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Very weird 1998 Ranger ABS issue


masnecar

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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.

 
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masnecar

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Something to add

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.*
 

Dirtman

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I have no answer for you, someone definitely will soon. Im just not an ABS guy... But can I use your post as a "how to ask for help" example in another thread? Long story short, im trying to explain how details matter in a "help" post, and you are the prime example of a perfect help post lol.
 

masnecar

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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.

Dirtman, Yes you may. I've worked in a shop for years and fully know the details matter. Thankfully I have a way of being able to relay what I am experiencing to a keyboard lol
 

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masnecar

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update

Ok so that seemed to fix the constant ABS activation issue, now I have it more pinpointed. If i hit the brakes over 30, it doesn't activate. If the speedometer crosses 35ish with my foot on the brake, it activates. If i press the brake between 35 to 15 it activates. under 15, no abs activation.
 

Bgunner

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Possible weak sensor. The wheel sensor may have enough magnetic pull to tell the the wheel is spinning the same as the others in certain circumstances but at certain speeds the magnetic pull is to weak to accurately read the wheel speed causing the issue.

This is sort of a stab in the dark but seems more likely with the tests you are doing. worth a look into. If your scanner has a graph option for wheel speeds run it while the vehicle is in motion and see if the signal drops off on one, or more, wheels when the ABS kicks in.
 

masnecar

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Its nearly impossible to get a graph of the ABS sensors when it is activating - which starting today it has a new issue. I can hear the pump buzzing around 45mph when my foot is off the pedal. It goes BRRR for about 10 seconds then stops. I did uncover what appears to be a failing rear axle sensor though.

From my understanding of the ABS system on these trucks, the speedometer gets its data from the ABS module, that calculates the speed based on the rear wheels. The speedometer works perfectly fine, and never stutters. After I switched the modules, I had a code for the VSS in the PCM, so I am going to inspect (and bypass) the truck wiring from the rear axle to the abs module and see if that clears things up.

Does anybody know if the 7.5 and 8.8 share the same speed sensor? I have the 8.8 rear end about 50 miles from me and can get it next time I head that way, otherwise I might just buy a new one. I also have two extra ABS sensors for the live-axle front end attached to the live-axle spindles. The transfer case has some play between the front and rear axles, and the air-hubs have some play too. I believe the tone ring is on the CV ends that go into the hubs, so if the axles are bouncing back/forth while rolling, that could freak out the ABS too.

Currently I have the big 50A fuse for the ABS removed from the fuse box to prevent the ABS module from overriding the brakes while I'm in traffic to prevent an accident. I'll mess with it more tomorrow. I went to bleed the brakes today and got the rear line flushed, but the front right bleeder is clogged so I stopped there.
 

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Bgunner

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The peaks in the rear wheel speed sensor graph are indicating there is an issue there but it is still unknown if the the sensor is going, tone ring has issues ( i wouldn't think so unless that differential had issues at one time like chipping a gear or grenade the diff gears) or wiring/connection issues going from the sensor to the module. But progress has been made since you have found an issue there at the rear.


As for bleeding the breaks, you are aware you can just turn the bleeder out more and let the fluid come out the threads for them? This still allows air to escape but takes a bit longer to do the bleeding.
 

Ranger850

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I'm no expert. But your explorer computer thinks it has a 8.8 rear end, and you're running the ranger 7.7 rear end. That might be throwing something out of whack.
 

masnecar

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I'm no expert. But your explorer computer thinks it has a 8.8 rear end, and you're running the ranger 7.7 rear end. That might be throwing something out of whack.
Yes, the 7.7 and 8.8 have different tone ring counts, if the computer is not updated to recognize the tone ring count of the 7.7 and thinks it is on the 8.8, the speedo will read slower than actual, and the computer will think the rear wheels are locking up, causing the abs activation issue I was having.

The peaks in the rear wheel speed sensor graph are indicating there is an issue there but it is still unknown if the the sensor is going, tone ring has issues ( i wouldn't think so unless that differential had issues at one time like chipping a gear or grenade the diff gears) or wiring/connection issues going from the sensor to the module. But progress has been made since you have found an issue there at the rear.
A week has gone by, and the problem HAS BEEN FIXED! The sensor came apart, looks like it had an impact on the bottom. Unsure if this was the cause, or if the casing from the sensor began to fall in and struck the tone ring, causing the complete failure.

Just installed a new sensor, truck stops like new!

If anyone has a C1102 abs code, get your hands on a OBDLink MX (usb OBD2 adapter) and download Forscan to a laptop, take a drive and graph out the speed sensors. Mine had an intermittent drop out, each time the signal dropped out the ABS computer thought the truck was slowing down and would activate the ABS. Very weird indeed.

Codes that I had:

C1102 (Acceleration switch circuit failure
--Caused because ABS computer was confused if it was stopping or not, the erratic wheel speed sensor signal made it think it was stopping or accelerating rapidly, and the acceleration sensor was not producing matching data.

C1237 - Wheel speed rear input signal missing (open circuit)
-- Was caused when the sensor coil made contact with something in the rear diff

C1230 - Wheel speed sensor rear center input circuit failure (short to power or ground)
-- When the sensor coil made contact with something in the rear end, the computer detected a ground condition on the sensor wires, which are isolated from ground under normal conditions.

Hope this helps the next guy. That was the very last bug I had to work out with this truck electrically.

Some useful information I found out while fixing this problem. The 7.7 and 8.8 rear ends both use the same speed sensor (aftermarket from autozone). If the rear speed sensor is disconnected, the ABS will estimate vehicle speed based off of the front wheels. Problem is, its not accurate, like at all. I was doing 65 according to GPS, speedo said 70ish. When actual speed is 100mph, speedometer recorded 110mph, and speed limiter kicked in. Pretty cool that the speedometer still functioned with a dead rear axle sensor. What was really interesting is it changed my shift points and made it shift sooner.
 

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