back firing

[nameskreen]

I have a 98 Explorer 5.0 with 280,000 miles on it. It had a slight stumble at idle and began to miss during acceleration. I replaced the plugs with Motorcraft and the wires with Duralast as I did the last time I tuned it up. There is no improvement in the idle, the miss during acceleration is only very slight now but it now back fires under moderate to hard acceleration. I double checked the wires, they are on tight and in the correct position ( I replaced them one at a time) I also cleaned the MAF sensor but no change. Any ideas? Thanks

 

[koda2000]

does it backfire out the exhaust or out the intake?

 

[nameskreen]

I think out of the exhaust

 

[koda2000]

it could be a leaky fuel injector dumping too much fuel into a cylinder. Pull the spark plugs and see if one look black and sooty. The other possibilities are a burnt exhaust valve or possibly it has jumped time, although I think these are less likely. with 280,000 miles, stuff wears out.

 

[nameskreen]

I'm gonna pull the plugs back out tomorrow and see. I don't know if I have a defective plug or wire, knocked off a vacuum line, or something more serious. I'll post back tomorrow.

 

[nameskreen]

The # 5 plus ( driver front) was either defective or I cracked it going in with all the brake lines and shock tower in the way, but I replaced it and everything is good.

 

[koda2000]

The # 5 plus ( driver front) was either defective or I cracked it going in with all the brake lines and shock tower in the way, but I replaced it and everything is good.

Congrats! I'm glad it was something simple. I've cracked a plug or two in my time too. It's not hard to do.