e30m3 conversion Abs problems

[g22]

I've got an '89 325i that I've swapped on a complete e30 M3 suspension including the brakes. I'm having problems with the ABS light coming on.

When I start the car the light is off but after driving for a minute or two the pedal will pulse and the light will come on.

I've checked the sensors, which are clean and there doesn't appear to be frayed wires. The abs worked with no problems prior to the suspension swap.

I was under the impression that the abs from the 325 would be plug and play with the e30m3 suspension and brakes.

Is there something else I need to change? What else should I look for?

[Vethen]

If you turn the wheels it doesn't pull any cables, sensors loose does it?

[g22]

I've not looked at that specifically. They all seem to be intact. I'll have my GF help me with that tonight.

Otherwise, this should be plug and play abs, correct?

[gazellebeigem3]

^ yes, if its all e30 m3 parts.

[s52e30m3]

Sounds like a bad sensor.

[Van Westervelt]

Pull the sensors off your 4 lug and put them on your car if you havent. Also, inspect the abs rings to make sure they are in decent condition.

[Massive Lee]

What ABS computer are you using?
Are front and rear tires with equal rolling diameter?
Are ABS ring diameters the same between M3 and 325?

The pulsating indicates a "wrong" situation, not that sensors are bad.

You probably know that the M3 and 325 don't have the same number of teeth on the ring.

[Van Westervelt]

My 88 325 abs computer and sensors have worked just fine on the e30 m3 suspension for over 60k miles.

I think the teeth on the rings are the same if I am not mistaken.

[g22]

Just had a frustrating day of attempting to get the abs to work.

All sensors are from the '89 325 and the abs worked perfectly before the conversion. I am also using the abs computer from the 325. The tires are identical. (brand / size)

All the new suspension is from a e30 m3.

All the sensors have been cleaned with brake cleaner, inspected for frayed wires as well as the abs rings sprayed down with brake cleaner and blown out. I tested all the sensors using a mult meter at the connection inside the fenders or below the rear seat. It appears all are open circuits / no resistance? Is that correct? (Hard to beleive all 4 sensors would blow)

The abs light comes on after about 30 seconds of driving.

What now? I'm at the extent of my knowledge

[etxxz]

they are Hall sensors. They flow current creating a magnetic field. When the teeth of the wheel hub/abs rotate, a differential voltage (oscillating) is generated and monitored by the abs computer.

In order to make the ABS work in my car (e36M/318ti) i have to shim the sensors away from the hub so that the signal matches that which it was with e30 hardware. I would have needed to record what the signal was with an o-scope and match it after with the e36 hardware.. i didnt so no abs for me. You shouldn't have any problems though.

i don't know how ot help you. just wanted to clear up why you measured no resistance.

[StereoInstaller1]

Have you checked your ABS overvoltage relay?

[g22]

Have you checked your ABS overvoltage relay?

This is the relay over the computer, correct? I checked it an the small copper wire is intact. Is there something else to look for?

So i went out today to start from the begining becuase I convinced myself that it was a sensor given the light comes on after driving. I thought i had it when one of the rear sensors was pretty dirty.

I removed both rear sensors from the hubs and cleaned the abs rings and sensors. I also used electrical tape and ran it all the way up the wires since the insulation was falling off. I also checked the relay under the dash.

Now the light comes on at start up and STAYS ON!

I'm not thinking clearly due to the steam coming out of my ears, what do I look at next?

[g22]

Okay, first off, many thanks to Dominic and Justin coming over to help this week.

Here's the latest. I swaped out the following known good parts: Under dash relay, the abs computer and all four wheel sensors. I also double checked that the rings weren't damaged and clean.

Any ideas?