PO300 Misfire Code

[Lost Hog]

I have had a problem with my wife's 98 S10 Blazer 4.3L for a year now and have done everything to my knowledge to fix it.

 

Here is the problem, When accelerating,passing or going over a bridge it starts to run rough and stalls. If I pull off the road and let it sit for a min or two it starts up fine and runs well until I need to pass again.then same thing. The code its throwing out is PO 300 (random misfire) We have already replaced:

Plugs,Cap,Wires roter,ECM module,camshaft sensor,crankshaft sensor,Fuel Pump,Fuel Regulator, Fuel Filter, MAP, Idle control valve, Catalyst, Fuel pump Relay, Fuel Injectors have been serviced twice,

 

Could it be the PCM It seems like the fuel system cant adjust properly when under load or cant recover from it...Iam really lost

 

I dont know if its connected but when we fill it with fuel it smells of gas fumes quite a bit until it goes down about 1/4.

Thanks Gary&Sherri

[SONOMA 4.3]

I have a remedy for the po300 code.

Most have answers, no reply with results. I have a 1996 GMC Sonoma with 115,000 miles.

I have read so many posts on the multi misfire code PO300 and probable cause. Fuel injectors always seem to get the blame.

What I have found is it's the distributer. The gear wears out and you get some up and down play in the shaft.

For $89 i bought a reman and all my codes are gone and the truck runs like new.

Wish I had taken pictures of the distributer gear to show how bad it was worn. hope this helps someone, because I know it was a pain in the butt to diagnose.

[Lost Hog]

The P0300 doesn't help much in this case.  You already know it's missing and running rough and that's all the code tells ya.  It doesn't help narrow it down to what is causing it.  Sounds like you replaced just about everything!

 

Lots of EGR problems with those, but none of the conditions you have to meet to make the problem occur really  doesn't fit a stuck open EGR.  And, once stuck with a piece of carbon like they do, shutting off for a few minutes and restarting doesn't clear it out.  Still, it's something to look at.

 

I highly doubt the ECM/PCM is involved in this problem, but anything is possible.

This needs to be driven with a scanner on it that can capture all the engine data when the problem occurs to see what's going on.  Probably only a dealer will be able to do that.

 

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Thanks for taking the time to respond.

[GM-Tech]

The P0300 doesn't help much in this case. You already know it's missing and running rough and that's all the code tells ya. It doesn't help narrow it down to what is causing it. Sounds like you replaced just about everything!

 

Lots of EGR problems with those, but none of the conditions you have to meet to make the problem occur really doesn't fit a stuck open EGR. And, once stuck with a piece of carbon like they do, shutting off for a few minutes and restarting doesn't clear it out. Still, it's something to look at.

 

I highly doubt the ECM/PCM is involved in this problem, but anything is possible.

This needs to be driven with a scanner on it that can capture all the engine data when the problem occurs to see what's going on. Probably only a dealer will be able to do that.

[95Sierra2500]

What brand of cap and rotor did you use? My fiancee`'s '99 Jimmy (basically the same truck) we discovered doesn't run well on anything but high-quality parts (in this case, at LEAST AC Delco replacement parts). Cheap replacements from Autozone or Advance won't do the trick.

 

Also, what brand of catalytic converter did you replace your stock one with? If you also simply got the 'universal' replacement from a local auto parts store, then it might be the wrong size. This is a lesson I have also learned from my fiancee`'s truck. The only good thing about it is that this universal converter has a lifetime warrenty, and I've already had to replace IT twice. I might suggest taking it to a shop and having a slightly larger catalytic converter installed.

 

Also, by 'serviced,' what exactly do you mean? The fuel injectors on these trucks really have one problem, the poppet nozzles at the end. They can stick either open or closed. If they are stuck closed, then servicing the system will clear up the problem (I recommend that they use the 'top engine cleaner' over anything else). However, if they are stuck OPEN, then no amount of cleaning or servicing will fix the problem unless the nozzles are replaced.

 

Just some lessons I've learned over time. Oh, GM also knows that this fuel injection system has serious problems, and last I knew if the vehicle was built for/sold in California originally, it came with like a 10 year/200,000 mile warrenty. The rest of the nation has to pay for it out of pocket.