, if it's consistently just the one side the camshaft is the only factor that's different (unless there is a faulty plug wire, injector etc..)

Need to remember the L-Jet system is a very "loosely" tuned system, it works fine for how under-powered this engine is and all factors for a stock car.

Toss a bunch of boost down its throat any tiny differences are amplified. This is why no 928 should be boosted unless everything, no exceptions, is running 110%. This is why I was working on adjustable cam gears for the 16V so I could further dial in such things for my boosted 81.

j.kenzie@sbcglobal.net

Eric, would you redo the timing belt for one tooth? I kind of think I've looked at everything else.
Thanks,
Dave

j.kenzie@sbcglobal.net

Hi Eric,
I guess you kind of answered my question. With one cam off by one tooth, the engine is certainly not 110%. I don't think fixing it will be too bad, I've done the TB 2 or 3 times, and the SC is just more stuff to R & R. I've got all Winter, and if it's still got different AFR's on the two cylinder banks, then it's something else.
Also, neither Greg Brown nor Sean nor Stan nor you nor any pro mechanic is ever going to say that one tooth off on cam timing is "close enough".
Thanks for the support,
Dave

hacker-pschorr

I don't see the need to re-do everything. Put the engine at TDC, use some close pins or other non marring type of clamp to hold the TB to the drivers side cam gear and loosen up the belt, adjust cam gear accordingly, put back together.

I did a passenger side cam tower gasket on my 80 without taking the belt off. Yes I was lazy......

Show a picture of both timing marks. The "catch" with these engines is sometimes it's as close as you can git and going the other way will just be a tooth off in the other direction. To get them closer you need to order up some offset woodruff keys.

j.kenzie@sbcglobal.net

Yeah, I agree, Eric. It shouldn't be too bad. It's the DS cam that's off, but I will use spring clamps and see if I can move the belt a little. Unfortunately, with a PKsnr, I think I need to pull the center cover to release the tension. I'll look and if I can release the tension without pulling the center cover, that would be great. I think I am just a little under on tooth off, by the marks, so I hope this will improve things.
Thanks,
Dave

j.kenzie@sbcglobal.net

Hi guys,
Well it's after the New Year, and I had a little time to work on the 928. I decided to try to correct the one tooth timing error on the DS cam sprocket.
I was able to release tension on my PKsnr by loosening its mounting bolts and letting it swing away. I had locked the flywheel and the PS cam to the belt, I released the tension and jumped the DS cam one tooth to the position I had marked on the belt. I compressed the tensioner slowly while held vertically in a vise, and reinsterted its pin. I reinstalled the tensioner, pulled the pin and unlocked the flywheel. After about 20 crank revolutions the cam sprocket marks and the OT mark on the crank damper are all exactly on their marks. I am going to quit for tonight while I'm ahead. Tomorrow I'll put things back together. BTW I turned the crank with a strap wrench on the supercharger pulley, after removing the spark plugs.
I a couple days, I'll get an idea if the AFR's are now equal on the two cylinder banks.
Thanks,
Dave

j.kenzie@sbcglobal.net

Success!
One cam tooth off gave me 1.5-2 AFR units difference between the two cylinder banks.
After correction the two banks are within 0.5 on AFR. (Crazy that I have two WB O2 systems.)

It was really hard to see the error, but fixing the problem was not really too bad.
Thanks for all the help,
Dave

Mrmerlin

glad you got things sorted out, Keep em Flying!

FredR

As a matter of interest for the bank that was off by one tooth was it advanced or retarded?

j.kenzie@sbcglobal.net

Hi Fred,
DS cam was one tooth advanced.
Dave

FredR

Hi Dave,

The interesting question is whether the symptoms are explicable. As the cam timing is advanced it should favour low/mid rpm range performance at the expense of top end. To perform better it needs more air flow and fuel to match but if the mix was rich at low/mid range that possibly suggests less air flow. I am not too familiar with the engine management system on your model year but it would be interesting to see if anyone can explain how your symptoms came about because of the cam error.

I suspect the 32VR cam timing tool does not work on your model given its name but for the 32 valve models it is a must for DIY enthusiasts. No idea if there is an equivalent device for your model year but if there is I bet you might consider buying one!

Either way well done albeit it took some time to get there. One cam tooth out is 15 crank degrees- folks playing around with cam timing tend to vary about 10 degrees retard tops looking for more top end so your error factor should be significant.

hacker-pschorr

Nope

Years ago Ken made a batch of modified cam hubs from 32V's to fit the 16V to allow for cam adjusting. Outside of that it's either one extreme or the other with a set key or get some offset woodruff keys.

I inquired with a couple of places on making some custom two piece cam gears which are common in the import crowd, cost wasn't horrible but I haven't pulled the trigger on a set yet.