dan25

hi to all i have an 85 mustang gt with a 5.0 throttle body i've been having this problem now for quite sometime it backfires and its not just small ones its loud big ones that blow my mufflers right up the problem seems to be only when the vehicle is at operating temperature i rev it and thats when it backfires or if i would horse it a little bit and not shift fast enough it will backfire i changed the spark plugs timed the motor back and now i have no clue where to look.


would anybody have an idea as to what could be causing this? thanks.

dan25

last week i toke a compression test i have 120 on every cylinder and also changed my exhaust for a '90 exhaust with flowtech mufflers the backfires seem a little less loud and at least don't destroy these mufflers
i was wondering if my problem could be all with the throttle body or injectors
what do u guys think cause i really don't lknow where to look anymore and i'm about to change the motor and put it all carburator if i don't find what is causing this thanks

VAEM

Sorry for the late reply. I was going to reply sooner but .... well, I forgot.

Incorrect timing as well as spark plug wires hooked up incorrectly at the plugs or the distributor, among a number of other things, could cause your 5.0 to miss or backfire.

It could also be the ignition control module (the little gray box with a wiring harness plug on the front of the distributor) or your timing. I know you said you timed the motor back on your Mustang. Im not sure if you did this but when timing a 5.0L motor, you have to unplug the sprout connector BEFORE you time it. You'll find the sprout connector on those wires that come from the ignition control module. When you time a 5.0L and the sprout connector is plugged in, it will make the timing look like it is set at roughly 18 degrees. However, if you unplug the sprout connector, you will see the timing is actually set at roughly 12 or 13. You need to time it correctly with the sprout connector removed. Time it to 12 or 13 degrees. After you are done, plug the sprout connector back in and you should be ok.

Here are a couple of threads that'll help you out:

https://www.cmoc.ca/forums/t13758/
https://www.cmoc.ca/forums/t13759/

If the backfiring is in the intake, the motor is running lean or the timing is very retarded. Try running premium gas.

Let us know if this helps at all.