Need 930 help

[5.7 GT1]

I just purchased a 88 930 and the fuel pumps were wired bypassing the relays and fuse block. I noticed the fuel pump on the fuse block was missing and block damaged, so I did the dual fuse bypass to the two fuel pump relays. The fuel pumps still did not work, I then discovered the brown and red wire that triggers the relays was not functioning. When I simulated that circuit (which is a negative trigger) the fuel pumps worked. I used the factory manual to track down that wire and it looks like it connects to the DME relay controlled by the DME. I know there is not supposed to be a DME, but that is what the factory manual calls it. Is there a factory fuel pump cut off that could be triggered by the alarm? I'm not sure where to go at this point with out getting much deeper into it. Anyone have experience with this problem?

Anyone??

[RarlyL8]

I believe the DME the manual is referring to is the Lambda O2 electronics located under the driver's seat. If memory serves the boost cutoff switch goes through that system. The cutoff switch functions by shutting down the fuel pumps so it stands to reason that the fuel pump wiring has a connection to this unit as well.
Others should chime in as my experience in this matter is a sidebar to knowledge gained by defeating the Lambda system.

[JFairman]

Yes, on your car it's under the driver seat. It's called a "speed relay" if you take the part number on it and do a search here in the pelican parts - parts section.

It is the relay mounted farthest to the left and closest to the driver door on a 1988 USA car. There are a bunch of wires going to it and one or more of them probably goes to the alarm system box under the cowl near the glove box.
It is also the factory rev limiter that disconnects the ground to the two red fuel pump relays in front around 7000rpm.

It seems that it also interfaces with the overboost switch circut and alarm system to disconnect the fuel pump relay grounds. If you set a working factory alarm in the driver door jam and then open a door or the front trunk until the interior or trunk light comes on the fuel pumps will not run along with the alarm horn next to the steering rack honking away.

[5.7 GT1]

Would it be worth starting by just replacing the speed relay? I did notice the factory alarm control unit behind the the blower fan up front does click on and off when I open the drivers door for about 10 seconds as if it has some type of built in relay for the horn. The only issue is; I purchased the car with the horn assembly missing, so I'm not sure if the alarm is sounding or not and the car has been re-keyed with out the alarm key switch in the drivers door. I have no control over the factory alarm.
Any suggestions?

[RarlyL8]

Thanks for adding that Jim, clears some things up that I have been fortunate enough to not have issue with yet, ha!

[5.7 GT1]

That's really interesting. It sounds like the factory alarm does not cut the fuel pumps if triggered?
I would really like to remove all of that junk wiring and stuff under the seat and at the engine. Do I need to re-wire any thing at the engine harness in back? I know there are a few needed circuits like the oil senders, WUR, boost signal, and ?

Would I need to change to the MSD or is that what you used just to limit your RPM and will the stock ignition system work?

Are there any good threads on this topic? The more crap I can get rid of in this car the better!

Thanks!

[OSI930]

Have you looked at Mark's post # 12 on the sticky, "My car doesn't start" ?

[mark houghton]

Originally Posted by JFairman

I don't know the answers to all your questions. My friend xbmguy removed all that stuff like I tried to describe before when he installed EFI so maybe you should ask him. I was reluctant to mention it and i guess i shouldn't have.

Actually Jim, it's a worthy topic of discussion. My personal experience, though, is that if you unplug just the speed relay and leave the lambda computer plugged in (whether or not you're using the O2 sensor loop) the pumps won't run...at least not in my '87 when I had the seat out a week ago for some relay PM work. I haven't tried unplugging everything, all wire harness connections, under the seat though.
I figure that speed relay just provides an interruptable ground loop and should be a simple matter of finding which lead in the plug is the ground...and grounding that sucker forever.

Need to hear from xbmguy if there's more to this work-around than just unplugging that stuff. But I do agree, it's really not needed and is just another source of failure. And vs. the cost of a special order $325 relay, it's a good option that if I had been patient last week while the seat was out, I should have taken the time to figure it out.

[5.7 GT1]

Thanks for all your recommendations guys. I will start with the speed relay and see what I can figure out. I'm pretty sure the fuel pumps are not supposed to run as soon as I turn on the ignition and continue to run without starting the engine.

That is how I have them wired now as I have bypassed that relay ground circuit.

That would also mean the fuel pumps are not currently cutting on over boost and rev.

It seems like a simple problem to solve yet a hassle when I don't know where to source it.

Someday I hope to be like most of you with a standalone EFI system.

Thanks to all for your help!