ABS help

[Boris3]

3/1990 build 325i now mainly a track car. Issue is a non working ABS system and could use some trouble shooting advice.

My abs light comes on when I turn the ignition, and goes off once the car starts. But no matter how hard I brake I get no abs and the abs light doesn't come on.

Late model car so if I understand the threads correctly I don't have the relay fuse issue. With no lights coming on during braking the issue is not one or more wheel sensors. So where do I start looking?

[Boris3]

Ok, if I'm reading these correctly according to the wiring guides/ trouble shooting manuals for 1989, 1990, 1991, it looks like the wiring was changed.

The early production 1989 had an abs 'over voltage protection relay'. Then the wiring changes (from the ignition switch and power distribution to the abs ecu) and this relay is no longer included from late model 1989 on.

The relay is not moved to the pump. The pumps look consistent with valve and pump relays.

So back to the puzzle... Abs light works at ignition and goes off at start up and stays off under hard braking but I have no abs.

[IAmGary]

My ABS doesn't work either. I pretend it's a good thing. But monitoring this thread for ideas...

[jlevie]

The ABS light behaving normally, but no ABS could be a bad ABS module or a bad ABS unit. I'd swap the ABS module first as that is a lot easier than swapping the unit. Then take the car out to an empty wet parking lot to test.

On track are you locking up and flat spotting tires?

[Boris3]

Much appreciated. I'll give the module a try. Any sense of why they dropped the relay, or how they adjusted things to still protect the system?

On track, the only lockups/flat spots have been when I've had to go both feet-in.

[jlevie]

If you aren't getting wheels to lock up under braking, you aren't using the brakes hard enough, don't have the right pads, or have some other problem with the brake system. The stock brakes on an E30, when using track pads, are more than enough to overwhelm R-compound tires and lock up a wheel(s). So something doesn't sound right.

When you have to go "both feet in" the car is sideways and the noise from the tires (and flat spotting) may be from them sliding sideways rather than being locked up.

[Boris3]

PFC 06s for a few years and now 08s. More likely me not braking hard enough to lock them up on track.

Question is in situations with both feet in should I be feeling abs?

[jlevie]

If you have enough pressure on the pedal you can feel the action of the ABS. But that may be difficult to discern in a "both feet in" event. There is too much going on with the rapidly changing angles and varying traction.

Those pads are certainly capable of lockup up the wheels if the brake system is working correctly. I suspect you just aren't getting deep enough into the brakes. Push harder when straight line braking and see what happens.