Scratching my head on this one.
97 GCV, 199K miles

P0300 / Random misfire.
Probable cause;
-Ignition system fault (plugs, wires, coil)
-vacuum leak
-injector fault
-high or low fuel pressure


Shudders and back fires if you get on the gas too hard.

I have replaced;
-Spark plugs (Wires look good)
-Vacuum lines that looked bad
-PCV valve and hose
-Up-stream O2
-and today I replaced the fuel pump assembly (pressure regulator) with one from a GCV that I scrapped out.

The fuel assy that I removed looked to have a new pressure regulator already on it.
The locking clip for the fuel pump wires was broken so I suspect the pressure regulator was replaced not to long before we bought it.
The previous owner said it had thrown a serp belt and damaged the camshaft sensor, and he had just replaced it.
The van also came with a spare coil pack. It would run for a while and then die. He replaced the coil pack, gave up and sold it to me. I replaced the crankshaft sensor and fixed that problem.

This random misfire is bugging the crap out of me!
I'm waiting for the engine to cool down and I'm going to inspect and clean the EGR system.

I just can't believe there is a problem with an injector because the DTC didn't point to any one cylinder.
I was sure it was too much fuel pressure, but on the way up to refill it with gas, the misfire returned 100' out of the driveway.

Any suggestions?


Thanks,
PinCup

 

Cross wires, EGR, bad cam shaft, push rods on the rockers or broken rocker tower. Just a few.

 

Update;

Today I replaced the intake plenum and all it's parts.
TPS, intake air sensor, EGR, idle control, throttle body.

It has fixed the misfire.
Not sure which part was the fault, but it runs better so I'm not going to lose sleep over it.

Thanks MT,
PinCup