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2021 Mach 1 Differential Overheating on track

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Hi All - took my new Mach 1 to Summit Point main this weekend with my son. The car ran well, though it needs some work to truly go fast.

I ran into an issue I didn't expect, and wanted to ask if anyone else has seen this. After about 10-15 minutes at speed, I got the dreaded Rear Axle overheating error. Looking at the gauge and it's close to 300 - this was on a ~90 degree day. The car is stock, so I plan on changing the diff fluid to 75w140 soon, but has anyone else seen this with the GT350 or GT500?

This car is supposed to be running the diff cooler from those cars, so the overheating issue was completely unexpected. I'm hoping a simple fluid change will fix it, but wanted to find out if people had to go to more extreme measures for track cars?

I've read lots of horror stories about folks without a diff cooler, but most with the cooler seemed to be fine. I was driving my friend's 350R on track at speed and it was fine as well.
 
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Hi All - took my new Mach 1 to Summit Point main this weekend with my son. The car ran well, though it needs some work to truly go fast.

I ran into an issue I didn't expect, and wanted to ask if anyone else has seen this. After about 10-15 minutes at speed, I got the dreaded Rear Axle overheating error. Looking at the gauge and it's close to 300 - this was on a ~90 degree day. The car is stock, so I plan on changing the diff fluid to 75w140 soon, but has anyone else seen this with the GT350 or GT500?

This car is supposed to be running the diff cooler from those cars, so the overheating issue was completely unexpected. I'm hoping a simple fluid change will fix it, but wanted to find out if people had to go to more extreme measures for track cars?

I've read lots of horror stories about folks without a diff cooler, but most with the cooler seemed to be fine. I was driving my friend's 350R on track at speed and it was fine as well.
Your cooler's not working. Get it to the dealer and get it fixed. Fluid change won't help. Personally, I wouldn't run a 75w140 on a car with a cooler because it makes the pump work harder.
 
Your cooler's not working. Get it to the dealer and get it fixed. Fluid change won't help. Personally, I wouldn't run a 75w140 on a car with a cooler because it makes the pump work harder.
You might be right - seems that neither exhaust valve is working either, and they seem to be tied into the same harness. Starting to feel like an electrical issue.
 
You might be right - seems that neither exhaust valve is working either, and they seem to be tied into the same harness. Starting to feel like an electrical issue.

the exhaust issue seems to be a blown fuse. Not sure why, though. Fuse for the diff pump is good, so that isn’t it.

anyone know how to test the pump? I tried forscan, but the R_DIFF_PUMP pid wasn’t available in the pid selection.

I read in the instructions for theford performance gt350 diff cooler that pulling the temp sensor plug and jumping the terminals will allow the pump to prime. Anyone tried that?

I might try that tomorrow.
 
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What tires? When running Hoosiers/Pirellis, I have to change my fluid more often due to heat. I’ve seen 330 at Road Atlanta before I shut it down.
 
301
360
Exp. Type
HPDE
Exp. Level
3-5 Years
Raleigh, NC
You were running the car in 2 different run groups, correct? Is that too much for our stock cars' drivetrain? I ask because I'm thinking of trying it. But afraid of overdoing it.
 
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...anyone know how to test the pump? I tried forscan, but the R_DIFF_PUMP pid wasn’t available in the pid selection...
The PID is available on Forscan for the GT350, so it's surprising that it's not there for the Mach 1. On the early cars, it's an ECU PID, but it's possible that Ford moved it, maybe to the BCM. Have you checked other modules to see if the PID's somewhere else?
 
You were running the car in 2 different run groups, correct? Is that too much for our stock cars' drivetrain? I ask because I'm thinking of trying it. But afraid of overdoing it.

That was the plan but we never made it that far. I overheated the rear axle on my first run group of the day, on both days. As I run red group, I was the first run group. We didn’t try back to back after that.
 
The PID is available on Forscan for the GT350, so it's surprising that it's not there for the Mach 1. On the early cars, it's an ECU PID, but it's possible that Ford moved it, maybe to the BCM. Have you checked other modules to see if the PID's somewhere else?

Yeah, I went through the entire list of pids looking for it. Both control and read. I couldnt’ find anything labeled “diff” in any of them.
 
301
360
Exp. Type
HPDE
Exp. Level
3-5 Years
Raleigh, NC
That was the plan but we never made it that far. I overheated the rear axle on my first run group of the day, on both days. As I run red group, I was the first run group. We didn’t try back to back after that.
Gotcha. I think I must have talked to your son right after the first overheat.
 
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pilot sport cup 2. Trying to learn what this car can do before moving on to more mods.
Hmmm...hard to say without seeing the conditions the car was in, but it is doable to overheat the diff in my experience. I will admit, it does seem unlikely on Cup2s. I would definitely recommend making sure that the diff pump is working as JAJ said.
 
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Yeah, I went through the entire list of pids looking for it. Both control and read. I couldnt’ find anything labeled “diff” in any of them.
Have you checked to see if there's actually a diff cooler installed on the car? It's supposed to be there, but is it?
 
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Ha ha - yes, I've checked. All of the components are there. I haven't checked the diff fluid level yet as I simply haven't had time, but the cooler/pump etc are there.
So, there's a far-fetched explanation and a simple one: first, the totally wacko one: the ECU software is not configured correctly, which would explain why there's no pump action and no PID. Next, the simple one: the pump is defective and the PID is there but with a different name. Now, the second one is simple but unlikely - the GT350 service manual shows the pump wiring connections including a "DIAG" connection and a "SPEED" connection to the ECU, so if the pump is not connected or if it's not working, the ECU should be aware of the problem and there should be a stored DTC in the ECU.

So, I think the problem is one that IDS can diagnose but Forscan can't. So, a trip to the dealer is in order...
 
So, there's a far-fetched explanation and a simple one: first, the totally wacko one: the ECU software is not configured correctly, which would explain why there's no pump action and no PID. Next, the simple one: the pump is defective and the PID is there but with a different name. Now, the second one is simple but unlikely - the GT350 service manual shows the pump wiring connections including a "DIAG" connection and a "SPEED" connection to the ECU, so if the pump is not connected or if it's not working, the ECU should be aware of the problem and there should be a stored DTC in the ECU.

So, I think the problem is one that IDS can diagnose but Forscan can't. So, a trip to the dealer is in order...

I thought of that, but wanted to avoid the dealer if I can - or at least get as far as I can without it. Haven't had luck with the dealers.

Has anyone seen this: https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4000-M8SGT350.PDF

Based on these instructions from the install, the last page indicates you can jump the temp sensor to force the pump to turn on. I haven't tried it yet, but was considering this option to simply test pump functionality.

The pid thing is also somewhat shocking to me, as I literally checked *every single pid* available in Forscan (and I have a new beta version of for scan I'm testing for the FS guys to try and disable my airbag and seatbelt monitor lights on the car).
 
Update - I checked the diff fluid and it's at the appropriate level. My son is out driving the car now to generate enough heat under normal conditions to test to see if the pump is working.

Second update on the exhaust - well, I discovered why it shorted out the valves on the exhaust. Seems the exhaust pushes into the body under certain conditions and has rubbed the electrical connector to short... In a car with < 500 miles. Ugh. Pic attached. Will post a separate thread for people to check.

Guess it has to go to the dealer no matter what at this point, but might as well know if it also has a bad diff pump.

exhaustvalve - 1.jpeg
 
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I thought of that, but wanted to avoid the dealer if I can - or at least get as far as I can without it. Haven't had luck with the dealers.

Has anyone seen this: https://performanceparts.ford.com/download/instructionsheets/FORDINSTSHTM-4000-M8SGT350.PDF

Based on these instructions from the install, the last page indicates you can jump the temp sensor to force the pump to turn on. I haven't tried it yet, but was considering this option to simply test pump functionality.

The pid thing is also somewhat shocking to me, as I literally checked *every single pid* available in Forscan (and I have a new beta version of for scan I'm testing for the FS guys to try and disable my airbag and seatbelt monitor lights on the car).
I think the FP instructions are based on a switch type of temperature sensor. The way they talk about it, the sensor in the kit switches on the pump if the temperature is high enough, and the on-off switch on the dashboard is essentially a "master switch" to disable it entirely.

According to the section on the diff cooler in the Ford service manual for the GT350, the sensor is an NTC thermistor and if you short the it the ECU will detect it as a fault and set a DTC.

One thing that I hadn't thought about but that's in the troubleshooting section is making sure that there's no obstruction to the airflow through the cooler. All it would take is a plastic bag or something to get into the airway and you'd have an overheated diff with the pump working fine.

Did you find any ECU (PCM) DTC's? There are four:

1628625494278.png

Of course, who knows if the Mach 1 is the same. Can't help you there.
 
I think the FP instructions are based on a switch type of temperature sensor. The way they talk about it, the sensor in the kit switches on the pump if the temperature is high enough, and the on-off switch on the dashboard is essentially a "master switch" to disable it entirely.

According to the section on the diff cooler in the Ford service manual for the GT350, the sensor is an NTC thermistor and if you short the it the ECU will detect it as a fault and set a DTC.

One thing that I hadn't thought about but that's in the troubleshooting section is making sure that there's no obstruction to the airflow through the cooler. All it would take is a plastic bag or something to get into the airway and you'd have an overheated diff with the pump working fine.

Did you find any ECU (PCM) DTC's? There are four:

View attachment 67267

Of course, who knows if the Mach 1 is the same. Can't help you there.

I tried shorting the pump method, but all that did was throw an error on the dash. My son is out driving it to heat it up, so we'll see. Worst case, I guess, I'll put my heat gun on the temp sensor until it gets pretty warm.

I checked for airflow blockage and it was 100% clean. That was my first thought at the track, all good. Other thing is when my son was on track, the car was able to maintain temps. So I feel like the pump was working, but I'd like to confirm it at this point.

I did have a P188A code but that was all.
 
Another update - my son just got back from driving the car and got it up to 210 on the street. I got under the car and the pump was not running as far as we could tell (no noise, no vibration when I touched it). We then put a heat gun on the diff cover near the temp sensor and got it to read 275 on the dash. Again, no activity from the pump whatsoever.

I'm not sure if the pump is designed to only run when the car is moving, but it definitely wasn't on when we were testing it.

I also went through all of the pids in Forscan while the car was running, and couldn't find anything for the diff.
 

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