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1999 Chevy Tahoe 5.7. Just put in a rebuilt engine with new

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plugs, wires, cap, rotor, and...
1999 Chevy Tahoe 5.7. Just put in a rebuilt engine with new plugs, wires, cap, rotor, and injectors. Runs good when cold but when it warms up it misses and throws a P0304 code. Replaced the # ***** plug and wire but still does it. Old engine overheated and blew head gaskets then sat around for 10 months before I replaced the engine. Could it be o2 sensors or is it injectors or what else could it be?
Submitted: 2 years ago.Category: Chevy
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9/15/2015
Chevy Mechanic: Jerry Newton, Chevy Technician replied 2 years ago
Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4,831
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Injectors are problematic on these engines, so much so that GM redesigned the injection system. You can replace it with the updated parts, it's a chunk of money to do so, though.

It's NOT oxygen sensor, MAF sensor, MAP sensor, or anything like that. None of those things can affect just one cylinder.

You can technically test these injectors if you have a high end scan tool and a fuel pressure gauge. The scan tool test allows the technician to measure the precise amount of pressure drop in each injector, and by comparison, you can see if #4 is failing to contribute. Anything short of this diagnostic procedure is simply guess work.

Techron is a fine product, endorsed by GM, for cleaning these injectors. I would put a bottle of that into the tank and just drive it for a few hundred miles to see if it improves. If not, then more diagnosis is needed. But don't overlook conventional causes: vacuum leak, low compression, burned valve, etc.

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