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Which is my over boost or air pressure relay?

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Last edited by jwakil; 02-05-2017 at 05:41 PM..
Old 02-05-2017, 05:39 PM
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Quote:
Originally Posted by jwakil View Post
I'm sure the battery is fine. I will remove the overboost switch next.
I went back to using jumpers to get power directly to pin 87 of the fuel pump relays and started the car. With the car running, all electronics work fine;horn, windows, lights.... so back to square one. I'm wondering why the voltage is lower even in the key off state for fuses 5&6, which are actually tied together in parallel on my fuse box. And I was wrong about the interior lights. They do work normally, even if the car is off. The horn however seems to work when the car is running, but doesn't work with it not running.
I suspect that all of your various components/relays are most likely fine. This power failure to multiple things (horn, windows, pumps, etc) reeks of bad ground. At low voltage (engine not running and alternator not putting out) the amp draw across any circuit increases dramatically. High amp draw will cause voltage drop anytime a circuit is energized. Check and clean all grounds, just to make sure, but you apparently have good enough connections to run the starter and start the car.
I'm not sure....someone else knows for sure...but does the main power to the fuse panel start at one of the connection points on the starter?
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Old 02-05-2017, 06:04 PM
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I'm at the point of doing what one of the previous posters suggested which is to just run a power source directly to the fuel pumps with a manual switch, and forget about all this relay crap. Just wondering if there is any drawback to doing this, like burning out the fuel pumps or something.
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Old 02-05-2017, 06:23 PM
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^^^

I believe that was JFairman. He stated that he only used as an emergency backup to get home. If there was a fire and the engine was shut off the fuel pumps would still be running.

Electrical is definitely NOT my forte but I like two of the suggestions.

1) weak battery; maybe if you jump the battery with another car you could test that theory? You did say that you got the car started and all the lights worked...running off of the alternator as opposed to the battery?

2) Find and clean all of your grounds. Maybe someone has a list of grounds to clean.

I would start with the battery because it is easy and can be eliminated as a probable cause quickly...even if you know it is good. I think that taking it to a parts store to do a load test would be best.

Rahl

Last edited by 356911930; 02-05-2017 at 07:02 PM..
Old 02-05-2017, 06:54 PM
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If u post a pic of your motor we might be able to help u more...

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Old 02-05-2017, 07:21 PM
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I'm not sure how helpful these pics will be but here they are. And for the last time...the battery is fine. It is new, it cranks the engine effortlessly, I have check the terminals and I'm SURE it is not the battery. If someone has a list of grounds for the early 930s, it would be very helpful.




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Several other daily drivers not worth mentioning...
Old 02-05-2017, 08:09 PM
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There are a set of grounds back behind the battery.Maybe u can take a closer shot of your fuse pannel

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Old 02-05-2017, 09:08 PM
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What the inline fuse for comming out of your fuse box??

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Old 02-05-2017, 09:13 PM
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It looks like maybe some one did a modification yo #6 fuse if u are counting from the left of the fuse block,also i have red relays for the fuel pumps,wich are the ones closest to the windshield...

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Old 02-05-2017, 09:19 PM
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The relay,witch is red in my engine compartment is also tied to the fuel pumps

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Old 02-05-2017, 09:21 PM
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I ended up taking all the wires out of the fuse pannel 1 at a time and stripped off the old wire until i had new strand then saughtered the ends and reinstalled,your car being a 81 model i am sure are corroded,mine were,if they are not making a good connection the wires tend to get a little toasty..

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Old 02-05-2017, 09:25 PM
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Also with the key on check to see if u have power at the wur

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Old 02-05-2017, 09:30 PM
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Relay g is the red one on the engine compartmen,your over boost is under your intercool the one with the black and white wire,the one with the orange cover that has a spring around it is your boost gauge,i would try and ground out the overboost wire then try starting it.

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Old 02-05-2017, 09:36 PM
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The fuel pump relays are supposed to be red. Not sure if your model year is any different than the later models, though. Black won't work on my car.
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Old 02-06-2017, 04:42 AM
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your panel looks different than mine.

here is mine,
my overboost relay is the yellow one on the edge of the pic.
it goes in the empty socket to the left.

if you have a non stock IC someone may have deleted the overboost relay and directly grounded the wire that goes to it.

you need to look for a sensor screwed into the IC with one wire going to it.


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Old 02-06-2017, 05:02 AM
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My car has always had the black relays for the fuel pump. I did bypass fuse #4 with an inline because it was corroded and couldn't get the screw to turn and didn't want to break the block. I'm beginning to suspect that my missing overboost relay or bypass someone put in might not be working. The red one in my engine fuse panel seems to be the same location as the black one in T77911S's post. I thought that one was for the heater blower or something. As I said, I already tried unplugging the plug from the airflow housing and grounding the overboost switch wire, however, if the missing overboost relay is stuck in the open position, or the bypass is broken, then I wouldn't have any current going through that circuit meaning my fuel pump relays would not switch to power the fuel pumps. I need to find this mysterious overboost relay or bypass.
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Last edited by jwakil; 02-06-2017 at 07:13 AM..
Old 02-06-2017, 07:03 AM
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here is a picture of my 1981 930 rear fuse panel area

also the 2 relays from the left near the windshield are RED on my car
Old 02-06-2017, 07:32 AM
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Old 02-06-2017, 07:33 AM
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in the engine compartment

the small silver relay ( i believe is)

Relay ignition cut off, 911 turbo 1977-1989

part number 930.617.117.01
sk 6455
88 12v max 10a

.................................................. ........................

the larger silver relay ( i believe is )
relay rear window heating

part number 911.615.115.00
Old 02-06-2017, 07:46 AM
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The earlier Euro cars have the much simpler wiring as the very early USDM cars as far as I can tell. Ain't a yellow relay nor anything to be found under the seat in my 84.

I was chasing something similar recently. I was super frustrated until I found the amazing wiring diagram already shared here. It turned out to be an intermittent fuse connection. I replaced ALL my fuses (most of them original) and cleaned the contacts a bit, and she fired right up.

I also found a few more minor things started working after the new fuses.

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Old 02-06-2017, 08:25 AM
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