This has been driving me nuts for months and I am finally throwing in the towel and asking for help.

I have a 1998 Ranger 4x4 that I swapped a 5.0 AWD into. All explorer wiring from the back of the cab forward (including engine bay). Speedometer functions, so rear sensor is good. Ranger was 4 wheel ABS, explorer was 4 wheel abs, both of same year.

I was using the Ranger 4x4 ABS module for the build, and it worked sort-of c1102 code kept getting thrown, however I did notice that two of the wires are different between the explorer harness and ranger harness (data wires to PCM), so I assumed the ABS module was incompatible electrically, and installed the known working module from the explorer. Both vehicles had 0 abs issues before the swap.

I have the ranger front hubs and ranger 7.7 rear end on the truck, using the ranger sensors. I have the frame sensor from the explorer, plugged into the factory ranger wiring, which is wired correctly under the driver seat to the explorer wiring. I had ABS code C1102 for the frame sensor, after replacing the ABS module which is electrically compatible with the wiring, the C1102 code is cured.

This is where it gets weird.

I have Forscan and can graph out, in real time, all three wheel speed sensors (front left, front right, and diff) and went for a drive around the block to see which sensor was dropping out. All sensors report as normal, until I hit a bump, then the scanner loses connection with the module, all sensors drop to 0, and the abs activates (pulses the pedal, can hear the abs motor spinning under the hood), and brake force is reduced almost always doubling the stopping distance.

It sounds like a bad wire, possibly ground or power to the unit, but what throws me off is the ABS is under full activation like a wheel is stopped, while im doing any speed. If it was a bad ground or power, the ABS module wouldn't be able to bypass braking force or spin the ABS pump, if it was a bad data line, it would throw a code for loss of communication to module.

I did a KOER shake test of all under hood wiring to try to replicate the loss of communciation issue with my scanner. I can access the PCM module and Airbag module while driving with 0 issue when I hit bumps. I lose connection to the ABS module when I hit bumps.

To be clear, the ABS activates at ANY speed, and speedometer functions 100% of the time. Brakes work normal half of the time, the other half of the time the pedal buzzes regardless of speed (any speed. 70mph, 2mph, it doesn't matter), and while applying the brakes, I can view wheel speed, until a bump is hit, then the scanner loses communication, and the pedal starts buzzing. Next stop, no issue.

I unplugged the ABS module plug, sprayed contact cleaner, and applied dialectric grease - no change. My next best guess is the main 3 plug firewall bulkhead connector could have a poor connection on one of the lines.

I'm tearing my hair out over this one. HELP!!!

Here is a wiring diagram if it helps

 

Something to add - I was doing some scouring of the internet and think it is common for Fords to lose data communcation with a scan-tool during abs activation as the computer in the ABS module is devoting all available resources to controling the brakes and doesn't have enough processing power left over to send data back over the data bus. Also, the frequency of the pedal buzzing does change with speed. Goes from a buzz at high speeds to a thump-thump-thump at low speeds.

After changing the tire diameter in the ABS module using Forscan, my speedometer is incorrect by about 5MPH. When I did this with the ranger ABS module, my speedometer was 100% correct to GPS. The Ranger ABS module has a section in the code to program the tone ring count inside the diff, as does the explorer.

I may have figured it out now. I switched the ABS module from the explorer into the Ranger because of the data communication issue with the PCM. That is now fixed, but it has a wheel slip issue. The Explorer 8.8 that the ABS module is programmed to has the 108t tone ring, while the 7.5 that is on my truck has the 102t. This might be enough to freak out the ABS module and would also explain my 5% speedometer discrepancy. I changed the option from 108 to 102, will report back tomorrow.