94 Mustang Gt Backfire In Exhaust

94 gt/cobra · Feb 29, 2016

i have a 94 mustang sn95 just bought it about 2 weeks ago. It misses and bucks and backfires in the exhaust only at cruising speed from 1000 to 3000 rpm if I'm just barely giving it gas if I get in the throttle it completely clears up. I put new cap and rotor on it, new 8mm plugs wires, new iridium plugs, new air filter, new fuel filter, checked the timing, cleaned the maf, checked all vacuums, replaced pcv valve. Can't figure out my problem, the o2s have been bypassed. It has e303 cam, cobra upper intake, edlebrock lower, trickflow heads, stroked to 306, pro m racing maf, deleted egr and a/c. Maybe a tuning problem? Please need some insight before I sink more money into it.

stykthyn · Feb 29, 2016

If you haven't tuned out the ecu to run without o2s then there's your issue. Same with the egr.

stykthyn · Feb 29, 2016

Also check your timing. Pinging or backfiring at cruise is a symptom of being out of time.

94 gt/cobra · Feb 29, 2016

Double checked the timing and surely with everything done to this car they programmed it only problem is I don't have a tuner and I've heard the tps would cause the same issues?

stykthyn · Feb 29, 2016

Do you have a chip on the ecu? If not it hadn't been tuned. Where is your timing set? Surely I'm sure they took short cuts, didn't tune it and then sold it. Let's start with the basics and work our way up. Verify timing and install o2 sensors assuming the bungs are still in the mid pipe.

94 gt/cobra · Feb 29, 2016

14 degrees and they're welded shut

94 gt/cobra · Feb 29, 2016

It ran the smoothest at 14 when holding at 3000

stykthyn · Feb 29, 2016

Have you dumped codes?

94 gt/cobra · Feb 29, 2016

Yes does have an ecu not sure what kind can check that tomorrow

94 gt/cobra · Feb 29, 2016

Showing 31 and 67 can't remember which one but I know one is a/c and other is egr

Mustang5L5 · Mar 1, 2016

Bypassed O2's? Why? Did you have a chip burned to account for that.

Backfiring is usually sign of a mixture issue, usually lean. The O2's help regulate this condition, but when them gone and no tune to compensate, it's pretty much certain you will have lean/rich issues. EGR is also a contributor to this when bypassed.

Also ditch the iridium plugs. Go back to copper plugs. The ignitions on these older 5.0's tend to not handle the platinum/iridium plugs all that well. They seem to thrive with copper plugs.

Adding the O2's with getting the EGR functional will cost you 0 HP, but make the car run much better. The alternative is a $300 chip and $300 dyno tune session.

94 gt/cobra · Mar 1, 2016

It has Bama chip in it and it is running pretty rich burning more fuel than should I'm going to get tune done this weekend but it has a msd street fire coil and dizzy and an accel ignition control module should I still go back to copper? Like I said I just bought it 2 weeks ago and I'm trying to get everything right.

jrichker · Mar 1, 2016

Did the person you bought the car from have floppy, oversized shoes, a red nose and frizzy red hair? No emissions, no tune, no O2 sensors means that the Bozo you bought the car from was one frizzy hair away from being dangerous around cars.

All 94 and later Mustangs use 3 digit codes; the fact that you got a 31 (EVP circuit below minimum voltage.) and a 67 code (clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. ) tells us that there is a 1986- 1993 year model computer of uncertain origin in your 94 model car.

This is going to be a soap opera with boatloads of money spent trying to get the correct computer and sensors back in the car and then get it tuned so that it runs decently on a consistent basis.

stykthyn · Mar 1, 2016

jrichker said:
Did the person you bought the care from have floppy, oversized shoes, a red nose and frizzy red hair? No emissions, no tune, no O2 sensors means that the Bozo you bought the car from was one frizzy hair away from being dangerous around cars.

All 94 and later Mustangs use 3 digit codes; the fact that you got a 31 (EVP circuit below minimum voltage.) and a 67 code (clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. ) tells us that there is a 1986- 1993 year model computer of uncertain origin in your 94 model car.

This is going to be a soap opera with boatloads of money spent trying to get the correct computer and sensors back in the car and then get it tuned so that it runs decently on a consistent basis.

Oh.snap.

mikestang63 · Mar 1, 2016

jrichker said:
Did the person you bought the car from have floppy, oversized shoes, a red nose and frizzy red hair? No emissions, no tune, no O2 sensors means that the Bozo you bought the car from was one frizzy hair away from being dangerous around cars.

All 94 and later Mustangs use 3 digit codes; the fact that you got a 31 (EVP circuit below minimum voltage.) and a 67 code (clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. ) tells us that there is a 1986- 1993 year model computer of uncertain origin in your 94 model car.

This is going to be a soap opera with boatloads of money spent trying to get the correct computer and sensors back in the car and then get it tuned so that it runs decently on a consistent basis.

Snort, floppy shoes That's funny right there.

.. Can I add a BAMA chip? Take that POS off and it will run better I bet.

94 gt/cobra · Mar 1, 2016

So If I get a 94 gt computer from salvage yard, fix welded bungs add my o2s back in and get a tune session I should be good then because I know the egr valve will not cause the problems I have and also I didn't realize you could put a fox computer in the 94 and it even run at all

94 gt/cobra · Mar 1, 2016

Because as of right now my only issue is its running rich and it pops in muffler when barely giving gas as soon as I get in the throttle it clears up still running rich but I should have way more problems than this from the way yall are acting and the Bama 4 bank is a pretty nice setup don't get me wrong I know the car has issues but it's a solid build just seems like they didnt know much about the sn95

jrichker · Mar 1, 2016

94 gt/cobra said:
So If I get a 94 gt computer from salvage yard, fix welded bungs add my o2s back in and get a tune session I should be good then because I know the egr valve will not cause the problems I have and also I didn't realize you could put a fox computer in the 94 and it even run at all

You can't... It takes a different computer harness to run the T4M0 or W4H0 computer that is normally found in a 94-95 5.0 Mustang. Add the computer and wiring harness to your shopping list plus some diagrams of the CCM module that probably got hacked up in the switch.

94 gt/cobra · Mar 1, 2016

I just don't see someone replacing factory wiring harness what's the point?

jrichker · Mar 2, 2016

94 gt/cobra said:
I just don't see someone replacing factory wiring harness what's the point?

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