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weird fuel pump problem... dodgy ECU?? 

 

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 Post subject: weird fuel pump problem... dodgy ECU??
Posted: Sat Jul 14, 2012 6:23 pm 
Getting Side Ways
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Ride: BA XR6T (mix of BA, BF and FG)

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WA, Australia

Hi all,

I have a dual fuel car that currently doesn't work on petrol.

I thought the pump was dead and was about to pull the pump out when I thought I'd better test the power to it first. No power when switched to petrol and ignition in.

* No fuses or fusable links are broken.

So anyway, from testing it appears that power is supplied to both the switching side and the power side of the fuel pump relay and the relay is triggered by a negative feed to the brown/green wire on the relay harness. If I feed a negative to this wire manually with a bit of old speaker wire the relay trips and power is measured at the fuel pump.... so the main circuit seems to be ok.

I checked the ECU harness and there is another brown/green wire in there... pin 22 I think... I tested continuity and sure enough when I feed a manual negative in there.. the fuel pump relay kicks in. That tends to indicate the whole harness is fine in that respect.... is there any input that would tell the ECU to stop feeding out a negative on that line?

So... the ECU is supposed to output the negative trigger to the fuel pump... .. but it isn't doing so. It is working perfectly in every other sense though.

I had to fly to QLD to deal with my fathers death in a car accident in bundaberg... and the car sat for 3 weeks.... it was working when I left.. only works on gas when I got back.

Are their surface mount relays in the ECU one of which may have gotten stuck? Or is it a blown transistor?


I guess for now a quick test would be to find my spare EL ECU and see if the fuel pump gets 12 volts with that one in.

anyone had this happen to them?

cheers

Frank
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 Post subject: Re: weird fuel pump problem. dodgy ECU? (ECU fuel pump trigger)
Posted: Sat Jul 14, 2012 6:37 pm 
Getting Side Ways
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Age: 45

Posts: 3440

Joined: 23rd Dec 2007

Gallery: 32 images

Ride: BA XR6T (mix of BA, BF and FG)

Location: Perth
WA, Australia

OK.. put my spare EL ECU in and it has the same problem.

Car runs fine on GAS, but it doesn't feed a negative down the brown/green wire to trigger the fuel pump relay.

That makes me think the ECU needs to receive another trigger before it does that...

Anyone know what that other trigger is? I imagine if I find out what that is, I'll find that the LPG setup has cut it and isn't rejoining it when it is supposed to. (ie when it's on petrol)

Anyone know what the trigger to turn on the fuel pump would be on the ECU?
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 Post subject: Re: weird fuel pump problem... dodgy ECU??
Posted: Tue Jul 17, 2012 3:27 pm 
Getting Side Ways
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Age: 45

Posts: 3440

Joined: 23rd Dec 2007

Gallery: 32 images

Ride: BA XR6T (mix of BA, BF and FG)

Location: Perth
WA, Australia

Was hoping someone would know what the problem was..

I've just checked the GAS module behind the ECU and it is currectly cutting the injectors as expected.. it doesn't look like my gas setup does anything at all to the fuel pump line.

Presumably the ECU turns the fuel pump on and off by internally switching a negative to the brown wire with green trace. doing so manually correctly feeds out to the fuel pump. but for whatever reason, the ECU isn't feeding out a negative on that line.

So I thought perhaps one for the earths is bad.. but not according to my multimetre, and besides, I doubled up every earth point when I got the car.

So now I'm left wondering... what could cause two EL ECU's to both stop outputting a negative to the fuel pump relay? The wire is not cut anywhere at all because feeding a negative in at the actual ECU plug.. triggers the pump. so the wire isn't cut anywhere else. The ECU just isn't feeding one out as it should. And it's not just one ECU, it's both.. so now I'm stuck.

Anyone else had something like this happen?

regards

Frank
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 Post subject: Re: weird fuel pump problem... dodgy ECU??
Posted: Tue Jul 17, 2012 9:08 pm 
Getting Side Ways
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Age: 45

Posts: 3440

Joined: 23rd Dec 2007

Gallery: 32 images

Ride: BA XR6T (mix of BA, BF and FG)

Location: Perth
WA, Australia

OK.... fixed.

I can't explain why there was no negative going out to the relay on the trigger wire..

But it turns out after all that, that the both my fuel pump in the car, and the spare I had were both stuffed... I thought maybe the ECU had detected a short and stopped triggering the relay.

Anyway, since my spare was dodgy... I had to put my walbro 255lt/h pump in... I did and it's now working fine. I still don't know why their was no voltage at the pump when I tested it.. I did so several times and had nothing.. so it's a mystery.

problem solved though... so I'm happy. and I have one less job to do when the time comes to put my charger on.
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 Post subject: Re: weird fuel pump problem... dodgy ECU??
Posted: Tue Jul 17, 2012 9:59 pm 
Getting Side Ways
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NSW, Australia

Well done mate.

Good to see you sorted it out.

Cheers
BenJ

 

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