Sick 91 z34 rough idle, stalling & no power

[portsider44]

Car is 91 z34 bought from orig owner 4 years ago with 71K, no has 95K. Prev owner was a maint freak & detail freak. Kept written log of all work done (which I've seen b4) but htis guy even listed dates of washes & waxing. Timing belt was replaced at 60K, before I bought it. My daughter drives the car & it has been a pretty good car with very little work needed.

About 6 mths ago the car stopped down shifting & will not go into low gear. So she has been manually shifting & things have been fine. Then the car started to stall (just died) after heating up. When it would cool down it would restart, however car didnt seem to have power. So I changed the Crank postition sensor, but warm stalling didn't go away. Read on hear about bad wiring going to ECM, I checked & my wire seemed balloned & I replaced it.

At this point started it up & ran fine. So I thought my problems were solved however after a long test drive car started cutting out at speed & would not idle. Let it set & it will start & idle fine until it heats up. Idle will bounce all over the place & disconneting the IAC does nothing. Also when its running good pulling plug wires does not always cause the car to have a mis or stumble. Really only when I pull #4 & #6 do I notice a problem.

So crankps, radiator & spark plug were replaced at same time. I am getting fuel but have not checked pressure or done a compression check. I am getting spark at all 6 & fuel pump is working & fuel filter was replaced 9 mths ago. Plus I did the paperclip trip & all I get is code 12.

I pulled the timing belt cover & the belt looks good & is tight. So I don't think it could have jumped timing. What would be the best place to check next?

[mrl390]

The fact that the problems occur after the car heats up leads me to believe that maybe the cat is clogged. At that age and 95000 miles it doesnt surprise me as long as its still the original converter. The loss of power after it warms up and the trans acting funny are symptoms of a bad cat as well. You should be able to have a new one welded in for a reasonable price at an exhaust shop.

[portsider44]

??? Didn't even think about that I will give that a look this weekend, thanks for the reply

[RedZMonte]

OR if you can, unbolt it and bang the guts out of the cat and see if it fixes the issue... the DP to catback bolts are probably pretty rusty.

you can also check the cat with a lazer temp gauge.. should be about 150* hotter on the back side of the cat as the front..

[Schurkey]

What is the fuel trim, O2 crosscounts, and IAC position when this stuff happens?

First Guess: Until you connect a proper scan tool, you'll throw parts at it until you go broke without actually fixing the true problem(s).

[86FieroSEv6]

I'm gonna put my shiny quarter on the fuel pump or it's relay.

[portsider44]

Don't have a scan tool so I am guessing but trying not to just throw parts at as I don't have the $$ for that. For now I think a cat removal & bang out might be a fairly easy & cost effective thing to try.

[portsider44]

**update 8/1/10

Well I would like to say I am making progress but I don't think I am.

So the cat converter is not the problem, plus I put a fuel pressure gauge on it & when running its showing 42 lbs at the fuel rail shcrader valve. I also double checked vacuum lines & ended up replacing a couple that were weather cracked, however they did not appear to be leaking.

When testing fuel pressure should it be done with the vacuum line connected or disconnected from fuel pressure regulator? Also if the pump is going out is it possible that the FPR with still pressurize the system (correct psi) but the pump can't keep up with the demand? Should I test it at the filter location & get a reading of the pump psi before the FPR??

FOr now the car can be hard to start with out using starting fluid. Once it starts will actually idle pretty well but does not have any power. If in drive or OD, transmission doesn't automatically downshift into low & manaully putting into low only puts in to 2nd. (keep in mind transmission problem has been like that even before motor issues started). So if you let idle it does good until motor heats up & then it starts missing & will stall & may or may not restart. However it does not throw a code or trigger SES light.

At this point I wonder if it has to do with with coming out of closed loop? Also would a scan tool help pin point computer, ICM or coil issues? What scan tool options are out there?

I have spark at all plugs
I have fuel
I guess next is to check for compression

[portsider44]

Update question on ICM

Well I have some time to work on my daughters car this weekend. I put it on the charger wednesday to make sure the battery was up. Tried to start it & it would not start. One shot of starting fluid & it started. I let it idle & run for 10-15 minutes then killed it.

THursday evening just for the hell of it I tryed to start it & it fired up. Idle was decent, however on short test drive car still has no power. Once home THursday idle became erratic, the car died & would not restart.

Friday check for spark & have it all 6. Put fuel press gauge on fuel rail reads 40 with key on & when started. When giving it gas it drops to 38lbs however when you rev it up to 3K & the rev limit kicks in it goes up to 42lbs as the motor bounces off of the rev limiter.

Now idles for 10-15 mins waiting for it to sputter & die but it doesn;t until I turn on the a/c. Car dies fuel press is at 40 & with key on not running after 5 mins fuel pressure goe sup to 42 & stays there. Even after 10 minutes, I turn off key & fuel pressure does not change even after 10 mins.

So I have spark & it appears I have fuel & no leak down issues. Vacuum line at map for FPR does not appear to have smell of gas.

What all does the ICM do? does it only tell to fire or does it also control timing advance? SInce I am getting spark does that rule it out as being bad?

I have a lap top so would free scan be a low cost option for a scan tool & if so where is the best place to order the cable?