Hi guys,

I have a problem with my 96 z28. The car run great, for about 1 or 2 minutes, gives a big drop in rpm and then shuts off. No codes are stored, no engine light, I checked all of the sensors and connectors and they look fine. The fuel pressure is around 41 IKON and 32IKOFF. Changed the fuel filter and still, got the same pressure readings. After the car shuts off, it will start right up every time without hesitation and then dies about 2 minutes later every time. Put a reader on it and the problem is occuring in open loop, so it's not a closed loop problem. I never had this problem before, just can't figure it out.

 

ur fuel pressures are fine, so its most likely not a fuel system related problem...what kind of reader are u using to diagnose that its an open loop problem? also, after it stalls do u have a hard time starting it back up? any smell of unburnt fuel?

 

It starts back up fine. No continous cranking at all. And I don't smell unburt fuel. The car actually runs with a smooth idle for a couple of minutes and just dies.

I used an actron CP918O with data playback capability, o2 monitoring, sensor data, fuel trim (which reads 0.00 on all fuel trims), and it says my car is in open loop. It can't run long enough to get it in closed loop. So that's adequate preesure? I was kinda hoping that it wasn't.

 

yeah the pressure is fine...for my build i have a 255lph pump in the tank and with key on/engine off the pressure is 40psi, key on/engine on the pressure is 42psi, and when shut down, it drops to 35 and holds for a long time...i mean 32 is a little low, but not any indicator for ur problem unless it continues to drop, then it may be leaky injector, bad check valve in fuel pump, or faulty fuel pressure regulator. with that said, u would smell unburnt fuel on start-up and it would be a little hesistant to start...
now im stumped with your problem, assuming ur fuel pressure holds, and would probably look to the ignition system to be at fault...hopefully someone else can chime in and help out as well...

 

Is it possible its running about 205 seconds (timer value to closed loop, assuming coolant temp is above 140*F and O2 sensors are active), and then dies as it attempts to switch to closed loop?

 

When I first start it up, it shuts off around 84 degress and the o2 sensors fluctuate roughly from .001-1.00 volts. If I keep starting it back up the temp will slowly rise eventually, after about 20 starts of course.

The opti, plugs and wires are not even a year old. But the coil hasn't been changed since 03 and the FPR is actually from 96 so I'm wondering if one of those could be bad.

 

if the FPR was bad, you wouldnt see your fuel pressure holding after the car shuts down...so my guess is that it isnt your FPR...
you can test ur coil according to shoebox's website. here is a link for it...
http://shbox.com/1/coil_testing.jpg

heres another link to his website for testing the opti, and also the ICM while your at it...
http://shbox.com/1/4th_gen_tech2.html#opti_test

 

Thanks, coil tested good, but what I've just noticed (after doing another pressure check) the pressure is not holding steady at all. Within the first 2 minutes the pressure drops under 30psi, and eventually in the 20's. Would this be the check valve in the pump or bad regulator?

 

that's a symptom for both of those problems...to test though, pull the vacuum line that attached to the base of the regulator (it runs from the FPR to the side of the intake manifold) and see if it smells like gas at all. if it does, its a good indicator that your FPR is bad, and a stock replacement is best until you are making serious HP and need to play around with the pressure you're running. if not, then your fuel pump may have gone, and now would be a good time to upgrade to something like the walbro 255lph pump offered from Racetronix....the other possibility from the fuel pressure leaking down is leaky injectors, but i dont think that is the most likely for causing your car to stall...my guess is that its the fuel pump, but test/check and make sure first...start with the FPR

 

84*F or 84*C? The O2 readings will swing back and forth between 0xx-9xx mV's, but it will only do that in closed loop. It can't go into closed loop at 84*F. It will go into closed loop at 84*C.

 

have you checked your maf? if you disconnect it I am pretty sure it goes to a closed loop??? Maybe someone else knows a lil bit more about this??? Just a thought.........

 

Disconnecting the MAF sensor does not force the PCM into closed loop. It forces the PCM to run in speed-density. Nothing else changes.

 

I am now having a very similar problem with my car (see sig.). Fortunately, (if you want to call it that), it has just now started showing DTC's 42 and 36 when I scan it. My optispark is an original GM Delphi unit purchased from "thepartsladi" last July with only 1,200-1,500 miles on it, and I'm now convinced it is the the opti that's bad. Where did you get your "year old" opti from?

 

Sorry I've been away guys. Been having computer problems, but to answer the questions asked, the car shuts off around 84 degrees F. The opti was bought at Jegs though I don't think it's the opti. FPR line appears to have no signs of fuel. I'm thinking it's the check valve.

I went to AZ website and noticed that they have a fuel pump check valve repair kit for $20. Does this kit solve the problem that causes the fuel pressure to drop.

 

The check valve closes to hold fuel/fuel presssure in the line, when the engine shuts off. Once the engine starts, the check valve has nothing to do with the fuel pressure. Its just "open". Have you checked the regulator. There is no reason for the fuel pressure to drop gradually to 20psi, unless the regulator is bad, or the pump is failing.