2002 Silverado Mis-fire at idle???????

[Dbrasco]

Hey I have a 2002 Chevrolet Silverado with the 5.3 L (120,000) miles. Truck has a mis-fire at idle when it's in gear. I have replaced the fuel filter and it did not help. Has anyone had a problem like this and if so what was the fix? Thanks

[67ChevyRedneck]

Plugs, wires??? Bad coil pack? Any SES lights?

[Dbrasco]

Truck is not throughing any engine codes, check engine light is not on. Plugs were also replaced in the last 30,000 miles. Was thinking about replacing the wires but I wanted to see if anyone else had run into this problem. Thanks

[truckdude239]

what kinda of plugs did u use? and how where they gaped? these trucks run a platinum plug that you don't gap using a normal gaping tool gap should be set to .060 if gaped wrong you can mess up the platinum tip causeing a miss fire

[Dbrasco]

Hey, I used the same plugs that were removed from the truck. I gapped the plugs per the spec under the hood. Thanks for the info.

[Josh]

Does it misfire under a load like up a hill? If you hold the brakes in gear and lightly load up the drivetrain with the gas pedal does it miss worse?

Josh

[oz's74 project]

noticed that my 04 has slight miss only noticeable at idle.

[truckdude239]

i've noticed most of the 5.3 s and 6.0 that come thought my shop have a slight miss at idle

[Dbrasco]

If I stall it up it does not mis. At idle in gear and sometimes when I am taking off. Plugs have 30,000 miles on them and they were the same plugs that were removed. I have also replaced the fuel filter but I did not expect that to fix it. I'm leaning towards LS1 plug wires, fuel sending unit, fuel regulator. I have also read something about fuel injectors. Still thinking about it. It would be better if it were throwing a code. Thanks

[DirtyLarry]

A stumbly idle is indicative of fuel injectors not firing cleanly especially when it clears up under load. You may want to run several injector treatments though it and if that doesn’t clear it up then pony up for 8 new injectors.

[Dbrasco]

That's what I was thinking. I will try some injector cleaner and see what happens. Thanks

[truckdude239]

take it and have a full fuel system cleaning done. i know my shop does it for 59.95

[Dbrasco]

Ok I'll look into that. Thanks

[LEEVON]

If you suspect the injectors then a cheap start is to removed them and soak them overnight in Seafoam. Some guys have done that with success. You could also take it to a shop for a fuel system cleaning as suggested (not sure what they do there) or send them off to a injector cleaning service such as:

http://www.witchhunter.com/index.php4

Wonder if a bad coil pack could cause this also?

[Dbrasco]

Up-date on mis-fire. Bought some stp injector cleaner and added it with a full tank of gas. Removed all the plugs and checked the gap, they were good at .060. Removed the plug wires and ohm-ed them out. They were between 388-450 ohms. Tighten down the intake a little. Truck is now running good and I have not noticed the mis at idle as of now. Will see what happens next....

[truckdude239]

you tighten the intake manifold???? i would be looking at a new intake gasket set asap

[Dbrasco]

If it starts missing again I will look into that. If I was wanting to install a 6.0L from say a 2005 could I use my ecu, trans, etc or would I have to use the ecu that the 6.0L was removed from. Could the ecu from the 5.3L be flashed to except the 6.0L. If I installed a 6.0L it would get a bigger cam and maybe a different intake (lsx). Also long tube headers. I would like to put electric fans on this truck and get rid of the fan/shroud. Any info would be great about a 6.0L conversion to replace the 5.3L. Thanks

Here are a couple pictures of the 2002 and another project that i'm working on. It is a 71 cheyenne 10. Picture of the truck complete is before I started and picture of the truck stripped is what it looks like now. I'm converting a lwb into a swb.

[LEEVON]

nice trucks man. Are you gonna keep it orange/white?

My wife's 02 Tahoe had an intake gasket leak, apparently they are common at around 100K...caused really bad idle when cold, missing and poor mileage. But it threw several codes that's why I didn't mention it before with yours. The gaskets are expensive (revised GM green gaskets), throw in the other stuff and your looking at about $200 but it's a simple job.

[Dbrasco]

I'm going to see how it runs for a couple weeks to see if that really fixed it. I did'nt want to start replacing stuff until I figured out what was really wrong. As far as the color on the 71 i'm not sure. I like the factory orange/white but I was also thinking about red. Not sure yet. I'm going to start a build thread for the 71 in a couple days. Thanks...

[truckdude239]

you would have to use the 6.0 computer but other then that i think everything else is the same

[justcuz]

I had a guy tell me it was the TPS. I have the same miss, just at idle in gear, runs smooth at speed or loaded. Oil stays clean but uses a quart between changes. Also has minimal coolant usage, maybe a pint between oil changes and the tailpipe has gotten darker. Used to be tan, now dark. I'm thinking the engine is running richer (TPS). Has not negatively effected fuel mileage much maybe 1 to 2 mpg overall. Plugs cleaned and regapped recently, need to check plug wires.

[Dbrasco]

Thanks for info on 6.0 computer. Also thanks for the info on the TPS. Seems like i've seen several guys with this problem and a couple different fixes. Thanks again.....

[truckdude239]

if your using antifreeze look at the intake gasket to be leaking sounds liek your getting to much air in. these trucks are bad about intake gaskets leakin

[bwood]

Originally Posted by truckdude239

if your using antifreeze look at the intake gasket to be leaking sounds liek your getting to much air in. these trucks are bad about intake gaskets leakin

The Gen III LS engines do not have coolant running though the intake. The intakes on these trucks are prone to air leaks but not coolant leaks. What is common on these engines for coolant leaks is for the water pump to leak where it mounts to the block. Most of the time it is just gaskets (although, if you take it to a dealer, you will pay $600 for those gaskets to be replaced but the good news is they throw in a new pump for free). It will leak a small amount over time and is more pronounced in the cooler months when the temp swings are much bigger.

The engines with that are prone to intake coolant leaks are the Gen I Vortecs (96-02 OBS Trucks and vans).

As far as using a 6.0 in a 5.3 truck, you can have your ECM reprogrammed/tuned for the 6.0 and also have some of the GM "torque managment" or whatever it is called programmed out. If you use the ECM from a 6.0 truck, it will have to be reprogrammed for the trans (the 5.3 used the 4L60E and the 6.0 will use a 4L80E), gear ratio and still need to be tuned for the best performance.

[Dbrasco]

Thanks for all info on the GEN III engines. Looks like I could go both ways with the computer just depends on the tune afterwards. This is very good info. Thanks again Dbrasco