ABS warning light

[brokencase]

Once in a blue moon, and usually after hitting a bumpy section of road, I would get the ABS warning light to illuminate.
No big deal, after shutting down the car and re-starting all was good.

Experience with a prior Scorpio has eluded that this is typically an indication of a failing ABS sensor on one of the wheels. Usually one of the front wheels. Basically the wires fray from repetitive suspension motion. This failure seems to happen around 80-90k miles.

Now, as the cold temperatures have arrived, I am beginning to see an occasional flashing ABS light on vehicle startup. Once I drive to somewhere and then restart the car the flashing light is gone.

According to the IMON archives, this is also an indicator of a failing ABS wheel sensor:

"
=========================================================================
Date: Thu, 7 Nov 1996 23:57:30 -0500 (EST)
To: Merkur Owners List
From: Eric D Wulf <[email protected]>
Subject: Re: Scorpio ABS idiot light problem

Kent,

Does your ABS light blink at roughly 1-2 second intervals at startup? If
so, the ABS computer is definitely finding a fault in the
system. I had this same problem in my '88 Scorpio and found an ABS wire
that was worn through toward the right rear of the car.

Good Luck,

Eric Wulf
Eric D Wulf <[email protected]>
=========================================================================
"

Fully anticipating this eventual failure I began looking for an affordable ABS front sensor replacement as was discussed a while ago on the forum here: https://forum.merkurclub.com/forum/view ... 53#p349353

The substitute sensors are from a Ford Transit. Purchased from China via banggood.com for about $10 each. The sensors are almost a drop in, the connector only requiring a change.

At that time I test fitted the sensor and measured a proper signal at it's output while spinning the rotor. But I decided not to install the sensor at that time since I would only very rarely get a warning light at that time.

Well, I think I am now getting close to the time to swap in the Transit ABS sensors.

Stay tuned...I believe Ed was anxiously awaiting a full confirmation that the Transit sensors were applicable to the Scorpio case.

Now, Should it turn out that my problem is more than just a simple wheel sensor problem, then I have a "Plan B", Yes, I like to "future proof" things to ensure Scorpio bliss will persist in perpetuity.

"Plan B" is more involved.

It entails the removal of the original Teves ABS system entirely.

I have previously purchased a 1990 Crown Vic ABS pump/computer unit ($50 - used) along with a universal 7" compact Vacuum power booster ($25 NOS) and a Crown Vic master cylinder and reservoir tank from Rock Auto ($5 clearance).

This installation will involve running an additional brake line to the rear such there is an independent line to each rear wheel.

The original Scorpio computer gets tossed and an adaptor connector is fabricated to route the ABS wheel sensors to the Crown Vic ABS unit.

This is a drastic change, but is totally reversible should it not pan out. But if it does work, then I am blessed with not only a more modern ABS system but I also get traction control.

But first we start with the sensor swap. It is also time for a brake fluid flush.

[Ed Lijewski]

I installed Jeff Herson's new front wheel sensor cables (pricey) on my '89 (didn't resolve the ABS light On issue).

YMMV

[DPDISXR4Ti]

My ABS has never worked. I know Darren (previous owner) spent some time on diagnostics - even found the Rotunda tool - but never got anywhere. FWIW, I get an assortment of clicks from the ABS, most often on start-up. The brakes otherwise work fine, so digging into this has never made it to the top of my priority list.

Semi-recently I spoke with an old-time Scorpio owner (Chris Cleeland) who indicated he fixed his Scorpio's ABS simply by removing the sensors and cleaning out the dried, hardened grease. He seemed to think he even documented that experience on IMON, so you might want to search that if you're so inclined Dean.

[brokencase]

I suspect it is a wire or connection issue. Simply from the fact that the "blinking on startup" only began once the temperatures have dropped.
As we all know, temperature drop means metal contracts.

Once the car warms up, like when I drive to the store, and I get back in to drive home there is no longer a blinking ABS light.

So it could be one of the ABS wheels sensor wires or connectors (most likely), connector the to ABS computer, or connector to the Teves unit itself.
Worst case would be a cold solder joint in the ABS computer.

I'll pull the connector of the Teves unit and give it a blast of contact cleaner.

There is great improvement with the Crown Vic ABS unit. The computer is built into it and there is only the one connector. As opposed to the Scorpio setup that has the separate computer under the dash and associated cabling. So the number failure points is much reduced.

It does not seem so hard to install the Crown Vic unit. Perhaps not as difficult as converting a Scorpio to MAF and EDIS?

I've already checked and the vacuum booster and Crown Vic master cylinder will join up and fit into the existing area. I will have to do some bracket engineering to mount the ABS unit somewhere low around the master. I will probably have to fabricate an adjustable connecting rod from the pedal to the new vacuum booster.

The tricky part will be procuring (or machining) an aluminum junction block so that I don't have to alter the existing brake line positions. I then just fabricate smaller brake lines from the ABS unit to the junction block and to the master cylinder (six lines). I see several options online for junction blocks but I think the Scorpio fittings are metric.

Then a harness must be made to get the eight ABS wheel sensor signals from the ABS connector from under the dash over to the Crown Vic unit. In addition power, traction control switch, and the abs dash warning light.

Well, maybe it is just as difficult as converting a Scorpio to MAF and EDIS.

What I really need is a fully staffed "Jay Leno" style garage where I can just lay down my plans and have the talented staff execute them. Wouldn't that be nice?

[DPDISXR4Ti]

What I really need is a fully staffed "Jay Leno" style garage where I can just lay down my plans and have the talented staff execute them. Wouldn't that be nice?

Yes, certainly. You and I both have no shortage of ideas and plans - just need more time to execute them.

I sometimes come across a seemingly random box of parts - hmmm, what's this!? Oh, right, that's all the stuff I gathered up 14 years ago for the ZBD project.

Any way, like the idea of the Crown Vic ABS, but you need to go first. The EDIS swap sounds easier, at least for my skill-set.

[Ed Lijewski]

My ABS has never
Semi-recently I spoke with an old-time Scorpio owner (Chris Cleeland) who indicated he fixed his Scorpio's ABS simply by removing the sensors and cleaning out the dried, hardened grease. He seemed to think he even documented that experience on IMON, so you might want to search that if you're so inclined Dean.

Did that long ago. Found sensors clean (nothing metallic on the Hall Effect tips). No grease need be applied (grease collects crud...).

YMMV

[brokencase]

Yes, certainly. You and I both have no shortage of ideas and plans - just need more time to execute them.

Yeah, I'll accept a Time Machine in leu of the fully staffed Jay Leno garage. So long as it allows me to compress 60 hours into one day and all the while prevents me from aging.

[Ed Lijewski]

My ABS has never worked. I know Darren (previous owner) spent some time on diagnostics - even found the Rotunda tool - but never got anywhere. FWIW, I get an assortment of clicks from the ABS, most often on start-up.

Did the Rotunda tool come with yout car purchase?

What clicks do you hear?

On start up there shouldn't be any clicking from ABS relays. If you hear clicking after the pump has pressurized the accumulator (length of time depends on condition of the accumulator) it likely is from depressing the brake pedal one or more times lowering accumulator pressure with the pressure switch signaling the relay to start the pump again.

^^That commonly would reoccur while operating the car.

That's the only ABS-related clicking I've heard. It's typically resolved by installing a new/good used accumulator.

YMMV

[Ed Lijewski]

Once in a blue moon, and usually after hitting a bumpy section of road, I would get the ABS warning light to illuminate.
No big deal, after shutting down the car and re-starting all was good.

Possible wiring connection/contacts to the brake fluid reservoir/level sensor, the two on the "cap" of the reservoir. Also, the reservoir float can act sticky and send a wrong level signal.

YMMV

[DPDISXR4Ti]

Did the Rotunda tool come with yout car purchase?

No. I'm pretty sure Bart has it.

On start up there shouldn't be any clicking from ABS relays. If you hear clicking after the pump has pressurized the accumulator (length of time depends on condition of the accumulator) it likely is from depressing the brake pedal one or more times lowering accumulator pressure with the pressure switch signaling the relay to start the pump again.

^^That commonly would reoccur while operating the car.

That's the only ABS-related clicking I've heard. It's typically resolved by installing a new/good used accumulator.

I suspect that's what I'm hearing. I do have a couple of spare accumulators, so it's probably worth trying one (or more).

Good thread here with diagnostics and details on depressurizing the accumulator...
https://forums.merkurclub.net/forum/vie ... hp?t=22528

In short, pump peddle 40 times with power off and then un-screw.

[Ed Lijewski]

40x is unnecessary. I've removed many. Many.

If still pressurized (your case) the pedal "feel" will become harder as it diminishes and loses power assist. 15x-20x is adequate.

In the event some little pressure remains (unlikely) I wrap a shop cloth around the base of the ball to catch any fluid exiting.

A failing pressure switch is also a possible reason for excessive relay clicking.

YMMV

[brokencase]

Since the Scorpio has a separate ABS sensor on each rear wheel then I don't understand why they only ran a single brake line to both rear wheels out of the ABS unit.

[Ed Lijewski]

My assumption is the engineers thought activating rear wheels together was better for the driver to maneuver the car under ABS operation.

YMMV

[brokencase]

I'm guessing it was a cost savings tradeoff.

The basic logic is: "During braking, if a wheel is locked up pulse pressure to that wheel".

I think about 70% of braking is biased to the fronts, in addition steering control is needed.

But for the backs they have made the compromise "If one wheel locks up, pulse pressure to both".

However such a compromise could have equally been applied to the fronts as well, without much detriment to overall performance.
Just like the old adage on pre-abs cars "if you start slipping while braking - pump the brakes"

The newer Crown Vic ABS unit has a separate line for each rear wheel. This is required for traction control during acceleration (if one wheel starts spinning then pressure is applied).

I wonder with the Crown Vic unit if the independent control of the rears functions in the braking mode.

My new Ranger has an ABS unit like the Crown Vic's (w/traction control) But I've never perceived it's operation. I've driven in 4wd in the snow but the operation of ABS and Traction control seems invisible. I'll have to investigate this more closely the next snow storm. Part of the problem is the past few winters have been very mild.

OTOH, The operation of the Scorpio ABS system is very perceptible to the driver. You really feel the vibration in the pedal.

[brokencase]

I found the following info in the book "CAR BRAKES - A GUIDE TO UPGRADING, REPAIR AND MAINTENANCE" by Jon Lawes

"Modern ABS systems can be of a four-channel design, with each wheel
having individual wheel sensors and actuation, or a three-channel system
using four sensors but modulating the rear wheels as a pair. This system
lacks some of the finesse of the four-channel system for a relatively minor
reduction in cost. A variation on this system, primarily used on rear-wheel
drive cars, uses individual sensors on the undriven wheels and a single
sensor for the driven axle mounted on the differential. The relatively
uncommon two-channel system, mainly used in American vehicles, has
largely been phased out. This system would split the ABS into paired wheels
and was therefore less able to control individual wheel slip. The cost savings
did not justify the reduction in capability and today most systems are three-
or four-channel."

This is a pretty good book. He cites the Scorpio as one of the early production ABS systems and this is the reason it attained "Car of the Year" in Europe in 1986.

However he fails to mention that early ABS systems used inductive sensors at the wheels and only later did they switch to Hall effect sensors.
I think the industry switched to Hall effect for several reasons. A Hall effect sensor is solid state and less prone to fail compared to a coil with fine windings when experiencing the heat near the hubs. They also eliminate the need for more expensive coaxial cable that inductive sensors require due to thier weak signals. The sensor interface in the ABS computer is specific to the type of sensors used.

I am fairly certain that the 2000 year Crown Vic ABS unit I have acquired is expecting inductive sensors like those used on the Scorpio because the schematic I have appears to indicate this is the case. In addition, the Crown Vic ABS sensor part numbers (and prices) transition in 2003 (according to RockAuto). But I will have to do some more investigation to verify this is the case.