Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Morgan Plus 8 EFI fuel pump circuit fault

Hi
I hope there is a car electrics wizard out there that can help. My '99 plus 8 started developing an intermittent fault, stopping then after a few minutes it would restart, I realised the fuel pump wasn't cutting in when the ignition was turned on, so whatever the issue was it was related to the fuel pump circuit . Because of the intermittent nature I have ruled out a fuse.

The car doesn't start at all now, because of the age of the car I have ordered a new relay for both the fuel pump and the main(ECU) , they should be here tomorrow but I don't think the relays are at fault because I have done some basic testing these are the results
1) The main relay operates ok and when I swap it with the fuel pump relay ( same part number) it also works ok
2) when I put a jumper wire (ignition on) across the relay switch terminals (30 & 87) the fuel pump runs continuously ( normally cuts out after a few seconds until the engine is started) so the pump is ok
3) When I put a multi meter on to the relay coil supply (86), I can see this supply voltage switching as the ignition is switched on and off.
4) when I put a multi meter on the earth side of the relay(85) it is dead- no continuity to earth & no voltage regardless of the ignition switch
The relay wiring bears no relationship to the diagrams on GoMog
This what I have
30- purple/ white (12v supply)
87 - White/purple, black, 2 X white/orange( lambda sensors)
86- white/green(12v supply)
85- blue (dead )
The spider immobiliser unit has been has a bypass link fitted
Help

First off find where that missing earth to the relay is.
Second and I can't be certain as regards Morgan +8, if the oil pressure drops (or, more likely no signal so effectively low / no oil pressure) then the fuel pump loses signal and stops to prevent engine destruction. This low/no oil pressure applies to cars/4x4 from Rover/Land Rover...

Good luck!

The earth side of the relay is switched to ground by a transistor in the ECU. So when the relay is removed, and you check the voltage on the earth side of the relay, it will show no voltage. If you put the relay in the socket and check the earth side it will start at something like 1 volt when the ignition is turned on (the relay is on) then it goes to 12 volts when the pump has run and the relay gets turned off. Once the engine is started the earth side of the relay will be back to around 1 volt when the engine is running.

Good luck

Mike Smith


don't forget the inertia switch is in the circuit to the pump, and I have seen a few of these with very dodgy connectors.

when I wrote

So when the relay is removed, and you check the voltage on the earth side of the relay, it will show no voltage

I did of course mean checking the socket pin for the earth side of the relay

Mike

I won't be able to do any fuurther testing till this evening, thanks for some of the prompts. I had forgot to mention I had already checked & linked out the inertia switch so that's discounted , I wasn't aware of the oil pressure safety cut out but because the engine won't start i.e. No oil pressure availible i'll also discount that.

I'll carry out Mikes test ( thanks Mike) then Looking at the EFI schematic, the earth side of the relay returns to the ECU Multi pin connector terminal 16, and there are 3 earths at terminals 4,14, & 40 so it'll be continuity testing, can't wait ! access is bad enough without the dashboard hanging in bits.

I read somewhere there is a fuel tank pressure sensor? What is that about , any idea where it is ? Could the charcoal filter thing prevent stating - wouldn't have thought so as it needs the engine running - but it's not safe to try and second guess Lucas Logic!

Re the charcoal evap system. I have a 2002 car with Gems system. I did get the MIL light on due to a fault registering. The car started ok though. Try gomog for a download of the Gems system "manual". There is a decent description of what it monitors and how. The oil pressure drop is definitely mentioned.

Every thing checks out ok, seems like it's some component degrading, it's the 14CUX system and there's no engine fault warning light showing , so I've sent the immobiliser green box away to be checked out (£25 including return postage, can't get vexed at that)

It was that 14CUX reference that got my grey cells going. Ten years ago my 1993 14CUX Plus 8 failed to start . There was no warning of imminent failure, nor any fuel pump whirring. Wiser heads than mine suggested relays, but having replaced same there was still no start. Then, I was pointed in the direction of a 20amp fuse, NOT in the fuse-box, but hidden behind/above the glovebox. Found and replaced, the pump whirred and away I went. Might be worth looking to see if your later car has the same fuse ?

Andrew Green
Glorious Devon

What I found was all the circuitry tested fine and by linking out the fuel pump relay the pump ran fine , as the -ve side of the relay returns to the ECU. This was chief suspect. I had ran the battery down so after reconnecting the ECU(removed for circuit testing) I connected the battery charger & left on overnight. When I went to the garage today i discovered 2 cock ups ,

1 ) I hadn't switched on the batter charger at the wall socket 2) I must have accidentally switched on the lights. This left the battery totally dead, I charged the battery , turned the starter and It fired first time and ran till the cooling fan cut in then I switched it off and restarted it again without issue.

This leaves me with 2 scenarios. Disconnecting the ECU has reset something internally, which I doubt as I had tried this a number of times, although the ECU contacts looked mint, it's possible there could have been a high resistance across one or more of them. The fault may still be with the ECU but-hidden and may return to but me in the backside. tomorrow I'll put the car back together and take it for a spin and see what happens? Over winter I'll send the ECU Away for a check up for peace of mind - I hate when something like this happens and there's nothing to show what the fault was. At least Ive gained a better understanding how the EFI system works.

[quote=smudger1 I hate when something like this happens and there's nothing to show what the fault was. At least Ive gained a better understanding how the EFI system works.
[/quote]

Fortunately My +8 is so old that I do not need EFI for Emission Regs. I use a 4 barrel Carb and a mechanical dizzy. I am not the only one that does this on the U.S. West Coast. Not that I am not interested in EFI. I have a GEMS that I have been going to hook up to My 3.9. But other than a bit better mileage and possibly a few more HP I see little to gain by doing so. But I feel I will loose the ability to diagnose problems with EFI. Not that I am doing very good with a Carb/Dizzy. But so far I can get it running.