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fuel delivery problem-electrical
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caleb
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PostPosted: Sat Jun 30, 2007 3:18 pm    Post subject: fuel delivery problem-electrical Reply with quote

1986 2.1 westy weekender GL, now heres the problem, while driving occasionaly, like two or three times a week, my van will start sputtering and the amount of time and harshness of sputtering will vary. Last night driving home and i had to pull over 4 times because the van would stop running, while pulled over i would turn the key but the fuel pump wouldn't do one long pump and stop like normally but it would pulse and it wouldn't stop until the key is turned off. Turn it on again and it just pulses. so today i got out the Bentley and started checking fuel injection electrical components. it seems like there is a bad connection somewhere in the system.
-continuity between the relay and pump
-coolant temp sensorII 1600 ohms, not driven since last night so i think its within specs
-fuel pump is within specs
-relay is new and good
thanks for any help
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riceye
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PostPosted: Sun Jul 01, 2007 9:25 am    Post subject: Reply with quote

How old is your ignition switch?
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devesvws
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PostPosted: Sun Jul 01, 2007 10:58 am    Post subject: Reply with quote

sounds like a pluged up filter/or crap in the pump
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caleb
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PostPosted: Sun Jul 01, 2007 6:17 pm    Post subject: Reply with quote

i have never replaced my ignition switch, and i don't think it is a clog because when i turn the ignition to the on position with out starting the fuel pump sound isn't constant, it is a surging sound and if i put my ear by the relay in the engine compartment its contacts are clicking on off on off on etc.
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caleb
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PostPosted: Mon Jul 02, 2007 8:58 am    Post subject: Reply with quote

it also seems to happen more when the engine heats and i drive for a while
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tencentlife
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PostPosted: Mon Jul 02, 2007 9:08 am    Post subject: Reply with quote

Well then you've found the problem, by the sound of it.

When you described in your first post how the pump runs intermittently when you key on, I immediately thought it's the primary Digifant power relay. When you key on, this relay passes power to the ECU, the injector positive bus, the PCV warmer and O2 sensor warmer. The ECU then grounds the coil of the secondary fuel pump relay, but if there is a no-start the ECU shortly opens that circuit. That's why when you key on without cranking, you hear the pump run for a couple of seconds and stop.

What it sounds like yours is doing is the primary relay is closing, but the coil strength is weak so the contact flutters open and closed. Each time it does the ECU sees it as a new key-on and closes the pump relay coil circuit. Whether the pump relay reaches time-out or the main relay opens and closes again, the result is the same: the pump runs, stops, runs, etc. The clicking you hear is the root of the problem.

It's not impossible that the ignition switch is a contributor, but in that case the behavior would be much more erratic, probably more like it runs one day, and won't run the next, quits running unexpectedly, then restarts and runs fine 5 minutes later. There would be no discernible pattern with the ignition switch. What you have is a pattern that points to the main FI relay.

It is the left of the two relays inside the box on the left wall of the engine bay. If you're replacing one, just do them both since they are undoubtedly of the same age. They are pretty cheap, any FLAPS 4-pin Bosch-style relay will do. Then you've ruled that out and if the problem persists, you can take the time to hunt for other causes, like resistance in the positive supply chain or grounding.
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caleb
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PostPosted: Mon Jul 02, 2007 1:48 pm    Post subject: Reply with quote

i have already replaced both relays inside the box but they weren't replaced with vw or bosch just generic brands.
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tencentlife
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PostPosted: Mon Jul 02, 2007 4:25 pm    Post subject: Reply with quote

The brand shouldn't matter much, the cheap ones work, too, just maybe not for as long. Did you already replace them as a response to this same complaint?

If you suspect them, and to rule them out as still being a possible cause, just try swapping them one for the other. Is the behavior the same? If so, then it's probably not the fault of the relays. You can also by feel tell which relay is clicking, and trade it for the load reduction relay, lowest row second from the left on the main fuse panel,which is the same type and easy to get at.

Check out the bundle of ground connectors under the ignition coil. Make sure they are all clean and tight. Also check the ECU ground connector under the back seat. Remove the nut that holds the ECU carrier to the firewall, and remove and clean the dedicated ground that attaches to a M6 stud there. If you remove the ECU multipin connector to make this job easier, make sure the ignition is off when you remove and replace the connector. While the connector is off, use electrical contact spray cleaner on all the ECU and connector pins. You can also use a sharp scribe to tweak the connector's female pins for better contact. Careful not to bridge accidentally between any of them. To be safe, you can disconnect the battery ground while working in here.

Still have the problem? Pull out the fuel pump relay (in the box, on the right). Jumper the white and the red/white wires to that relay, the two pins that make a letter "T" to each other. Listen for the fuel pump. It should run steadily as long as the jumper is in place. This is independent of the ignition circuit, so it will run no matter what position the key is in. If it's still fluctuating, you should check and clean the power connectors at the pump, and track down and clean the brown ground wire from the pump to where it grounds on the chassis.

If your pump operation is still intermittent, you should run basic fuel delivery volume and pressure checks. You can use the jumper to run the pump while performing the tests. The delivery volume test is key here; pressure is actually controlled by the pressure regulator. I don't know the spec, but without regulation the pump should be able to produce a pretty high pressure into a blocked line. Some folks have said theirs have made 90psi. I would think at least 70psi. If it still operates intermittently and/or fails the delivery volume test, you're in need of a new pump. Delivery volume should be at least 1 liter per minute on an open line.

If jumpering the pump relay makes the pump run steadily, you can start up and run the car. Don't worry, you're not damaging anything. The igntion will be controlled at the key, so it will shut down when you key off, but the pump will run constantly until you remove the jumper. If you can start up, drive around and all else works normally, and you've cleaned up all those grounds, you can try another fuel pump relay, but the fault may be the pump relay grounding function in the ECU.

There are other power supply tests if these are inconclusive. Do the stuff above and let us know what happens. Other points where you could rule out bad connections in the positive power routing are where wires are ganged on the starter #30 positive pole, the B+ pole on the back of the alternator, and there is a positive connection on a stud inside the wiring connector box on the forward engine bay wall. The relay socket connections for both Digifant and fuel pump relays could also be loose. It is also very common to have an overheated main #30 connector on the back of the main fuse panel, which can cause all manner of problems.
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caleb
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PostPosted: Tue Jul 03, 2007 9:12 pm    Post subject: Reply with quote

something else i just noticed today driving home from work. the van always seems to have the problem at the same place. its about 7 miles from my work to where the problem occurs. today replaced the fuel filter( needed a new one anyway) and the ignition switch, neither of them worked. i still need some time to try the things that tencentlife mentioned, thanks for the help.
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devesvws
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PostPosted: Wed Jul 04, 2007 5:48 am    Post subject: Reply with quote

ok here is a shot in the dark check all the connector wires at the alt Confused i had a 86 syncro with a broken wire at the alt and it kinda did the same thing. and one day it just would not start at all . btw is there a bump or railroad crossing or big pot hole you hit near your work that would jolt the van ? how long have you been driving the van? hang in there it just takes time to get to the bottom of the problem. and most of the time its somthing simple Smile
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tencentlife
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PostPosted: Wed Jul 04, 2007 10:24 am    Post subject: Reply with quote

Yup, it's true. It is usually something simple.

Quote:
something else i just noticed today driving home from work. the van always seems to have the problem at the same place.


You should find a new route home from work.
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caleb
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PostPosted: Wed Jul 18, 2007 7:33 pm    Post subject: Reply with quote

ive got more clues to the puzzle. i think it may be the ECU or the ECU ground. i think this because while driving i break down, so i start checking things with DMM and i put my ear next to the fuel pump relay and it is clicking a million times a second so i go to the ECU and and give a gentle tap, nothing, tap it again and the fuel pump operates normally so i tap it again and it works good again so i start up the van and drive no problems all the way to my destination. since then it has had the problem so i tap the computer and its fixed. the ECU makes a high pitch/ high frequency sound, not sure if that means anything. the ECU has yellow junkyard marker that says 1VW. should i try an ECU that i know works to try to eliminate that as the problem? thanks for any help
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tencentlife
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PostPosted: Wed Jul 18, 2007 8:57 pm    Post subject: Reply with quote

Absolutely. try a known working ECU. Make sure it is '85 or later, that the part numbers agree (except a last letter, they can vary).

I was kind of afraid it might be in there.

One test you could do if you can catch it oscillating, is to pull any injector connector, and put a testlight between ground and the hot pin in the injector plug. One of the pins will be hot, but it should be steadily hot. If it also flickers, the problem isn't the ECU but somewhere in the main FI power supply circuit.
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