My 99 F-150 4.2 5 speed with 13,000 miles has been backfiring lately. It happens about once a week and may only do it once on the day it happens. Could it be the gas? I use 87 octane that Ford recommends. I did mix brands once although the octane was the same. Any ideas are surely welcome!!

 

Backfiring or pinging??? What are symptoms or conditions??? If it's pinging it could be the gas. I've never heard of a fuel injected backfire, although I've seen nitrous related fuel inj. backfires. Your intake would have to get hot enough to ignite fuel, and there would have to be some way for fuel to puddle or other wise collect to cause a backfire(not possible(sey) in a DPFI system). Check your spark plugs, as they will tell you a lot.

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1999 F-150 4.2L
-just bought it, have to mod it-
1987 Mustang LX Hatchback
351W
"Strictly strip, 250 shot nitrous, going for broke"
NEEDS TRANNY!

"Burying the competition, one bowtie at a time"

 

It's definitely not pinging. It's a loud "pop" or explosion. It usually happens when i'm accelerating and shifting up. It's just one loud bang. At first i thought it was the car next to me but the next time it happened, i heard it from my truck.So, you think it might be the plugs. I'll probably take it into the dealer and have him check it out since it's under warranty.