14CUX Problem - non starting TVR 4.0

[firestarter_phil]

Hi there V8 people
I am a Newbie to this forum and have a Bowler with a TVR Cerbera 4.0 v8 in it. It's not been used for over a year and I am struggling to get her started now.
I have an ECUMate which I have plugged into the OBD1 and it is not able to connect with the ECU at all and I can see that my Fuel Relay is not firing and therefore Fuel pump is not priming/running.
I appear to have power to the places that I would expect it, including permanent 12v to the ECU on pin 15 and switched 12v to the ECU on pin 19.

My immediate thoughts are that I have got an issue with the ECU but wondered if anyone has any tips or techniques for working that out.

I have swapped out the fuel relay with a known working relay and that has not resolved my issues, I have put on a new fuel pump as my immediate thought was that my problem lay there, but that was not the answer either.

It seems odd to me that my ECU would have blown as I know there are pretty resilient but I can't see what else it might be.
If anyone has any pointers as to what I could test next, I'd be massively appreciative.
F_P

[GDCobra]

What about the main power relay?
When the switched power is applied to the unit it turns on the main power relay.

I’d also suggest checking all fuses to see it they’re blown or perhaps have corrosion or not seated properly.

I personally would not bother replacing components which can’t be part of the problem like your fuel pump, if the relay is not switching and you’re not getting power to the pump it can’t be part of the problem.

I don’t know if you’re aware but power is only supplied to the fuel pump for a second or so on initial power up and only turns on again when the ECU gets a pulse from the ignition system so it knows the engine is turning.

You should also get a short buzzing sound from the idle speed control valve when you turn the system off.

If that doesn’t help post back and I’ll dig out the wiring diagram and see what else to suggest.
Whereabouts are you located? I have a spare 14CUX (or 6) which you could eliminate the ECU with if you are close enough.

[DaveEFI]

If you've been swapping relays, are you certain you have the correct ones? There are different configurations of 5 pin relays that will fit - but not work correctly. Although, if like the 4 CU, this really just applies to the main one.

[GDCobra]

If you've been swapping relays, are you certain you have the correct ones? There are different configurations of 5 pin relays that will fit - but not work correctly. Although, if like the 4 CU, this really just applies to the main one.

That’s a good point, some also have diodes in which I think are needed to protect the ECU from getting voltage applied when the field in the coil collapses.

[firestarter_phil]

Many thanks for the responses everyone
Ref the Main relay - I have checked this both off and on the vehicle and this is functioning correctly. With the relay that I have been swapping out from a fuel relay point of view, yes I have been swapping like for like on these (Bosch 0332014112)

I was aware that the fuel pump doesn't permanently run prior to the engine running and have a multimeter across the terminals but the voltage doesn't do anything when I turn the ignition on, or engage the starter motor.

Am at a little bit of a loss TBH

One thing that I have notices, is an anomaly at the ECU pins and, when the ignition is on, I have a +ve on pin 16 also which is Fuel Pump Relay Ground. I can't quite tell if that is right or wrong! Should I have a 12V +ve on that pin?

[r2d2hp]

Thats because the ECU will pull to ground when triggered and until that happens you will see 12v on both sides of the relay coil

[firestarter_phil]

Thats because the ECU will pull to ground when triggered and until that happens you will see 12v on both sides of the relay coil

That makes a lot of sense.....thanks

Am going to work through some other ideas in the morning.......I need to work out what is needed from the ECU for the OBD1 to start working so I can get some sort of communication with it

[DaveEFI]

The priming pulse sent to the pump relay at switch on is automatic. If you are sure that isn't happening by checking at the ECU output (to eliminate the relay and wiring) and you're also sure the ECU has power and ground, there must be an ECU fault, I'd say.

[GDCobra]

and you're also sure the ECU has power and ground, there must be an ECU fault, I'd say.

Good point in Dave's post, your initial post indicates you've checked for power but what about ground?
Most if not all of the ECU functions switch a ground rather than supplying a live so if the unit is not grounded switching won't occur.

What happens if you supply a ground to the fuel pump pin? Does the pump run?

I just noticed your location, didn't see that previously, obviously too far from me to try substituting the ECU!

[GDCobra]

.......I need to work out what is needed from the ECU for the OBD1 to start working so I can get some sort of communication with it

The diagnostic connector uses pins 9, 18 & 31 according to the wiring diagrams I've seen. As far as I can tell, 31 is a ground which would make one or both of the others signal wires, possibly one for transmit and one for recieve. Was this port working previously? If so it can only have stopped now due to a wiring or ECU fault.

Apart from the fuel pump starting up briefly, the other "sign of life" you should observe is the idle control valve buzzing on shutdown (and possibly start-up) do you get this?

Looking at the wiring diagram there are a number of pins which connect to ground, some appear to be related to specific sensors, pins 14 & 40 appear to be the main grounds as far as I can see.

Grounds
4 - At Lambdas
14 - Paried wtih 40 - Main ground?
27 - At tune resistor
31 - Connected to groud when diagnostic plug cover replaced
40 - Paried wtih 14 - Main ground?

[r2d2hp]

Not sure if this link will help you at all https://www.legionlandrover.com/manuale ... 20(v8).pdf

[firestarter_phil]

I just wanted to let everyone know that it turned out I did have a duff ECU - found a replacement and it started up straight away. I will send it off to find out what is wrong with the ECU and let people know.

I know it's taken me a long time to respond, but wanted to bring closure to the request for help.
Thanks everyone.
F_P