Backfire through exhaust under load...

cougar_68 · May 29, 2010

Like the title says, my car backfires through the exhaust under load. It stalls until you cram on the pedal. The whole time it is at about 30% power. You cram on the pedal and it stalls and then lurches forward and backfires through the exhaust.

It generally does this when I first start it up (with the car hot or cold). After driving for a couple miles it will stop doing it. It’s really messed. It will be acting all crazy then like flipping a light switch, it is just fine and runs like a top.

I have absolutely no clue what could be causing this. Anyone have this happen before?

See my signature for my setup…

Almost forgot, I can rev engine (in neutral) all day when it is doing this and there isn't any problem at all!!!

87steed · May 29, 2010

sorry not any help but your not alone ...I have basically the same issues with mine , ive checked for vac leaks, codes, sensors but still have this issue everytime i restart hot or cold about 10-12 minutes of driving and it runs fine
hopefully someone has an answer

cougar_68 · May 30, 2010

87steed said:
sorry not any help but your not alone ...I have basically the same issues with mine , ive checked for vac leaks, codes, sensors but still have this issue everytime i restart hot or cold about 10-12 minutes of driving and it runs fine
hopefully someone has an answer

This is soooo frustrating...think I'm going to put my car on ebay.

cougar_68 · May 31, 2010

Bump.

thethirdeye88 · May 31, 2010

wow, that sucks...i'd like to know what would cause that...

cougar_68 · May 31, 2010

thethirdeye88 said:
wow, that sucks...i'd like to know what would cause that...

So would I!

I need to see if I can make it over to autozone and see if it will throw a code. Can they do that on this older EFI? I'm assuming they can.

Mustang5L5 · May 31, 2010

Autozone can't read eel-iv codes.

What year is the car? You can do this yourself with a jumper wire

cougar_68 · Jun 1, 2010

It's a 68 cougar, but the efi is from a 90 Mustang. I don't have a check engine light. Is that required?

marine_80 · Jun 1, 2010

you must have a electric fuel pump, what is the pressure at?]

cougar_68 · Jun 2, 2010

I do have an electric fuel pump. How do I check the fuel pressure? You think the pump may be going bad?

nick6690 · Jun 20, 2010

anyone ever figure out what the problem was? I have the same problem.

jrichker · Jun 20, 2010

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 19-May-2009 to update drawing for dumping the codes on 86-88 Mustangs with no check engine light.

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the way 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. You watch the flashing test lamp or Check Engine Light and count the flashes.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

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. You watch the flashing test lamp or Check Engine Light and count the flashes.

See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

Strype · Jun 21, 2010

Tell us some more about your setup...

Do you have the correct MAF for 24lb injectors? Do you have the correct computer? It sounds to me like when you pop it into drive it's losing time.

Have you checked the timing when it's screwing up?

cougar_68 · Jul 2, 2010

I do have the correct injectors for the MAF. I have not checked the timing when it's acting up. After a few minutes of driving it returns to normal. After that I can put it in/out of gear over and over, so I’m not sure if that is it.

I would not be too surprised if the fuel pump was bad. It's weird that it only does it right when you start it up (hot or cold). I’m thinking maybe the fuel pump is just dieing on me and can’t keep up at first, but then maybe it gets warmed up and it’s ready to go? Does that makes sense?

cougar_68 · Jul 17, 2010

I went out on a limb and purchased a new ignition coil today (el cheapo from advanced auto). It seamed to help, but I'm not sure if it was just better because it was really hot outside. It still did some wierd things.

For example, I pushed the pedal to about 75%. It sped up, but then it learched forward, held the acceleration, learched forward again, held the acceleration again, it did this about three times. If you could see the acceleration curve, it was like it was stair stepping (is this the computer re-learning?). Pretty crazy (maybe it was the v-tech kicking in???) . It felt really strong though, maybe stronger than before?

It also backfired a few times through the exhaust, but came out of it much quicker. Last time I drove I was about 20 miles from home and it was kicking, spittering, and sputtering the whole way. So this was a great improvement. Come to think of it, it was super hot that day too. Maybe my ignition (stock, except for spiro pro 8mm wires) isn't up to par?

What do you guys and gals think?

cjrpony · Jul 17, 2010

Sounds like a timing issue to me. But you say it returns to normal so that would make me think it wasn't the dizzy not timed right. Check the harness for the SPOUT plug and make sure that is ok. If the computer can't see the SPOUT plug in place (bad wiring or loose plug) then it won't advance the timing. And double check the timing anyways. I dealt with a simular issue this spring for a couple days and discovered I had accidently set the timing at 10 deg ATDC instead of BTDC. OOPS.

cougar_68 · Jul 17, 2010

You may be onto something...

This was a pre-labeled wiring harness, the plug that says "Spout" on it has a gray "cap" plugged into it. Is this thing supposed to plug into the distributor some how? There is also a cover over the place where I would guess this would plug into on the distributor...I'm going to go take a pic real quick...

cougar_68 · Jul 17, 2010

Here is a picture of the blocked off spout connector and distributor...

Haus · Jul 17, 2010

that cap is suppose to be on there. When you adjust the timing. you remove it then when you get your base timing, you put it back on

cougar_68 · Jul 17, 2010

So that connector doesn't need to be plugged into anything? Bummer, I was hoping that was going to solve the problem...

Backfire through exhaust under load...

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