What's so special about the magic yellow relay?
12-01-2006, 03:41 AM
#1
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What's so special about the magic yellow relay?
I've been chasing an intermittent start problem for a while. When I turn the key and hear the fuel pumps start, the car starts right up. If I turn the key and don't hear them, it doesn't start until I try again a few more times and the pumps come on.
I have worked through the following steps:
Check/clean fuse
Check/swap fuel pump relays
Replace electrical portion of ignition switch
Check/bypass alarm box
Pull paddle switch plug from CIS dist. (pumps run any time the ignition switch is on)
Look suspiciously at yellow relay
Read wiring diagrams
Look suspiciously at yellow relay
From what I have read, is seems that magic relay is inline with my ground for the fuel pumps. I don't quite understand how it get's it's signal from the boost sensor, but apparently something back there is holding my fuel pumps hostage intermittently.
The relay has a ground pigtail and a fiberglass circuit board on the bottom between the pins. It must be special in some way since it's $172 for a new one. That seems a little steep for a test and I'm kind of stuck in the troubleshooting at this point. Am I barking up the wrong tree? Can that relay be replaced with another more common Porsche relay? What's the magic? Delay? Sensitivity? Color?
I have worked through the following steps:
Check/clean fuse
Check/swap fuel pump relays
Replace electrical portion of ignition switch
Check/bypass alarm box
Pull paddle switch plug from CIS dist. (pumps run any time the ignition switch is on)
Look suspiciously at yellow relay
Read wiring diagrams
Look suspiciously at yellow relay
From what I have read, is seems that magic relay is inline with my ground for the fuel pumps. I don't quite understand how it get's it's signal from the boost sensor, but apparently something back there is holding my fuel pumps hostage intermittently.
The relay has a ground pigtail and a fiberglass circuit board on the bottom between the pins. It must be special in some way since it's $172 for a new one. That seems a little steep for a test and I'm kind of stuck in the troubleshooting at this point. Am I barking up the wrong tree? Can that relay be replaced with another more common Porsche relay? What's the magic? Delay? Sensitivity? Color?
Last edited by ayglass; 12-01-2006 at 03:44 AM. Reason: I can't type.
12-01-2006, 07:27 AM
#3
Drifting
I'm just curious, so if you hear the fuel pumps running with the ignition switched on - car not actually started - then that means the safety wiring on the back of the fuel/air metering housing must be disconnected. See this thread for a picture:
https://rennlist.com/forums/911-turbo-930-forum/306621-fuel-pump-question.html
If you check it and it *IS* connected then the sound you might be hearing when the key is switched on, is the CDI box and not the fuel pumps, which might point to something else being your problem.
I'm just throwing it out there as another possibility. It's no biggie to have had the wiring I mentioned disconnected...many people do it.
https://rennlist.com/forums/911-turbo-930-forum/306621-fuel-pump-question.html
If you check it and it *IS* connected then the sound you might be hearing when the key is switched on, is the CDI box and not the fuel pumps, which might point to something else being your problem.
I'm just throwing it out there as another possibility. It's no biggie to have had the wiring I mentioned disconnected...many people do it.
12-01-2006, 09:57 AM
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ayglass,
I had a similar problem, except that mine would only do it when I was driving! That magic relay is certainly a key factor in the system and shuts your fuel pumps if the overboost switch is activated (ungrounded). My issue turned out to be the overboost switch connector itself. I simply disconnected it and cleaned it up real nice, put some di-electric grease on it and re-connected it. Before I did that though, I also took apart that yellow relay and re-soldered the joints as they did seem a little dull (cold solder joint) which eventually leads to cracking. Try those two things... or as a test, you can ground the white wire coming from the overboost switch and see if it does it anymore. If not, you know that is where your issue is (relay or connection).
From a safety perspective, once you have this issue licked, I would recoonect the plug on the fuel distributor, you just never know.
I had a similar problem, except that mine would only do it when I was driving! That magic relay is certainly a key factor in the system and shuts your fuel pumps if the overboost switch is activated (ungrounded). My issue turned out to be the overboost switch connector itself. I simply disconnected it and cleaned it up real nice, put some di-electric grease on it and re-connected it. Before I did that though, I also took apart that yellow relay and re-soldered the joints as they did seem a little dull (cold solder joint) which eventually leads to cracking. Try those two things... or as a test, you can ground the white wire coming from the overboost switch and see if it does it anymore. If not, you know that is where your issue is (relay or connection).
From a safety perspective, once you have this issue licked, I would recoonect the plug on the fuel distributor, you just never know.
12-01-2006, 01:00 PM
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Hey All,
JBL: I've been reluctant to open it up until I knew that it was the problem. I was concerned that I would botch the disassembly and have to buy one for my clumsiness :-) If I open it up I will carefully compare it to other Bosch relays and give a report. $172 is highway robbery if it's the same as a fuel relay inside.
Sand_Man: I gave that connector a try when I was looking for a solution. If I pull it, the pumps will run all the time and the car *always* starts. With it connected again I only get the pumps sometimes. The bizarre twist is that if I leave it disconnected, my speedo doesn't work!!! It's bizarre.
Mark: I wonder if you are onto something there. I have a Kokeln intercooler and the overboost switch is threaded into it. If the intercooler wasn't properly grounded that might cause an intermittent signal from the switch... I'll check the ground on the intercooler!
JBL: I've been reluctant to open it up until I knew that it was the problem. I was concerned that I would botch the disassembly and have to buy one for my clumsiness :-) If I open it up I will carefully compare it to other Bosch relays and give a report. $172 is highway robbery if it's the same as a fuel relay inside.
Sand_Man: I gave that connector a try when I was looking for a solution. If I pull it, the pumps will run all the time and the car *always* starts. With it connected again I only get the pumps sometimes. The bizarre twist is that if I leave it disconnected, my speedo doesn't work!!! It's bizarre.
Mark: I wonder if you are onto something there. I have a Kokeln intercooler and the overboost switch is threaded into it. If the intercooler wasn't properly grounded that might cause an intermittent signal from the switch... I'll check the ground on the intercooler!
12-01-2006, 01:15 PM
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Something else you can try.. is when you turn the car on and don't hear the pumps.. go back there and flick that yellow relay around... if you hear the pumps come on, you know what it is.
But certainly check the ground.
But certainly check the ground.
12-01-2006, 02:22 PM
#7
Drifting
Originally Posted by ayglass
Sand_Man: I gave that connector a try when I was looking for a solution. If I pull it, the pumps will run all the time and the car *always* starts. With it connected again I only get the pumps sometimes. The bizarre twist is that if I leave it disconnected, my speedo doesn't work!!! It's bizarre.
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12-01-2006, 02:25 PM
#8
Drifting
Originally Posted by mark '87 930
Something else you can try.. is when you turn the car on and don't hear the pumps.. go back there and flick that yellow relay around... if you hear the pumps come on, you know what it is.
But certainly check the ground.
But certainly check the ground.
12-01-2006, 02:42 PM
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When you install the Kokeln you lose the ground (earth) as it is so well insulated for heat. The other possibilty is that it is the switch itself at fault. You can test this by grounding the white wire.
12-01-2006, 05:53 PM
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ayglass,
I replaced/cleaned everythig you did PLUS the majic relay and STILL had problems. The little culprit wound up being a bad socket the relay plugs in too. Apparently over the years the pin-to-wire conections broke and weren't making good contact. The fix was a new socket w/harness prt# 90161233300 for $20
I replaced/cleaned everythig you did PLUS the majic relay and STILL had problems. The little culprit wound up being a bad socket the relay plugs in too. Apparently over the years the pin-to-wire conections broke and weren't making good contact. The fix was a new socket w/harness prt# 90161233300 for $20
12-02-2006, 03:28 AM
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This just in...
I gave the intercooler the ground check. I clipped the test light lead on the fuse block hot side and put the tip in the intercooler fins. I then bumped the intercooler around a bit and couldn't get the light to go out. I then started the car (sometimes the pumps came on, sometimes they didn't) and the light stayed on. Therefore I'm going to conclude that the intercooler is grounded. (though an improved ground might be worth doing)
Nathan, I did try grounding the switch wire, but I was able to get intermittent fuel pumps with it grounded. I guess that rules out the sensor.
To clarify some, according to the wiring diagram when the CIS paddle switch is connected like it was from the factory, there is a contact that turns the pumps on when the ignition switch is in the "start" position. They only run in the "run" position when that paddle switch is disconnected. I can always get them to run when I disconnect the paddle switch, but I'm trying to get this beast to operate correctly when wired as the factory intended. (if possible)
jwl: Thanks! I'm gonna find something solid to strike my head against if I find out that it's a $20 socket for the magic relay ;-) I'll check it thoroughly!
New data from this evening's scratching:
The pinout of the magic yellow relay is the same as the pinout of the regular red fuel relay. I violated all sorts of safety rules this evening and plugged a red relay in where the yellow one was. THE CAR STARTED!!! Now granted, all sorts of other things might not work, overboost might not shut down the car, the relay might overheat after a while, chickens may lose their feathers, and PCNA may come to my house if I discourage you from spending $172 for that yellow relay... But, this opens up a whole new troubleshooting option. I could buy the extra black and red relays that I should be carrying around in the car anyway and put a red one back there for a day or two. If that cures the intermittent starting and the fuel pumps come on every time I start the car, we now know that the magic yellow relay was intermittient!
The question then, of course, is do I buy a magic yellow relay for $172 or do I just buy a regular red one for $26???? I believe in quality, but I'm not prone to spend my tire money on relays...
I gave the intercooler the ground check. I clipped the test light lead on the fuse block hot side and put the tip in the intercooler fins. I then bumped the intercooler around a bit and couldn't get the light to go out. I then started the car (sometimes the pumps came on, sometimes they didn't) and the light stayed on. Therefore I'm going to conclude that the intercooler is grounded. (though an improved ground might be worth doing)
Nathan, I did try grounding the switch wire, but I was able to get intermittent fuel pumps with it grounded. I guess that rules out the sensor.
To clarify some, according to the wiring diagram when the CIS paddle switch is connected like it was from the factory, there is a contact that turns the pumps on when the ignition switch is in the "start" position. They only run in the "run" position when that paddle switch is disconnected. I can always get them to run when I disconnect the paddle switch, but I'm trying to get this beast to operate correctly when wired as the factory intended. (if possible)
jwl: Thanks! I'm gonna find something solid to strike my head against if I find out that it's a $20 socket for the magic relay ;-) I'll check it thoroughly!
New data from this evening's scratching:
The pinout of the magic yellow relay is the same as the pinout of the regular red fuel relay. I violated all sorts of safety rules this evening and plugged a red relay in where the yellow one was. THE CAR STARTED!!! Now granted, all sorts of other things might not work, overboost might not shut down the car, the relay might overheat after a while, chickens may lose their feathers, and PCNA may come to my house if I discourage you from spending $172 for that yellow relay... But, this opens up a whole new troubleshooting option. I could buy the extra black and red relays that I should be carrying around in the car anyway and put a red one back there for a day or two. If that cures the intermittent starting and the fuel pumps come on every time I start the car, we now know that the magic yellow relay was intermittient!
The question then, of course, is do I buy a magic yellow relay for $172 or do I just buy a regular red one for $26???? I believe in quality, but I'm not prone to spend my tire money on relays...
12-02-2006, 09:05 AM
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If the overboost switch still cuts the fuel pumps and when that other connector is plugged in the CIS the pumps only run when the engine is cranking/running I would just buy a red relay and see how it goes. Also make sure that when you switch off the ignition that the engine continues to run for a second or so like it is supposed to.
12-03-2006, 10:47 PM
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I said to heck with it all, and set up my two fuel pump relays on a grounded inertia switch (one wire at the back of the relays does it). This takes out all the BS in the back. If there is ever a shunt, the inertia switch will cut the pumps off.