Drivetrain Fox Power Loss While In Gear

[J_5.0_VERT]

1990 5.0L Manual T5 - Will try to keep this short.

Car is effectively “dying while driving” in all gears. Happens randomly at any rpm and speed, feels like the motor is heavy engine breaking mid gear and on the accelerator. Saw the rpm jump up like a blip as it happened this morning. The first time it happened i took it out of gear and put it back into gear, worked fine all the way home.

Now everytime i drive it it does it. Except now it has turned the motor off, but still has electrical power when rolling. It’s like it’s stalling mid drive, and a puff of white smoke and something else banged under the backseats after this (comparable to the sound of a rock hitting the undercarriage). This time it didn’t die and i drove it home cautiously.

I’m not sure where to even start now, transmission fluid shows no signs of excessive wear in fluid, has been topped off and changed, tested fuel pressure with engine on and off, results were within normal range.

Any advice or idea of what’s happening here? Going to get under the car tonight to see if the car losing power twisted my driveshaft or broke a ujoint. Would make sense given that the car is effectively dying at 50mph sometimes while in gear still clutch out. I really hope this isn’t the case.

 

[Noobz347]

Pull OBD Codes. It's easiest with an OBD 1 scanner, cheap, from Amazon but there are are instructions here to pull them without a reader:


clicky clicky

Electrical Thread 'How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs'

Jan 27, 2016

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it...



Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

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...

• jrichker
• Replies: 10
• Forum: Fox 5.0 Mustang Tech

• 

After that, I would begin to suspect the following components (in no particular order):

TFI Module

Fuel Pump

Distributor PiP sensor

Let's see what codes you get, first.

 

[J_5.0_VERT]

Will check the engine codes, last time i ran them i didn’t get anything back from it…

Also does the problem have to occur during the same “session” that i run the code test?

In any case, i’ll run the engine codes again and we’ll start there, will update today before the end of the night - got the kiddo at home to appreciate before submitting myself to diagnostic torture on this thing lol

 

[Noobz347]

It does not. The CEL light will only show those codes associated with emissions problems. We're looking for any stored codes.

Something along the line of O2 sensors or MAF sensors out of limits, etc... can help point in a direction. If there are truly no codes then that indicates an issue as well. We're looking for an [all clear code] at minimum.

 

[J_5.0_VERT]

It does not. The CEL light will only show those codes associated with emissions problems. We're looking for any stored codes.

Something along the line of O2 sensors or MAF sensors out of limits, etc... can help point in a direction. If there are truly no codes then that indicates an issue as well. We're looking for an [all clear code] at minimum.

Copy that, I believe i had a code 10 which was the finalized clear test code last time, either way will run test and give results soon

 

[AeroCoupe]

If you do not get any codes including Code 11 or if it will not run the KOER diagnostics I would suspect the ECU. If it returns clear for both KOEO and KOER then most likely the PIP in the distributor. I would get this tester:

Pardon Our Interruption...

 

[Mcmahst]

All good advice from these two Mustang Masters. Based on your description, it sounds like it’s losing spark at some points, and then recovering that spark. That would give you the feeling of loss of power and even engine braking, And then after recovering the spark, that noise out back could be the muffler burning those fuel vapors that didn’t when you lost spark (bang). Good luck.

 

[J_5.0_VERT]

It does not. The CEL light will only show those codes associated with emissions problems. We're looking for any stored codes.

Something along the line of O2 sensors or MAF sensors out of limits, etc... can help point in a direction. If there are truly no codes then that indicates an issue as well. We're looking for an [all clear code] at minimum.

So ran the test last night - on a cold engine - so i was surprised to not find a code (21 i believe for an out of range coolant temp?) However the only codes to show were 11, 10, and 11c. Last week when i ran the codes i received 11, 24, 21, and 67.

Also checked underneath the car to see if the banging after the power loss in the rear could’ve been my ujoints locking up or some sorts when the engine cut while in gear, could not find any damage so hoping it could’ve been backfire from unburnt fuel upon respark like @Mcmahst said. There’s only so many things that move back there so..

Going to put in the TFI module today seeing as I didn’t have time last night.

Was really hoping for some sort of confirmation with a solid engine code crumb trail to follow….

 

[J_5.0_VERT]

All good advice from these two Mustang Masters. Based on your description, it sounds like it’s losing spark at some points, and then recovering that spark. That would give you the feeling of loss of power and even engine braking, And then after recovering the spark, that noise out back could be the muffler burning those fuel vapors that didn’t when you lost spark (bang). Good luck.

Really hoping that’s the case, would explain the puff of white smoke after it died the first time burning off whatever else was left of the fuel.. This definitely sounds in the right direction though, but hey at least it’s not looking like a mechanical issue like synchros or the clutch stalling out the car being misaligned or something !

 

[J_5.0_VERT]

If you do not get any codes including Code 11 or if it will not run the KOER diagnostics I would suspect the ECU. If it returns clear for both KOEO and KOER then most likely the PIP in the distributor. I would get this tester:

Pardon Our Interruption...

Just posted an update on the OBD1 scan i did last night - however i may order one of these, didn’t even know they existed so I’m a little excited to think this might solve this for me. Does this just plug directly into the TFI module?

Unsure on how this tester works or where it all plugs into but i’m intrigued.

 

[AeroCoupe]

It has instructions and is super simple to use.

 

[J_5.0_VERT]

It has instructions and is super simple to use.

Thank you, i’ve had too many times where i buy a tester of some sort and there’s no clue on the use of it lol, will buy one of these

 

[Mcmahst]

I marked mine in my wish list and the guy sent me a discount offer. Just saying.

 

[J_5.0_VERT]

I marked mine in my wish list and the guy sent me a discount offer. Just saying.

Just purchased, should be here around Saturday at the earliest - will try this new TFI in the meantime, worst comes to worst i test them both if i dont get a positive result from either.

 

[J_5.0_VERT]

@Mcmahst @AeroCoupe @Noobz347

Update - put in the new TFI Module today, I also cleaned the MAF sensor last night, and added dielectric grease to all the spark connections on the distributor cap for extra care. Brand new sparks all around as of earlier this week.

Ran a test drive off the new TFI Module, before I made it off my road, got a CEL. Turned the ignition off and back on again and gone. The test drive went good, relearned its idle at the same time, did not die or hesitate which is good news! Will take it to work tomorrow just to be sure we're solid.

However, after running home and running the codes again, got a 11c as normal, a 10 again, but now I receive a 41c and a 91c - O2 sensors... even though I've never gotten that code nor did I touch them lol.

I could tell while I was letting the car idle up to operating temp after TFI change it did smell a bit rich - a little confused but car is drivable so far at least. I did have to rotate the distributor after loosening the hold down bracket bolt to get to the TFI screws, however I did mark it as instructed and it's back in it's exact prior position. Is there a possibility that the distributor is the very slightest off and threw off the mixture somehow? I'm diving into new territory...

 

[Noobz347]

Clear the codes and run it to work tomorrow as planned. Pull them again that evening.

 

[J_5.0_VERT]

Clear the codes and run it to work tomorrow as planned. Pull them again that evening.

Copy that, will see what happens

 

[Mcmahst]

It must feel great to be finally getting somewhere. I’ll try and not jink it. If it turns out to be the TFI module, after you tried quite a few, it will be great you’re driving your car, but sucky that we all have to worry about this in the future. Like lots of folks, I carry a spare and the tools to replace it in my car. I’d pay a premium to any company that could produce a 99.5% probability good TFI module. Good luck driving tomorrow.

 

[J_5.0_VERT]

It must feel great to be finally getting somewhere. I’ll try and not jink it. If it turns out to be the TFI module, after you tried quite a few, it will be great you’re driving your car, but sucky that we all have to worry about this in the future. Like lots of folks, I carry a spare and the tools to replace it in my car. I’d pay a premium to any company that could produce a 99.5% probability good TFI module. Good luck driving tomorrow.

Not gonna lie, a bit nervous ever since the rough banging towards the rear of the car ever since that happened. Nothing of note besides a little shake at 2k rpm but its subtle.

I am keeping that old TFI in the car along with the tools to replace it roadside if neccessary. I've heard alot about the crappy TFI manufacturers reading up on it.. I was still running the original Motorcraft one before today - may have to buy another one just to keep in the car like you said in case it fails me early.

If only Motorcraft kept producing these - I've always had good luck with their parts and get their brand whenever I can.

Thank you for the good luck, will see what happens tomorrow. Really hope it was that and not the PiP in the dist, those are a bit more expensive to replace and I'd probably try to get ahold of an MSI one if anything.

Will update tomorrow!

 

[AeroCoupe]

The O2 harness connects to the ECU harness just below the MAF. Make sure that connection is solid. My car did this once and it took a couple days to track that down.