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99 silverado 4.8 multiple misfires


Wes.bond

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Ok so I've been trouble shooting this for about 3 weeks and still have yet to solve it.

 

My truck runs fine 50% of the time. Get cil when it starts to run bad. Take it to orileys / advanced/ and auto zone and all show that it's showing multiple misfires. Have replaced o2 sensors,fuel pressure regulator, fuel filter, spark plugs and wires. It doesn't seem to have a rhyme or reason for when it starts to run rough. Can be hot, cold, just started, running for 20 minutes etc. It will back fire occasionally. I have checked for loose connections, replaced an injector connector wire that had been butt spliced several times. I really don't know where else to look. I don't have a computer that will show real time diagnostics or I'd be able to locate what cylinder the misfires are occurring on and swap coils etc. I'm left to think it's either a coil or injector. Anything else I can check? I'm running out of ideas and cash. Thanks in advance

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Hmmm ... were the plugs oil, carbon, or fuel fouled?

 

I wonder if the 2 banks of coils are controlled by 2 different drivers? That would point to ignition if so, and plugs would be fuel-fouled.

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These things like to be in the upper 50's to 60 psi if I remember right. Tough to say if that's a real problem, or the gauge's accuracy is questionable. Would have to test the gauge to be sure. I don't trust any tools like that from auto parts chains. I could see them purposely selling gauges that read low, just to move fuel pumps or regulators. The way of the world today. Usually they won't even start when far out of specs. I hear there's a fine line too. Every vehicle is different though, so maybe this is your issue.

 

About your ignition: I wasn't suggesting your coils are bad - I was wondering if each bank had it's own driver. I just read that each coil has it's own driver these days, so that is out. Not sure what is common in the ignition on one bank, since all the coil primary wires head to the ECU.

 

About your catalytic converter: I was going to say in my last post that your cat is probably going to be smoked if you were finding heavy fouling on the sensors and plugs. If you live where they do not test for emissions, I wouldn't worry about it - could punch it out and leave the shell, or remove it altogether. If you live in a state that governs like mine does, your going to be out quite a bit of cash, if it is indeed bad. If your not getting either of the P0420,1 codes, then the cat is probably fine.

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Interesting! That's why I always say - nothing is a given in this line of work! No matter how long you work on things, you'll still get surprised ... especially with 21st century equipment. :)

 

Glad you got it fixed. :cheers:

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This may not be your problem ... but every time I've seen a P0300, it was due to leaking intake manifold gaskets. You're in that year range of the crap ones. An internet search on the issue will give you plenty of ways to check for that.

 

Shocked they made it this long, as most failed nearly 10 years ago. Maybe you're on your 3rd or 4th set.

 

With these modern electronic crapboxes, you really have to take some serious time to troubleshoot. You've just wasted $100's of dollars in unnecessary parts. That sucks. GM thanks you, and will use your hard-earned money to continue producing garbage for us suckers to purchase. :sick::(

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They look to be fuel fouled. I've pondered coil packs but all on the passenger side were fouled so I doubted al four coil packs were bad. I need to pull them again and see if here all fouled again or just 1 or 2. That is why I looked at o2 sensors. I'm also starting to wonder if my cat is blocked on the passenger side.

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Wouldn't leaking coolant be a symptom if there were bad intake manifold gaskets? I'm just asking because that's what I've been reading. I have zero issues overheating or with coolant leaks

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Not all the time. Just like a leaking head gasket doesn't always leak coolant either outside on the block, or into the crankcase.

 

My '00 Jimmy leaked air only at light throttle cruise (high vacuum). At idle or full throttle, the vehicle ran perfectly (low vacuum). Made sense in hindsight. I got so angry with that POS, I parted it out.

 

Wasn't until I yanked the intake manifold for a carburetor install (for my '89 S10 Blazer) that I found the actual cause of the code. The intake gaskets were physically trashed. Plastic framed gaskets. Total junk.

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What I did notice when I was doing all of this:

 

Cylinders 2,4,6,8 all had fouled plugs.

When I changed o2 sensors I found that bank two sensor two was the worst. Bank two sensor one was not great.

Bank 1 sensor one and two looked fine.

 

After replacing plugs wires and sensors I found a wire harness by the Ecu that was unplugged. I plugged it back in and then rewrited cyl 2 injector wire and plug.

 

When the truck starts to run rough it will get to the point it's hardly running at all. Constantly stalling and half power. I threw in a cleaned up old o2 sensor in bank 2 sensor 2 and it ran like a champ for about 10 minutes then reverted to running rougher.

 

Should I be looking at cleaning injectors?

I want to set fire to this truck.

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