Thread: 5.0 L tuning help needed

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I have built my 32 Ford with a 5.0 L mustang engine. I had a superchip burnt for it by the local mustang shop. It has a GT 40 lower intake, explorer upper, 42 # injectors, 90 MM mass air, 65 mm accufab throttle body . It has a .569 lift cam with trickflow heads. I have set the timing at 10 deg. BTDC with the spout unplugged.
I got it running today but I am having problems. It runs perfect when its cold but as it warms up it starts to idle rough and by the time the fan kicks in it will back fire when you rev it up and sometimes it stalls. I am going to phone the guy on Monday who burnt the chip but I thought I'd ask what you think it is. My gut is telling me that it is running too lean. Opinions? Thanks.

I was thinking a lean condition as well. Backfiring is often a sign of that.

The gauge says it's about 180 deg. but the gauge sender is at the back of the engine. The fan switch is at the front of the engine, and I think it's a 190 or 195 deg. switch. All the sensors on the engine are new except for the coolant temp sensor for the EEC. Maybe I'll try swapping it out with a spare one and see if it helps. Any other ideas ? Obviously if it runs good when cold then it goes lean when hot so it is either a sensor or incorrect program correct ?

sounds like a bad programing job or a bad o2 sensor to me. my 87 mustang with a 5.0 did the same thing to me and it was the o2 sensor... also you might want to change that fan to a switchable fan instead of sensor run, they're sposed to kick in at 195, but i went through 12 sensors from 5 different sources and they were all opening at 210.... which is a little hotter than you want that motor goin to

I had the guy re-program the chip with two program. One a forced open loop ( no O2 sensor ) and the other a closed loop. It ran good on the open loop until it got hot then began to miss and backfire. The guy at the mustang shop says it sounds like a vacuum leak or miss fire. So I think I have a misfire condition. I am going to reset the rocker adjustment since I wasn't the one to do it when I bought the long block and do a compression test. Beyond that I will try and see if I got a bad plug or wire. If that doesn't cure it I will have to trailer the car down to the mustang shop to get it diagnosed. Why did I get into hotrodding anyway ? At least I got the coolant and fuel leaks fixed, but now I noticed a rear main seal leak

maybe it should be put on an oscilliscope, to see whats causing the misfire... not too many techs use scopes anymore... but they can give a LOT of info on whats going on in your cylinders

42 # injectors? Is there a power adder I missed. Thats a lot of injector if its a stock bottom end. Sounds like its way over injected for what it is. 19# will support 325hp. I'd look for some smaller injectors and then retune.

later

Dennis

Originally posted by DennyW
http://images.google.com/imgres?imgu...LG:en%26sa%3DN

That's alot of Jet-Hot coating there.

I know nothing about power adders. so I'll shut up so I don't make a stupid comment. Nice mustangs.

Later Dennis

coogan,
I have to agree with 53fatfndr about the injector size being too big. When I built my turbo 1.8L motor I was talked into putting 45# injectors in. Although I do have the so called power adder (turbo), I found that the 45's were way too large and controlling flow down low was a problem. At WOT it is no problem, but after a high rev run and coming back to idle my motor would load up on fuel and stall. 35# injectors have solved all these problems. For shorter pulses (idle to off idle) the volume of fuel is much more controllable and at WOT there is still more than enough to go around. Another thing to check is your pressure regulator. Are you recirculating fuel back to the tank or just regulating pressure? If things are too rich (so much fuel pressure that you are pressing fuel past the injector, or it is dripping) you could end up with unburnt fuel in the exhaust system which also leads to nice bangs! My 45's gave me plenty of opportunity to experience that.

Man, EFI is a bitch, or it is awesome! It just depends on whether it works or not!

Regardless of the problem, the plugs ought to tell you all you need to know. To rich they are wet, too lean they are whiteish. Next time you get it warm and it starts back firing, while in the backfiring stage, turn the key off and immediately pull a plug, or many plugs. This will give you a glimpse into that moment in time as to what is really going on in your cylinders.

Good luck. I went from adujst it with a screwdriver "webers" to EFI, and tuning with a laptop while fun, is just a whole different frustrating world. I can sympathize with you.

Brian
www.myturboalpine.com

Injectors sound a little big to me also

I started another thread saying what the problem was with my car after 3 months of hair pulling but I guess the mods did not like me saying the painless harness was at fault and they deleted my thread. Nice to be censored for telling what happened.

The thread you started on the Painless harness isn't closed, just off the active threads page.....

Thanks for that, I thought maybe the mods were worried about slander or something. Not sure why I couldn't find it.