Microbus fuel pump relay keeps failing

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jlronning
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Microbus fuel pump relay keeps failing

Post by jlronning »

1994 VW Microbus shut down and had to be towed in. An auto electrician replaced fuel pump relay, worked OK for a couple months, then it failed too. It was a used relay, so I had a new one put in. It also failed after a short time. Don't want to put another R800 down the hole if something is causing the relays to fail. Any ideas? Also, where is this relay located, if I want to try it myself? It's not with the other relays with the fuses, it's not behind the right rear light where some other relays are located. Thanks for any help. Presently I have the fuel pump wired to the hooter circuit so it's on when the ignition is on but there's a safety issue with that in that it won't shut off when the engine shuts off (i.e. in a collision it'll keep pumping).
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Re: Microbus fuel pump relay keeps failing

Post by MK2 G60 »

The relay is behind the right rear light.There is a number of others too.
Check maybe it blew the fuse there.Remove all the relays and clean the holders for them.They get dirty due to water entry.The fuses do the same thing.Check the relay inside for water too.
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jlronning
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Re: Microbus fuel pump relay keeps failing

Post by jlronning »

g60 Golf - thanks for the tip. The relay was where you said it was after all, and I did find a blown fuse (looks melted due to bad connection). With new fuse, fuel pump relay works after all.
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Mark Taylor
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Re: Microbus fuel pump relay keeps failing

Post by Mark Taylor »

What is the part number/identity no. on the fuel pump relay .... Thanks
Billypaton
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Re: Microbus fuel pump relay keeps failing

Post by Billypaton »

What does fuel pump relay on microbus 2.5caravelle look like
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Re: Microbus fuel pump relay keeps failing

Post by missioner »

Billypaton wrote:What does fuel pump relay on microbus 2.5caravelle look like
It looks like a relay. It can be found next to other relays and some fuses.

'87 Golf 1 Olde Skewl OEM+
Billypaton
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Re: Microbus fuel pump relay keeps failing

Post by Billypaton »

It may have sounded like a silly question but there is a large one with a double relay pin attached to it. Others are a single relay type. If you're a kombi person you may understand.
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Re: Microbus fuel pump relay keeps failing

Post by missioner »

Billypaton wrote:It may have sounded like a silly question but there is a large one with a double relay pin attached to it. Others are a single relay type. If you're a kombi person you may understand.
If you still have the owners manual it will have a fuse and relay diagram in it.

It's a known thing that relays burn out after some time on a high current circuit, replacing it will sort out the problem 90% of the time.

Usually it will be a 4 pin relay. Almost never 5 pin. The circuit only has to power one single component, the fuel pump.

To work out which relay it is will take some time, some brains and some testing tools. This will be a multimeter and a jumper wire. First check the fuses, fuel pump is normally a 30A fuse. Remove the suspected relay (based on research and some RTFM), look at the pin diagram on the relay housing ( or at least the pin numbers) to determine which pins are needing to be bridged to test the circuit.

They go like this
30 Battery +be
85 control switched
86 ground
87 output.

Confirm with the multimeter before proceeding.

Bridge the 30 and 87 pins and the pump should run. If you crank the motor it should start, if all else is working. Don't leave it too long as a KJet motor will flood if the pump stays on.

If the pump doest run and you have power across the bridge, pull it out immediately and disconnect the wires on the fuel pump. Rebridge the relay socket and test the voltage at the pump wiring. If you have 12V, go buy a new pump. If the old pump is seized and it doesn't blow the fuse, it will make lots of smoke come out of the wiring, be cautious.

To test a relay connect pin 85 and 86 to a battery and test for continuity between pin 30 and 87.

If the relay is old and you are installing a new fuel pump, it's not a bad idea to get a new one at the same time. Make sure it's rated for 40Amps and not lower. The lower amp relay will burn out from the load of the fuel pump. Use high amp relays for fans, lights, pumps etc. Pay more for a brand name like Bosch or Hella, etc, it's worth the money.

Happy hunting
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Re: Microbus fuel pump relay keeps failing

Post by missioner »

Make a jumper like this oneImage
'87 Golf 1 Olde Skewl OEM+
dam003
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Re: Microbus fuel pump relay keeps failing

Post by dam003 »

I have a 2.2 Audi k-jet in a '81 Kombi bakkie. The fuel pump doesn't stop after a second or two when ignition is turned on but engine not started. The relay have numbers 15 (ignition), 30 (battery), 31 (neg.), 31b (coil -) and 87 (pump). What controls the stopping of the pump? Any help appreciated!
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VAG Fan
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Re: Microbus fuel pump relay keeps failing

Post by VAG Fan »

I've driven both the 2.2 K-Jet and the 2.3 KE-Jet Audi engine. Unfortunately I have much more experience with the electrics of the latter, and very little with the former (which was in my early student days). But perhaps we can get you sorted anyway.

1) Did the fuel pump relay switch off properly previously, after 1-2 seconds? Did you change anything before it stopped working?
2) On my old 1978 Audi 100 (K-Jet), at some stage the fuel pump stopped "priming" completely. It wouldn't run when switching on the ignition. It would only start once you engaged the starter, or push-started the engine. (Which is obviously the opposite problem of yours - yours doesn't stop.) I never bothered to trace the problem, but you should definitely repair yours, to prevent e.g. flooding after an accident.
3) I also know from my old Golf 1, which had the same type of Hall sensor ignition ("TSZ-H") like the K-Jet Audi, that the TCI ignition control unit monitors the RPM signal from the distributor, and stops drawing current about 1-2 seconds after the RPM signal stops. I could always see this on my Golf's ammeter. After switching on ignition, or after stalling the engine, the ammeter would read about -2 A, then go to zero after about 2 seconds.

Putting all of this together, I think it's quite possible that the TCI unit on the 2.2 K-Jet Audi has an output signal which is used to drive the fuel pump relay.

So, if you didn't change anything else (see question 1), and the system just failed on its own, then I would suggest replacing the TCI unit (they're not very expensive, Goldwagen should be able to help).

That's my 2 cents, but I hope Missioner will also chime in.

Edit: I think the TCI unit is also sometimes referred to as a "TP35" or a "TP" with some other number.
Mark R.
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2004 VW Golf TDI, type 1J, AHF, 317k (2016-current) --- daily
1990 VW Fox, type 16, HM, 304k (2005-current) --- spare runaround
Previous:
1992 Audi 500 SE, type C4, AAR (2001-2020) --- nice while it lasted
1983 VW Golf GTS, type 17, FR (1992-2005) --- most fun car I've ever had
1978 Audi 100 GLS 5E, type 43, WC (1991-92) --- died in the side of a Rekord who cut me off
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dam003
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Re: Microbus fuel pump relay keeps failing

Post by dam003 »

Thank you very much VAG Fan, I removed the relay, and it had a "X" scratched on it, replaced it with a good quality one and it works as it should. Thank you for the explanation.
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VAG Fan
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Re: Microbus fuel pump relay keeps failing

Post by VAG Fan »

Glad you're sorted, and thanks for the feedback.
Mark R.
- - - - - - - - - -
2004 VW Golf TDI, type 1J, AHF, 317k (2016-current) --- daily
1990 VW Fox, type 16, HM, 304k (2005-current) --- spare runaround
Previous:
1992 Audi 500 SE, type C4, AAR (2001-2020) --- nice while it lasted
1983 VW Golf GTS, type 17, FR (1992-2005) --- most fun car I've ever had
1978 Audi 100 GLS 5E, type 43, WC (1991-92) --- died in the side of a Rekord who cut me off
- - - - - - - - - -
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