Miss fire at # 5 cylinder only under load

[[email protected]]

Thanks for the luck I think I am going to need it.
New msd dist, coil, and wires. Did find that the new Msd coil was bad and replaced with a good one.
Keep you posted, Hope only a matter of time before I find why.

 

[L31MaxExpress]

There was a thread here sometime back about a distributor getting out of kilter under load. I think it was a bad bearing or something and the truck would run rough when under load but at no other time. I wonder if you don't have early symptoms of that issue. I have no idea how you test for it but surely someone will have an idea. Good luck!

I had one that the drive gear became knife edged. It would misfire at highway speeds at light throttle.

 

[stutaeng]

Are you getting a code? I've got a basic Innova 3100 scanner that gives freeze frame when codes are set...things like engine RPM, speed, fuel trim data, MAF information,stuff like that.

You need more information to properly diagnose the problem.


You may need a better scanner with live data and needs to taken for a drive to look at data.

 

[Gary Mettus]

I had the same issue in a different car but did the same things you have done to track it down. I thought to myself no way could it be the spark plug, didn't look any different than the others and they are 100k mile iridium plugs with only 40k miles on them. Well, it was the plug.

 

[Gary Mettus]

I had the same issue in a different car but did the same things you have done to track it down. I thought to myself no way could it be the spark plug, didn't look any different than the others and they are 100k mile iridium plugs with only 40k miles on them. Well, it was the plug.

What really threw me off was it only happened under load, I could rev the engine out of gear and not a blip.

 

[semperfi]

Replace distributor cap. Check youtube videos on this problem. Use A/C delco.

Sent from my SM-G930R4 using Tapatalk

 

[stutaeng]

OP mentioned new spark plugs, and checked distr. rotor... You always swap plugs to make sure if problem persists, though.

 

[Erik the Awful]

It's specifically the #5 cylinder, which means it's secondary ignition, fuel injector or wiring, or a mechanical issue. The plugs, wires, and injectors are new. You said you checked the distributor cap, but didn't replace it. That's where my money's at.

 

[lxe4]

i chased this kind of thing around the ignition and fuel for a couple years once. intake gaskets fixed it. One clue would be the misbehaving cylinders spark plug getting ashed up from the oil its sucking in from the lifter valley. My oil consumption also reduced to a manageable level, mind you it had been leaking for a couple years slowly getting worse.

 

[stutaeng]

That's a good point lxe4. Maybe OP should perform a vacuum check?

I just checked my k3500 because I had a lean code and suspected intake leak or vacuum leak. However, vacuum test indicated normal vacuum.

The test is so simple yet gives so much information about the health of an engine... I'm not sure why a lot of people like me didn't know about it.