Hi All
I've been chasing an intermittent starting issue with my 1991 Range Rover 3.9 EFi for a while now. Since my car has an LPG conversion, my first port of call was a forum I was already on and some history to the issue can be found in the following post
LPG Discussion Forum • View topic - Range Rover Classic 1991 3.9 EFi - what LPG system is this?

To cut a long story short , after a little fun off road including a bit of deep water, the problem became permanent which has helped me realise why the car was hard to start. I believe there was an intermittent short in the loom causing all 8 petrol injectors to remain stuck open and therefore massively overfuel. Now the short is permanent and the battery runs down overnight and if the petrol pump is left running, the engine overflows with petrol (see the trumpet on number 8 cylinder which had overflowed!!)
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Investigated further by removing the ram housing and injector rail and proved that it is all 8 injectors that flow permanently with ignition and fuel pump on. The half plastic bottles all filled in a matter of seconds with the pump on!!!!
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I have a Haynes and see that on the 14cux hotwire, pins 11 and 13 of the loom provide the signal to the right and left bank of injectors respectively, and that pin 2 completes the circuit. I'm trying to figure out if the injectors should get a permanent +12v from pins 11 and 13 and are then grounded through pin 2 to pulse, or vice versa? How to best test if the issue is in the ECU itself or in the loom? Am I correct in thinking a short could cause this fault? Could it even be a knackered ECU?

points that may be relevant (or not!)
- EFi system shows the orange ! warning light on dash (not surprising)
- Pulling harness connector at each injector stops the flow at that injector
- Pulling the main relay for the EFi stops the flow of injectors
- Petrol Pump relay is bypassed to a manual switch, hence the pump can be run continuously rather than a few seconds without starting the engine (PO did this to stop unexplained petrol usage when on LPG)
-many sensors are currently disconnected from the loom i.e. fuel temp, stepper motor etc but I don't think this should matter?

Next step for me is to electrically isolate the LPG side of things from the loom and see if problem remains. This all a bit new to me :confused:
 
do I need exact like for like with a matching PRC number and or date code? (Mine says PRC9061 and Date Code 4790)

No, any 14 CUX should do.

The fuel injectors are earth switched so either something is causing the injectors to be permanently grounded or the ecu is is having a fit.

You should check all the sensors and get them connected up properly so the efi warning light (the orange one with a !) goes out otherwise it will drink petrol like you wouldn't believe (well maybe you would).
 
Thanks Kev. If the replacement ecu model number differs do I need to swap the map chips from original to replacement ecu?
 
Thanks Kev. If the replacement ecu model number differs do I need to swap the map chips from original to replacement ecu?

Not as far as I know. I have 3 14CUX ecu's, the original one had a socketed chip with an invisible fault - sometimes works, sometimes not, the one on the Rangie has a different number but works the same, no issues never looked back and then there is my spare which is a later one but again, I have tested it and it makes no difference at all.

I think it might be beneficial for you to properly disconnect the LPG system to troubleshoot the EFI. I have to admit to knowing nothing about LPG systems but if it has been spliced in to the EFI loom who knows what issues it could be causing. Get it going on petrol first then sort it for LPG is probably the best bet.
 
What is the impedance between 11 & ground, 13 & ground, 2 & ground, 11&13, 11&2, 13&2? Measured from the wire loom connector at the ecu?
 
Not as far as I know. I have 3 14CUX ecu's, the original one had a socketed chip with an invisible fault - sometimes works, sometimes not, the one on the Rangie has a different number but works the same, no issues never looked back and then there is my spare which is a later one but again, I have tested it and it makes no difference at all.

My search for a backup ECU begins :)

I think it might be beneficial for you to properly disconnect the LPG system to troubleshoot the EFI. I have to admit to knowing nothing about LPG systems but if it has been spliced in to the EFI loom who knows what issues it could be causing. Get it going on petrol first then sort it for LPG is probably the best bet.

You're right, that is my next step when I get the time. For the sake of moving a few wires and returning the loom back to factory connections at least it will prove whether the fault lies in the LPG system or not. If not, must be a knackered ecu or short to ground in the injector wiring.

A helpful guy on the LPG forum pointed out that there are factory splices in the loom where the right and left bank injectors split into 4. If these splices run along then transmission tunnel then they probably got wet so that is worth investigation. Anyone know where they are in the car?
 
What is the impedance between 11 & ground, 13 & ground, 2 & ground, 11&13, 11&2, 13&2? Measured from the wire loom connector at the ecu?

Will go and get a reading of these but can I assume you mean resistance? I have no way of measuring impedance.
 
With connector unplugged from ecu, testing at rear of connector
11-ground = open ciruit
13- ground = open circuit
2 - ground = open circuit
11-13 = 8.6 Ohms
11-2 = 4.6 Ohms
13-2 = 4.6 Ohms

I think this is as expected and means the loom is ok?

When I plug the ecu connector back in and do the same tests, results stay the same except this time
11- ground = 8.1 kOhms
13- ground = 8.1 kOhms

Possibly enough to be keeping the injectors open and pointing to the fault being the ECU (maybe it did get wet!! :()

With ignition on, there is aslo a constant 8V differential between pins 2-13 and pins 2-11, which is what must be holding the injectors open.

Does this make sense i.e., ECU buggered, loom ok?
Cheers
 
Ok, so replacement ECU came today and using this the injectors appear to behave normally. So there it is, the very first thing I looked at and which appeared to be ok really wasn't. Lesson learned. Now I just need to put it all back together and see if she runs!

Not all bad news because I'm taking the opportunity whilst there to relocate the ecu and relays somewhere higher in the car, changing all the spark plugs, changing oil, flushing radiator etc. I also took of the right hand rocker cover today and WOW, what a mess under there. Unbelievably sooted in there. Doesn't look like it's seen oil for years!!! is this normal?
 
I'm afraid that black death is only 'normal' when the engine hasn't had regular engine oil changes. :(

Ties in with the facet I can't get the effing sump plug undone! Car is all back together but I can't try and start her because the oil is full of petrol. So high it's reading right up to the top of the dipstick!! Now, where did I leave that syphon?:rolleyes:

not had a pushrod v8 before, should there be obvious signs of fresh oil under the rocker covers?
 

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