*JC*

I'm not sure if this is the right forum to post this, if not please forgive me.

The car is a 2002 LS1 Firebird with 26,000 miles. The engine is sputtering at partial throttle, bucks like it's missing or something and will backfire some. The fuel pump shows a soild 55 psi at idle. The fuel filter is brand new and the 02 sensors are good. The MAF is clean and working properly. The TPS is working correctly.

This problem just popped into exsistence overnight one day about a month ago.
There is no SES light on, no codes, and no misfires recorded. The only unusual thing is when it's at idle and holding steady RPM and the Cal load is steady, I notice the Adv Ing timing is going from 15 to as high as 23. That seems a bit strange to me, shouldn't it be holding steady or close to it, not spiking and droping that far at idle?

I'm at a loss as to what's causing the engine to run this badly? It went from running just fine, to this overnight. I feel like I'm chasing a ghost and I'm unsure what to check next. Any help and advice would be greatly appreciated.

silvershark

backfiring is normally bad timing either electronically or actual timing is off on the timing set. Another cause can be due to super rich condition/clogged cat.

SlasherVRGR

iTrader: (1)

I had a similar problem with my 3800 car a few years ago. The plug wires in the rear cylinders melted to the manifolds and the boots got dry rotted and cracked. Have you checked the plugs and wires?

*JC*

Anything is possible but the car doesn't seem to have a problem reving higher. It's only at idle there is an odd sounding miss sound. And when you go to drive it and put the car under load, it has that stumbling/sputter condition, It happens mostly around the 1500 rpm range. If you give it more gas the car takes off like a rocket.

This car has never been driven hard or taken to a race track, that of course doesn't mean something mechanical couldn't be at fault. Stuff used even nicely can and does break.

I'm really at a loss at trying to figure this out, that's why I'm asking. Thank you for the input.

*JC*

I have given the plug wires a visual inspection and nothing has ever touched manifold or melted. I suppose there might be some dry rot that I can't see? I did unhook most but not all of the coil packs to see if it might be that. Just from the ones I unhooked I noticed nothing out of wack. The behaved just as they should when I unhooked them and came back to life when I hooked them back up. I can't say it's still not a coil pack or wire, as there was some I did not unhook.

The plugs and wires are original to the vehicle. Supposedly the Plugs are good for 100,000 miles, or so the Factory claims. My car has only 26,000 miles on it, so the plugs should still be good. Seems to me a bad plug or plug wire should cause it to run poorly through all the RPM range. And the ECM has recorded no misfires or any codes (Say except for one's I created when testing).

Thank you for the imput

SlasherVRGR

iTrader: (1)

Mine would be good until the engine was under a big load, like going up a hill in a high gear. The miss wouldn't even trip the blinking CEL unless I was going up a pretty long hill in too high of a gear.

*JC*

I'll know soon enough, I ordered the GMPP Red Performance Wires 12495519 and some ACDelco 41-110 Iridium plugs . I'm sure there is much better stuff but I was looking at cost, and it's a stock engine. I figured if I'm changing plug wires I might as well get the red ones, for the added benefit of under the bonnet bling. And the longer lasting plugs so I'm not having to do this again in a year or 5 years or 10. I'm not getting any younger and crawling around under a car isn't as easy on me, as it used to be.

I'm not looking forward to changing plugs & wires, by the time your done you look like you fought a Tiger. All scared up and bleeding

But I have a sneaky suspicion this isn't going to resolve the problem. In the end I may have to take it to a shop?

silvershark

Since it has power up top, you can cross a clogged cat off the list.

JT2000WS6

I haven't had this problem on my LS car, but every other car where I've had this condition occur it ended up being the coil packs. Sometimes I lucked up and had a SES light for a misfire on a specific cylinder. More often I just replaced them all and it solved the problem. Not saying this is your issue, but based on the symptoms above new coil packs have worked on my non-GM cars.

Good luck.

1FastBrick

iTrader: (16)

You said you had 55 PSI at idle, what about under load?

Have you checked the fuel pressure regulator.

With only 26,000 miles on a 15 year old car, have you ever run fuel injection cleaner through the fuel system? You know gas goes bad when it sits and it can do nasty things when to the injectors sitting in the rails.