04 Silverado 4.8 random missfire

[Daphatdub]

So to start off I'm totally new to online posting so please excuse me if I do something wrong... I have a 2004 Silverado that I can not seem to find a solution for my problem. A little history on it. I d never driven the truck b4 it came into my possession but was told it was a good runner... it sat from there for another 2 years. I gave it a jump and she started right up. When driving to gain data for the etest I notice a bad vibration depending on deceleration or around 2000 rpm light throttle, wot there's slight hesitation but it moves pretty good, no missing noticed. With the missing at 2000 rpm or deceleration it shows a p0300 random missfire, with a scanner it shows 1568 cylinders with hundreds of Missis in the histories but none ever current. Since than thanks to a lot of reading on here (thanks) I've checked what I think is everything to do with this problem. Cleaned and added grounds new plugs wired intake gaskets swapped around and cleaned injectors and coils 2 new 02 sensors... I ve had it by a very good local mechanic who checked it out without really any conclusion. Apparently it has tune on the computer so trying the crankshaft relearn was not successful... what now ? I'm in the gta area Toronto if anyone specializesees in this and is Mobil with a tech 2 please reply !!! Anyone else that has even a suggestion please do any help at this point would be awesome.

[rdnkcpa]

How old was the gas in the tank? If it sat for 2 years, did you drain the tank and put fresh gas in? Did you check fuel pressure? Compression on all 8 cylinders? Mileage on truck?

 

If you have new spark plugs, & intake gaskets, and sure you have spark on all 8, that leaves fuel and compression.

 

Find a trouble shooting guide for P0300. Lots of variables with P0300.

[txab]

^^^^^^ +1

[Daphatdub]

Mileage is just under 200000, I ve done a compression test with results being 170 ish I just did a leak down test and it's with in acceptable limits. I had the valve covers off and no signs of the Cracks or coolent

[Daphatdub]

I got a computer from the scrap yard and want to try it out but I'm unsure of what is required by the dealer or if other scan tools can be used to link the new computer to the key or Vin whatever it is. But once that's done I be leave I could do the case relearn and see what happened there

[rdnkcpa]

Fuel pressure?

[anumber1]

I just noticed you said you "Swapped the intake gaskets around".

 

Does this mean you reused your gaskets or installed new ones?

[Daphatdub]

Oh thanks... no excuse me that should had a , maybe. New gaskets have pressure tested the intake it's good. I swapped around the cops and injectors. No matter what I do the missing stays with the cylinders 1 5 6 and 8. I find mixed opinions about changing the bcm at home, is this possible ???

[Daphatdub]

I'm good with the mechanical stuff. Spelling grammar and type talking to people not so much! Please excuse my fat numb fingers and lazy English

[Daphatdub]

Sorry rdnkcpa... the fuel pressure was checked at the rail and each injector was run with a snap on scan tool. The fuel trim is plus 5ish to -10ish

[rdnkcpa]

Another thing I thought of, since it was sitting for so long I'd clean up all the grounds as well. Corrosion on the grounds can cause problems as well. I'm out of ideas if your fuel pressure is good and each injector is firing on command.

[Daphatdub]

Yaaa that's it I'm just plain outta ideas tooo... yup cleaning testing and adding grounds all done.

[Daphatdub]

So ... FYI it was a crankcase variation relearn that solved the misfiring problem. The first to mechanics who try'ed it were unsuccessful because they were not doing the procedure correctly. The right guy with a tech 2 ... 5mins later it runs like a dream! Thankyou Scott@ Georges garage here in Markham