Photo request of ABS well for 1991. Here's mine.

[Torchred96]

I dived into this project already (inoperable ABS) with both feet, but this is approximately what my ABS well looked like. I am undergoing repair of my abs system and looking under here, I hope that's not a factory gm job :o

I am hoping that someone who has relatively untouched ABS Well would take a picture under the sound cover so I can try to put this back closer to the factory layout.

I've already pulled that harness out, because as you can see, it looks terrible, wire are broken and I get no light at all from ABS on the DIC even though the fuse is good..not even when jumping pins a and g on the aldl.

Thank you in advance. Here's the before pic. The ebcm (computer) is not pictured but is there and the connector was just sitting on top, so it looked plugged in but wasnt snapped in. You may be able to see the positive and neg large power wires are both disconnected and a couple broken wires...so I decided the easiest way was just to pull the harness out and repair it on the bench.
http://i1096.photobucket.com/albums/g328/sirlancair1/1991%20Corvette%20ABS/20150122_023630_zpso2colkco.jpg (http://s1096.photobucket.com/user/sirlancair1/media/1991%20Corvette%20ABS/20150122_023630_zpso2colkco.jpg.html)


I ordered a manual covering the 90 and 91 system, but it appears I can make some progress at least with a multimeter, checking relays, repairing the broken wires and applying 12v to the abs motor. It doesn't look good right now!

[Hib Halverson]

This article on C4 ABS may help.

http://www.corvetteactioncenter.com/tech/c4/abs/index.html

[Torchred96]

Thanks for the link to your article Hib, it was one of the first ones I read and it took the mystery out of the abs brakes..and gave me some courage too

I ended up taking out my modulator and harness. There were 3 broken wires..the orange one to the over voltage relay was corroded and was just hanging there, the main power lead had been spliced with a non factory connector and it wasn't crimped properly and broke (or was ripped off intentionally) loose and finally a third wire was snipped..i think to turn of the DIC light. Oh yes, the ECBM itself was not connected either, just laying on top of the connecter. My pump motor had rusted to death, so I took it apart in the name of science. While I had the harness out, I took the old tape off and re-taped the whole thing as it looked ratty.

I found that the corvette modulator, which looks identical to many others is around 250 to 300 on ebay, and even though I ordered one at that price, the seller emailed me to say he sold the one he had listed locally...so I bought a look-alike from 1994 mercedes e320 (a lot of other cars use a similar almost identical modulator/pump up to around 1997 or so even though they changed ours in 92) at a shipped cost of $35 The model from the mercedes was #265 200 043 and the one I swapped out was 265 200-059. There was a difference in the wiring plug, but I just swapped out the black electronics square box that holds the solenoid relay, motor relay and connector with the corvette plug and also swapped the feet (rubber shocks). If it doesn't work, I'll chalk up the 35 bucks to lesson learned, But I figured it was worth a try. The solenoids, motor and fluid connections are identical.

I'm still waiting on my braided M/C line but I was anxious to see if it was going to fire up..so I used the emergency brake to stop. With the key on, the ABS light, EBCM and associated relays clicked to life and went out after the appropriate 4 seconds. I backed the car out of the garage and about 20 feet later I heard the abs pump complete the test for the first time in probably over 10 years. I know some people hate it, but it makes me happy when things work the way they were designed..or better. Hopefully it will all work when I get the system bled (borrowing a tech 1a from a friend) after the MC line is connected. I'll keep you posted. :cheers:

[We Gone]

First time I ever had the sound deader out.

http://imageshack.com/a/img673/7831/y1Ch8M.jpg

[Z51JEFF]

I've got a bunch of ABS relays if you need to borrow some.

[Torchred96]

Steve, thanks for taking the trouble to do that for me. Yours certainly looks FAR better than mine did, I just had a hard time believing the factory would cram those wires in there in such as disarray. Hopefully mine will look a little better when I get it buttoned up.

Jeff, thank you for the offer for the relays, mine all tested good as far as I tested them and so far I don't have any lights. I won't know for sure for a week or so because the system is bled down awaiting for the MC hoses.

I still haven't been able to find out what that 4th relay does..In my picture it's the one at the top of the screen with the blue wire and my amplifier wire running behind it. The other 3 relays are talked about everywhere, but this on is illusive...maybe it powers the FX3 computer?

[WVZR-1]

Steve, thanks for taking the trouble to do that for me. Yours certainly looks FAR better than mine did, I just had a hard time believing the factory would cram those wires in there in such as disarray. Hopefully mine will look a little better when I get it buttoned up.

Jeff, thank you for the offer for the relays, mine all tested good as far as I tested them and so far I don't have any lights. I won't know for sure for a week or so because the system is bled down awaiting for the MC hoses.

I still haven't been able to find out what that 4th relay does..In my picture it's the one at the top of the screen with the blue wire and my amplifier wire running behind it. The other 3 relays are talked about everywhere, but this on is illusive...maybe it powers the FX3 computer?

There's no reference to a relay in the FX3 components locator. Is there a part # on the relay? Have you received an acknowledgement regarding the construction of the MC line? Maybe I missed you mentioning it elsewhere.

[Torchred96]

There's no reference to a relay in the FX3 components locator. Is there a part # on the relay? Have you received an acknowledgement regarding the construction of the MC line? Maybe I missed you mentioning it elsewhere.

The number on the relay is VF4-75F11-z01 14100455, Potter & Brumfield
I've seen different ebay ads list the part for abs, rear window defog, fuel pump, adjustable shock, and horn. Is is definitely wired IN the abs harness.

[Torchred96]

There's no reference to a relay in the FX3 components locator. Is there a part # on the relay? Have you received an acknowledgement regarding the construction of the MC line? Maybe I missed you mentioning it elsewhere.

Sorry, I put it in the for sale section. I sent it off to classictube.com in NY, and they called me with a quote for $36 a piece. The guy I spoke with Tim, said he had received my brake line and that the new ones will look different as the fittings are larger in diameter, but will function correctly. And I should expect them in 7 to 10 days.

[WVZR-1]

The number on the relay is VF4-75F11-z01 14100455, Potter & Brumfield
I've seen different ebay ads list the part for abs, rear window defog, fuel pump, adjustable shock, and horn. Is is definitely wired IN the abs harness.

That part # has an application for Brake Pressure Mod Valve Relay for a '91 MY only. It of course has applications elsewhere. It should be a 5 pin relay. A '91 differs from a '90 with there being an ABS ACTIVE relay that is in the image 8A-201-16 the FSM. '92 ASR was added so that would explain the '91 MY only application, it's also in the schematic 8A-44-2

It has applications in '91 also for a compressor relay, courtesy light relay and a fuel pump relay. Those are the only part # specific applications I saw for '91 but I didn't look real hard. That was a quick glance and those were what I expected. The BPMV harness is of course different for car with FX3 and with out.

[Torchred96]

That part # has an application for Brake Pressure Mod Valve Relay for a '91 MY only. It of course has applications elsewhere. It should be a 5 pin relay. A '91 differs from a '90 with there being an ABS ACTIVE relay that is in the image 8A-201-16 the FSM. '92 ASR was added so that would explain the '91 MY only application, it's also in the schematic 8A-44-2

It has applications in '91 also for a compressor relay, courtesy light relay and a fuel pump relay. Those are the only part # specific applications I saw for '91 but I didn't look real hard. That was a quick glance and those were what I expected. The BPMV harness is of course different for car with FX3 and with out.

Yes! It did not click at Key ON (feeling relay with my hand for click), but it did click when the pump cycled on after I moved the car. Thank you, the manual I bought doesn't even show this relay.

Also, I untaped the whole abs/fx3 harness in that well and saw that in actuality, the blue connectors of the fx3 are completely separate from the ABS harness with the exception of 2 wires. I can't remember them off-hand but I think I took pictures. I've read the FX3 adjusts shock setting with input from vehicle SPEED, but I couldn't find where it gets that input from. I imagine only one wheel sensor is needed if indeed that is the source.

[Torchred96]

Btw, seeing how so many of us modify our engines/suspensions, sound systems etc, I found surprisingly little information on the web delving into the inner working of the bosch ABS system in our cars or any other for that matter.

While there are some really good articles (like Hib's) demystifying ABS, I really didn't find much information on modifiying the BPMV or reprogramming ebcm for better threshold braking, or for whatever reason, hacking into it etc., yet there is a ton of information upgrading to larger rotors c5 brakes etc. Just a thought.:blahblah:

[Torchred96]

Well I'm almost done. Certainly looks better than it did. That's the Mercedes pump, and the main connector was a little different.


http://i1096.photobucket.com/albums/g328/sirlancair1/Mobile%20Uploads/20150212_205543_zpsgpsh6ifa.jpg (http://s1096.photobucket.com/user/sirlancair1/media/Mobile%20Uploads/20150212_205543_zpsgpsh6ifa.jpg.html)

[We Gone]

Nice job, You going to make BG his year? I have a room for ya if you need to stay a nite in Atlanta.