My '93 indicates ~65 when actual is ~60 (roadside radar, several samples). Will re-check with a borrowed GPS.

My cluster says I still have the full six recalibrations available. Current constant value is 995.

I've read several different methods to determine the needed calibration constant, but they all seem pretty foggy, and they're all for non-Aeros.

Does someone know the number of teeth on the 7.5" tone wheel? Or, even better, a method to use the info I have to determine, on the first try, the correct new calibration constant? Preferably a method that someone has actually used.

I know how to set it, just not 100% sure on how to obtain the number, with an Aero's 7.5" rear axle.

 

I'd like to hear the whole procedure if it's DIY-able. I've read Ford can do it with their scan type tool. Both my Aeros read about 4 mph too high & I'm not gonna change tire size back anytime soon. Let us know if you find the whole truth. I imagine any speedometer shop could do it too.

 

You can recal the speedo/odo (Programmable Speedometer/Odometer Module) via grounding the labelled PSOM wire located behind the passenger side kick panel, then using the Reset and Select buttons on the cluster. You can search on "recalibrate PSOM Aerostart", either here at ford-trucks or Google. There are many articles detailing how to do that.

Unfortunately, there are many different versions of finding out exactly which number to plug in.

You can determine your current calibration constant without grounding the PSOM wire. Also can find out how many recalibrations you can do -- max is six.

 

I have one friend in Cherkassy, his business is Speedos and Tachographs. I asked him how too, he ansvered me that I need Uniprog for EEPROM chips. All the speedos and tachographs have constant saved there. This is 2 bites only, number of pulser per 1/10 of mile ore km. He does all the speedos and instrumental clasters I ever sow.

I tried to search over FTE and got one thread.
https://www.ford-trucks.com/forums/1...eedometer.html

 

A special programmer is not needed to reset the calibration constant on the '92-96 speedometers, but only six resets are allowed.

If all six are "used up", one has to use either the Superlift (~$180) or Dakota Digital ($80) external correction box to change the number of pulses which reach the PSOM.

I am trying to determine how to ascertain the correct new constant. I know how to get it into the PSOM, but not too sure how to get the right number the first time.

 

Ford considered the Aero speedo to meet accuracy specs if it reads between 58>67 mph indicated at actual 60 mph.


SPEEDOMETER INACCURATE -- TEST C


C6 MEASURE TIRE DIAMETER


l To determine the conversion constant perform the following procedure:

-- Hoist vehicle.

-- Measure tire outside diameter (TOD).

-- Note number of rear axle speed sensor teeth, speed sensor ring diameter, or axle capacity/tape group.

-- Verify speed sensor ring diameter with identification tag attached to rear axle cover retaining bolts. If tag is missing manually count teeth.

l Is outside diameter greater than 25.2 inches?



NOTE:
7.5-inch rear axles have 102 teeth and 8.8-inch rear axles have 108 teeth.

Yes
Use formula revs/mile = (1528 - (28x TOD) to calculate SAE average revs/mile. GO to «C4».

No
Revs/mile = 20,850/TOD. GO to «C4».

C4 VERIFY CONVERSION CONSTANT AND DISPLAY MODE


l Check whether the conversion constant in the speedometer is correct with the following procedure: (does not apply to Aerostar EIC)

-- Press and hold the RESET button on the front of the speedometer while turning the ignition switch 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 (MPH) graphics. A lower case "o" signifies an overseas (KMH) graphics. 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 or the constant calculated in C6.

-- Turn off the ignition switch to exit this test.

l Is the programmed conversion constant the same as that displayed on the chart or the constant calculated in C6?

 

Speedo reading vs . (borrowed) Magellan GPS:

 

96_4wdr and asavage: The Aerostar reference librarians for the world! You guys constantly amaze me with your ability to pull out the most esoteric technical information.

The "speedo vs GPS" test was great. After blasting past radar traps all these years with no tickets I became convinced the Aerostar was either a stealth vehicle or had a cloaking device. How humbling to find invincibility is only an illusion.

 

it's the fiberglass hood and liftgate.
absorbs radar ether waves and doesn't reflect laser light waves



the real stealth gear on the Aero are the kicker panels, they rust off and the cops can't even see an Aero from the side

 

I thought it was because whenever they looked at the speed, they thought that their radar/laser gun was on the blink, because there is no way a mini-van could be doing that.

 

There seem to be a few vids on YouTube of people breaking 100 MPH in Aeros. I watched a couple and shrugged: this is remarkable? I've done that easily in mine, even with the little 3.0l .

Of course, this is with the 10% error on the speedo on the '93.

My '89's digital dash's speedo was spot-on though, according to streetside radar checks. Too bad it would only read to 85 MPH It had spent a lot of time reading 85