'84 930 Turbo Relay question

jriera · 11:23 AM

I have a red cable soldered to the red relay marked in red in the attached picture (thanks beep beep for the pic)

As one may imagine that is not factory original and has caused me some trouble in the past (i.e. leaving from TRE got stranded in rush hour traffic on the left lane of 134, car just died)

What that realy does and why in the heck a cable is soldered to one of the relay pins??

Planing on taking that apart and crimp the cable to the relay harness.

Thanks

jriera · 03-05-2006, 08:36 PM

Help ... please ...

magic930 · 03-05-2006, 09:20 PM

I think that relay will cut off fuel if not wired properly. By grounding your previous owner was defeating it and trying to ensure that it stays on. I can't remeber if is either part of the overboost sensor circuit or the CIS pressure plate switch circuit.

jwmarc · jwmarc's Garage

Does the red wire go back to the BOV plenum and terminate in a single pole switch ( over boost sending unit) ? The over boost sending unit is generally connected with a single white wire from there back to the fuse realy panel on the left engine bay but goes to a larger yellow relay on my 86-930.

If the relay is bad and shorts the circuit as if it were getting a signal form the Overboost sending unit it would cut out the fuel pumps and leave you stranded. I had that happen to me on my 86 . I took apart the relay at the suggestion of a pelicanite and found the solder welds were cracked and at times were enough to cut out the pumps.

jriera · 03-06-2006, 10:09 AM

Not sure where the red wire goes/terminates, so far goes back to the loom on the 14 pole connector. Will take the intercooler out and follow the cable. Dave at TRE mention about the yellow relay but the one I have is red (and I cannot find any references to a yellow relay).

Thanks everyone, more to follow.

sand_man · 03-06-2006, 10:27 AM

I'm pretty sure that in my '87 the Overboost Relay (if that's what we're talking about here) is yellow. It's also an ice cube relay (sort of rectangular in shape), not round.

sand_man · 03-06-2006, 10:33 AM

NOT my car:

sand_man · 10:39 AM

Of course if it's just a relay and if the one you have has the correct rating and fits, it probably doesn't matter if it's the color of a baboon's @zz.

jriera · 03-06-2006, 11:43 AM

Thanks, here is mine:

Tyson did a very handy work with the soldering iron!!

Also in the process to replace the 3 fuses with ATO fuses.

So far getting to the base of the relay is not as easy as it was looking last night ....

tiorio · 03-06-2006, 12:42 PM

Here's my guess. The original overboost relay died. The PO saw the $$$ compared to a similar (but not directly swappable) relay for $ and made a modification.

You should have a rectangular overboost relay in there and you do not. When this relay fails or you overboost, it cuts fuel supply. Looks like the PO must have defeated it in either situation, which may lend some clues to what is going on with the other relay...

OSI930 · 03-06-2006, 12:51 PM

Do you have a fuel enrichment device on your car?

jwmarc · jwmarc's Garage

The yellow overboost relay is about $200.00. The red relay is $25.00. I would tell you to trace the white wire from the overboost sending unit in the back of the BOV plenum. If it marries up with the red wire in the harness then it is jury rigged as everyone says. The yellow overboost relay has a PCB board with a nos. of resistors and some other components and is much more sophisticated in its currant processing than the basic red / and black high currant relays. take the wire off the over boost sending unit with the motor running and ground it... the red relay should cut the power to the fuel pumps and car should die. One other thing is the yellow relay is supposed to act very quickly to the over boost condition and reset very quickly. I am not sure if the red relay can operate that fast...

OSI930 · 03-06-2006, 02:39 PM

In reviewing my Porsche pet CD, I am not sure that an '84 even has yellow, cube type, overboost relay. I know that earlier versions of the turbo had the ignition delay relay which I can see in your photo. They also had an air flow sensor/charging pressure relay which was a round red relay. 1986 might be the first year turbo to use the yellow, cube type, overboost relay. Do you have a wiring diagram specific to an '84 or do you have a 1984 owners manual for your car? That should specifically i.d. your relays and fuses.

jriera · 03-06-2006, 04:53 PM

I have the '84 Owner's Manual and it says:

Relays in engine compartment
- Manifold pressure limiting switch and air sensor contact
- Rear window defrogger
- Slow-acting relay

But it also says that I should have one fuse for the rear window defrogger and I have 3 ...

I will try to 'chase' the wires tomorrow. The car runs fine (until the red cable disconnects)

tiorio · 03-06-2006, 05:05 PM

The owners manual is...uh...not so accurate on what relays are where. It's missing about 5 that are on my car in various places...

RarlyL8 · RarlyL8's Garage

It is #1 on the above list - manifold pressure limiting and air sensor contact.

You don't need it. Bypass and be done with it. Overboost is rare and you'll know very quickly if it happens. Mount a good boost guage with a tattletale needle and you become the relay.

jriera · 03-06-2006, 07:08 PM

I'm all for simplicity specially if it means not getting stranded anymore ... so dumb question how to bypass it??

OSI930 · 03-06-2006, 08:00 PM

Did you get a chance to trace the red wire in your photo? I am not sure how to tell you how to bypass the relay because I am not sure how it is currently wired.

jriera · 03-06-2006, 08:21 PM

No, not yet... got sidetracked with work today .. go figure.

mark '87 930 · mark '87 930's Garage

Not to hijack this thread, but jwmarc, you said you took it apart and reviewed/fixed it... Can you elaborate on that? If you can Pm me, that would be be great. My car cuts out for a 1 second or a little more, and then on again.. No backfire when it comes back. Changed the Fuel pump real, and now onto the OB relay,, bu If I can fix it, then I will.