Been awhile since I've posted 2 any Z site but I've gotta problem that has me STUMPED!!

1991 Z-24 3.1 V6 5spd
Crank pulley, Down Pipe, HI Flow Cat, Full Exhaust
FastChip installed
Run 91-93 Octane
130,000 Original Miles

When I was getting on the highway last week very fast thru a corner my car ended up dieing on me, felt almost as if the throttle cable had snapped in that the gas pedal had no effect on the engine RPM whatsoever. Figured I may have run out of gas since I was goin 2 get gas and had about 2.5 gallons left, friend got me gas so I was able to get 1 gallon into it but nothing, after awhile the car started would idle but any time I blipped the throttle it would die.

Car was towed home.

Some Symptoms I've noticed

- Next day car started fine but blipping the throttle would cause it to die but I was still able to get it into our garage and onto the lift.

- You can start the car whenever the engine is cool or cold but when it is warm or has already stalled out not always able to start it right away.

- The car will sometimes be idleing fine but then without warning, just die.

- If you press the gas to the floor it will increase in RPM by about 1000 drop 1000-2000 (depending on the rpm you started at) and increase again by 1000 drop the same amount and then go up by the same amount, repeating itself untill it stalls or you let off the gas.

- Blipping the throttle still causes it to want to die or to die and it sounds like the car is gasping for air.

- Only when the car is off and the ignition in the ON position, the Check Gages (NOT CHECK ENGINE) light illuminates, will go off, come on, go off, and come on, and sometimes stay on but the gages read normal

- I've smelt unburnt fuel from the exhaust for a few years now but have alwasy passed emmisions and only smells at startup (running a FastChip Chip)

- For the past 2.0 months the idle at startup has been kindof ruff as in when you step on the gas it does not have a smooth sound but would clear after a minute or so to the point where it sounded normal

What I have checked and what has been replaced
I've used an AutoXray ScanTool for GM Vehicles set up to scan the 91 Z24

Fuel Pressure - OK
Fuel Pump - New, less than 6000mi
Fuel Filter - New, installed today, 0mi
Fuel - added 2.5 Gallons of 93 Octane
Fuel - added STP Fuel INJ Cleaner
Air filter, 10" K&N Cone filter, Cleaned, less than 2000
NO Obstructions in air intake or TB
PCV Valves removed 7 years ago, No Problems
ECM - Checked with known Good
Mem Cal - Checked with known Good
CPS (Crank Pos Sen) - Checked with known Good
MAP Sensor - Checked with Known Good
MAP Hose OK and when disconnect will set code.
Ignition Module checked with known Good
Coils Tested and alll 3 are within SPEC
New Plugs and Wires less than 2000mi
TB was cleaned and regasketed less than 2000mi
IAC Motor checked with known good
All vacum lines from TB were checked for cracks, still need 2 look at the ones going to the charcol canister
Cleaned TB with STP TB Cleaner
TPS registers proper voltage and shows correct throttle angle %
CTS and IAT temperature readings when compared are within limits
O2 Sensor, fairly new less than 4years old (LOW MILEAGE) adjs itself accordingly when engine is running.

SO WHAT IS IT?

I will not rule out ignition or fueling problems, could it still be the pump even though its a new BOSCH?

ANY IDEAS or what I can check next would be greatly appreciated, I know someone has delt with this before,

Thanks every1 for your help and ideas

- PETE


<img src="http://registry.gmenthusiast.com/images/91cavaliergtrz/personal_pic.jpg">
DON'T BOTHER...the emblem is GONE!!

Step 1: Pull out the FastChip and put in your stock PROM. See if anything changes.




1989 Z24 Convertible - Dust Covered
2006 tC - Dust Covered, but driven more

^^ I was going to just say that..

If that doesnt work, try onther ecu all together. and if that doesn't do anything, I would try another ICM.

To be honest.. it sounds like the computer is freaking out or not getting enough voltage. If you've ever had your voltage regulator go out, and voltage starts to drop too much.. the car does things like your laking about sometimes.

Just a thought

Could it be a weak spark that gets blown out when you stomp the gas? Maybe reducing the gaps a bit will help?

I'd look at injector pulse widths next. You can do this with a simple RC filter and a DMM. That will narrow down your issue to fuel or spark.

2002 Cavalier 2200 5spd

Yeah I already covered the whole ECM thing, thought that might B it since its on ECM #2
I figured what I did eliminated the possibility of a problem with the ECM and the MemCal
I pulled the Fast Chip put in the OEM Chip -NO Change
I pulled the ECM and placed in a Known Good ECM with both the OEM and FastChip chip, NO CHANGE - Everytime I disconnected the + and - terminals

Voltage Regulator, where is that located on the 91Z? I figure something must regulate the voltage but is it a standalone unit or built into something like the alternator?
Scan tool shows my voltage at normal charging rate.....but last year I experienced what you were talkin bout...........got stuck in traffic for 3hrs at the beach on a HOT DAY where the only way I could keep the car running was by keepin my foot on the gas....otherwise the rpms would drop and then die........turns out the WALMART batt. shi+ the bed on the way up to NH and then decided to let me know in traffic.............that

All coils checked out well within spec and the gaps on all 6 plugs were set to factory spec about 3000 miles ago, maybe less, whatever the mileage was from CT to NOPI NATS 2006 back to CT and some extra miles.........the next topic I was gonna read about was the whole fuel and injector section in the Fac. Serv. Manual..........without lookin there right now do they tell you how to check it with a DMM.............or if you know do you have a link to how to set up the test with an RC filter and DMM?

Earlier today checked the Fuel Press again...........turn the pump on about 43psi.....run the car under load or blip the throttle about 38psi.......

KEEP THE IDEAS COMIN.......Eventually I'll get it


<img src="http://registry.gmenthusiast.com/images/91cavaliergtrz/thumbnail_personal_pic.jpg"> DON'T BOTHER...the emblem is GONE!!

Quote:

Earlier today checked the Fuel Press again...........turn the pump on about 43psi.....run the car under load or blip the throttle about 38psi.......

Wait a minute.... the fuel pressure should be higher under load and when applying the throttle, than it is at idle... not the other way around.

Even that being the case... It "probably" wouldn't cause your problems since most cars run ok with the FPR unplugged. That's strange though.

The voltage regulator is in your alternater, but if the car is charging OK, that prob isn't it either. You could always check it out with a volt meter to know for sure I guess.

Have you tried using a different ignition control modual yet?

In the originalpost I stated the stuff I have already tried, I tried a known good module to no effect.

Gonna try removing the EGR valve tomorrow since some of the symptoms I've been having relate to a defective EGR valve.......that and since my HC and Nox levels have been getting worse with each subsequent emissions test and unpluging it does not trip the CEL it'd B worth a shot


<img src = "http://registry.gmenthusiast.com/images/91cavaliergtrz/personal_pic.jpg"> Don't Bother The Emblem IS GONE!!!

I removed the EGR completely and then started the car. Didn't think of what would happen until it happened and then......OH YEAH!!

Basically the car made a large sucking noise then the RPMs shot WAY UP like you had the TB wideopen......funny thing is no CEL came on and the car didn't die right away (I probably shut the car off before it would die)
I then completely blocked off the EGR opening and if there was any diff. it was very slight......so im guessing the EGR is not at issue.


<img src = "http://registry.gmenthusiast.com/images/91cavaliergtrz/personal_pic.jpg"> Don't Bother The Emblem IS GONE!!!