the flyin' scotsman

how are the ISV hoses? connector?

SeanR

Colin, since you have the intake off this will be easy. Cut the harness back about 6 inches from the MAF connector boot, the majority of the issues I was fighting on mine was due to a bad wire that far up in the harness. Butter after I fixed that.

Mrmerlin

also ask the owner what was the last thing he touched prior to the engine running poorly maybe he moved the pod or was messing in the CE panel or was adjusting the pod lights or anything else that may seem inconsequential

FredR

Is Lizard a "nome-de-plume" for Agatha Christie?

Come on Colin- the suspense is killing me!

Regards

Fred

Lizard928

Sean, I disconnected the MAF and LH then put 12V through LH wires and measured voltage at plug wiggling everything around and up/down. I didn't get my change in voltage. I also checked the other wires as well, no cross over at all.

I put the intake back on, and a new CPS as the connector was breaking on the old one.

I'm heading there this morning to see how it runs when cold.

Lizard928

So the car is running better, and I can now get the car to idle reliably without any stalling/near stalling.

Car still runs rough cold, but smooths out much quicker.
However if I bring the RPMs up, and then let it return to idle it runs rough.
I can disconnect each of the injectors while running rough and they all have the same effect.
While running smooth the vacuum is a very steady 15" Hg (big cams, so this is acceptable). When running rough the vacuum drops to 3-4" Hg then slowly comes back up, as it smooths out.

When running rough the O2 adj goes up to -12%, the HC goes up (1200-1500), the CO can go up to 1.5 (likely just due to the accel enrich). So what I deduce is that the cylinders are randomly misfiring/being blown out/not igniting.
Did a compression test and all cylinders are 190-185 with cylinder 7 being the lowest at 182PSI.
When I watch the inj PW in the ST, they go a little higher when running rich, but remain steady. Listening to the injectors with the stethoscope confirms all are functioning the same, and I can hear no missing pulses.
A timing light shows all cylinders are firing, though it is nearly impossible to see if a spark drops out.
An oscilloscope on the drivers side coil shows no missing pulses.
I cannot get a read out on the final stages signal with the oscilloscope, but obviously they are working.

I have tried known good final stages, coils, leads are new and ohm checked all of them, new plugs (2 sets).
Now the interesting thing is that I found a condenser on each of the positive leads to the ignition coils when I swapped in new coils.

I am going to be doing a leakdown test first thing in the morning when it is cold and the vehicle tends to run the roughest.

Additional note, there is no smoke out the exhaust, no black, blue, or white at all...

John Speake

Maybe a problem with the tank vent system valves ?

AO

Hi Colin,
Although rare, I did recently see a bad EZK cause all kinds of problems. The car ran, but not well. Have you tried a different EZK?

The other thing that comes to mind is some kind if intake leak. I have a tester that I made out of a PVC end cap with the same diameter as a MAF and a quick connect fitting. Hook up the air and pressurize to about 10 psi. Any leaks should reveal themselves.

the flyin' scotsman

what triggers 4 cyl/limp home mode? is that sensor/circuit healthy?

69gaugeman

That sounds a lot like valve trouble. broken spring, sticking valve or bad lifter.

Lizard928

AO,
Have run with 4 EZK/LH. Two factory unrebuilt, 1 JDS, one Electronic repair, all work perfectly in my car.....

Malcolm,
Ignition monitoring system has a bypass relay in it.

Rod,
Lifters are new INA lightweights from Roger.
Springs are new, and if one or more was broken I could trace it to one specific cylinder. I've had that before. There was also a notable drop in vacuum for the cylinder that was missing/not firing and it wouldn't fire until cylinder pressures came up.
Not sure I understand sticking valve though. On a pushrods the rod will bend, with our over head design it really doesn't have that option......

the flyin' scotsman

indeed, which is triggered by the thermo couples in the exhaust:

Tom. M

Just a FYI... 89 had the temp sensors in the 4/8 position.... in 1990 Porsche moved them to 3/7 for better reliability.....

Also, Colin...double check your ign monitoring bypass relay.. maybe it's bad?

69gaugeman

Valve can stick open with carbon build up, valve spring breakage, bent valve, etc, etc.

Just sounds like a valve timing issue when it loses vacuum like that.

the flyin' scotsman

thx Tom.....the change was noted in the 1991 service book but as the car is exJapan it maybe a bypass cct unique to the model......perhaps?