Misfire HELP

[Raptordude]

Hi guys, my 2001 Silverado 2500HD with the 6.0 and 4l80e started misfiring this morning. The service engine soon light is flashing. The motor runs, there is no metal on metal type of noises, just a misfire. The spark plugs and wires were done at 100k currently at 117k and I checked that the boots are snug on the plugs and they are.

 

What could cause this? A buddy is coming in a little to pull the codes, just figured I'd get it out there in case we don't have any luck.

 

My guesses are

 

-crank position sensor

 

-cam position sensor

 

-knock sensors

 

What do you think?

 

 

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[dewfpo]

Depending on the code, if it's a single cylinder misfire, swap the spark plug and wire with another cylinder and see if the misfire is still there at that cylinder, if it is, then you likely have a bad ignition coil or coil wiring, or a sticking fuel injector. If it's a random misfire code then it could be a vacuum leak, low fuel pressure issue, or possibly the crank sensor.

 

We'll know more when the codes are read.

 

DEWFPO

[Formulabruce]

Crank sensor "Dirty" IMHO.. good luck!

[Raptordude]

Well my buddy plugged in, and as these things go, the problem magically disappeared. It did say "misfire detected" but it was the generic P0300 code, it didn't specify a cylinder.

 

I drove the truck about 20 miles to get some work done and didn't have an issue.

 

I'm hoping it's the crank sensor, I will probably order an AC Delco one and get rid of the advance auto cheapo one that's in it now.

 

The crank sensor is by far the easiest to replace between the cam sensor and knock sensors

 

I can check the fuel pressure but I just put in a brand new fuel pump and filter a year ago so I doubt it's that

 

 

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[Raptordude]

When I put in the new crank sensor last year, I did NOT re-learn it. So doesn't that mean it can't be the crank sensor? Because I think since I didn't re-learn it, it wouldn't know to throw a P0300 misfire code

 

 

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[Swimmer8366]

I would start with relearn. Than go from there.

 

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[Raptordude]

I'll try that and see what happens. Can the knock sensors cause this?

 

I really don't think it's fuel related, and the plugs/wires/coils are good. I'm betting it's either the crank or cam sensor

 

 

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[dewfpo]

A bad knock sensor can cause the ECM to pull ignition timing and in some cases maybe even add fuel but I doubt it will cause a misfire.

 

DEWFPO

[Raptordude]

Ok thanks, I'm hoping it's not them

 

 

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[Raptordude]

Truck acted up again this morning. I put in a new crank sensor, but it seems to only do it in the morning. I'll start it up tomorrow and see what happens

 

 

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[Raptordude]

Problem is still there with the new sensor, I'm going to have it re-learned

 

 

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[Raptordude]

For anyone still reading this, re-learn did not solve the problem. I put in a new CAM sensor now. Seems to be ok so far but we'll give it some time

 

 

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[Formulabruce]

If it cant be isolated, could be Throttle plate and area dirty. I have had this cause similar issues

[Raptordude]

Could the MAF cause this? If it can, if I unplug it and it gets better, that means that's what it is right?

 

 

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[Raptordude]

My 2001 Silverado with the 6.0 is misfiring. It seems to do it on a cold start only. If I shut it off and restart it twice, it will be fine the rest of the day.

 

Here is what I did so far:

 

-fuel pump

-fuel filter

-crank sensor

-cam sensor

-crank re-learn

-fuel pressure regulator is good

-plugs and wires done at 100k, currently at 117k

-unplugged MAF while it was misfiring and no change

 

Where can I look next? I'm getting fed up with this

 

 

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