z280utlaw

I'm going to paraphrase the story on my 93 Z28. The car has minor bolt ons, CAI, Muffler, HyperTech chip and thermo, blackouts etc.

About a month ago after the first snow had let up I went to drive my car to put it in storage for winter, rolled down my driveway and the car died. I though hmmm, tried restarting it and it wouldn't start. I had let it run for about 15 minutes before I tried leaving. Had the car towed out to our shop and put a new starter in (other one was cracked in half) Car fires right up, work the gas build up out, and we're off. Pull out of the shop and head towards the end of the driveway and the car is running like crap again. Dies, restarts, dies, restarts, until it won't start anymore. Pull it back into the shop and run some fuel injection cleaner through it, change plugs, no codes being thrown, no SES light.

Car starts right up, runs awesome... drive it to work and back, let it sit for an hour and go to put some gas in. Starts right up, idles kinda funny... then when I rev it the car starts to spit, sputter, and shake very badly, espically in the lower RPM's, but if you stay on it the car kicks out of it. Let it sit for 15 minutues, starts right up again, head to the gas station and the car runs fine. Put gas in, start it up, same shaking, sputtering, backfiring and all. Still no codes, no SES Light, car just runs like **** espically when u put it into gear and try driving, feels like there is no power even when you floor it and the car feels like it's stalling when u tap the gas.

I'm debating on what this could be, I've been thinking Opti but if it was the Opti wouldn't the car start a little ruff? It could also be injectors maybe, because after the fuel injection cleaner the car ran awesome for a little while then could have clogged back up. Or could it be a bad fuel pump?

Any suggestions or advice would be great, considering I've been without my baby for over a month and it's really killing me not being able to drive it when the weather is nice, plus I have some performance parts to install. I really love my car, and want to get this resolved. I'm hoping I can get some better information on her as opposed to LS1Tech.

Thanks in advance and sorry for the long write-up.

Gripenfelter

Could be bad gas. I had something similar happen to me when I ran Shell 91 octane.

turbo_Z

Yeah this is the place for LT1 questions.

Id start looking into the ignition. In fact next time it dies on you, check to see if its getting spark. Its really the downfall of the LT1.. the constantly failing ignition system but not always because of the opti. Another somewhat common problem is the ICM(ignition control module) which is that square sensor bolted down right beside the coil. Being that its in almost direct contact with the head, it gets pretty damn hot. So heat gets the blame for it failing all the time. The ICM will work when its cold but once everything gets to operating temps its believed the sensor will sometimes fade in and out giving irratic idles, stumbling and evenually cause the motor to stall completely. Anyway Id definitely put it up there pretty high on your list of culprits and its fairly inexpensive from what I remember. Hope ya figure it out.

z280utlaw

The problem is, the car no longer dies on Me, it actually idles pretty decent with a little stumbling from time to time, it's when u hit the gas that it really starts running badly. The car will start up and run forever, it just has no power, stumbles, backfires, the works. But it hasn't died since I changed the plugs and ran fuel injection cleaner. I will look into the ICM though. I've also heard that it could be O2 Sensors, I would really like to have this figured out before the end of December... I might just start trying little things like the coil etc. Does the ICM have the same function a MSD 6A would have? If so I would just do MSD, instead of replacing with factory parts.

z280utlaw

For the record, I can hear the fuel pump priming when I turn the key. My wires are fine, but the car does smell like it might be running a little rich.

droptop z

well, I had similar problems this afternoon, my car started smokin horribly (white). My head gasket blew keep an eye on your coolant level.

96SLPTransAm

I say that it might be the EGR valve. If the valve is sticking open then its going to burn rich and you will feel the loss of performance. My cars EGR is sticking open and when you floor it it kinda sputters a little and it burns VERY rich. Check the hoses connected to the EGR and clean them out with some carb cleaner and then put them back on. But if you put a new EGR valve on it and it still sticks open then you might want to check and see if your cats are clogged like mine cause that is what is causing the problem. Good Luck.

ptown

I had a similar problem and found that the fuel pump was dieing

Blown_Red_97z

same with mine, fuel pump problem. Under light throttle, runs fine, under half or more throttle, runs like crap. Hook up a mechanical fuel pressure gauge to the shrader valve on the back on the intake and watch the fuel pressure as you drive and put a load on the motor. Anything less than like 35 psi you should look into replacing the fuel filter and/or the fuel pump.

SSConceptz

If you ask me, it's the MAF Sensor, it caused the problem on me, if you start it you have to give it gas for a few mins before it will idle on it's own. Just get the car started, then when it's running go tap kinda hard on the MAF Sensor with a screw driver, if it dies then the MAF is bad if it don't then I'd see about the fuel pump.

Injuneer

He has a 1993 Z28 = speed-density = no MAF sensor.

Check the fuel pressure.

6SpdLT1Z

Sounds like what happened to me when my fuel pump went out (just last weekend)


Check the fuel pressure.

wrd1972

I had a similar problem.
Start the car and it would cough and choke and would not reach idle.
Turn it off and restart and it would eventually act right.

Upon removing the Bosch spark plugs they were totally carboned up and black as can be. Obviously a serious rich condition. I also noticed black spray shooting out the exhaust pipe.

I had recently replaced the EGR and I dont think it was that. I then replaced the Bosches plugs with NGK and replaced the O2 sensors and have not seen the problem sense.

I also ditched my hypertech PP in favor of a madz28.com tune.

z280utlaw

Thanks guys, I'm going to be replacing the fuel filter tomorrow, then I can see how that looks. I doubt that will solve the problem so I will try to hook it up to a fuel pressure gauge and see what happens. If my fuel pressure is below 35 PSI, is it for sure the fuel pump. I don't want to spend the money unless that it is, but it wouldn't be so bad considering a fuel pump is cheaper than some other things that could be wrong. I appreciate all the advance, the guys on LS1Tech aren't helping as much as usual, I'm going to start posting here more often.

SSConceptz

Didn't think about that LOL.