Z28 Running Poorly

**cm86414** · 05-24-2009, 07:17 AM

I am at my wits end! My car is still not running properly. It runs fine when you first start it but when it is restarted after it has ran a while it acts like it is missing out. It has no power and sputters along for a few seconds. After it does that it runs fine until you restart it again and put it in gear. I have had a tune up, changed the fuel filter, cleaned the MAF, cleaned the air filter, and always run premium fuel. I don't have a SES light on so I really don't know what it could be. I don't have cats and have rear O2's deleted. Could it be the pre cat O2's? Again I don't have a SES light though. Coil pack? I just don't know. Again it will only do it when the car has been warmed up and restarted after shutting it off. Please Help!! Thanks.

**Y2KPewterSS** · 05-24-2009, 09:49 AM

It could be a front 02 sensor, but usually those will throw a SES code. Try swapping your front 02 sensors out for another one and see if that fixes the problem. Have you also checked to make sure all your plug wires are connected well?

**Cutlass** · 05-25-2009, 04:43 AM

Sounds like it only happens for a short period of time? Are you able to isolate it to a specific cylinder or cylinders?
Maybe a fuel injector cleaning service would help.

**pajeff02** · 05-25-2009, 11:13 AM

Almost sounds like it is vapor locking...

**0rion** · 05-25-2009, 11:15 AM

how's your temp gauge reading? Something else to look at is the ect sensor on the drivers side head right by plug number 1.

**cm86414** · 05-25-2009, 02:35 PM

Originally Posted by 0rion

how's your temp gauge reading? Something else to look at is the ect sensor on the drivers side head right by plug number 1.

The temp guage reads normally when the problem occurs. It does do it for a short period of time and I mainly focus on the RPM's because they are low. I have not been able to pinpoint it to a specific cylinder again because the problem only occurs for such a short time. I am planning on having a fuel pressure test and compression test done soon and maybe that will open a door with a definite answer.

**Cutlass** · 05-26-2009, 03:36 PM

A GM Tech 2 scan tool has a "Misfire display" that will show what cylinder is misfiring...usually. Do you know anyone at a GM dealership?

**JoshieDoom** · 05-27-2009, 03:36 AM

Kinda off vehicular topic but ive had the same issues outta multiple gm vehicles(buicks, chevys, etc) turned out to be fuel pressure. The pump would get hot from running and provide less pressure. The longer it run the cooler in got swishing around in the tank(my theory)

Try changing out your IAT sensor since it is very cheap as well. Ive read on some of the ls series engine in other vehicles(ls4 etc) have hot starting issues. The IAT gets hot ass piss when the vehicle is turned off. When restarted its has to cool off the sensor to get proper timing etc.

Just a couple of thoughts.

**pajeff02** · 05-27-2009, 04:09 AM

+1 on the IAT getting hot. Mine will heat soak after the engine has been shut off, but it comes down quickly once re-started. I believe with a 72 degree air temp, the heat soak was up around 110 degrees not too long after shutoff. I think it would only be a problem though if the IAT were acting up or sluggish to respond. Probably not a bad idea to clean these also when you do the MAF as a layer of crud could act to insulate the sensor, giving a false reading to the PCM.

**cm86414** · 05-28-2009, 12:55 PM

Originally Posted by JoshieDoom

Kinda off vehicular topic but ive had the same issues outta multiple gm vehicles(buicks, chevys, etc) turned out to be fuel pressure. The pump would get hot from running and provide less pressure. The longer it run the cooler in got swishing around in the tank(my theory)

Try changing out your IAT sensor since it is very cheap as well. Ive read on some of the ls series engine in other vehicles(ls4 etc) have hot starting issues. The IAT gets hot ass piss when the vehicle is turned off. When restarted its has to cool off the sensor to get proper timing etc.

Just a couple of thoughts.

Thanks for the input from everyone. I just replaced my IAT sensor today so fingers crossed that fixes the problem!