Engine Missfire Help

[marshall_mosty]

Guys,
Took the car to the track yesterday and it ran well except it seemed to be stumbling a bit climbing through the RPM band. Nothing to fall on its face, but enough to hear/feel from the driver's seat.

Today, Michael and MFW took my car to the dyno and they didn't get the car above 5K due to the horrible popping/missfire.

I changed the plugs/cap/rotor and bad wire since the last enduro.

Car still put down 288HP/315TQ with stopping at 5K, so I'm sure it would be around 310HP or so.

The miss didn't seem to hurt the power, but did make the dyno graph look a bit funny.


What would be the first thing to look at? Apparently the car ran fine from 2K to 4K and then started to fall apart (graph wise).

[mitchntx]

Guys,
Took the car to the track yesterday and it ran well except it seemed to be stumbling a bit climbing through the RPM band. Nothing to fall on its face, but enough to hear/feel from the driver's seat.

Today, Michael and MFW took my car to the dyno and they didn't get the car above 5K due to the horrible popping/missfire.

I changed the plugs/cap/rotor and bad wire since the last enduro.

Car still put down 288HP/315TQ with stopping at 5K, so I'm sure it would be around 310HP or so.

The miss didn't seem to hurt the power, but did make the dyno graph look a bit funny.


What would be the first thing to look at? Apparently the car ran fine from 2K to 4K and then started to fall apart (graph wise).

Sounds like an opti-spark is dying. 8)

[AllZWay]

Sounds like an opti-spark is dying. 8)

But I am thinking that is probably not his problem...although I don't know much about Fords. :P

[evarner]

TFI module? During the popping and misfire, was the tach bouncing needle bouncing around?

Mass Air car? Could always check the 2nd filament wire on the meter (if you can see it) for any debris.

Fuel Pressure was steady and didn't drop off approaching 5k?

Reset the computer by disconnecting battery and leaving the ignition on "run" for about 5-10min. Connect battery and then start the car - leaving it run without touching the throttle for 10min (fast EEC learn).

I've had to do at least one of the above on my drag cars when they had the same symptoms as what you described.

.02

[marshall_mosty]

TFI module? During the popping and misfire, was the tach bouncing needle bouncing around?

No, tach is stable.

Mass Air car? Could always check the 2nd filament wire on the meter (if you can see it) for any debris.

I'll check that.

Fuel Pressure was steady and didn't drop off approaching 5k?

Don't know. Didn't have a guage hooked up at that point.

Reset the computer by disconnecting battery and leaving the ignition on "run" for about 5-10min. Connect battery and then start the car - leaving it run without touching the throttle for 10min (fast EEC learn).

Don't know if this one will work since I just have the master disconnect, toggle switch for the EFI system, and the starter button. The one toggle powers the EFI and the fuel pump.

One thing I will look at is the fuel pump/strainer. Since I've had lots of issues with this in the past, it might have been fuel starving at high RPM if the strainer fell off or is plugged.

[Rob Liebbe]

Make sure the battery voltage is good and the alternator is charging. I recently had a similar problem on another Mustang. He changed the fuel pump and got resolution.

[AI#97]

we hooked up a fuel pressure guage...FP was steady at 40 at idle and held firm at 48 during the pull and never waivered. I am guessing a bad coil or some sort of valve problem from the enduro.

For reference from the first pull. a/f was in the low 11's and dipped to 10.8 once. We pulled plugs and they weren't fouled. I backed the FPR out 1/4 turn and the a/f was better on the second pull in the low 12's high 11's but steady at 12.2 during the pull. started breaking up at 4200, bad at 4500-4600 and we killed the pull at 4800.

I was perplexed and we swapped the modules with a spare from micheals pit box. Car cranked perfectly every time and didn't sound weak...but the bendix was a cranky when we put it on the trailer...but still cranked strong. I ran out of knowledge at that point and the dyno operator was actually the previous shop owner of Modern Mustang Performance and even he was scratching his head. Great guy too who was interested in CMC!!!!

Oh, and 1 chambers are f'n loud!!! LOL! :lol:

[Rob Liebbe]

I'm still going with low voltage. Easy to check.

[Todd Covini]

I'm going to go with Throttle Position Sensor (TPS) for $100, Alex.

[AI#97]

I'm going to go with Throttle Position Sensor (TPS) for $100, Alex.

You know, that is one thing we didn't check but could be checked with a volt meter in about 30 seconds. are the 5.0's 1-5v with wide open being about 4.8v..? and closed being 1.0v? Pretty normal for most cars I think.

Marshal, the more I think about it I am coming down to no alt output or bad coil. If it were doing what it did today on Sunday, you would have brought the car in which tells me its something that is getting slightly worse...my money is on alternator at this point.

I do hope you figure it out though and it's great to sort it now instead of at the track!!!! Good luck!