03 avalanche 5.3 internal problems

**sportred04** · 03-28-2010

so my parents have and 03 avalanche with 125000 easy miles. my father was driving it in town the other day and it just started running REALLY rough. took it to a local family friend owned reputable shop. they put the scanner on it. missfires on all 8 cylinders. they pulled the spark plugs and all eight were soaked with gas. did a compression test. all were good except for one. no oil in coolant or coolant in oil. there pulling the heads on monday for further investigation. its kinda odd that all 8 spark plugs were soaked. he said it started doing it with out any warning. no sputter, shudder, shake. gas mileage was usual. any thoughts?

**wulfpack06** · 03-28-2010

something electrical im sure sounds really odd though

**sportred04** · 03-28-2010

sounds very odd to me. electrical sounds possible but the no compression is internal. either way there pulling the head to figure that out. the whole thing is very odd to me

**JESSEGOTTA GP GT** · 03-28-2010

It could be something electrical telling the PCM to give the engine more fuel, and its just choking out. I've never heard of 5.3's having any problems.... my dad had a 02 silverado that he hauled a trailer around to job sites for 6 years and sold it with 210k miles and ran like a top.....

**sportred04** · 03-29-2010

thats also what i was thinking bout the fuel. would the fuel not back off when the one cylinder isnt firing and just keep putting the same amount in. but none of this explains the one cylinder not having any compression. i thought it was odd when they called me and told me it was having problems.

**sportred04** · 03-30-2010

anybody else?

**JESSEGOTTA GP GT** · 03-30-2010

Think it might have to do with the fuel pump sending unit? maybe the pcm is telling it that it's priming, like when you first turn the key on?

**sportred04** · 03-30-2010

yea its possible. should no something later today. i think the low compression on the one cylinder might have been an after effect from the engine running at low RPMs and oil pressure being low. Hmmm.

**JESSEGOTTA GP GT** · 03-30-2010

That's crazy, them 5.3's are bullet proof. All my brother company trucks all have 250k+ miles and they beat the piss out of them.

**sportred04** · 03-30-2010

i o what you mean. my brother in law has a 2000 with 225000 that he uses for his construction company truck and it runs like a top. i think its just a freak incident. im still goin with it having low oil pressure from not running right. well find out

**sportred04** · 04-01-2010

so we found out that the problem was just a broken valve spring. got really REALLY lucky the valve didnt drop into the cylinder. dont no how it didnt but it didnt. the pcm was feeding the engine fuel to try to make it keep up with wat was being asked of it from the throttle. got it fixed and out the door for just under 500 bucks.