When i had my truck scaned at the shop it said my problem was a miss on # 8 cyilnder. I have changed the pluggs wires cap and rotot. and no help it still backfires and shakes. i ran some sea foam through a vac line and thro my tank nothing. i had a mechanic pull my injectors and he says there fireing fineat idle at least. i dont know what to do next can you help?? the dealer told me it may be my computer causeing all my touubles and it should be re flashed would that really help? please any thing will help

 

Have the converter pressure checked. If it is clogged, misfires are caused on #6 and #8. Many muffler shops will do that for free.

 

that is a good help cuz my converter rattles so its on its way out. ill have that checked any thing else?

 

Nope. I'd almost bet a week's pay that is your problem since it is rattling. I would also recommend you replace the O2 sensors as well.

 

Don't let that dealership touch your PCM. All they'll do is retard the timing and tell you it's fixed without correcting the real problem. Then you'll still have the problem and a slug-truck.

 

I need more help with this guys any one have anymore ideas? i have checked the compression. hollowed the converter changed the plugs wires cap and rotor. i have had the injectors pulled and i was told they work fine Enen the dealer in confused on this one... please help!

 

There is a TSB regarding the spark plug wire routing. Inspect the insulation on the plugs to insure there isn't wear in the insulation and that it is making 100% full contact on the plug and the cap. Route the wires properly. Misfires can also be caused by a stuck valve.

 

This may sound dumb but make sure you've got the wires on the right point on the distributor, I had the 5 and 7 mixed up once and she bucked like hell.

 

if its shaking at idle then it should have a pretty dead miss. First thing to do is verify which cylinder is missing. (they can be reported wrong, have seen it before)

start by disconnectnig the electrical connector on each cylinder until you find the one that doesnt change rpm.

After you isolate which cylinder it is it should be easy. Check for strong spark, if you have spark take a test light and check for power at the injector harness for that cylinder, then if it has power, clamp the test light to the positive terminal of the battery and check the other terminal on the injector harness. With the truck cranking or running the test light should flash. If it doesnt then you would be looking at wiring or more likely a pcm.

also make sure you check compression on multiple cylinders to ensure there is no major difference between cylinders.