What's a PSOM & how do I "P" it??? - Page 15 - Ford Bronco Forum
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post #281 of 300 (permalink) Old 10-03-2014, 09:30 AM
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Thanks Steve! Been running 32's for 2 years and just went to 33's. Got pulled over last night for doing 9 over in a 35 and the cop liked the Bronco so much he let me go with a warning! Easy to do, took me about 5 minutes and per GPS, I'm dead nuts now.
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post #282 of 300 (permalink) Old 08-20-2015, 12:56 AM
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Just checked my PSOM. It read ...."0 08 6" so I know that it hasn't been changed yet. My "conversion constant" number said 972CAL. Doesn't that seems a bit high for my Broncos original stock tire size of P265-75R15SL that was on my door sticker??? I don't know what brand they were originally but I used the TireRack site to check the rev/mile of the 265's and the 6 tires available were 679 rev/mile.

so.....679x108/8000=917....BUT mine is set to 972.... it doesn't make sense to me???

972CAL is more along the lines of between a 225 and a 235 tire.

It had 31's on it when I bought it and I just put 33's on it. The SPEEDO seemed to be right on with the 31's on it according to a speed reader unit near my home when I was driving at 30mph. It might have been off at higher speeds but I didn't notice. I have noticed a 5mph difference with the 33's though at 30mph and possibly more at higher speeds.

My new BFGoodrich T/A KO 33x12.5x15's have a rev/mile on the TireRack website of 636 rev/mile.

so.....636x108/8000=859.....Should I just go with that??? What do you think Steve?
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post #283 of 300 (permalink) Old 08-20-2015, 12:38 PM
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Originally Posted by Sturgeonsurgeon View Post
Just checked my PSOM. It read ...."0 08 6" so I know that it hasn't been changed yet. My "conversion constant" number said 972CAL. Doesn't that seems a bit high for my Broncos original stock tire size of P265-75R15SL that was on my door sticker??? I don't know what brand they were originally but I used the TireRack site to check the rev/mile of the 265's and the 6 tires available were 679 rev/mile.

so.....679x108/8000=917....BUT mine is set to 972.... it doesn't make sense to me???

972CAL is more along the lines of between a 225 and a 235 tire.

It had 31's on it when I bought it and I just put 33's on it. The SPEEDO seemed to be right on with the 31's on it according to a speed reader unit near my home when I was driving at 30mph. It might have been off at higher speeds but I didn't notice. I have noticed a 5mph difference with the 33's though at 30mph and possibly more at higher speeds.

My new BFGoodrich T/A KO 33x12.5x15's have a rev/mile on the TireRack website of 636 rev/mile.

so.....636x108/8000=859.....Should I just go with that??? What do you think Steve?
Steve isn't going to answer, he's no longer with our group.

Are you sure the PSOM wasn't swapped out before? 265's are equivalent to 31's and stock cal for that is 918. Therefore the reading of 972 makes me think someone swapped it before.

Your math looks correct. You should be at 859
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post #284 of 300 (permalink) Old 08-20-2015, 03:10 PM
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Steve isn't going to answer, he's no longer with our group.
What happened with Steve??

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post #285 of 300 (permalink) Old 08-20-2015, 04:20 PM
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What happened with Steve??

tim
Steve83?
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post #286 of 300 (permalink) Old 08-20-2015, 05:22 PM
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Thanks, had no idea. I have been busy and haven't been on as often lately. I was just surprised and curious too I guess.

Oh well,
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post #287 of 300 (permalink) Old 08-20-2015, 09:46 PM
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Originally Posted by sackman9975 View Post
Steve isn't going to answer, he's no longer with our group.

Are you sure the PSOM wasn't swapped out before? 265's are equivalent to 31's and stock cal for that is 918. Therefore the reading of 972 makes me think someone swapped it before.

Your math looks correct. You should be at 859
Thanks
I was wondering if my PSOM had been replaced. It could have been I guess. My PSOM read 0 08 6. That indicates Canada I believe. My VIN starts with a 1 which indicates made in USA?.......hmmmmm
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post #288 of 300 (permalink) Old 08-20-2015, 09:50 PM
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20 years is a long time for nothing to be swapped. Especially since the bronco has such a wonderful online forum of knowledge available, anything is likely to have been done over 20 years. I always keep a spare instrument cluster just in case and for trouble shooting.

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post #289 of 300 (permalink) Old 08-23-2015, 01:08 PM
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20 years is a long time for nothing to be swapped. Especially since the bronco has such a wonderful online forum of knowledge available, anything is likely to have been done over 20 years. I always keep a spare instrument cluster just in case and for trouble shooting.
My 94 Bronco has 315000kms on the Odometer(195000 miles). I was told that the motor had been rebuilt when I bought it 9 years ago. My Bronco sat for 8 years during that time. I guess the PSOM may have been replaced by PO with a 92-97 Econoline or Aerostar PSOM as they may have come with the smaller 225-235 stock tires which would account for my High 972CAL #???
I can't imagine that a F-Series or Bronco came stock with that small a tire though?
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post #290 of 300 (permalink) Old 08-23-2015, 07:29 PM
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My 94 Bronco has 315000kms on the Odometer(195000 miles). I was told that the motor had been rebuilt when I bought it 9 years ago. My Bronco sat for 8 years during that time. I guess the PSOM may have been replaced by PO with a 92-97 Econoline or Aerostar PSOM as they may have come with the smaller 225-235 stock tires which would account for my High 972CAL #???
I can't imagine that a F-Series or Bronco came stock with that small a tire though?
Can you post a picture of your PSOM?
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post #291 of 300 (permalink) Old 08-24-2015, 10:11 PM
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Can you post a picture of your PSOM?
Here's the front:

and here's the back:
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post #292 of 300 (permalink) Old 11-25-2016, 05:51 PM
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Steve83 saving the day again! I imagine he's gone from here because he seems very short tempered with the noobs on here, but he's a wealth of knowledge to say the least! I found this thread by accident and I'm glad I did. My 94 has BF Goodrich A/T 33x10.5x15 and they are not stock. I've only have the truck for about 6 months and I've noticed the speedo has been off by about 5 mph at highway speeds. It bothered me a little but I just compensated (when I remembered). Thanks to this thread, I was able to check my current CAL settings and found it to be at 918 with 6 changes left. I, very easily, changed it to 864 based on the 640 revspermile I found at Tire Rack and using the formulas in this thread.

The speedo is now spot on up until about 55mph. At 60-70 it's off by 1-2 mph which is acceptable in my book. (Verified against the GPS on my phone)

Thanks again! Love this site!

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post #293 of 300 (permalink) Old 02-10-2017, 01:22 AM
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In Post #1 there's nothing but a link to a photo. I thought the useful information from the post was just gone entirely and I was feeling unhappy. Clicking the photo opened up a new window with a picture that didn't look remotely useful, as I'd come here hoping to learn the steps to take to reprogram the cluster in my '95 to display accurate speed and mileage count while running larger tires. I'm not terribly swift sometimes, and it took me a moment to realize that the linked photo was marked "#2 of 10," so I clicked "previous" and voila, there is a picture with a very lengthy caption describing the reset procedure along with a few other things. I'm sure there was no need for me to make this post, but maybe it will help someone. Photo #1 is the one with all the info.

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post #294 of 300 (permalink) Old 02-12-2017, 11:36 PM
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Well, I followed the steps properly, but my speedometer doesn't seem to be accurate. Wondering if I did something wrong somehow, or if this is the way it's supposed to be.

With these new tires, but before having made any changes, the speedometer was showing about 6-7 mph less than I was actually going, for instance it would show 60mph when I was doing 66-67.

(My previous tires were BFG 31x10.50R15 on stock size rims. No known accuracy issues with my PSOM at that time.)

My tires now are Goodyear Duratrac 33x12.50R15, so I got my Revs Per Mile from the manufacturer's website. The Revs Per Mile is stated as 635, which I plugged in to the formula (RpM) x 108 / 8000, giving me 8.5725, which rounds down to 8.57. I double-checked using the formula on this page, (RpM) x 0.0135, which also gave me 8.5725.

Connected my ground, changed my PSOM (e 08 6) to 857CAL.

GPS shows I'm doing about 2mph less than the speedometer now says. If the cluster reads 30mph, gps says 28. If the speedometer says 60, gps says 58. The trip odometer shows a discrepancy as well; what my cluster reports as a 16.0-16.1 mile trip, the GPS reports as 15.8.

It *appears* to be accurate between 40 and 50 mph, but not on either side of that range.

Based on my math, using what I in good faith believe to be the correct Revs Per Mile, the conversion constant of 8.57 should be right, which means that what I'm seeing right now should be normal...? Do I leave things as they are, or waste one of my changes to set the conversion constant at the commonly-cited 8.59 (based on BF Goodrich 33's)? If that doesn't work to fix the accuracy, I'll have to waste ANOTHER change to set it back to 8.57, because I at least know that's what it "should" be.

Please advise. I don't want to let this go for too long.

1995 Eddie, 5.8/E4OD, 232K, BDS 4" Long Arm Lift, 33" Duratrac on Black Daytonas, Warn Premium hubs, WAAG brush guard, Wolo air horn, Alpine/MTX audio, 2.5" Super 44 exhaust, AutoMeter gauges, Westin step bars, factory cargo shade

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post #295 of 300 (permalink) Old 02-13-2017, 01:25 AM
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Well it looks like you got closer to your goal! If you run through the procedure WITHOUT grounding the PSOM connector, can you verify that your changes did in fact save? Your PSOM should now read e 08 5 if the changes were accepted... Just a thought. Without the PSOM grounded, you can't inadvertently use up one your "changes" while in programming mode.

Also, if you read back through the thread, I recall reading somewhere that +/-3 mph is supposed to be "within spec" for the PSOM... Perhaps you're spot on with your calculation.

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post #296 of 300 (permalink) Old 02-13-2017, 01:38 AM
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Here's a pretty good read about speedometer accuracy in general.

Speedometer Scandal! - Feature - Car and Driver

Your tire pressure and ambient temperature also plays a role in the accuracy, as mentioned. The article sums things up by saying "allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph."

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post #297 of 300 (permalink) Old 02-13-2017, 02:07 AM
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Well it looks like you got closer to your goal! If you run through the procedure WITHOUT grounding the PSOM connector, can you verify that your changes did in fact save? Your PSOM should now read e 08 5 if the changes were accepted... Just a thought. Without the PSOM grounded, you can't inadvertently use up one your "changes" while in programming mode.
I ran through the verification procedure, and the changes are in, I have only 5 remaining attempts now.

The only other number I could think to change it to would be 859 (it's at 857 now) based on the cited example 33x12.50R15 BFG tires (which, by the way, aren't at 859 in the real world anymore anyway. When these writeups were made, the BFG tire had a revs per mile that put the conversion constant at 859, but the new KO2's have a revs per mile of something like 640, making the conversion constant around 864).

I know I followed the steps correctly. I've even triple-checked the revs per mile [here] and triple-checked my conversion constant [here]. I used an alligator clip test lead to ground my PSOM single-wire connector to the ground on my cigar lighter. I did everything as instructed, and let's be honest, this isn't hard to understand. I know I did it right, and if my Revs Per Mile is right (and the only thing I didn't do was personally mark the tire itself and physically count the rotations) then the number I plugged in should be good.

The only thing I can think of, other than the stated revs per mile being an approximation over the life of the tire (and at that point, it's overthinking. The instructions said get RpM from the tire manufacturer's spec page, and that's what I did) is that these are mounted on a 15x7 stock size rim. This tire is rated for 8.5-11 inch rim range, according to the manufacturer. Maybe that's the problem?

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Originally Posted by jtetterton View Post
Also, if you read back through the thread, I recall reading somewhere that +/-3 mph is supposed to be "within spec" for the PSOM... Perhaps you're spot on with your calculation.
Even if the numbers are right, and the 3 mph discrepancy is within spec, it's still throwing off my odometer a tiny bit. Over time, it will show more mileage on the truck than I've actually driven.

1995 Eddie, 5.8/E4OD, 232K, BDS 4" Long Arm Lift, 33" Duratrac on Black Daytonas, Warn Premium hubs, WAAG brush guard, Wolo air horn, Alpine/MTX audio, 2.5" Super 44 exhaust, AutoMeter gauges, Westin step bars, factory cargo shade

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post #298 of 300 (permalink) Old 02-13-2017, 02:14 AM
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Here's a pretty good read about speedometer accuracy in general.

Speedometer Scandal! - Feature - Car and Driver

Your tire pressure and ambient temperature also plays a role in the accuracy, as mentioned. The article sums things up by saying "allowable range on an 85-mph speedometer is 3.4 mph, and the acceptable range on a 150-mph speedometer is 6.0 mph."
That article sure uses some fancy language. I'd need to read it a couple of times to really digest what they're saying, but I think I get the general drift.

My tire pressure *should* be at about 35psi (which I think is the manufacturer's limit for these anyway) but they were mounted new at a shop I trust, by guys I know personally, only about a month ago, meaning I believe the pressure is about where it's supposed to be, although I have not checked. As for ambient temp, it's a few degrees above freezing today, for whatever that's worth.

It's just that I've been reading this and other threads on this PSOM recalibration, and it seems that when people successfully input the new conversion constant, they always post back with how perfectly accurate the speedometer is. Because mine is questionable, that's why I think there's a problem.

1995 Eddie, 5.8/E4OD, 232K, BDS 4" Long Arm Lift, 33" Duratrac on Black Daytonas, Warn Premium hubs, WAAG brush guard, Wolo air horn, Alpine/MTX audio, 2.5" Super 44 exhaust, AutoMeter gauges, Westin step bars, factory cargo shade

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post #299 of 300 (permalink) Old 02-13-2017, 09:37 AM
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That article sure uses some fancy language. I'd need to read it a couple of times to really digest what they're saying, but I think I get the general drift.

My tire pressure *should* be at about 35psi (which I think is the manufacturer's limit for these anyway) but they were mounted new at a shop I trust, by guys I know personally, only about a month ago, meaning I believe the pressure is about where it's supposed to be, although I have not checked. As for ambient temp, it's a few degrees above freezing today, for whatever that's worth.

It's just that I've been reading this and other threads on this PSOM recalibration, and it seems that when people successfully input the new conversion constant, they always post back with how perfectly accurate the speedometer is. Because mine is questionable, that's why I think there's a problem.


Mine's about 1-2 off above 70mph. My BF Goodrich 33x10.5x15s are max rated at 50psi and that's how I run them.


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post #300 of 300 (permalink) Old 06-09-2017, 03:40 AM
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I just read this and to my relief the 6 is in my favor not against. I did watch Bronco Bobs video too only thing that threw me was my tires are 35x12.5R15 and i knew that number wasnt right on the revs so luckily and for once being patient i found the conversion chart on Goodyear which in the metric system changes it to 318/80/R15 which gives me 778 and add the 30 and i got 808 ...but i didnt round up i see you guys posted 809...Its midnite here so i will punch that number in tommorow ill ground it to the antena and hopefully everything will be copasetic.. By the way my Bronco is a 93 XLT Half Ton with a 4 inch lift. I bought it to be me and my sons Project Vechicle. Thanks for the post guys it was very helpful before i tried anything. Steve your trial and errors helped me if thats any constalation [IMG]
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