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Fuel pump problems, maybe ECU? 88 Vanagon
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VanagonT3
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PostPosted: Wed Aug 04, 2010 5:45 pm    Post subject: Fuel pump problems, maybe ECU? 88 Vanagon Reply with quote

I have an 88 Vanagon with a fuel pump that does not want to start up. I took the fuel pump out and tested it and it works fine. The only way I can start my van is by bump starting it. I unplugged the ECU and plugged it back in and it worked the 1st and 2nd time but not again. Do you think this is just an ECU problem or can it be something different?
Thanks
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pioneer1
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PostPosted: Wed Aug 04, 2010 5:50 pm    Post subject: bump Reply with quote

Hi: If the engine runs after a bump start then you are getting fuel,right? What happens when you turn the key? ie-does the starter turn over the engine? Hows the battery?
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VanagonT3
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PostPosted: Wed Aug 04, 2010 5:54 pm    Post subject: Reply with quote

Yeah, that's why I was thinking! When I turn the key I usually hear the fuel pump start to pump fuel but not anymore. The starter turns over the engine but it just won't start. You know, it very so could be the battery. Let me get back to you on that one.
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VanagonT3
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PostPosted: Wed Aug 04, 2010 5:55 pm    Post subject: Reply with quote

But then again, why would it start if I unplugged and plugged back in the ECU?
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914 mike
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PostPosted: Wed Aug 04, 2010 6:32 pm    Post subject: Reply with quote

I had what sounds to be the same problem in my 91 Carat. I could hot wire the fuel pump to get it to run, I could hot wire the fuel pump relay (located in the left black box in engine bay)....both relays checked out fine....everything was pointing to the ECU....I think its pin #3?....anyways, swapped out an ECU from a parts van and the problem was solved....

Good luck...
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stevey88
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PostPosted: Wed Aug 04, 2010 6:33 pm    Post subject: Reply with quote

Try jumping the fuel pump relay in the black box above the ign coil. It is the right hand side relay. Remove the relay and jump terminal 87 and 30 of the socket and the pump should come on even the ign key is off. If the pump does run try starting the engine. You can also swap the left relay to the right to see if that makes a difference.
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VanagonT3
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PostPosted: Wed Aug 04, 2010 9:07 pm    Post subject: Reply with quote

Thanks for all the help guys. I bought a new fuel pump relay this morning and I am putting it in Tomorrow. But I still think it could be the ECU...
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pioneer1
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PostPosted: Thu Aug 05, 2010 4:00 am    Post subject: bump Reply with quote

Hi Again: Can you explain to me,for future reference,how the engine will run if it is bump started but the key will not start it and the fuel delivery system is defective? Thanks Confused
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914 mike
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PostPosted: Thu Aug 05, 2010 9:12 am    Post subject: Reply with quote

Not sure I can answer your question, but here it goes....

When you turn the key to the 'on'position, it triggers the fuel pump relay (located in the black box above coil in engine bay) and thus activates your fuel pump. You should hear it 'prime' the fuel system for a brief second. When you start the motor, the fuel pump is constantly on delivering fuel (quite noisy if its like mine Sad ). If the fuel system is bad, it could be a bad relay.....you wont hear the fuel pump working at all. You can jumper the relay as described above and you should hear the fuel pump working.....it will always be on however, even when you shut everything off....so its more of a 'testing fix' than anythig else. You can also just switch the two relays in that box to test for a bad relay as described above.
You can run a jumper wire from a 12v source (battery) directly to the fuel pump and get the same effect....again, it will always be on until you disconnect.

So, basically, you are just trying to get the fuel pump to turn on due to the ECU not working to do this. Once the fuel is flowing and assuming you have spark/good ignition, you should be able to now start the engine.
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pioneer1
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PostPosted: Thu Aug 05, 2010 1:39 pm    Post subject: fuel pump Reply with quote

Hi Mike: In the initial description there was no talk of jumper wires or wiring the pump direct. He turns the key,no pump noise and yet the engine runs when push started... huh?
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914 mike
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PostPosted: Thu Aug 05, 2010 8:52 pm    Post subject: Reply with quote

Ah....just re-read it....my bad. Embarassed
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VanagonT3
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PostPosted: Thu Aug 05, 2010 10:40 pm    Post subject: Reply with quote

I am still a bit confused on what the problem is. It isn't the relay and not the fuel pump, pretty sure it's not the battery... Oh dear.
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crowinghen
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PostPosted: Fri Aug 06, 2010 7:53 am    Post subject: Reply with quote

I can't really help you other than to point you to the Digifant manual where you should find some helpful troubleshooting info.

http://www.loam.org/vw/Vanagon/VanagonProTraining/DigiFant/

I had a similar experience with fuel pump, except my engine would never start-- turned out to be the ECU. That is on an 84 though which is a digijet, not a Digifant.

Hope this helps,
Susie
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tencentlife
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PostPosted: Fri Aug 06, 2010 9:13 am    Post subject: Reply with quote

Quote:
You can also swap the left relay to the right to see if that makes a difference.


We used to suggest this around here, I think I'm guilty of it myself, but if you understand the sequence of events in powering up the system it becomes clear that this will only serve to confound you further. The reason is, if you suspect it's the fuel pump relay not closing, putting that presumably inoperative relay in the main FI position will just mean that instead of the pump not getting powwr, now the ECU won't get power. Since the ECU has to power up and then it triggers the pump relay, now that won't happen so if you're listening for the pump to cycle you will observe no change in behavior, so it essentially tells you nothing.

If the oposite is true, that the main FI relay is bad but the pump relay good, as I said above you would not hear the pump cycle, and after switching them you still would not hear the pump cycle.

Basically if you're using the pump cycling as a quick diagnostic aid, both relays have to be good. If either is bad, the pump will never run.

So for me the quick way to isolate the problem to either relay is to jumper each one in turn, simulating that relay closing. If jumpering either restores normal operation then you know that that relay was bad. There are other ways to ascertain this but for me this is very fast and definitive.
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Syncro Pilot
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PostPosted: Sun Dec 15, 2013 8:30 pm    Post subject: Reply with quote

Old post, new feedback.....

I had a no start, no fuel pump situation this weekend. (luckily in my driveway)
Temperatures in the mid to low teens (Fahrenheit)

Swapped in a new spare fuel pump. No fuel pump action. I had bench tested the new pump already. The old one was definitely sluggish by comparison. Anyway, check continuity on the power and ground to the pump. Tested good but still no joy. Swapped in new relays, both ECU and Fuel pump. Nada. Jumpered power to the pump and it runs...... Still could not figure this out so I went for swapping out the ECU with a known good one.

Sure now it runs and starts. Funny thing is that the old ECU also runs and starts.

The only difference that I can think of is that by plugging/unplugging the ECU's and reconnecting the grounds, is that I caused a marginal connection to improve and the new pump and relays just helped it all work like it should.

I did use de Oxit spray on all the contacts as I progressed through the repair. None of the contacts were obviously corroded.

My summary of the problem is that the low temperatures and the marginal fuel pump and some possible corrosion on the ECU contacts, maybe tired relays as well added up to a no start fuel pump failure.

Just some more reference for the collective. The logic of electrical troubleshooting I can deal with, but the sometimes fickle nature of electrical contacts makes this kind of repair seem like voodoo sometimes.

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