RX-7 ABS troubleshooting FD 1993

[ZGN]

My ABS light is on, any helpfull tips to determine the cause of this malfunction other than the fuse?

[93rx7r1]

Have you recently done any work around the front hubs? The wheel speed sensors wires are very easy to break.

[Herblenny]

Did you do any brake bleeding?

[ZGN]

Not recently, the light has been on for 2 years+
Just swapped out the abs pump, old one was leaking slighly. About to jack up the car and bleed the brakes. I'll check the speed sensors also.

[ZGN]

we posted about the same time,

[BigIslandSevens]

I have all the sensors if any of yours are bad. Let me know if you need them. Free because we have the same birthday.

Dave

[ZGN]

Thanks, none of the appear broken. Do they every just go bad? Any way to test?

[BigIslandSevens]

I'd have to check the manual on testing them. I would imagine a resistance reading is the standard.

I also have 2 ABS computers. a 93' and a 94' As wel as a 94 pump

[93rx7r1]

Originally Posted by ZGN

Thanks, none of the appear broken. Do they every just go bad? Any way to test?

Originally Posted by BigIslandSevens

I would imagine a resistance reading is the standard.

Unplug the speed sensor and measure the resistance between the terminals on the speed sensor side of the plug. The resistance should be between .8-1.2 k-ohms

[ZGN]

Originally Posted by 93rx7r1

Unplug the speed sensor and measure the resistance between the terminals on the speed sensor side of the plug. The resistance should be between .8-1.2 k-ohms

Thanks, I'll test them later today and also reseat the ABS computer connections!

[Lilfreddie]

Whats up! I have the factory ABS test equipment that plugs where the ABS ECU goes. If you need it let me know.

[ZGN]

Yo man, have not heard from you in a while hows it going? ABS is on hold for now... blew my motor at DGRR 0 PSI on front rotor and 58 on all the faces on rear. Almost have the motor out. Just one stuck exhaust bolt to remove and it's comming out!

[cewrx7r1]

My ABS light would come on when the car started to move after a startup.
ABS would not work
(1) The wheel speed sensors had not been cleaned in years so that was my first check. Removed and cleaned all four of them, and they were very dirty. Problem remained.
(2) Pulled and checked the ABS motor and valve relays, and diode. All were good.
(3) Disconnected the two ABS hydraulic unit connectors. The main control one had a little dry corrosion, cleaned it.
(4) Check voltages at hydraulic unit. They were good.
Reconnected everything and the problem went away and the brakes worked fine for two weeks. Then.

ABS light remain on after startup and before moving.
ABS would not work.
(1) Swapped ABS control units located in the left rear of the hatch area.
Problem remained.
(2) Check all ABS wiring from the rear control unit to the front hydraulic unit, and the voltages from the battery at the rear. All were good.
(3) Check out each sensor at the control unit, static and dynamic tests were done. All were good. Problem remained.
(4) Used a Mazda ABS checker. Ran the test three times and it would give different multiple problems every time but always said the LF solenoid was stuck open. But it never completed the complete test criteria as listed in the manual. Something is fishy! This did not make sense to me because neither the motor or solenoids were making any noise. Maybe the test unit had "SECRET and HIDDEN" analysis features not show in the schematics.
(5) Manually cycled the ABS motor and the three solenoids while the brake pedal was floored. All 4 functioned. Now I am getting pissed off! ABS still does not work.
(6) Removed the diode and replaced with a test diode. The problem remained so I reinstalled the stock diode.
(6) Checked the hydraulic unit voltages again at the ABS hydraulic unit. Now the 12 volts coming through the 15 amp ABS fuse was low, but it was fine before.
(7) Started testing the wires from the fuse to the hydraulic unit. Found that if I wiggled the 12v wire between the connector and the unit, the voltage would fluctuate.
(8) Pulled that pin out of the connector. It is a square box female design and the spring side was totally missing. One edge of the male pin was very slightly burned.
(9) Pulled the same type of female pin out of a new unused connector in my parts bin and repaired the connector. Evidently that one pin was not real tight and over the years the extra resistance slowly burned it up until it failed.
PROBLEM FOUND AND FIXED, ABS FUNCTIONS AGAIN.

[ZGN]

Thanks for the info. As soon as I get my FD back on the road again I'll continue to troubleshoot this issue and should have it resolved!

[alavochin]

Originally Posted by Herblenny

Did you do any brake bleeding?

If I did some brake bleeding and my ABS failed after.. what could it be?

I was installing an engine brace that required I remove the ABS pump. Reinstalled the pump and bled the brakes. Could not get get a real hard pedal, so it would take a couple brakes pumps for stiff pedal. Since I could not figure it out, I took the car around the block to see how it brakes while driving. ABS light came on. Back in the garage, I realized that my big front brakes had 2 bleed valves and I was only bleeding one of them. Fixed my mistake, rock solid pedal, but now the ABS light will not turn off and ABS system is not functioning.

What do you think happened and how could I fix it?