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Fuel question

I have a no start problem and I just finished reading a couple of posts here but got a few questions.

Should the fuel pumps come on after removing the metering plate switch?

Last edited by 1fastm70; 08-14-2010 at 10:28 PM..
Old 08-14-2010, 10:25 PM
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Ok I unplugged it, turn the ignition on but pumps won't run unless I move the metering plate. Got any ideas on why this is caused? Thanks for the help shadetree930.
Old 08-15-2010, 07:41 AM
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You removed the plug from the connector (circled in picture) and with the ignition "on", the fuel pumps do not turn on? But if you reconnect the plug, turn the ignition "on" and move the metering plate, the fuel pumps turn on? This really doesn't make any sense. Did Porsche change the type of switch in the metering plate housing in certain vintages?

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Old 08-15-2010, 07:51 AM
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You removed the plug from the connector (circled in picture) and with the ignition "on", the fuel pumps do not turn on?
Yes, they don't come on.

But if you reconnect the plug, turn the ignition "on" and move the metering plate, the fuel pumps turn on?
With the plug on or off, if I move the metering plate with my hand the pumps come and I am able to start the car. Hope this helps to calrify.


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Old 08-15-2010, 08:16 AM
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What year is your engine/car?
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Old 08-15-2010, 08:23 AM
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Quote:
What year is your engine/car?
both 1979.
Old 08-15-2010, 08:46 AM
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None of that makes any sense. You unplug, the pumps should run. The switch in the metering arm I think is normally closed and opens when the arm is depressed. Pulling the plug should mimic the same condition as an open switch. Got a weird gremmlin lurking back there.
I'm leanng toward your relay in the rear relay tray. Later cars the relay was rectangular and yellow, earlier I think they were your standard round relays.

You also said this: "With the plug on or off, if I move the metering plate with my hand the pumps come" That is pure magic. If the plug is disconnected, then there is nothing for the switch to send it's "message" through. Are you sure you're not unplugging something else back there (the only other thing might be the frequency valve, but I'm not sure you have an O2 emissions Lambda system in the '79 (thus no frequency valve).
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Old 08-15-2010, 05:22 PM
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Ok so I ordered a new overboost relay and now the car starts fine but dies after a second or two. Now if I remove the metering plate switch the pumps turn on with the igniion on. Guess it was a bad relay but there's still something else. Looked for relays under the seats but nothing was found.
Old 08-16-2010, 11:51 PM
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Ok, making some progress. Go through the normal littany of stuff - overboost sensor wire connection or the sensor itself maybe bad (put the wire to ground and see if that fixes the stalling problem), fuel pump relays and fuse and wire connections up front in the main fuse tray. Will the car continue to run if you start it with the plug to the metering plate disconnected?
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Old 08-17-2010, 04:54 AM
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Grounded the overboost sensor wire and still starts but dies. Same result with the metering plate switch connector removed. I cleaned the fuses and relays in the front fuse box and it stayed on more than before but still died. Now say I crank the engine, it starts but dies. I try to starts again but it only cranks no start. I have to wait about 10 seconds to be able to start it.
Old 08-17-2010, 09:22 AM
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Quote:
Originally Posted by 1fastm70 View Post
Grounded the overboost sensor wire and still starts but dies. Same result with the metering plate switch connector removed. I cleaned the fuses and relays in the front fuse box and it stayed on more than before but still died. Now say I crank the engine, it starts but dies. I try to starts again but it only cranks no start. I have to wait about 10 seconds to be able to start it.
Hmmm.....

You also said: Looked for relays under the seats but nothing was found.

Does your car not have an oxygen sensor/lambda control system? I'm not familiar of when these were put on the US market cars, but all the control stuff would be under the drivers seat...including the speed relay which can at times be the fault (my understanding is that that's where the white wire from the overboost sensor terminates, so a bad connection there would stop things).

I had a similar issue for a short spell where the car would start and run for a second then shut down. Cleaned with electrical contact cleaner both fuel pump relay female plugs and also replaced both relays just because. Problem went away...so far. Recommend disconnecing the wires to the relays at the fuse box, cleaning the wires, then re-torquing them back in place. And maybe a couple new relays as well. I hate to throw money at things unless absolutely necessary, but at leas the relays are relatively cheap ($14 IIRC).
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Old 08-17-2010, 11:15 AM
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I was looking for that speed relay but there is not a single thing under any of the seats.
I installed new pump relays thinking that might be the culprit but nothing changed. I also cleaned all relay contacts and fuse wires just to make sure.

I started the car but I had to push the metering plate down a little to keep it on. If I would let it go it would die, feels sort of like if the engine wasn't sucking enough air to move the plate on it's own. Can the metering plate be adjusted somehow?
Old 08-17-2010, 12:43 PM
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Is your car a 930 or an SC with a 930 motor in it... because that could change everything as far as tracing this problem.

1986 was the year the 930 was sold in the USA again after 1979. Thats when it got the lambda emission sytem along with better AC ducts, and slightly upgraded evaporator along with a bunch of other little things.
Old 08-17-2010, 01:26 PM
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Car is a 79 930.
Old 08-17-2010, 01:32 PM
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Quote:
Originally Posted by 1fastm70 View Post
I was looking for that speed relay but there is not a single thing under any of the seats.
I installed new pump relays thinking that might be the culprit but nothing changed. I also cleaned all relay contacts and fuse wires just to make sure.

I started the car but I had to push the metering plate down a little to keep it on. If I would let it go it would die, feels sort of like if the engine wasn't sucking enough air to move the plate on it's own. Can the metering plate be adjusted somehow?
Ahhh....another tidbit of information....

So, even with your metering plate switch plug un-plugged, you find that the pumps continue to run but the car won't stay running unless you push down slightly on the metering arm? There really isn't any reason for any adjustment to be needed unless the pivot point is worn/corroded/sticking or something bent the arm...which it shouldn't be but who knows? You can adjust the arm to deliver more or less fuel (see the mixture adjustment screw on top of the fuel distributor) but I'm not sure that would be a good idea (yet) as it could just compoud your problem. If you want to try that, then turn the screw clockwise about 1/16 of a turn and see if the car will keep running. Each time you turn it, you'll be going richer. Keep track of your starting point.

Does/did this seem to occur only with a cold start, or also when hot starting? Did this problem just crop up out of the blue, or slowly became a hard-to-no-start issue?

Make sure that your fuel control and system pressures are correct - easy to check with the correct gauge setup. Could be that your WUR is causing fuel delivery issues (i.e., too much control pressure, not allowing the arm to deflect enough to deliver fuel). Could be your cold control pressure is too high, indicating an issue with the WUR.

Finally, you might have nothing more than a nasty vacuum or air leak somewhere on the intake. Don't forget to look for the obvious first.
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Old 08-17-2010, 01:41 PM
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Ok I don't want to mess with the adjustment just yet because before the car started doing this it ran like a champ no problems whatsoever. It just didn't want to start one day. Don't know about it having trouble staying on when warm because I get tired of holding the metering plate for it to warm up.

Since I have to push the metering plate down to keep it running I noticed that when I push it down and am not holding it sturdy enough it will push it back up. Not sure if this is how it's supposed to be.
Old 08-17-2010, 02:01 PM
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"Can the metering plate be adjusted somehow?"
Yes it can and according to Larry Fletcher at CISFLOWTECH most of the CIS airflow sensor plates he's seen on older cars need adjusting and most people don't know it.

With the fuel pumps running so control pressure is pushing the plate up all the way while the motor is off the sensor plate should be right even with the narrowest point of the venturi cone, and it has to be perfectly centered.
You check for it being centered all the way around it with a feeler gauge.

To change the sensor plate hight at rest while fuel pumps are running there is a small interference fit pin under the fuel line inlet on the airflow meter housing. You have to remove the fuel line to get at it but you can see it by looking at the left side of the fuel line inlet on the fuel head.

If the plate is too high, take a small drift punch and hammer and tap it downwards slowly and carefully to lower it. If the plate is too low or you drive it downwards too far then it becomes alot of work....
You then have to remove the whole CIS airflow meter housing that is held in by only 3 nuts and bolts and then split the thing top from bottom. you will need a new gasket when reassembling.

Once apart, you drive that pin upwards or outwards from the housing. Then put it all back together and with the motor off and pumps running so control pressure is pushing the plate upwards you tap the pin downwards until it is even with the narrowest point of the venturi cone.
If that narrowest point of the venturi is not a point and is a small flat area about 1mm long, the plate should be even with the top of it.

hth.
Old 08-17-2010, 02:09 PM
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You can see the sensor plate height adjustment pin on the top of the air flow meter housing under where the fuel line inlet would be if the fuel head was mounted on it in this diagram if you look for it.
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Old 08-17-2010, 02:25 PM
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Don't make any adjustments. It seems the reason it runs for a few minutes is because the cold enrichment is on and then after a couple of minutes, it turns off and returns to normal control pressure. The air leak is such that a rich condition will allow it to run, but when it returns to normal, it leans out and dies.
I with Shadetree930....sounds like an air leak.
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Old 08-17-2010, 03:37 PM
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Then I shall check again for air leaks just to make sure. I didn't want to make any adjustments just yet because the car was running fine before it did this.

Could it be possible for the warm up regulator to be causing this? Does this thing give out just all of a sudden or does it start giving problems little by little?
Old 08-17-2010, 05:56 PM
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