car ran fine...now it back fires

[ECU5.0]

alright, i already did a search and found nothing that would help me out. my car has been running great since i put my intake and rockers on 2 weeks ago. today when i got in it to go to practice it started back firing. timing is correct, fuel pressure is right at about 33 or 34 psi vac on and rotor, cap, plugs and wires have maybe 10k on them. WTF? i feel like im driving a POS. it back fires every time i left off the gas to shift. its not the normal popping that you get from an off road pipe either. any suggestions or solutions? thanks

i already posted this in TALK and didnt get that much of a reply...please help me. i already checked all the obvious stuff.

 

[ECU5.0]

anyone? please help

 

[BlackGT89]

Are you talking about backfiring through the intake when you get on it, or through the exhaust when you are letting off ? Have you had a chance to run any stored codes ? If you're backfiring when you get on it, I'd suspect ignition or fuel delivery problems. I'd check for any vacuum leaks as well. Once you backfire through the intake there's a good chance some vacuum lines have been blown off. Good luck.

Sorry, just re-read, it's when you shift. Probably you're fuel mixture has changed for some reason.

 

[ECU5.0]

alright, ill check it out today and see what i can do. thanks

 

[ECU5.0]

well...i checked everything i can possibly think of. i dont have a tester to pull any codes and nobody around here does it and i dont have the money to get one right now. all the vacuum lines are hooked up. fuel pressure is good. timing is good. i just unhooked the battery and im gonna let it sit for a little bit to see if it will reset the computer and than run like it was before. any other advice?

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

 

[IMissMy93Fox]

Can't you just go to autozone or a similar place near you have have them read for free?

 

[BlackGT89]

I thought of something else, check and make sure the pipe from your air pump going back to the H-pipe is still there and connected. Also check for other exhaust leaks, sometimes that will cause a backfire or puttering sounds. Is your car running poorly, or just sounds bad ? If you have cats, could they be clogged ? Let us know...

 

[autoXr1]

In addition to what the others have said, you may be running lean.

I know many road racers will tune a little on the rich side because of this issue...when you let off the gas in a corner, the engine will run lean for a moment, and may cause a backfire. Heck, I've seen some of the Trans-Am racers run so rich it blows a 10 ft. ball of flame out the side of the car when they are in the braking zone and let off the gas. Drag racers using nitrous will often run a little rich to reduce the chances of backfire.

Perhaps running your fuel pressure closer to 40 psi may help. It just seems to me that 33-34 psi is a bit low, but I don't know your engine, either. Your injectors are calibrated at 40psi, and during closed-loop operation, a properly working computer will adjust the duty cycle of the injectors to maintain a normal air/fuel ratio. So, even if you are running a higher psi, you won't run rich during warm idle or cruise (it may when it's cold). That extra PSI may give you that little bit of fuel at WOT and between shifts and may reduce the chances of backfire.

My .02

 

[ECU5.0]

im running 34 psi vac on...so im pretty sure im not running lean. no cats...so those arent clogged, and my air pump isnt hooked up anyways. i unhooked the battery for half an hour today and than drove it around and it doesnt back fire as bad....but still does it. ill have to pull the codes. how do you do it with a paper clip. oh yeah, i dont even think my check engine light works because ive never seen it on. where is it?

 

[noslow5_0]

yeah your runnin a tad lean.... your suppose to set the fuel pressure with the vac line off of the f.p.r.. I had that exact same problem as you, and cranked up the fuel pressure to about 42 psi with the vacum off (you reattach it once you've set it) and it runs like a raped ape!!!!

 

[ECU5.0]

yeah, the fuel pressure is at like 42-43 vac off. well see how it runs on the way home tomorrow. thanks for the help fellas

 

[BAERSysteMAX]

another vote for fuel pressure

 

[ECU5.0]

well what should i set it at. ive already got it at 42 psi vacuum off. ill just crank it up a little more i guess. like 45 or so. thanks for all your help guys

 

[BAERSysteMAX]

Yea, keep steppin it up little by litte....with my 255 and 30 pounds injectors, my systemax kit liked to have 46psi with the vac off. and this was on the dyno

 

[noslow5_0]

do you still have the stock injectors and fuel pump???? Ive heard that as you mod these motors more, and start to push the safe workin capacity of the injector cycle, you may need to crank up the pressure to support the injectors flow up top.... there was a guy on here who had his runnin at 57 psi!!! it all depends man.... good luck!