I'm going through calibrating my PSOM due to my larger tires. The original value was 9.84.

The calculations I have found rely on using the tone ring tooth count to set the value. I have found the tooth count for the Bronco's is 108 and the F250/F350 is 120.

Does anyone know the tooth count for the tone ring in a 93 E250 with a Dana 60?

I would assume it was 120 because of the similarities in the F and E series, but using the PSOM calculations I found, based on the stock tire size of 225/75/16, it makes no since why the stock value is 9.84.

That would mean the tooth count would be around 110-112.

 

I can't verify how many teeth are on the tone ring, but I can relate my experience.

vehicle: 1996 E350 5.8l, 225/75x16E tires.

The speedo has always been 3mph high @ 60mph, so about 2 weeks ago I finally got
brave enough to reprogram the PSOM. I calculated that the CAL value should be 10.68.
I was expecting the factory calibration to be about 10.33, surprise! it was 10.65. I think
I expected 10.33 because that's the CAL for the 245 size tires, std. on some models &
the math for 225 to 245 worked out to a 3mph diff. @ 60mph. So, I wound up setting
the PSOM CAL to 11.00(the highest setting), checking my new setting against my GPS
revealed that I was correct in the change(+.35), speedo is spot on!

I hope this helps in some way, DDK

 

What calculation were you using to get your calibration number?

The one i found on another site (1983 Ford Bronco PSOM picture | SuperMotors.net)
ConvConst = RevsperMile x ToneRingTeeth / 8000

With my stock setting of 9.84 and 120 teeth, it matches up EXACTLY with the F-Series trucks having LT235/85/16 tires and 120 teeth which are significantly taller than the stock 225/75/16's (31.7" tall vs 29.3" tall)

Also your van having that calibration being totally different than mine is strange. Yours actually is very close to what the calibration should be vs WAY WAY off on mine.

With the fact that mine matches exactly with a F250 calibration, I wonder if my PSOM was swapped out with a new PSOM due to the referenced TSB for jumping speedo but without setting the calibration correctly. It still has all 6 calibrations on it.

 

So I went ahead and changed it based on 120 teeth. My calculation for my 285/70/17 tires came out to be 9.525. I changed the calibration to 9.53 and took her for a test drive and the Speedo was dead on the money compared to the GPS on my phone. Before it was off by about 2 to 3 mph.