Random Cylinder Misfire

[98chevy2500SS]

For some reason, my truck is having a random cylinder misfire, on the Vortec 5700. Had it scanned and gave me the P0300 code.

Just replaced the injector spider about a little over 2 years ago.

Checked the fuel pressure and would stay at 52 psi idling, and runs like crap. Doesn't sound right.

Would the fuel pump be causing this? I am going to try a fuel filter tonight to see if that is getting plugged.

I really want to drive my truck badly, but I can't with this horrible mess.

 

[east302]

Factory spec is 60-66 psi with ignition on, so it would be worthwhile to swap out the filter...could be a restriction causing the pressure drop.

Does the pressure hold when the ignition is turned off?


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[98chevy2500SS]

Yes the pressure does hold.

Just replaced the filter now and didn't make it any better. We are beginning to think it is my cracked cylinder head - cylinder 4. I will replace that soon and let you guys know how it went, might be a while though.

 

[Blaine Cornelius]

Yes the pressure does hold.

Just replaced the filter now and didn't make it any better. We are beginning to think it is my cracked cylinder head - cylinder 4. I will replace that soon and let you guys know how it went, might be a while though.

Did you change your distributor cap? These are notorious for failure. spark jumping through the plastic aftermarket caps causing all kinds of stupidness. Causes same symptoms described.

 

[98chevy2500SS]

Yes I did that too, put a brass one on, instead of the plastic, which I had on previously. Still didn't work.

I did get new ACDelco plug wires a while ago.

 

[Blaine Cornelius]

Well crap brother... I hope you trace it down. I doubt you are having issues with only one cylinder though with the multiple misfire code. It's gotta be something dumb. Have you checked your O2 sensors? Those will cause the funky misfires too


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[Blaine Cornelius]

Just saw your 52 PSI statement. I've seen these trucks not run at all at 49. I'm going to say it's your fuel pump. Mine always check between 56-60.


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[CoolDude1975]

For some reason, my truck is having a random cylinder misfire, on the Vortec 5700. Had it scanned and gave me the P0300 code.

Just replaced the injector spider about a little over 2 years ago.

Checked the fuel pressure and would stay at 52 psi idling, and runs like crap. Doesn't sound right.

Would the fuel pump be causing this? I am going to try a fuel filter tonight to see if that is getting plugged.

I really want to drive my truck badly, but I can't with this horrible mess.

I racked my brain for months trying to figure out what was causing my random misfire because I had just done a full tune up on it and it turns out that my distributor cap had failed on me. I can almost guarantee that it's something simple like that.

 

[CoolDude1975]

I racked my brain for months trying to figure out what was causing my random misfire because I had just done a full tune up on it and it turns out that my distributor cap had failed on me. I can almost guarantee that it's something simple like that.

Your best bet is to get access to a higher end scanner that allows you to view the diagnostics in real time. That's what I did with mine and found that my number 6 cylinder had missed thousands of times and then I had a general idea of where to start.

 

[TruckinAin4Sissies]

I had the same exact problem. It is without a doubt your distributor drive gear.
Check my profile, I posted some pictures and details on how I replaced it with a MSD one.

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