dlpalumbo

I have a 90 C4. The traction control and ABS lights came on, so I had my favorite tech read out the problem with a 9288. He reported that the lateral accel was bad. As a new one is $2,250, I researched the forums for other possible causes. Several people recommended cleaning the accel. This accel is a mechanical pendulum whose motion is sensed. This is done so it can sense constant acceleration (as opposed the dynamic) which most OTS accels cannot do. In the forums, there was also some confusion as to which accel was which (there's an identical longitudinal accel as well).

Available documentation is even conflicting with Streather (pg 403) showing the lateral accel to the rear and Technical Data w/o Guesswork showing it towards the front. The proof is removing the accel, popping the top and seeing which way the pendulum swings. I removed the forward accel (the consensus opinion) and, indeed, it was orientated to sense side-to-side motion. It didn't seem to need cleaning of any sort, so I tried to clean contacts to no avail. I ordered a new (used) accel which I installed and tested last night.

The PDAS still squawked. This meant that either the new unit was bad, there was a wiring problem or the PDAS was bad (ouch). None of these options seemed good. This morning I resolved myself to comparing the new unit to the known good longitudinal accel. I removed the accel and opened it up. Low and behold, its pendulum was jammed with metal filings (from God knows where) so that it couldn't move. And, just as I had thought, when I replaced the driver's seat, I bumped the console and dislodged the pendulum so that it was offset, reporting constant acceleration (this is when problem first occurred).

I put the 2 good accels in and all is well. This leads me to the conclusion that the 9288 is reporting the wrong accel (or the documentation is wrong). This would also explain why Streather and others thought that the rear accel was the lateral accel. Replacing it fixed the problem indicated as a bad lateral accel.

I hope this helps clear things up.

Dan

Indycam

Did you ever find the part numbers on the things ?

HoBoJoe

I'm actually getting ready to remove mine and clean them. My code came back stating my longitudal one had failed. I was just going to clean them both though.

Indycam

HoBoJoe
I was taught to do one thing at a time .
Do one , get the results . Good , bad or indifferent . If good go on . If bad redo .

amr89c4

I had a lengthy experience with the accelerometers back in Nov. What I found was that the AFT Accel has an externally exposed pendulum and mine was jammed up with what looked like metal drill shavings of a brass colored material.

The FRONT Accel, when opened up was of a completely different design and was sealed internally. I wasn't brave enough to go any deeper into it. I blew it off, gave it a gentle shake, hoping something I might dislodge anything that might be interfering with its "magic movement" and stuck it back in. Low and behold the lights all went out and the PDAS has been working fine since. Go figure. Keeping fingers crossed.

I did not have a hammer and thus had no codes to offer as further evidence of incorrect referencing in the diagnostics or reference manuals.

Its great that you solved the problem!!! When you get 3 warning lights and a warning horn, you generally get a $inking feeling. I started with the basics, ie checking all the grounds and worked my way up to the expensive components it paid off as I was only out my time and I learned a lot about the entire PDAS/ABS system.

HoBoJoe

Ok, so which one is the longitudal?

aeroman

You can get those used for 100 bucks if you know where to look. Several Rennlisters have gotten them same place.

dlpalumbo

The longitudinal is towards the shifter (rear). My accels were identical with part #993.606.153.00. I got mine from a used parts shop (there's one in L.A. and one in North Caroline, maybe more). I paid $450. The accel senses in the direction parallel to the short dimension of the box.

amr89c4

Search me!

Here's my take on it. And its just an opinion, guys. If memory serves me correctly, the AFT one was the one that you could see the pendulum once you got the cover off. Teh Accel body is situated (mounted to the car) with its long axis perpendicular to the driveline. The pendulum arm is also perpendicular to the driveline and in this orientation will move fore and aft and my guess is it doesn't have to move much either. Logic says that is the Long Accel. But then I'm just a country boy.

The Forward Accel body is mounted with its long axis parallel to the driveline. Since my FORWARD one was completley sealed once I got into it, I can only venture a SWAG as to how it is constructed inside. The tiny PC board and its circuits were visible, but there was no pendulum, so it must have been inside the inner body or uses another method to sense motion. One would presume, perhaps incorrectly, that it is constructed the same way as the other accel. If so, then its pendulum would swing left and right slightly on side g loading. Thus being the Lateral Accel.

Thats my story and I'm stickin' to it.

gfunk

I don't need one but for future reference do you care to share where to look?

thanks,

Greg

PS - My sensors were identical except for all the extra metal filings in the longitudinal one. I'd be interested if anyone had an explanation for why the longintudinal sensor gets clogged up but the lateral one stays clean. Perhaps it's just more frequent movement of the longitudinal one?

amr89c4

I want to know where all those pieces of metal are coming from. Those Accels are sealed and there is no way for anything to intrude into the sealed body. The one I cleaned was packed with metal. You would think that a PC board and sensitive assy like that would be a clean room assy. There is nothing inside the Accel that could have produced the shavings.

The other question now rises as to why my FORWARD Accel is different from my AFT one. There was absolutely no moving parts visible once I opened it up. In fact, as I recall, the FORWARD one is unsealed from the end of the module and the PC board unit slid out and there was no pendulum, like in the AFT one.

Maybe the FORWARD one had already been replaced with a newer version. I don't know. Strange.

aeroman

I believe the newer ones are different and don't have moving parts.

dlpalumbo

My longitudinal accel had small metal filings stuck to the magnet. The pendulum looked twisted so that it might have been scraping the magnet, producing the filings over time. Besides poor quality control, I can only guess that the hunks of tin Lynn found in his accel came from poor quality control on assembly. I can picture the actual circuit board being constructed under somewhat pristine conditions, then put in the box in some other part of the plant where QC wasn't quite up to snuff.

Interesting to note that Lynn's car (89 C4) has different accels, mine and Greg's are identical. I have a 90 C4. The parts diagrams also show these parts as identical.

Dwane

I hate it when people "SAY" they know how to get parts for a great price, yet do not share the info with anyone else!

amr89c4

I have to agree. If they don't want to tell the world, thats fine, but don't say you know where/how to get something and then not at least PM a requestor with the info. Tahts my two cents.