87 5.0 backfires 1st - 2nd shift high rpm

[Jay5_o]

Got a problem with backfire under load when shifting from 1st to 2nd 4500+ rpm. sounds like a gunshot going off, and its embarrasing when im raceing.
I got newer rotor ,cap ,spark plugs, wires
what would cause this? leaky injector ? wrong kind of spark splugs ?timing ?
any input would be helpfull to fix this problem

 

[89rdgt]

Well the off road h pipe doesnt do you any justice in that feild. It give a spot for extra fuel to burn after it leaves the engine. With no cats you tend to get a little backfire out the tail pipe. a bad injector could do it too.

 

[281pony]

i had the same problem. had an exhaust leak from mufflers to h-pipe

 

[5.0Droptop]

Chek to be sure you vac line is still connected to the map sensor If you still SD. Make sure your Spout is plugged in also. Just a couple small things to chek.

 

[Jay5_o]

"Chek to be sure you vac line is still connected to the map sensor If you still SD"

huh ? explain

 

[TheUser]

If you have a timing light, check the timing. I believe that MAP sensor is on the firewall to the right of the upper intake and it has a vacuum line connected to it...check to make sure that it's in tact and not leaking.

 

[5.0Droptop]

"Chek to be sure you vac line is still connected to the map sensor If you still SD"

huh ? explain

On Speed Density mustangs the MAP sensor reads the vacume from the manifold. If the line is off, kinked,leaking, etc it will cause problems. The map sensor is a black box next to the vacume tree its not in the center of fire wall but close to it.