I have a video of my brothers fox body here with a weird nitrous backfire. It goes off at the top end of the track where as all of the other ones I've seen go at the start.


http://videos.streetfire.net/video/8...ang_162001.htm

 

without knowing more information, I would venture a guess that the car went lean due to fuel pressure drop.

Would help to know the following:
1) bottle pressure
2) fuel pressure
3) A/F ratio
4) timing
5) spark plugs

with it being fine on the 100 but having issues on 150, my guess is you exceeded the pumps capability and went lean.

 

Is it a stock fuel pump? What kind of plugs are you running? What solenoids? Answer Ray's questions and you'll be able to get a better answer

-Will

 

Its running your Brand X kit (awesome kit by the way). 1 heat range colder with a little less gap plugs. We pulled 4 Degrees of timing. The stock fuel system and full bottle pressure of 1050. But im assuming ford put real crappy pumps in them if they cant handle a 150 shot.

 

If its still on the stock fuel system I would look into a higher flowing pump. Did it have a fuel pressure safety switch on it?

 

Yeah but I think its for a carb'd one because it didnt cut the spray.

 

I had that happen in my '86 fox, It was do to fuel that had puddled up in the intake.

 

High RPM lean backfire would be my guess, ask me how I know, lol. Though backfires can be lean or rich, but higher rpms tend to be lean. Being a Stang it was probably a wet kit?
Robert

 

Lots of unanswred questions. I would like to add is there a windowswitch and did he tag rev limiter?

 

Often a back fire is blamed on fuel puddling due to misunderstandings of hwat actually happed.

Odds of the fact of your back fire being because of fuel puddling is slim to none.. Unless your tune up was so rich that the car was drowning on fuel. The mixture is pulled through that motor so fast that there is no way for it to puddle for nay other reason than the one I listed.

What is common with the fox body intake is a backfire at hp levels over 175 due to the runner design. You end up with a lean cylinder causing a backfire. Since the fuel vapors are in the intake the back fire is more violant.

Other reasons of a back fire is lean pops due to not enough fuel. Overly rich conditions. No window switch.

 

Thanks with the responses. The car is a new strong automatic so no rev limiters but i did some research on my own and its an 88lph fuel pump from the factory and with 200k miles Im going to say it went lean and didnt shut off with the fuel pressure one since The fuel pressure switch we have is for a low pressure system that we got from a friend.