I have a 96 Camaro 3.8/5 speed that has given many issues/problems over the last 6 months. It was a gift that was not running & was in sad shape when I got it... as you'll see from the list of parts required to get it this far.

Right now, I've got the car down to ONE lone P0300 trouble code that has it backfiring out the exhaust ONLY under load. It will idle beautifully, can rev to 3-4000 rpm perfectly, but as soon as you put it on the road under any kind of load, it backfires constantly. 166k miles on the odometer.

Here are parts/issues that have been replaced/repaired within the last 6 months (not exactly in this order):

flushed radiator with Everclear (reg. radiator flush didn't work)
3 new coil packs
Swapped ICM with known good one
All 6 injector connectors
3 new fuel injectors
Replaced injector o-rings
MAF sensor
New PCM
New Air charge temp sensor
New fuel pressure regulator
New intake gasket
New IAC
New TPS
New coolant temp sensor
replaced throttle body (original was egg-shaped)
throttle body gasket
replaced all vacuum hoses
replaced alternator
replaced fuel pump
new fuel filter
new air filter
new pcv valve
new vacuum canister
new MAP sensor
new vacuum purge solenoid
new plugs & wires
new clutch/flywheel/release bearing
replaced cat. converter with temporary straight pipe (new cat will eventually be going back in)
replaced broken air intake tube

If I can just figure out this last issue, the damn thing should run like a brand new car. lol

Any ideas??

 

This is an afterfire, a back fire comes through the intake. This is caused by raw fuel being sent into the exhaust. P0300 is a PITA to repair since there are so many different things that can cause the code. This is usually from ignition not occuring, but the injector still firing like normal. I would check the plugs and wires first, see if one or 2 look different. The 3.8L has a bad habbit of burning plug wires.

Massey

 

This was my first thought also, replaced the plugs & wires with a (second) new set last Saturday with no change.

 

Look for bad grounds then. I believe the ground for the ICU are on the front driver's side of the engine.

Massey

 

Have you done a compression test? Exhaust valves that aren't seating well will cause a poor burn in the cylinder, and unburnt fuel would get blown out the exhaust. If it was an intake valve issue, you would be popping out the intake.

 

DTC P0300 (random multiple misfires) is either due to an ignition malfunction which affects all cylinders or a lean fuel mixture. If it was due to a single cylinder misfire, then the PCM would set a P030X code, X indicating which cylinder was misfiring. Being that you changed most ignition stuff now would be a good time to take a good look at the fuel system. Check fuel pressure, especially when engine is pulling hard, check the O2 sensors for proper activity.

A code P0300 may mean that one or more of the following has happened:

• Faulty spark plugs or wires
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector(s)
• Low fuel pressure under load
• Burned exhaust valve
• Faulty catalytic converter(s)
• Stuck/blocked EGR valve / passages
• Faulty camshaft position sensor
• Defective computer