Anyone know if ABS can be enabled/disabled by pulling a fuse on an NA 88 944/924s? Getting a spec car and was thinking of leaving ABS on for the first few events.

 

Pulling the relay would disable it for sure. But I think doing so will illuminate the "!" and "ABS" warning lights on the dash (but thats for a 85.5+ 944 dash/instrument cluster - not sure what warning light the early style dash has). Didnt know/think ABS was an option on the 924S, are you sure it has ABS?

If it does, you probably want to wire in a shutoff/reset switch, which is basically necessary with ABS for track use. With stiff suspension and stiff tires, the ABS will fault out when hitting rumble strips and curbing, so you will want to be able to reset it w/o having to turn the ignition off.

 

If rules allow you to keep the ABS, I would recommend keeping it and perhaps installing the reset as Jim notes above. I went from a non-ABS 944 NA to the ABS 968.

Hated it!

Gave it a bit of time to see if it would grow on me.

Sure as heck did. It's actually become quite a handy feature. Much lower risk of flat-spotting expensive tires, more braking/trail-braking options, advantagous when diving in on non-ABS cars in your class...

Yup, I kinda like it now. Oh, and it is awefully nice to have now that the car is wearing snow tires and slogging to/from the office.

 

Just put a switch on the power lead to the ECU, as noted.

 

Whats stiff mean to you? I was looking at either 375 or 400 lb springs on the front and a 30mm bar in the back. Shocks are koni yellows. Is this stiff enough to fault ABS also?

 

My 88 924s doesnt have ABS.

 

924S's did not come with ABS.

 

I'm WAY north of those spring rates and don't currently have any issues on track or on the street.

I was having an intermittent fault, but found it to be a loose ground in the passenger foot well near the ABS box.

I have heard a number or 944/951/968 folks state that you'll need an ABS reset, just doesn't seem to be happening to me.

Method that was described to me was a toggle switch run back to the fuse...

 

Maybe you're doing a better job of staying off the rumble strips than most...

 

I have never had the ABS fault out on either of my 89 Turbos during DEs, and I was running Turbo Cup springs on one of them.

But in my last PCA Club race, I was having to reset the ABS 2-3 times per lap in my track car, and that was not hitting rumble strips - just pavent irregularities/cracks through the high speed sections of the track. But I do think I have a bad wheel sensor. Havent had time to troubleshoot it yet to confirm. Regardless, the reset switch is a pretty good idea to install.

I dont remember specifically, but the fuse that the ABS circuit is on, probably is also wired for other circuits - like "brake lights, cigarette lighter, and trunk light". If you read the fuse box diagram, its pretty common to have various components on the same fuse - so probably not a good idea to just pull the fuse w/o making sure other systems would not be affected.

For putting in a reset switch, there is probably more than one location to splice in. There are two power wires, one going to the hydraulic unit, and one going to the ABS control unit. Putting a switch in either of those wires will not reset the system, unless you cut both. I recall I ended up putting the switch in the relay ground wire - break the ground, and the relay stays open, sending no power to either the hydraulic unit or the ECU.

 

The only one that matters is the ECU - the valves on the HU should not need a power reset. You're trying to restart the ECU.

 

Yes, I thought I had a bad sensor as well. Checked them all during my next brake overhaul, then the fuse, then the relay...

I was all set to put in a reset switch as the ABS was faulting just about everwhere... on the street, on the track, smooth surfaces, rough surfaces... UGH!

So, I go to inspect the brain box in the passenger foot well. Hey! It's not there!

Turns out the cage builder had relocated it to allow for the cage coming through the vents (which is nice). While I'm poking around down there, I see a simple round connector wire that is just 'a spinnin' around the bolt on the chassis to which it is attached.

Tightened it down and have not had a single ABS fault since. No idea how it came loose, but I suspect it is not uncommon.

When I discussed the issue (prior to the fix) with a pretty solid race shop, they completely dismissed the notion that stiffly sprung Porsches will trip the ABS. He said "something's loose, trust me". He was right.

Jim - Which car color/number are you in F-stock? I would imagine we've been running around Gingerman, Road America, Autobahn, or Blackhawk together. Apologies in advance if I've just forgotten (getting older)

 

Actually that doesnt work. There is a crossover power wire from the hydraulic unit to the ECU (from the wiring diagram - why I dont know, buts its there), so if only the power to the ECU is cut, it still will not reset the system. My first attempt at installing the reset switch was to install it in the ECU power wire, but it didnt work as a reset. I then put an additional switch in the power wire to the hydraulic unit. Tried them both - each switch individually will not reset the ABS, both had to be turned off at the same time. I then moved a switch to the relay ground, and it kills power to the entire system and resets it.

 

I have not ruled out a ground problem, or even a bad wire here or there. The sensors and the connectors were from a donor car, and are not in the best condition. Thanks for the tip.

I have some factory info, copy of a letter sent from Porsche Motorsport to PMNA regarding the Turbo Cup and US Escort cars in early 1987. Porsche AG was telling PMNA that they were having ABS fault problems on the Cup cars in Europe, and had diagnosed the problem as rear hub deflection under load - so they gave a measurement spec of a max allowed distance between the sensor tip and the ABS pickup ring on the rear hub. Thought it was interesting info.

I had a gray #58 944 Turbo F-stock. Car was wrecked at BIR last year, and I did not get it rebuilt this year. Will have it ready to go next season as a D car. I will try for TRAC 07.

 

Doesn't surprise me - thanks for the info.