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2002 silverado 1500 5.3l Misfires

So this is gonna be long and I will do my best to explain without confusing. So I have a 2002 Chevy Silverado 1500 5.3l vin t with 127000 miles on it. It has been randomly misfiring for 2 months now. It all started as a cylinder 2 misfire and was so random and sporadic and only really happened after the truck was one and I accelerated hard I didnt think much of it but tried to fix it anyways. Well after a couple unsuccessful attempts It eventually became a misfire on all of bank 2 and was getting consistent but it never misfire at idle so I kept working at it. Now it Misfires on cylinder 6 and 4 at idle cylinder 6 being the worst. At 1000 to 2000 rams Cylinder 4 becomes worst then 6 all the while 2 and 8 might read 1 or 2. Once you rev it up to 2500 rpms or more Cylinder 2 becomes the worst and cylinder 4 and 6 start to get a lot better and 8 stays around 1. Once you let the rams down to idle it starts idling rough and sometimes cylinder 5 will start misfiring for a cycle but then it will stop. I have literally replaced and tried everything I will list everything I replaced in the order I did it just hoping someone can tell me something I didnt think of.

Spark plugs and wires
ignition coils
intake gasket
TPS Sensor
MAF sensor
Camshaft sensor
Crankshaft Sensor
Fuel regulator
o2 sensor
Ohmd all the wires
Fuel Pump
Fuel Filter
Throttle body gasket
Fuel rails
Wiring harness for injectors
The crossover fuel line in top of intake
Spark plugs and wires again (they were fouled)
Intake gasket again (overnighter it and smashed the gasket)
Intake manifold
Checked the lifters none were sticking and moved like they should
Scoped out the pistons they were all good except minor oil residue on cylinder 6.
And i think thats it other then checking for vacuum leaks and replacing various o rings.
The truck had all new fuel lines 3 months prior went through and checked them all anyways the fuel line into the rails had a bad clip and o rings so I replaced it still nothing.
As a side note 90% of those parts were all failing or bad upon removal and yet it still misfires.
My buddy has an HPTuners so we checked everything through there very thoroughly. We are both at a complete loss. Also I know about checking the head gasket but so far the engine doesn’t overheat and no coolant has gotten into the oil so we are pretty sure thats okay. Also checked the cat and it appears to be functioning normally.
Other then that we checked endlessly for fuel leaks and vacuum leaks and have come across a few and have fixed them all but still no luck.
So any advice I can get will be highly appreciated. Also as a side note the truck doesn’t have an egr didnt have one from factory I bought it off my friends dad eho has been helping me who bought it new 18 years ago.

Sound like you need to go back to the basics.
Did you run a compression test? What were the results?
Have you hooked a vacuum gauge to the engine while running? What were the readings?
You replaced plugs a 2nd time because they were fouled. Fouled with what? Oil? Carbon?
What error codes have you been pulling from the truck? Pxxxx what?

haven’t run a compression test due to the variation in the misfires we don’t think its possible. we haven’t hooked up a vacuum gauge yet will have to try that. And the plugs were burnt out on bank 2 bank 1 were fine. and I’m just pulling an p0300 code for multiple random misfires. we are going to check all the wiring again from the computer to all the sensors.

That is completely incorrect. Pull the spark plugs, open the throttle body, insert the compression gauge and crank the engine. If you don’t know how to run this test, go to Youtube and watch a video or 2. You are wasting your time and money if you don’t run this test.

Same advice for a vacuum test. Google it, watch a video, report what you see on the gauge.

What in the world do you mean by “plugs were burnt out” ? Again… oil foul or carbon. Google that as well for pictures.

You are spending a LOT of time and money on this without doing the basics like a compression test and vacuum test.


Agreed with Muistangman; compression test is Step One. Or should have been after a check with a vacuum gauge.
The vacuum gauge can be connected in seconds and will tell you something instantly.

I’m having a hard time believing that 90% of all of those parts were dead or dying. The fact the plugs were fouled should have told you something and I have a feeling once a compression test (both dry and wet) are performed you are going to feel pretty low about spending all of that money and time.


well we are gonna run a vacuum and compression test tonight. And it was more of a carbon build up on the plugs. And no a lot of the parts were worn out cracked or threw a code as well. And I’m not worried about the money most of the parts I got were upgraded parts.

Sounds like you have an exhaust restriction on bank 2. Check the manifold vacuum at idle and at a steady 2500 RPMs, the vacuum should increase with engine speed.


Shouldn’t it decrease as the throttle is opened?

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should increase as the throttle opens and the exhaust is good compression came back good and vacuum was good checked them all

Manifold vacuum should drop to zero when the throttle is opened abruptly; assuming the gauge is tied into manifold vacuum and not ported vacuum.

So what was the manifold vacuum reading at idle? It should be around 20" with a rock steady needle.

And what are the compression numbers. Countless people have come onto this board with allegedly “good” numbers and the numbers they provide are anything but that.

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