Stumped

arielleon90 · July 8, 2017

Changed out the fuel pump and still no fix. Idles rough and not alot of power on take off. It sounds like something is clogged but can't tell wat it is. The check engine light flashes only code that comes out is the p0300 random misfire. I'm just bout to give up on this truck.

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muddkatt · July 9, 2017

Misfire on two cylinders could be several things. Start by pulling all the plugs and comparing them. Run a compression test on all cylinders.

arielleon90 · July 9, 2017

Compression test has been done it was all good. The plugs also have been pulled n checked they were good as well. I'm thinking of just pulling the engine n dropping another one in

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Indyman · July 9, 2017

Vacuum problem? You've replaced and checked almost everything else.

arielleon90 · July 9, 2017

No vacuum problems that's the first thing mechanic checked. So far the fuel pump fuel filter have been replaced next up would be those 2 misfiring injectors n if that doesn't it fix it then who knows. Switched out the coils that were misfiring and problem was still there. Compression was checked as well and was good.

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arielleon90 · July 9, 2017

Guess what guys turns out it had nothing to do with fuel. I went outside to check out everything once again. Pulled the spark plug from cylinder 5 and 4 which were misfiring. Also pulled 2 and 3 to compare. 2,3,4 looked all the same but number 5 had some kind of build up in and around it. So cleaned it out and sanded it down a bit to see how the truck runs n voila no more hesitation or vibration from the engine. Drove it around the block to see if maybe it'll come back but it didn't and the engine light wasn't blinking. So this coming up Friday I will be buying new plugs for it but a.c. Delco these that it has on are autolites so no bueno. But that still doesn't explain the 40 psi from the fuel. So one problemo down more to go. Thanks to the ppl that gave me their input. Should've checked this before anything the mechanic checked them but only a couple n thought they all looked the same. Here's a couple of pictures of the spark plugs the one by itself is the one with build up the other is comparison to wat the other looked like

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arielleon90 · July 9, 2017

Looks like they decided to go cheap and put copper plugs

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muddkatt · July 9, 2017

Well we are getting there.....I still say check the compression, especially interested in the cylinders that show to be burning oil.

Check the fuel pressure again with the new pump, hell the gauge you are using might be off 10 lbs.

New plugs for sure, Denso makes the AC Delco plugs. Use the 5090 plugs: http://www.rockauto.com/en/catalog/chevrolet,2000,suburban+1500,5.3l+v8,1361517,ignition,spark+plug,7212

they are 4.33 each or buy them locally.

If the miss comes back, you can clean the plugs that are fouling and swap them with 2 from other cylinders. No need in replacing the plugs I recommended because they are good for a couple of 100,000 miles unless they get mechanical damage.

arielleon90 · July 9, 2017

Will be doing that this coming up weekend as I have run low on funds for the moment. What plugs should I run platinum or iridium?

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muddkatt · July 10, 2017

Will be doing that this coming up weekend as I have run low on funds for the moment. What plugs should I run platinum or iridium?

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Iridium, see post above for correct part number.

arielleon90 · July 10, 2017

Yes just saw that right now thanks

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arielleon90 · July 23, 2017

It's been 2 weeks n truck has been running smooth bought the spark plugs just haven't put them on yet. Got the stock muffler removed n got a flowmaster in place but since then there has been a ticking sound coming from the exhaust manifolds(stock headers I think thats wat they are called) on both sides. Wat could cause this?

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muddkatt · July 24, 2017

Look for broken manifold bolts, they are notorious for breaking and causing the tick/hiss.

arielleon90 · July 25, 2017

Look for broken manifold bolts, they are notorious for breaking and causing the tick/hiss.

But why would it make noise after taking the stock exhaust off? Will look into this thou thanks

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swathdiver · July 25, 2017

My truck is a 2009 and calls for 43.5 psi and the TECH2 says the pump is putting out 43 psi and no lights or any kind of problems.

Compression test is good but a leakdown test is more thorough. I once bought a performance car for many thousands less than listed price because of improperly gapped spark plugs.

As for the exhaust, you either didn't/couldn't hear it before or shifting the pipes around during the muffler install caused it.