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3.73 to 4.88 Gear Swap Problems in 2020 Bullitt

L0566Bullitt

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On June 5th I bought a 2020 Bullitt. Love the car but first thing I noticed was how long the gears were. I could never do a pull and even get into 4th on the highway. That's ridiculous. What a waste of 4th, 5th, and 6th gear. So with only 1800ish miles on it, I took it to East Coast Gear Supply and had them swap the stock 3.73s for 4.88s. Completely different car, pulls insane and now it actually feels like a 500+ hp car. However, the PCM does NOT like the new gears. It's throwing all sorts of blindspot, parking aid, cross traffic, neutral switch shorted to ground, abs, and powertrain control module faults. I took it to the dealer and they have no idea what's wrong. They said somehow they're all tied in to the network and if one thing is off (like gear ratio), then it throws everything off. They said they put a request into corporate Ford for help. In the mean time, I took it home and hooked it up to Forscan which found all sorts of DTCs. In the BdyCAM there are two rows for "Axle Ratio". One row let's me manually enter 4.88 which is good, but the second one only let's you select 4.10 as the lowest gear ratio. Since I have the one above it set to 4.88, the one below reads something like "48800 - Incorrect or Incompatible Configuration" or some sort of error.

I have a few questions. Has anyone heard of a gear swap messing with the BLS/rear parking aid/cross traffic/ABS/neutral switch sensors? I will say that when I first drove it home off the lot, I noticed it never displayed the gear I was in like I had noticed in some videos previous to purchasing. I just thought I didn't have the display set correctly. It also had some faults show up but I just thought it was buggy software so I restarted the car and they'd all go away. Every once in awhile I'd receive some of the same faults and it wouldn't allow me to change drive modes and/or steering options. I once again just thought it was buggy and didn't pay much attention to it. But now that I'm getting the neutral switch shorted to ground fault, it's all making sense now. After I clear that DTC, as soon as I drive down the driveway about 50 feet, the neutral switch DTC is thrown and I lose my gear position indicator on the dash. Instead of showing N, R, 1st, 2nd, etc., it's just blank (see pics below).

Fast forward to getting the gears upgraded, and now it does this ALL the time. They drove it before and after and even they noted it was messed up. I told them not to worry about it because it had done it before so I just figured a simple reboot would fix the problem like before. But the difference is after they swapped the gears it does it ALL the time now. Question is, are there sensors down by the rear axle they could have broken and/or plugged in backwards?? Both the left and right Side Obstacle Detection Control Module (SODCMs) are throwing faults as well. I've used Forscan to do module resets on every single module I can, cleared DTCs, did PCM relearning, EVERYTHING I can think of to try and clear these faults but nothing makes them go away permanently.

I told the first dealer (where I purchased it from) it almost seems as if there's a wiring problem since I'm getting "shorted to ground" faults. He said that is definitely not uncommon for these cars. I was surprised to hear that.

A different Ford dealer also told me that changing the values in Forescan isn't enough and that the PCM actually has to be flashed for 4.88s to match what is set in the modules that Forescan can write to. This doesn't make sense to me; isn't Forescan writing values TO the PCM?

As a last resort, I purchased an SCT X4 from Steeda as they seem to be the only ones with a Bullitt tune so I'm hoping I can set the gears to 4.88 there. I'm not going to do anything else because I don't want to void the warranty. Everyone says SCT can do 4.10s and 4.56s but no one knows if it can do 4.88s. Anyone know if the SCT X4 can flash 4.88s as well??

In one of the pictures you can see I'm in 6th gear but there's no indicator in the center of the tach...it's just blank.

The other pictures are of the wires shorted to ground. I think it may actually be a wiring problem??

Any input is greatly appreciated.
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IMG_20200820_214903.jpg
IMG_20200820_214908.jpg
IMG_20200821_165530.jpg
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Elp_jc

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That tranny wiring issue might be causing all other faults. And even if it's not, you need to get that corrected first, to know what you need to fix due to the rear-end change. I know nothing about that, but once you take care of that problem, you should be able to get help with just the diff change. Noticed your car is displaying the correct speed already (my Bullitt would show over 90 mph at 2,600 rpm in 6th), so that's good news. At any rate, you haven't touched the tranny, so you shouldn't have any issues with a warranty claim for that. Good luck.
 

Bear_Stang

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On June 5th I bought a 2020 Bullitt. Love the car but first thing I noticed was how long the gears were. I could never do a pull and even get into 4th on the highway. That's ridiculous. What a waste of 4th, 5th, and 6th gear. So with only 1800ish miles on it, I took it to East Coast Gear Supply and had them swap the stock 3.73s for 4.88s. Completely different car, pulls insane and now it actually feels like a 500+ hp car. However, the PCM does NOT like the new gears. It's throwing all sorts of blindspot, parking aid, cross traffic, neutral switch shorted to ground, abs, and powertrain control module faults. I took it to the dealer and they have no idea what's wrong. They said somehow they're all tied in to the network and if one thing is off (like gear ratio), then it throws everything off. They said they put a request into corporate Ford for help. In the mean time, I took it home and hooked it up to Forscan which found all sorts of DTCs. In the BdyCAM there are two rows for "Axle Ratio". One row let's me manually enter 4.88 which is good, but the second one only let's you select 4.10 as the lowest gear ratio. Since I have the one above it set to 4.88, the one below reads something like "48800 - Incorrect or Incompatible Configuration" or some sort of error.

I have a few questions. Has anyone heard of a gear swap messing with the BLS/rear parking aid/cross traffic/ABS/neutral switch sensors? I will say that when I first drove it home off the lot, I noticed it never displayed the gear I was in like I had noticed in some videos previous to purchasing. I just thought I didn't have the display set correctly. It also had some faults show up but I just thought it was buggy software so I restarted the car and they'd all go away. Every once in awhile I'd receive some of the same faults and it wouldn't allow me to change drive modes and/or steering options. I once again just thought it was buggy and didn't pay much attention to it. But now that I'm getting the neutral switch shorted to ground fault, it's all making sense now. After I clear that DTC, as soon as I drive down the driveway about 50 feet, the neutral switch DTC is thrown and I lose my gear position indicator on the dash. Instead of showing N, R, 1st, 2nd, etc., it's just blank (see pics below).

Fast forward to getting the gears upgraded, and now it does this ALL the time. They drove it before and after and even they noted it was messed up. I told them not to worry about it because it had done it before so I just figured a simple reboot would fix the problem like before. But the difference is after they swapped the gears it does it ALL the time now. Question is, are there sensors down by the rear axle they could have broken and/or plugged in backwards?? Both the left and right Side Obstacle Detection Control Module (SODCMs) are throwing faults as well. I've used Forscan to do module resets on every single module I can, cleared DTCs, did PCM relearning, EVERYTHING I can think of to try and clear these faults but nothing makes them go away permanently.

I told the first dealer (where I purchased it from) it almost seems as if there's a wiring problem since I'm getting "shorted to ground" faults. He said that is definitely not uncommon for these cars. I was surprised to hear that.

A different Ford dealer also told me that changing the values in Forescan isn't enough and that the PCM actually has to be flashed for 4.88s to match what is set in the modules that Forescan can write to. This doesn't make sense to me; isn't Forescan writing values TO the PCM?

As a last resort, I purchased an SCT X4 from Steeda as they seem to be the only ones with a Bullitt tune so I'm hoping I can set the gears to 4.88 there. I'm not going to do anything else because I don't want to void the warranty. Everyone says SCT can do 4.10s and 4.56s but no one knows if it can do 4.88s. Anyone know if the SCT X4 can flash 4.88s as well??

In one of the pictures you can see I'm in 6th gear but there's no indicator in the center of the tach...it's just blank.

The other pictures are of the wires shorted to ground. I think it may actually be a wiring problem??

Any input is greatly appreciated.
IMG_20200820_214856.jpg
IMG_20200820_214903.jpg
IMG_20200820_214908.jpg
IMG_20200821_165530.jpg
Sounds like the wiring issue preceded all the other stuff. Unless dealer can prove the wiring issue was caused the install, they should fix it.

If not, reach out to James (the guy that made the steeda tune). Someone on the steeda sub should get you linked up with him. He might be able to can it so you can adjust for the new gear. Then just fix the wiring with a local trusty shop.
 
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L0566Bullitt

L0566Bullitt

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There were some questions as to the MPG I'd get with these 4.88 gears. I reset my trip when I left home and around 3 hours/210 miles into the trip, hit exactly 24.0 MPG. Speed limits ranged from 55 - 70 MPH so my speed ranged from 64 - 79 MPH (2,600 - 2900 RPM). I was hoping to get better than 24 and see maybe 24.1 but hit some mountains so by the time I arrived my final average was 23.8 MPG at 238 miles.

Pulling high vacuum/low load allows for a smaller fuel pulse which offsets the higher RPMs. I think the AFR is too rich at high vacuum/low loads and even better MPG could be achieved with a leaner AFR at high vacuum.

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PXL_20201218_204536072.MP~2.jpg

Cruising vacuum on the level
 
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Schwerin

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Sounds like a possible wiring issues, but you WILL need a tune(likely custom) for 4.88 gears. The built in Ford software ONLY supports the gears that Ford themselves sell/offer. Any well known Mustang tuner can make one for you. Tuning By James made the Steeda Tune, I'd reach out to him or Lund Tuning. Both have great tunes and will offer remote/phone support.

I'm actually surprised your RPM/MPH is correct, I wonder if the speedo measures actual axle speed now. As fast as the other systems are concerned they likely think your spinning way to fast and have a traction problem.
 
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L0566Bullitt

L0566Bullitt

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Sounds like a possible wiring issues, but you WILL need a tune(likely custom) for 4.88 gears. The built in Ford software ONLY supports the gears that Ford themselves sell/offer. Any well known Mustang tuner can make one for you. Tuning By James made the Steeda Tune, I'd reach out to him or Lund Tuning. Both have great tunes and will offer remote/phone support.

I'm actually surprised your RPM/MPH is correct, I wonder if the speedo measures actual axle speed now. As fast as the other systems are concerned they likely think your spinning way to fast and have a traction problem.
My most recent post is after having everything fixed/corrected by a Steeda tune.
 

driden

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My most recent post is after having everything fixed/corrected by a Steeda tune.
Hi. I was curious how things are going now. Still having issues or did you get them all lined out?

I wonder, what gearing is supported by Ford and is a tune needed? I guess another way to ask is what gearing is supported by the software?
 

RonsterGT

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I know the Ford Performance ProCal 4 device that came with the CAI and calibration kit for my 2020 GT allows for gear changes. It was an option in main menu. Has pre-loaded ratios or can enter custom ratio.

Maybe reach out to Ford Performance and buy a ProCal 4 for your car?
 
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L0566Bullitt

L0566Bullitt

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Hi. I was curious how things are going now. Still having issues or did you get them all lined out?

I wonder, what gearing is supported by Ford and is a tune needed? I guess another way to ask is what gearing is supported by the software?
From what I understand, anything lower than 4:09 is not supported by Ford. The SCT/Steeda tune (only tune available for the Bullitt at the time) corrected all my issues. Just had to select the 4.88 axle option when loading the tune and good to go.
 

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chesster51

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Correct. SCT/Steeda tune fixed everything.

And thanks! The 4.88s feel amazing. Perfect combo in my opinion.
It would seem first gear would almost be a granny gear now. I'm sure starting in second gear is no problem now. If I may, what did the gear change cost you?
 
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L0566Bullitt

L0566Bullitt

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It would seem first gear would almost be a granny gear now. I'm sure starting in second gear is no problem now. If I may, what did the gear change cost you?
First is really not that bad...perfect for stop and go traffic. Much better on the clutch.

Gears and installation were $1,579.30, not including the $641.95 Steeda tune. So all said and done, $2,221.25.

Starting in second isn't a problem, but I still usually start in 1st. The transmission is so incredibly high geared that even now 1st isn't too low...it's just right in my opinion.
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