[AlaskanBronco]

I've been troubleshooting some issues with the truck, Replaced the VSS and the ECM, but the issues continued. So I figured maybe the PSOM was the culprit and decided to try that. Since I've had a lighting gauge cluster lying around for the last 10 years, I decided to send it to a shop to get refurbished it, program the mileage, and calibrate it for my 32" tires.

Got her installed today and took the Bronco for a test drive, but unfortunately the speedo is WAY off. I don't know if the shop to account for this being a lightning speedo or what, but following traffic around 35-40mph the speedo is showing 60mph. Definitely needs adjusting.

My question for anyone who has done this swap or just knows how these clusters work, is fixing this as simple as going to the ford dealer and telling them my speedo is off? Or do I need to explain the speedo swap and tell them to program it according to the donor vehicle's repair procedure? (94 lightning).

I'd like to avoid multiple programming attempts since these apparently lockout after 6 programming's.

 

[Kingfish999]

look up revs per mile for the tires you use/plan on using

assuming its an 8.8" stock rear axle, it has 108 tone ring teeth. if swapped to a 10.25" then its 120

revs per mile X tone ring teeth / 8000 = what it should be set ofr

you can check what the current is set for and see if its worth changing.

 

[CrazyBRONCOguy]

My bet is the math it different for the lighning speedo. Good luck finding dealer that knows how to do this still.
I think you will have to fix yourself.

Oddly what you describe is almost exactly right if the lightning speedo didn't say 120. it is like the conversion constant needs adjusted to hit the 120 speedo correctly.

 

[Burntoutaccountant]

Don’t lightning have different gearing? I would think it needs reprogrammed.

 

[jermil01]

Lightnings were 4.10 from the factory.

 

[Burntoutaccountant]

Lightnings were 4.10 from the factory.

I have a feeling that is the issue. The PSOM is programmed for 4.10 gears.

 

[BigBlue 94]

I have a feeling that is the issue. The PSOM is programmed for 4.10 gears.

The PSOM does not see or care about gear ratios since the tone ring is on the carrier. Only tire size matters. Now if it were a vehicle with a transfer case mounted VSS or a cable driven speedo, then yes, gears matter.

Im with CBG, 60 on the lightning speedo is about the same place as 40 on the 85mph bronco speedo.

Otherwise, i cant be much help. I never recalibrated the one on my 94.

 

[Kingfish999]

i think Lightning use the same PSOM as the normal trucks. think the guage needle itself is jsut calibrated for the difference. cant find any info on this

first i would see what the current constant is at before we get too deep in this. he says it was calibrated by the rebuilder, doesnt mean it was calibrated correctly. find out what the current calibration is

also make sure it says E and not a lowercase o on the left on one of the displays before. E indcicates English and uses MPH. lowercase O indicated Overseas and uses KPH. 30-40mph is pretty close to the 60kph. maybe accidnetally changed it when rebuilt

Check whether the conversion constant in the speedometer is correct with the following procedure:

-- Press and hold the RESET button on the front of the speedometer while turning the key to RUN.

-- Release the RESET button. The pointer will prove out and some codes will appear on the odometer display. If an "E" is on the left side of the display, the module is programmed for English display mode and should have English graphics (mph). A lower case "o" signifies an overseas (metric) graphics (kph). Verify the graphics and display modes agree. (The number appearing after the type is the microprocessor revision level and is not used in this test.)

-- Press and release the RESET button again. The conversion constant and the word CAL will be shown on the odometer display.

-- Verify the programmed conversion constant is the same as that displayed on the chart. Refer to «Conversion Constants Charts» under Specifications in this section.

-- Turn off the key to exit this test.

 

[sackman9975]

I have programed one of these once.
Let me find out what I calibrated it too and we can do some math too get yours right.
I'll use his programming cal, and his tire size too figure it out. But I got his spot on first try.

What tire size you running?

And yes....I remember this being different than our PSOMs.

 

[sackman9975]

I have a feeling that is the issue. The PSOM is programmed for 4.10 gears.

PSOMs don't care about gear size, only revs per mile for tires. Gear change doesn't change that.

 

[rla2005]

I saw this recently on another forum: Simplified PSOM Calibration using GPS

 

[AlaskanBronco]

i think Lightning use the same PSOM as the normal trucks. think the guage needle itself is jsut calibrated for the difference. cant find any info on this

first i would see what the current constant is at before we get too deep in this. he says it was calibrated by the rebuilder, doesnt mean it was calibrated correctly. find out what the current calibration is

also make sure it says E and not a lowercase o on the left on one of the displays before. E indcicates English and uses MPH. lowercase O indicated Overseas and uses KPH. 30-40mph is pretty close to the 60kph. maybe accidnetally changed it when rebuilt

Alright, I just got home from work, here's the current calibration:

 

[AlaskanBronco]

I have programed one of these once.
Let me find out what I calibrated it too and we can do some math too get yours right.
I'll use his programming cal, and his tire size too figure it out. But I got his spot on first try.

What tire size you running?

And yes....I remember this being different than our PSOMs.

Appreciate the help!

Here's my tire size: 32X11.5R15LT
Revs per mile is 659 according to tirerack.

So when you say these PSOMs are different, do you mean the formula calculation is different?


Following king fishes formula I get the following:
659 x 108 / 8000
= 8.8965

My current CAL setting as programmed by ModuleMechanics is 9.20

 

[AlaskanBronco]

I saw this recently on another forum: Simplified PSOM Calibration using GPS

Cool idea, I'll try this in a little while and report back what I come up with.

 

[Kingfish999]

9.20 would be for ~30.5-31" tire. so thats off alittle. but not alot. (9.20 x 8000 / 108 = 681.5 revs per mile)

so heres the problem. the ECM still needs the correct speed signal in order to shift the trans correctly. so if you do the GPS method and scale the PSOM calibration so the speedo works correctly, then the ECM will see a much lower MPH than what your doing and it will shift weird

i would send it back and have them fix it

 

[sackman9975]

9.20 would be for ~30.5-31" tire. so thats off alittle. but not alot. (9.20 x 8000 / 108 = 681.5 revs per mile)

so heres the problem. the ECM still needs the correct speed signal in order to shift the trans correctly. so if you do the GPS method and scale the PSOM calibration so the speedo works correctly, then the ECM will see a much lower MPH than what your doing and it will shift weird

i would send it back and have them fix it

920 CAL would be for Lightning factory tires 275/60/17 if the CAL is still on number 6 setting

Factory Lightning tie side is 275/60/17 and has 673 revs per mile
673x108/8000=9.085 (909 cal)

So there's a little bit of difference
Need to reverse math so that 920 equals 673 revs and I figured this:

So 673 x 108 / 7900 ≈ 9.200
So you'll need to do the math as this

659 x 108 / 7900 = 9.009 (901 CAL)

This is all ringing a bell now and I'm confident that a 901 CAL with the 120mph Lightning PSOM will be spot on .

I will have more info as to what I programmed the other one too this weekend. He's going to check his CAL #

 

[Kingfish999]

if the PSOM is currently set at 9.20 and he needs 8.90 for his 32" tires, thats only about ~4% difference. like i said its off alittle but not alot

so regardless if he is truely off by as much as he is saying he is off, he needs to send it back to get it corrected.

if hes doing 35-40mph and its showing 60mph, thats a 50-70% increase. if he tried to scale the PSOM constant so the speedometer is accurate, then the ECM will have the wrong signal and the trans will shift at wrong times because it will also be scaled

 

[AlaskanBronco]

Sounds good Sackman! I'll wait for you to confirm with your man and I'll look up a good programing tutorial so i'm ready to go when we decide on numbers.

I just got back from testing out Rla2005s GPS method, here were my results.

Speedometer Reading​	GPS Reading​
35	25
45	35
60	45
75	55
85	65

So around town at slow speeds, the discrepancy starts at 10mph,goes up to 15 and gets as high as 20-off starting @ 55mph (And probably gets worse at even higher speeds). I'm a little concerned that the off ratio changes so dramatically at higher speeds, but I think I read in other threads on this topic it's normal for that difference to get worse at higher speeds?

Anyways following the gps calibration method from the ford-trucks forum gave me this:

Speedo/GPS
85/65 = 1.307

Current CALXXX number x above fraction
920 x 85 / 65 = 1,203.07 ?
= 1.2?

^^^Had to edit all this because i got some of the numbers backwards, but now i'm coming up with 1,203? I probably fucked that up.

 

[AlaskanBronco]

View attachment 209366

if the PSOM is currently set at 9.20 and he needs 8.90 for his 32" tires, thats only about ~4% difference. like i said its off alittle but not alot

so regardless if he is truely off by as much as he is saying he is off, he needs to send it back to get it corrected.

if hes doing 35-40mph and its showing 60mph, thats a 50-70% increase. if he tried to scale the PSOM constant so the speedometer is accurate, then the ECM will have the wrong signal and the trans will shift at wrong times because it will also be scaled

I went out and did a test with a GPS, apparently 35 actual is 45 on my speedo, so it's not as bad as what I first guessed from the eyeball test, but the difference does get worse at higher speeds. Though from what I read that's normal? but I'm fairly clueless about this PSOM stuff.

Are you suggesting that there is some baseline programming of the speedo that is messed up that can't be corrected by adjusting the calibration code? If so, what would I tell the company in order to help them program it correctly? Tell them my GPS speed test results and hope they can figure out what went wrong the first time? Or since it's not off by as much as I first thought, do you still think it needs to be sent back in?

 

[Kingfish999]

35 / 25 = 40% faster than actual
45 / 35 = 29% faster than actual
60 / 45 = 33% faster than actual
75 / 55 = 36% faster than actual
85 / 65 = 30% faster than actual

25 / 35 = 0.71
35 / 45 = 0.78
45 / 60 = 0.75
55 / 75 = 0.73
65 / 85 = 0.76

matter of perspective how you view it.

the faster you go when comparing them the more accurate it will be

a job of the PSOM is to convert the rear axle signal to tell the ECM how fast the truck is going. the ECM expects an 8000 pulse per mile reading which is where the 8000 in the forumla comes from.

so if you scale the PSOM constant to fool the speedometer to read correctly, now the signal to the ECM will also be scaled. this means it will shift the transmission at the wrong points. your trans would shift alot later than normal