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2003 chevy 6.0 wont idle and backfire through the intake?

bigbadchev84

bigbadchev84

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So I just picked up a 2003 chevy 3/4ton 6.0 about a month ago for a work truck. I drove the truck about 150 miles round trip today never an issue or a hint of one.

I was at the shop grabbing some parts and left the truck running outside for 10 minutes. I was walking back outside when I heard the truck stumble and sputter then it died. It has over 1/2 tank of gas in it. I went to re-start it and it took longer to crank before it fired up, then it runs really rough a couple seconds and dies.

It will stay running if I give it throttle, but it is slow to respond. I replaced the fuel filter and fired it back up and same thing, I revved it up a couple times and it is backfiring through the intake now. Is there anything I should be looking at? the only codes it shows is a p0300 random misfire.
 
How many miles on the engine? Assuming that no one caught you not looking and swapped a couple of plug wires, it sounds like it jumped time.

I would pull the distributor cap and check for a bad rotor, cap, carbon tracking, and if the distributor body will turn in the block.

But it really sounds like the timing chain jumped a tooth.
 
if its a 6.0 it wouldn't have a distributor, but it could have skipped a tooth on the timing chain. That or something happened to the cam sensor.
 
First, test fuel pressure. Second, ask this question over on ls1tech.com. If its not fuel related, im betting it pooped a cam/crank sensor.
 
I would be checking fuel pressure or suspecting a cam or crank sensor issue but those three items should drop more codes than just a P0300. However, sometimes when low fuel pressure it takes a bit before the lean bank1, lean bank2 codes appear. A timing jump is possible but I have my doubts.


Fordum said:
I would pull the distributor cap and check for a bad rotor, cap, carbon tracking, and if the distributor body will turn in the block.
Click to expand...

That is good one. Like checking antifreeze in a Corvair :haha:
 
[quote
That is good one. Like checking antifreeze in a Corvair :haha:[/quote]

Ahh, its what I get for just skimming the post. Didn't notice the year, barely noticed the size.
I saw backfiring through the intake, and went straight to a loose dizzy.

And, hey, nothing wrong with checking for antifreeze in a Corvair........If you find some you know you really got problems........:D
 
Would low fuel pressure cause backfiring through the intake? if it is a crank or cam sensor are they plug and play or do they need calibrated?
 
bigbadchev84 said:
Would low fuel pressure cause backfiring through the intake? if it is a crank or cam sensor are they plug and play or do they need calibrated?
Click to expand...

Yes, a lean pop through the intake. Sometimes it will even blow out the safety plug in the intake that is there for this reason.

The crank sensor has a relearn process but even if you don’t relearn the ECM after a sensor install, they will eventually figure things out after enough key cycles.
 
Different car, but I kept getting a random misfire with my dads car a few years back, ended up being a bad coil pack.

And yes, when the fuel pump on my TBI engine went low on pressure, that was a major thing that it would backfire through the intake and get real sluggish with throttle.
 
It's possible for it to jump time, but a more likely cause is something to do with spark or fuel. Potential causes include a bad coil, wire, or plug, or a malfunctioning injector. When the LS2 in my Corvette broke a valvespring, it threw a misfire code and idled poorly. Of course with that one the computer was able to easily pinpoint the cylinder, since it was happening constantly.

Faulty crank/cam sensor could cause similar problems, if the cam sensor fails completely, the engine should still run, but not real well. If the crank sensor completely craps out, it won't run because it will have no reference to establish timing. Each of these should have unique codes, but if they are just having intermittent errors, maybe not.

Good luck on tracking down the problem. Start with the easy and obvious first.
 
Well I was able to mess with it for just a bit between jobs yesterday. Fuel pressure with key on engine off was 54lbs engine running was 56lbs. I did notice a ticking or clacking in the passenger valve cover. I am gonna try to get it to my shop tonight and take a look under the valve cover and see if something is broke.
 
bigbadchev84 said:
Well I was able to mess with it for just a bit between jobs yesterday. Fuel pressure with key on engine off was 54lbs engine running was 56lbs. I did notice a ticking or clacking in the passenger valve cover. I am gonna try to get it to my shop tonight and take a look under the valve cover and see if something is broke.
Click to expand...

Ticking or clacking is often a symptom of rocker arm issues. A rocker arm that is loose enough won't actuate the valve properly. Mine made a clacking sound as well when the spring broke, because the rocker was bouncing around. Definitely pull the covers. I thought a broken spring would be the last thing to happen on mine (stock cam/valvetrain), but sure enough...
 
Well time to update this. I got the truck hauled back to my shop, I put the fuel pressure gauge on it again and this time it was only 48psi. Went and bought a new delphi pump for it and got the tank dropped. The previous owner had already been there judging by the orange and blue wirenuts to splice the cheapo fuel pump harness into it.

Got everything put back together and it ran marginally better, and by that I mean it ran like crap, but would hold a violent idle. I pulled the passenger side valve cover and found a broken intake valve spring.

Went down to the local machine shop and ordered a new spring for $5 plus the $10 shipping. I was able to replace it without pulling the head luckily. Got it all put back together and it now runs great.
 
Called it! The least likely culprit strikes again. I wonder if there's a trend of these 6.0s breaking valve springs.
 
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