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Need Help:- The Yelow Relay

I had problim starting my car after restoration the engen & the engen wir harnes, then I unplug the Relay for Air Flow Sensor Boost Pressure and mad a streat wir connection instead of the relay and the car starts.

I purchase new Relay for Air Flow Sensor Boost Pressure and the car works, I drive the car 5 times then I had the same problim agin !!!

What do you think regarding that, do you think my new Relay for Air Flow Sensor Boost Pressure is defected ???

Regards,

Fahad

Old 04-11-2013, 03:42 PM
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Make sure all the connections in the socket are clean, which you may have already done. That relay is just one of the things that can go wrong with the pumps running. I presume you also have under the drivers seat the overspeed relay (don't know what year car you're running). That relay can cause the problems you're experiencing as well as the yellow relay from hell, since they work in concert.

To get to the relay under the seat, you need to remove the seat (of course). Four bolts and it's out. Unbolt the relay from it's mount so you can move it toward the rear of the car for easy access short-term. Next time your car won't start, try tapping (or beating on) the relay. It may or may not start after that. Either way, pull the plug harness and clean it well.

If you haven't already done so, spend some time to read all the posts in the sticky "my car won't start". Most everything you need to know is in there somewhere. If still stumped, please do ask questions!
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Last edited by mark houghton; 04-11-2013 at 07:43 PM..
Old 04-11-2013, 07:34 PM
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Thanks, Mark
Old 04-18-2013, 01:07 AM
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Mark's on the right track. In my case, I thought that I had a yellow relay issue and replaced it; I still had problem. Replaced the overspeed relay under the driver's seat; end of problem. It's a fairly common issue. My original speed relay lasted 23 years.
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Old 04-18-2013, 06:09 AM
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I have a 79 930 and I dont have the yellow relay in my engine compartment electric panel. There is a normal red relay in the socket there under the black plastic panel cover.

Is this normal for my year car or did the previous owners make some changes to remove it?
Reason I ask, my car does run the CD box for a few seconds after switching off the ignition to burn any residual fuel from the chambers then it shuts off like it is designed to....so unless I am wrong, I thought the yellow relay controlled this aspect of the ignition.

Is my car modified or is this normal for a 79 US model? Where should the yellow relay be found then?

Thanks,
Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-18-2013, 06:41 AM
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The ignition delay relay is the one that keeps the CD on for a few seconds to burn off residual fuel after you turn off the car with the key. It's the small aluminum relay next to the larger aluminum rear window defroster relay that are both held in place by a screw or small bolt on the rear panel.

I don't know if your year car came with a yellow relay. If everything works good without it consider yourself lucky and leave it that way. Red relays are more reliable and a fraction of the cost of a yellow relay.

It's always good to carry some spare red ones in the glovebox or trunk to replace the 2 front red ones for the fuel pumps when they go bad and they work fine to replace any of the black ones too.
Old 04-18-2013, 07:02 AM
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Quote:
Originally Posted by JFairman View Post
The ignition delay relay is the one that keeps the CD on for a few seconds to burn off residual fuel after you turn off the car with the key. It's the small aluminum relay next to the larger aluminum rear window defroster relay that are both held in place by a screw or small bolt on the rear panel.

I don't know if your year car came with a yellow relay. If everything works good without it consider yourself lucky and leave it that way. Red relays are more reliable and a fraction of the cost of a yellow relay.

It's always good to carry some spare red ones in the glovebox or trunk to replace the 2 front red ones for the fuel pumps when they go bad and they work fine to replace any of the black ones too.
Thanks for the info.
Yeah, I keep a few spares in the door pockets....had one or 2 go out on the road on me....not fun miles from home.
One thing I have been having trouble with is the red relay in the trunk fuse panel working its way lose. It will get lose enuff over time to kill the car and then it either wont start or died at a light on me once. I tried bending the prongs out slightly to increase the press fit but it still is something I dont think should happen and I have to check on them once every few hundred miles to make sure they are tight.
Its one of those PITA things I put up with on this beast.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-18-2013, 07:09 AM
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There's a cut-off year somewhere in the 70's I think where they 'updated' (term used loosley)to the yellow relays, vs. a standard round black one. It seems that early on when I was troubleshooting what I thought was a yellow problem, that swapping it with a black one did not work...but then somewhere along the line I found the problem to be the overspeed relay under the seat. So I presume that round vs. yellow rectangular relays only work in the year of car they were wired for.

I took that overspeed relay apart and re-soldered all the points I would get to and fixed the issue. Have since found a used one that I got for $45, which now resides in my glove box. And of course I also have a spare yellow that I probably didn't need after all. Money pits, these cars, sometimes.

Fred, the yellow has nothing to do with ignition...just fuel.
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Old 04-18-2013, 07:28 AM
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the yellow relay is controled or energized by the AFM switch. with the key on and engine off, the AFM energizes the yellow relay, removing the ground to the 2 FP relays. that ground is of course the boost pressure switch.

here is how i would go about TSing this system: based on whats esiest to do first and each step does not fix it.
(if one pump runs and one does not, then the FP or the relay.)
both pumps not running:
i would reach around and pull the connector off the AFM. as soon as the key is ON, no start needed, the FP's should run.
then i would check to see if the boost pressure switch is grounded. with connector off AFM, ground the wire on the boost switch.
jumper 30 and 87a on yellow relay
jumper pins 1 and 2 on the speed relay
IF 1 and 2 run the pumps, check for 12v to speed relay
if 12v present, speed realy bad. bad solder joints is a problem on this relay.

a note for the yellow relay:
unlike most realys, the yellow relay runs the pump in the de-energized mode. so the coil can be bad and the pumps can run. you might consider popping the cover off and cleaning the contacts with fine sandpaper. i bet there are a LOT of good/repairable yellow relays that have been replaced.

the FP circuit was different for the years on the 930 from what i am told. the 87 has a fuse in the wire bundle itself that feeds power to the speed relay. it is a pain to get to....from what i am told.


fahad
you may have moved a wire that is not making good contact. you could also have a lose or bad contact in the yellow relay socket. you could do as i said abbove, clean the contacts on your old relay.
follow my trouble shooting. start with the AFM switch.
in your case, i might jumper 30 and 87a on the yellow relay socket first. make sure it is in a "no start condition"
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-18-2013, 09:39 AM
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The above post should be in the no start thread at the top of the page.
Good info like this gets buried and lost and it would be good to be able to find it easily.
Old 04-18-2013, 09:45 AM
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Thumbs up

T77911S:
I have been meaning to sit down and figure out the electrical mess/relays on our 930s, but have looked at it and HAVE ALWAYS HAD SOMETHING BETTER TO DO. I've copped out and, "replaced with a known good part". Thanks for the assistance!
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Old 04-18-2013, 10:39 AM
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this IS about the 4th or 5th time i have posted it. this one is a little different. maybe i will save it so i can just copy and paste. funny, the other post this is in is not far down from this one.
i have always wondered why when one topic comes up, there is another post identical to it right next to it.

my friend (mechanic) chased that fuse to the speed relay for about a week.

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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 04-18-2013, 10:46 AM
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