VN 808, was running, now no fuel relay voltage

Converting To Delco ECU From Carby Or Other Injection Systems
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VN 808, was running, now no fuel relay voltage

Postby Jag304 » Tue Sep 11, 2018 7:01 am

I have an older conversion, VN 304 with 808 into a 1973 Jag. This has worked for over 20 years but now I'm not getting voltage on the fuel pump relay. The ECU is getting voltage.
Do I have a dead ECU and if so where is the best place to get another?

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Re: VN 808, was running, now no fuel relay voltage

Postby oldn64 » Tue Sep 11, 2018 1:12 pm

Jag304 wrote:I have an older conversion, VN 304 with 808 into a 1973 Jag. This has worked for over 20 years but now I'm not getting voltage on the fuel pump relay. The ECU is getting voltage.
Do I have a dead ECU and if so where is the best place to get another?


My head is saying something about oil pressure but been a while since i have looked into this thing. I gather the car will crank over if the key is rotated. So if you supply +12v to the relay does it switch? Secondly if you bridge the relay so the fuel pump runs does the car start and run?

My hunch is that there might be a grounding issue. Remember your car was originally design by the prince of darkness. Therefore I would check the relay, the grounds and even the main wiring loom plugs. Normally the fuel pump should prime. I expect it is not even doing this.

cheers
oldn64

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Re: VN 808, was running, now no fuel relay voltage

Postby Dazza92VP » Tue Sep 11, 2018 2:27 pm

If it’s still got the wiring there you can crank it over until it gets oil pressure and this will power the fuel pump bypassing the relay in case of relay failure during driving but wiring may have been taken out during conversion as they usually have. The ecu grounds the relay so if you have no power to the solenoid side of the relay need to look at wiring

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Re: VN 808, was running, now no fuel relay voltage

Postby vn5000 » Tue Sep 11, 2018 2:56 pm

The 808 ecu supplies 12v to the fuel pump relay when engine is running or for a few seconds for priming when ign first turned on

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Re: VN 808, was running, now no fuel relay voltage

Postby Jag304 » Tue Sep 11, 2018 6:55 pm

Thanks guys,

The relay gets 12V for less than a sec, the pump doesn't have time to prime.

I turned it over till the oil light went out and the pump didn't run

I'll pull the ECU tomorrow and see if it smells brown etc

I'll also check if the voltage on the relay trigger is actually just floating or if it's been forced to earth.

Curiously this occurred just after I changed back to unleaded from E10 (I had a bout of stupid that lasted several years)

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Re: VN 808, was running, now no fuel relay voltage

Postby Jag304 » Wed Sep 12, 2018 10:34 am

ECU Fuel pump relay signal from A1 is good.

I had a bad relay that was dropping 2V. As oldn64 pointed out jags are not the easiest to fault find electrically, I'm finding multiple issues - I'm not seeing voltage at the pump but I may have introduced a fault as when I apply 12V to the pump it just gets hot and makes a disappointed low hum.

New pump on the way.

Thanks to all for their input.

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Re: VN 808, was running, now no fuel relay voltage

Postby Charlescrown » Wed Sep 12, 2018 2:59 pm

Apart from super high pressure there's only 2 reasons a pump would get hot. Poling armature or shorted winding. From my experience the quieter the pump the better and they mostly get noisy when the pickup side become blocked. A 2 volt drop is a huge amount. Sounds like good old Lucas electrics. Your not getting confused with the static and operating voltage are you.

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Re: VN 808, was running, now no fuel relay voltage

Postby oldn64 » Fri Sep 14, 2018 2:15 pm

Jag304 wrote:ECU Fuel pump relay signal from A1 is good.

I had a bad relay that was dropping 2V. As oldn64 pointed out jags are not the easiest to fault find electrically, I'm finding multiple issues - I'm not seeing voltage at the pump but I may have introduced a fault as when I apply 12V to the pump it just gets hot and makes a disappointed low hum.

New pump on the way.

Thanks to all for their input.


Hang on... a [pump is expensive to fault find with.... But yes is pointing to the pump. If you use a light globe (normal H4 would be perfect) in place of the fuel pump and then try turning the car over does the light stay lit for a small period of time (ie priming) then then go out and return on once the oil pressure is available? If not then while your pump might be an issue you have something else occurring as well. Last thing you want it to fry your new pump or your new pump not actually fix the issue.

Yes I have worked on many british machines. I suspect the youngest daughter is going to drag me into BMC products, which for me is the wrong marque :(! I dont mind the Jags, as long as it has either had the jag runnign gear removed or it is a v12 with a stupidly long bonnet ;)

cheers
oldn64

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Re: VN 808, was running, now no fuel relay voltage

Postby Jag304 » Mon Sep 17, 2018 8:59 am

The relay was dropping 2V across the contacts, checked with a multimeter across it's contacts, it's only a few bucks so I replaced it.

I am getting the priming voltage for a fews secs as measured at the ECU. I think my earlier result was incorrect as I was measuring at the pump or I just cocked it up.

I ran a wire from the battery directly to the pump and the pump doesn't run but gets hot. Earth is good.

Pump should be here in a day or two and I'll update with the outcome.

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Re: VN 808, was running, now no fuel relay voltage

Postby oldn64 » Fri Sep 21, 2018 11:23 am

Jag304 wrote:The relay was dropping 2V across the contacts, checked with a multimeter across it's contacts, it's only a few bucks so I replaced it.

I am getting the priming voltage for a fews secs as measured at the ECU. I think my earlier result was incorrect as I was measuring at the pump or I just cocked it up.

I ran a wire from the battery directly to the pump and the pump doesn't run but gets hot. Earth is good.

Pump should be here in a day or two and I'll update with the outcome.


Yep definitely sounds like the pump has had its day. Love to hear this once you have it running again :)

cheers
oldn64

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