Unleash the Fuel System Fault Diagnosing Anoraks

[The Moosehunter]

Hi Guys

Major sudden fuel pump electrical failure.

Started fine drove about 10 miles parked up all OK
Got back in 2 hours later everything electrical in the car appears to work OK ... except the fuel pump
After much mucking about checking fuses / relays etc fed a live wire from the battery direct to the pump all fired up and the car drives well for the 10 mile return home
Just checked the wiring to the pump tonight and the earth is good ( as proven by trip home with temporary live ), have continuity from the fuel pump to the fuel pump relay, so feed wire and inertia switch OK
Have glow fuses on every connection and have pulled them all to check for faulty items, nothing evident
Feed for fuel pump relay comes from ignition switch relay and everything else seems to work OK

When direct feed fed to pump it runs continuously when usually it switches off after a couple of second on switching on the ignition. Seems strange and may be contibutary

My car has developed a cold start issue where it runs very rich on start up which is not an issue if you leave it for 30 seconds to warm a little. If you touch the throttle at all in the meantime it instantaneously chokes itself to a stop. When engine is warm restarting is not an issue. Need to investigate this and am assuming that the two are not linked but thought I'd best mention it just in case

Anyone help in narrowing down why I appear not to have a positive 12v feed to my fuel pump relay. Sudden dropping out of supply wire at rear of fusebox unlikely and no passenger during trip to kick / dislodge any item in the footwell

Your on going bailing out of my least favourite part of working on any vehicle (ie electrics) is greatly appreciated

Cheers

Moose

[Loubaruch]

When turning on the ignition the The pump should initially prime for a few seconds and then switch off. This is normal.

When the engine turns over the pump will resume its operation.

If your car has the original immobiliser then the fuel pump is one of three items that are immobilised. If this is faulty it could explain your problem.

Send me a personal mail with your mail address and I will dig out the connections.

[Hoover.]

Moose from what you have said.... I concur with above that first port of call would be the imoboliser...

I had something similar with mine, which involved some re-wiring

[The Moosehunter]

Cheers for the reply and I am familiar with the starting priming behavoir being the owner of tempremental beast for many years. This however is a new one on me.

Nothing happens at all when immobilizer deactivated. The relay switches on but theres no feed getting to the high output incoming side of the relay

Something somewhere is dead

[Aussie John]

On my preserp the fuel pump relay has a fuse which floats in the loose wiring where the relay is located, this caused my problem.

[spend]

The Moosehunter said:

Cheers for the reply and I am familiar with the starting priming behavoir being the owner of tempremental beast for many years. This however is a new one on me.

Nothing happens at all when immobilizer deactivated. The relay switches on but theres no feed getting to the high output incoming side of the relay

Something somewhere is dead

From what I've read of your description it sounds to me like the power feed to the relay is not present (the ecu switching works OK ~ you could hotwire the battery to the relay feed for pump control as an interim rather than your battery to pump BTW). The POWER feed to the relay probably is cut by the immobiliser & an inline fuse (the inertia switch should be after the relay before the pump ~ but don't rely on that a lot of confused folks have hacked aimlessly at cables over the years ).

May give you some ideas ~ unfortunately you just have to work through it either forwards to find where the power is still present (battery ~ fusebox ~ immob ~ fuse ~ relay) or conversely backwards to check resistance [circuit / no circuit] (relay ~ fuse ~ immob...).

[blitzracing]

Its a 2 stage process you can hear from the two relays- The main relay basically switches the AFM, injectors and puts 12v onto the second fuel pump relay as you turn on the ignition. The fuel pump relay then switches this supply from the main relay when the engine rotates or first power on.

So it goes.

Ignition on- both relays close- listen to both them (or hold then and feel the click)- this shows the 12 volts is there and the ECU is working.

3 or so seconds later the fuel pump relay opens again with a click if the engine is not turning. This proves the pump relay is working.This shows the pump should be getting power. If its not you have a faulty fuel pump relay or wiring from the relay to the pump.

[EGB]

Fuel pump relay on mine is in the blue socket. Check this is ok and then the electrical connections on the fuel pump. These are very exposed to salty road dirt and need emery to briten up to make good live and earth connection.

[Aussie John]

Hi Andy, did you sort it?

[The Moosehunter]

Aussie John said:

Hi Andy, did you sort it?

Morning, am pleased to say that it kind of sorted itself.

When I pulled everything out to re-check the relays and the wiring ..... the pump worked !

Safe in the knowledge that there therefore must be a dodgy connection somewhere I then found these



As quite correct pointed out by Auusie John and EGB, the relay that controls the fuel pump and switches off after three seconds is indeed the blue one. Located on the floppy end of the dangling section of loom that they forgot to do anything with.

My diagram showing the 4.3 precat wiring loom clearly shows the fuel pump relay in the position that I have been checking on the main board which does activate once the ignition is on and the immobiliser cancelled out. It also has continuity to the positive side of the fuel pump, so its anyone's guess as to what this does. Sadly / happily there also appears to be another one that nobody tells you about, which is the one that appears to have caused the issue

Clean up of all of the terminals quick squirt of wd40 and so far every time I have switched it on and off it now works, so theory being.......problem solved (Gulp)

Thanks again to all of you for your kind input and please keep yourselves on standby in case the problem raises itself again. Or any other electrical issue come to think of

See y'all at the Growl ( assuming I make it )

Moose

Edited by The Moosehunter on Tuesday 16th April 07:57

[EGB]

Glad for you Andy. Worth carrying a spare relay in tool kit. Spray electrical contacts with Electrical Contact Cleaner (Halfords) and then pray!

[The Moosehunter]

The Moosehunter said:

it now works, so theory being.......problem solved (Gulp)

Oh ! How wrong was I !!!

Thought I'd celebrate today by taking my son to school in the early morning sunshine

Turned the key ...... no fuel pump

All relays clicking over OK

Shut the garage door ... swore a lot ... and took the family V8 runabout

Today I hate my car again

Grumpy Moose

[blitzracing]

The relays clicking means they are being activated- but its no guarantee the internal contacts are switching reliably and actually put a 12 volt feed to the fuel pump. You can open up the relay case with a small screwdriver (prize it off) and have a look at the contacts. You can use a little strip of wet and dry paper between the contacts to clean them, but if it is this causing the issue its time for a new relay anyway. You cant do much more testing without a test meter if its not the relay itself. From memory these relays are not the normal ones with 5 pins- they switch two pins live at the same point (ie two of the switch pins are on or off at the same point) so you need to get the correct one.

[EGB]

Silly question! Does the ignition light come on when the key is turned? If not, it could be the Vauxhall ig barrel.

[MPoxon]

Have you checked the contacts on the fuel pump itself? I has this problem with mine a while back and it turned out to be a loose connection on the fuel pump.

[ChimpOnGas]

MPoxon said:

Have you checked the contacts on the fuel pump itself? I has this problem with mine a while back and it turned out to be a loose connection on the fuel pump.

This is indeed a good starting point, it could also be a break somewhere in the rats nest loom buried in the passenger footwell.

But TBH it's just as likely to me the dreaded immobiliser.

The fuel pump & other circuits are routed through the immobiliser, which TVR wired back to front.

It sounds like your immobiliser is cutting the feed to fuel pump on the move, which is more common than you think.

PM me, I can help.

[Sardonicus]

Moosehunter in your Pic is that black wire secure on the blue socket? check its not loose in the spade terminals claw or hanging by a few strands

[Oldred_V8S]

Right the two metal capped relays look like the ECU and the fuel pump relay.

If when you cycle the ignition on and off, you do not hear the idle control valve cycling (whirring noise) then there is a good chance the ECU relay is duff or the immobiliser is not working. If you hear the ICV cycle then it could be the fuel pump relay. Do not be tempted to swap the two relays over. Some people have seen one is the fuel pump relay and swapped it with the ECU relay.

I had the same issue on my V8S this time last year when it came out of hibernation. It had been fine before that.

[The Moosehunter]

Hi Anoraks

Well ..... I have no ideas

Went out to the garage yesterday morning to have another go at it, having not moved a thing since last times failure to prime up the pump .... all works fine.

Drove it to work .... fine. Popped out to it 4 times during the day ..... fine. Drove it home via petrol station ... fine.

Checked it again this morning .... fine

Beginning to think it may indeed be an immobiliser issue.

Dodgy looking wire in the blue plug is very secure even if the outer is lacking a little

Both relays do click on off whenever igition activated

Terminals on the pump OK wiring to the pump connectors replaced two years ago rubber boots ok and continuity to the relay seems fine

The one thing I can not confirm as I have been so distracted with checking relays etc when it does not work that I can not guarantee that the top immoboliser warning light comes on at all when the oump fails to activate

I know how to connect pump directly now so have an emergency plan ( thinking of wiring in a ditect feed just in case of future issues with a rocker switch to isolate when working well )

Anyone know if immobiliser can reactivate the ecu and yet not activate fuel pump ? As when it first failed everything else worked ok and with direct feed to pump meant I could drive it home.

My how I adore intermittent electrical faults. I would say give me a smashed piston anytime as at least its obvious whats broken, but Ive had enough of that over the years

Cheers for your ongoing assistance

Moose

Edited by The Moosehunter on Saturday 20th April 08:20

[ChimpOnGas]

Andy, PM sent.

My money is on the immobiliser, but the wiring to the fuel pump is ratherVERY lacking too.

I recommend replacing the weedy gauge fuel pump wiring used by TVR, with beefier 30amp 44/0.30mm 3mm² twin core thin wall.

Running twin core allows you to connect the earth wire directly to the battery, both this and a heavier gauge supply wire will effect a massive reduction in resistance on the fuel pump circuit.

It will also give your fuel pump relay an easier life, with the original TVR fuel pump wiring this relay can get extremely hot ending in failures.

With your new lower resistance loom, for the first time your fuel pump will receive the volts and amps it needs to operate as designed.

The results of lower resistance in the fuel pump circuit can be a smoother less ragged hot idle, improved hot starts & a few more horse power at wide open throttle too.

Not to mention a cooler running (so longer lived) fuel pump, so ultimately far better reliability.

The pump itself is good quality & very reliable, the wiring supplying it & the immobiliser on the other hand are not

Edited by ChimpOnGas on Sunday 21st April 18:44