• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

random misfire P0300, many new parts

M

MarkB

New member
Hello all, I hope you can help me with this mystery - I have a 1997 3.8 supercharged, all stock, with random misfire code P0300. Starts fine, idles fine. at approx 2300 rpm, feels as if it is starving for fuel, as it approaches 3000 rpm begins to misfire/backfire. Disconnected supercharger belt, no more misfire but won't rev over 2800 rpm, and of course, no power...

installed new AC iridium plugs & AC wires, fuel pump, fuel filter, fuel pressure regulator, MAF sensor, coil packs, ignition module...no change.
Was setting P0301 misfire #1 cyl consistently after those changes, swapped #1 and #3 injectors to see of misfire would follow the injector - nope. Misfire moved to cyl #2.... Original injectors with 175,000 miles. car was a daily driver for two consecutive wives (not mine) and has not been driven hard.

Auto-zone's free scanner yields this:
DTC P0302
throttle position 55.6%
RPM 2468
load value 32.5%
air flow rate 78.84 gr/sec
MAP sensor 153 kpa
short term fuel trim1 0.8%
long term fuel trim1 3.9%
short term fuel trim1 3.9%
short term fuel trim3 -96.7%
long term fuel trim3 -70.2%
speed 33 mph
fuel system 1 open
fuel system 2 n/a

I tried removing the spark plug boot heat shields, still misfiring.

Tried locking it into 1st gear, gently increased throttle up to 3300 rpm - about as high as it will turn without misfiring, held it there for about 1/4 mile - temp guage quickly shot up to almost overheating range.....cooled it off, tried again, same result. Between 2500 rpm and 3500 rpm, still feels like it's starving for fuel... I'm thinking it's running hot due to lean condition? or could the cat be partially plugged?

What could the problem be?
 


AC iridium plugs i bet thats the problem boosted cars dnt like iridium plugs well atleast i know the gtp doesnt my car did the same and seems like its kr which could lead to a blown motor or something going bad
 
I'd say run a compression check, to either point or draw the blame away from major internal damage and then go from there
 
I think I found the problem, dead cat.
inlet brick collapsed, most of the holes in the next brick/mesh are fused shut. Time for a new cat.
 


You must log in or register to reply here.
Back
Top