Chuck Jones

Sandman: Was it the fuel pumps? I hear the same noise whether the green connector is hooked up or not....it's still that whirring sound that comes on most of the time, but not all the time. There are times when I turn on the key and listen...and just get silence...but the car starts just the same. I stripped out all the stuff from the front trunk...tire, carpeting, everything thinking that I could focus in on the sound...but I cant' seem to localize it. It almost has a ventriloquel (sp??) effect. But I just fired up the car and it starts instantly...have to take it for a drive...but I'm still a little spooky about it just dying again. I still haven't gotten to the root cause of that.

thanks again for talking me thru this. I have Brian's WUR and solenoid that will be going in as soon as Ben (M and K SSI's) and Rarely get me back my Y pipe with the dual 38mm Tial wastegates and dual inlet flanges that will hook up with the SSI headers. I'm also probably going to go with the Garrett turbo...and will most likely be selling off my K27 7200 that I had bought last year but never installed along with the 46mm Tial. I'm waiting to hear back from Ben when it's all completed.

Bottom line...it's been fun today digging into the guts with the help and input from you guys. This is almost therapeutic for me. I retired over a year ago and have been looking for something that I think would qualify as "fun"....and I'm finding that this seems to qualify.

nathanUK '81 930 G50

Chuck, you mentioned temperature seems to make the fault appear & reset itself.

In my experience this is usually the electronic ignition. I wonder if your MSD is faulty. It is possible despite it being new.

Chuck Jones

Just a quick resurrection of this thread becasue you folks who focused in on the yellow relay in the rear panel were right....it turned out that after all this time, there was a broken wire to one of the pins....most of the time it made contact, but every once in a while it would break contact by heating up or ??? and the engine would die. A good indy chased it down and also found that the fuel pumps were running all the time becasue of more wiring issues in that rear fuse panel....all good to go now....but your collective assessment of the yellow relay was right. I've been told it's a good idea to carry an extra one of those along with a DME relay too.

nathanUK '81 930 G50

+1 on carrying a DME relay although the 930 doesn't use one AFAIK. I have one in the glove box of my carrera though.

srf506

Chuck, glad to hear you're getting it sorted out. I hate electrical problems over all others.

I carry one black, one red, and one yellow relay in my "trouble box" in the boot, along with an assortment of fuzes, an assortment of light bulbs, a spare belt, a can of tire goo, jumper cables, a big flashlight, a couple of road fuzees and one of those reflective triangle things. Of course I have the ever popular Porscher tire inflator and tool kit up front too.

So far, (sound of knocking on wood here) I've never had to use any of it since i put it in there. Speaking of which I should probably replace the can of tire goo, replace the flashlight batteries, and check the fuzees.

A930Rocket

Ditto on the fuses and all relays. You just never know...

fiftyfive

Today my 930 showed almost exactly the same problem as Chuck's. The only difference was mine would cut off every couple of minutes, restarting after 30-45 seconds. My shop thought it might be a DME relay, which I thought the 930 doesn't have.

I looked at the black box under the driver's seat; in addition to it there are two smaller boxes, 930 618 123 00 and 930 617 131 01. Searching the Pelican catalog, the first is described as a relay, the second as a fuel enrichment unit. My copy of PET doesn't seem to show these parts, but the Carrera's DME relay is 911 618 154 00. In Pelican's description of it they say it may be applicable also to the Turbo. Does this mean that 1) the 930 has a DME relay and 2) the Carrera's version can be substituted?

Per the thread, I'm taking a look at the overboost relay, too.

Thanks,
John

JFairman

DME is short for digital motor electronics. There is no such thing in a 930.
A DME is part of the motronics used in a Carrera.

The other small relay under the seat near the K-jetronic box is the factory rev limiter.

fiftyfive

Thanks. So 930 618 123 00 is the rev limiter (relay) and 930 617 131 01 the the enrichment unit?

JFairman

Can't see the numbers on mine right now but I think the one on the left is the rev limiter and the one closer to the K-jetronic box is the full throttle fuel enrichment relay.

That one disconnects the lambda system/oxygen sensor from the pulse valve putting it into open loop mode which lowers control pressure a little >richening up the air fuel ratio.
That relay is triggered by the throttle position switch on the throttle body when at full throttle.

fiftyfive

Yes, the enrichment unit's closest to the K Jet box. Regarding the overboost relay, does it cut the fuel supply or the ignition?

Mark Houghton

I believe the over-boost relay cuts the fuel. It all ties in to those other mysterious (and sometimes yellow) relays that sometimes give us trouble with the pumps.
Oh...and to echo JFairman, all that crap under the drivers seat is to control that simple little oxygen sensor and the Lambda system. No DME on our 930's...that would be far to sophisticated for a car that does not have electronically controlled fuel injectors.

JFairman

It cuts the fuel pumps by diconnecting the grounds to the fuel pump relays up front, and the loss of power is instant.

The rev limiter is 7200rpm i think, and will cut the ignition out completely all at once but the fuel pressure remains.. when the ignition returns that makes an orange flash of light in the mirror at night.

fiftyfive

Thanks very much for the information. Then if either the rev limit or overboost relay fails or is intermittent, the same effect of instantaneous shut-off is felt?

When I restarted the car (daylight) I don't think there was any sign of accumulated fuel, i.e., backfiring, rough start, etc. It simply restarted.

fiftyfive

Between browsing Pelican's relays and PET5 (MG=9, SG=2), the overboost relay is 911 615 118 00.

However, there's another engine compartment relay, "Ignition Cutoff", 930 617 117 01. Taking the name at face value, would its failure/intermittency also kill the engine immediately?

MG=9 SG=1 shows the under-seat enrichment module and rev-limiter relay P/N's. My car also has item 1, DME box 911 618 111 05 (from PET5, didn't confirm actual box's number yet), with the harness plugged in. Is it simply a dummy?