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1996 Chevy 1500 5.7 Liter V8

3

3020 JD 15

Member
We changed the spark plugs and plug wires and now it idles real rough and back fires when you put it in gear. Any ideas why. Thanks!!
 
Did you change one plug at a time or did you take them all out then put the new ones in?

It sounds like to me that you have two plug wires crossed. Be sure to recheck the firing order.

Let us know what ou find.
 
I forgot to mention that when you check the firing order be sure to trace each plug wire to make sure it's on the correct plug.
 
Yup,something got crossed up somewhere.Distributor cap has cylinder numbers on the wire towers.
 
We put two new plugs in it on the left side and it started to do that after I put in them two plugs. Would the gap have anthing to do with it. Its at .60 and thats what is reccomended for it. Thanks!!
 
.060 used to be the recommended gap. There is a service bulletin from GM to drop down to .045. Make sure you have the wires on correctly. I've seen many of those flat top caps crack internally and cross fire.
 
If you hadda pull on them kinda hard, you mighta broke a wire even though the outside looks good. If they are all on right, check each with ohm meter. Should read almost zero, unless carbon would read couple thousand ohms. Sometimes they break right around terminals. Dave
 

Mighta broke plug wire. Test with ohm meter. Should read zero ohms or if carbon may be couple thousand ohms. This will not likely be visible. Dave
 
Based on what you've said so far, I would put either the original plugs or wires back on and see what happens. It could be you got defective wires, or overgapped the plugs, or both. BTW, a shop with an engine oscilloscope can probably find the problem in a few minutes.
 
Sounds like the wires are installed incorrectly
or the wires are defective. Note which way the rotor turns, then locate No1 plug tower on the cap and see if the plug wire is connected is connected to No1 plug. The numbers may be on the intake manifold then follow the firing order tracing each wire from the cap to the correct plug. Hal
 
The zero ohm wires are for antique tractors or race cars. The wires with a few thousand ohms are for cars and trucks, like the OP has.
It's tempting, but don't ever put a zero ohm spark plug wire on a daily driver.
 
My money is on crossed wires as other mentioned. The flat caps are bad for arching also . But if it ran ok before you changed wires, I'd bet a donut you got one crossed . follow #'s on cap . Shoot ,I cross them even when I think I 'm paying attention .
 
One more thought. Is the engine all greasy around the plug holes? A dab of greasy dirt bridging the plug gap will short them out. Same with a bunch of greasy paw prints on the porcelain on the outside.
 
There was alot of dirt around it. I know I had to get some dirt in the holes at the back because they were hard to get in there. Everything is wired right. And the Service engine soon light is now blinking and before it just stayed on but now blinking. Thanks!
 
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