thunderstruck
Babuinos Móviles
Cliff-notes below. 1995 TBI 5.7L, about 235,000 miles on original motor.
A few weeks ago on the way home from work, my 95 began stumbling/misfiring under load. As long as I stayed under about 1/4 throttle, it was okay. Getting closer to home, it began backfiring through the exhaust. Didn't have time to mess with it then, besides I had another truck ('06 Avalanche) to drive for the time being. The next day, I changed the fuel filter and tried the '95 again. Had no problems for the next two weeks, but I unfortunately had to put the Avalanche in the shop for transmission work during that time.
Now that my other vehicle is the shop for awhile, guess what decides to start f'in up again? While on my lunch break, truck begins misfiring under load again. However, it's not quite as bad as last time. In 4th gear with the TC locked, I could feel a slight miss with a little throttle. But if I hammered the throttle, after a slight hesitation, the truck would come back to life. Truck sat for the rest of the work day, didn't have any issues until about halfway home when it began stumbling again.
I'd guessed that it was safe to rule out a mechanical failure (timing chain, sticking valve, etc.) due to the intermittent nature of the misfiring.
Next day, again, halfway to work the truck begins stumbling again. At this point, I realize the failure is somewhat heat related. After work, truck's running fine again but I stop by O'Reillys and rent a fuel pressure gauge. Good call, because the truck barely makes it home from there, hardly able to do 60mph, backfiring through the exhaust like crazy. Next morning I checked fuel pressure, lowest reading was 11.5psi, highest was 13.5psi. I did replace the fuel pump with a Delphi unit about 30,000miles ago. I would have liked to run the truck for a while with the fuel pressure gauge, but couldn't because the damn gauge kit was so worn and abused it leaked fuel everywhere.
Now considering the fuel pressure seems good and I'm experiencing backfiring thru the exhaust, I'm thinking my problem is ignition related. Pulled all the spark plugs, looked fine although they were showing some wear on the electrodes. Some of them seemed to have some glazing. Pulled the distributor cap, cap and rotor looked fine. I had replaced the spark plugs, wires, cap and rotor about 35,000 miles ago.
Since the issue seemed heat related, my first suspect was the coolant temp sensor, which has never been replaced in the 8 years I've had the truck. I don't really like to throw money/parts at a problem, but it seemed reasonable to do so here. It might be all in my head, but after replacing the sensor, I felt the truck idled better and accelerated slightly better. Unfortunately, the stumble came right back after about 20-30 of driving.
Next suspect was the ignition coil. I had replaced it mistakenly about 25,000 miles ago trying to cure another misfire issue, which turned out to be the EGR. Decided to try yet another coil and replace the spark plugs. Installed the coil first, started the truck to test it. Truck idled great, but I didn't want to drive the truck until I changed the spark plugs.
Once I changed the spark plugs, I restarted the truck. Now it was missing quite a bit during idle. Not horribly bad, but the only time my truck ever idled worse was when the original fuel pump was going out. After the truck ran for a couple of minutes the idle seemed to smooth out. Took the truck out and drove it kinda hard for about an hour. It seems like I've fixed the misfiring issue, but the truck still feels a little weaker than it used to. Also once I got home, again, I experienced a rough idle. I let the truck sit until night so I could maybe see any arcs from the plug wires in the dark. When I tried later, the truck idled just fine and I couldn't see anything.
Any ideas? Did I screw up my plug wires when removing them to change the plugs?
Cliff-notes:
Had intermittent stumbling and backfiring thru exhaust when under load. Fuel pressure checks out, 11.5-13.5 psi. Replaced coolant temp sensor, ignition coil and spark plugs. Stumbling seems to be fixed, but now idles rough intermittently.
Fuel pump replaced about 30,000 miles ago with a Delphi unit.
Spark plug wires (Taylor) and cap & rotor (Accel) replaced about 35,000 miles ago.
EGR valve and EGR solenoid replaced about 25,000 miles ago.
TP sensor replaced about 40,000 miles ago.
O2 sensor replaced about 30,000 miles ago.
IAC valve and TB gasket replaced about 5,000 miles ago.
A few weeks ago on the way home from work, my 95 began stumbling/misfiring under load. As long as I stayed under about 1/4 throttle, it was okay. Getting closer to home, it began backfiring through the exhaust. Didn't have time to mess with it then, besides I had another truck ('06 Avalanche) to drive for the time being. The next day, I changed the fuel filter and tried the '95 again. Had no problems for the next two weeks, but I unfortunately had to put the Avalanche in the shop for transmission work during that time.
Now that my other vehicle is the shop for awhile, guess what decides to start f'in up again? While on my lunch break, truck begins misfiring under load again. However, it's not quite as bad as last time. In 4th gear with the TC locked, I could feel a slight miss with a little throttle. But if I hammered the throttle, after a slight hesitation, the truck would come back to life. Truck sat for the rest of the work day, didn't have any issues until about halfway home when it began stumbling again.
I'd guessed that it was safe to rule out a mechanical failure (timing chain, sticking valve, etc.) due to the intermittent nature of the misfiring.
Next day, again, halfway to work the truck begins stumbling again. At this point, I realize the failure is somewhat heat related. After work, truck's running fine again but I stop by O'Reillys and rent a fuel pressure gauge. Good call, because the truck barely makes it home from there, hardly able to do 60mph, backfiring through the exhaust like crazy. Next morning I checked fuel pressure, lowest reading was 11.5psi, highest was 13.5psi. I did replace the fuel pump with a Delphi unit about 30,000miles ago. I would have liked to run the truck for a while with the fuel pressure gauge, but couldn't because the damn gauge kit was so worn and abused it leaked fuel everywhere.
Now considering the fuel pressure seems good and I'm experiencing backfiring thru the exhaust, I'm thinking my problem is ignition related. Pulled all the spark plugs, looked fine although they were showing some wear on the electrodes. Some of them seemed to have some glazing. Pulled the distributor cap, cap and rotor looked fine. I had replaced the spark plugs, wires, cap and rotor about 35,000 miles ago.
Since the issue seemed heat related, my first suspect was the coolant temp sensor, which has never been replaced in the 8 years I've had the truck. I don't really like to throw money/parts at a problem, but it seemed reasonable to do so here. It might be all in my head, but after replacing the sensor, I felt the truck idled better and accelerated slightly better. Unfortunately, the stumble came right back after about 20-30 of driving.
Next suspect was the ignition coil. I had replaced it mistakenly about 25,000 miles ago trying to cure another misfire issue, which turned out to be the EGR. Decided to try yet another coil and replace the spark plugs. Installed the coil first, started the truck to test it. Truck idled great, but I didn't want to drive the truck until I changed the spark plugs.
Once I changed the spark plugs, I restarted the truck. Now it was missing quite a bit during idle. Not horribly bad, but the only time my truck ever idled worse was when the original fuel pump was going out. After the truck ran for a couple of minutes the idle seemed to smooth out. Took the truck out and drove it kinda hard for about an hour. It seems like I've fixed the misfiring issue, but the truck still feels a little weaker than it used to. Also once I got home, again, I experienced a rough idle. I let the truck sit until night so I could maybe see any arcs from the plug wires in the dark. When I tried later, the truck idled just fine and I couldn't see anything.
Any ideas? Did I screw up my plug wires when removing them to change the plugs?
Cliff-notes:
Had intermittent stumbling and backfiring thru exhaust when under load. Fuel pressure checks out, 11.5-13.5 psi. Replaced coolant temp sensor, ignition coil and spark plugs. Stumbling seems to be fixed, but now idles rough intermittently.
Fuel pump replaced about 30,000 miles ago with a Delphi unit.
Spark plug wires (Taylor) and cap & rotor (Accel) replaced about 35,000 miles ago.
EGR valve and EGR solenoid replaced about 25,000 miles ago.
TP sensor replaced about 40,000 miles ago.
O2 sensor replaced about 30,000 miles ago.
IAC valve and TB gasket replaced about 5,000 miles ago.
