3.9 '92 Classic wiring

Hi Guys, I am having to redo a lot of the wiring and I can't find the resister that's meant to be in-between the coil and the ECU - it's the 14CUX and according to the information I have it should have a 6.8k ohm resister in the wiring for the ECU somewhere? Can anyone give me an idea where it might be please?

Thanks!

(This is NOT a "Tune Resistor".)

When visually inspecting the EFI Cable Harness Assembly, one unusual component that's particularly conspicuous is the resistor that Rover included on the Engine Speed sense circuit. This resistor should NOT be confused with the Tune Resistor. This circuit is the only connection between the ignition system and the fuel injection system. A damaged or loosely connected resistor would likely result in an open circuit, leaving the ECU wondering about engine speed.

In our example system this resistor is marked "Lucas", "RD953066", "83630A", and "892Q". The resistor should provide about 6.8k Ohm resistance.

Shamelessly copied but mine's sat under the tunnel carpet just in front of drivers seat.

Thanks 3.5 - I had found that information but I couldn't find the resister - anyway I got brave and started hacking my way through the never ending layers of sticky black tape and eventually discovered it, rather worryingly it showed some signs of rust!

It's all on a part finished RR Classic part converted into a Dakar and the only loom I have is for the EFI unit, the injectors and the sensors so I have had to add wiring for the coil, alternator, fuel pump and the rest of the lighting myself - got a spark but no signal to the injects - yet! The coil signal is now wired into the EFI via the resistor but that didn't help unfortunately ............

ps the resistor was nowhere near the Y in the loom!

Cookee said:

the only loom I have is for the EFI unit, the injectors and the sensors so I have had to add wiring for the coil, alternator, fuel pump and the rest of the lighting myself - got a spark but no signal to the injects - yet! The coil signal is now wired into the EFI via the resistor but that didn't help unfortunately ............

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The injectors are earth switched so I would suggest check the earthing for the injection loom. Next do a continuity check on the wire to the coil negative, should be a white with black wire connected to pin 39(?).

Check the condition of the connector plugs on the injectors make sure they are clean and there is good contact.

The next thing to check is that the main efi relay is working. The "power" side of the injectors is fed off the main relay but also, if the main relay is not working then the ecu will be dead as well. HTH

classic kev said:

The injectors are earth switched so I would suggest check the earthing for the injection loom. Next do a continuity check on the wire to the coil negative, should be a white with black wire connected to pin 39(?).

Check the condition of the connector plugs on the injectors make sure they are clean and there is good contact.

The next thing to check is that the main efi relay is working. The "power" side of the injectors is fed off the main relay but also, if the main relay is not working then the ecu will be dead as well. HTH

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Checked all of that and done some diagnostics and I think it's missing a signal from something to energise the ECU - the fuel relay is refusing to energise as well making me think the ECU is faulty or there is something else not providing an input? The good news is I have a spark, the main relay is energising and all of the earths are fine as far as I can tell.

What inputs does the ECU require to fire up? I have disconnected the start in gear wire as it goes to earth when in gear - anything else I should check as an input?

Thanks!

Cookee said:

the fuel relay is refusing to energise as well making me think the ECU is faulty or there is something else not providing an input? The good news is I have a spark, the main relay is energising and all of the earths are fine as far as I can tell.

What inputs does the ECU require to fire up?

Thanks!

Click to expand...

Does it have cats?

1 - check fuel relay is not duff either replace with a new one (make sure it is the right type) or substitute the main relay for the fuel pump one and see if it goes "click" when your turn the ignition on.

2 - Faulty ecu is a possibility, test by substitution

3 - Check inertia switch, make sure it is closed.

4 - Check there is a power feed to the fuel pump relay, should be as it is bridged with the main efi power relay

5 - Ignore the having a good spark. The ignition system is totally separate from the efi system apart from the negative input from the coil that tells the ecu the engine is running and when to trigger the ignition pulse.

HTH

classic kev said:

Does it have cats?

1 - check fuel relay is not duff either replace with a new one (make sure it is the right type) or substitute the main relay for the fuel pump one and see if it goes "click" when your turn the ignition on.

2 - Faulty ecu is a possibility, test by substitution

3 - Check inertia switch, make sure it is closed.

4 - Check there is a power feed to the fuel pump relay, should be as it is bridged with the main efi power relay

5 - Ignore the having a good spark. The ignition system is totally separate from the efi system apart from the negative input from the coil that tells the ecu the engine is running and when to trigger the ignition pulse.

HTH

Click to expand...

No Cats
Relay is good
Don't have another ECU but I'll try and get one to swap.
No Inertia switch (yet) but isn't that after the relay?
Power is getting to the relay but no earth from the ECU which is earthed.
Ignition - got that (I put the wiring in for the coil etc) and I have connected up the -ve from the coil to the resistor.

Have you checked you are getting fuel to the fuel rail? and I know it might sound sarcastic but have you got enough petrol in the tank?

You might want to check for continuity from the injectors back to the ecu, IIRC somebody on here had an issue and found a broken wire in the loom so if you don't fancy swapping the ecu, try swapping the efi loom.

I have a tester on one of the injector plugs and the fuel relay isn't firing, I can fire the pump up separately to get pressure to the rail without the relay but that doesn't help.

Did you get running? Is the fuel pump priming for a second or two when you turn on the ignition?

cooltide said:

Did you get running? Is the fuel pump priming for a second or two when you turn on the ignition?

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Hi! Just got back from India on Tuesday night so haven't been near it for a couple of weeks. The fuel relay won't energise, it works and it has a live feed but the ECU isn't giving it an earth. I did some diagnostics before I went away and a number of things are up with the whole system so I'm going to put the ECU on a different vehicle to see if it works or not and go from there.

Next option is fit a mega squirt just for the EFI side - watch this space!

Silly question but has the ECU got the correct ignition live feed?

Cookee said:

Next option is fit a mega squirt just for the EFI side - watch this space!

Click to expand...

bit of a waste..since ms does so much more, best to sort lr ecu, besides ecu off ebay is £25..ms is a wee bit more..

cooltide said:

Silly question but has the ECU got the correct ignition live feed?

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Yes it has two feeds, one permanent and one switched by the ignition, the main relay is switching on but not the fuel relay.

The only Ebay 14 CUX ECU's I have found seem to be £120? Am I searching in the wrong place?

Another question - there are no wires to the ECU plug for the Oxygen sensors, can the hotwire system function without these? I have replaced the exhaust (well it didn't have one actually) and it doesn't have any Lambda's in the system. My concern is that there is a mismatch between the wiring loom, sensors and ECU?

Range rovers came without lambdas till 93ish. You'll know more when you do your substitution.

cant find the resistor,near the ignition coil?

Hi guys - making some progress but still no action from the injectors. Managed to get the fuel relay functioning and operating the fuel pump correctly. I put the tester on one of the injector plugs and both terminals show a voltage when energising the ignition, I have a injector tester plugged in and nothing flashes when I turn the engine over, the left and right banks from the ECU both return the correct resistance and if they are getting voltage it must be that nothing is telling the injectors to fire - I can't find a diagram that shows how the injectors are fired - help!

No Lambda wiring and no sensors (it's a '92) so that isn't an issue as far as I can tell - haven't managed to get another ECU yet but working on it.

Cookee said:

I can't find a diagram that shows how the injectors are fired - help!

No Lambda wiring and no sensors (it's a '92) so that isn't an issue as far as I can tell - haven't managed to get another ECU yet but working on it.

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Injectors are earth switched by transistors in the ECU as far as I know. The trigger signal is from the coil negative so maybe check you have a good spark so you know the coil is switching. Check the connections to the coil and the ignition amplifier. Maybe a red herring but check the battery is good and strong, low voltage can cause injection problems. HTH.

Maybe a member or your local garage can lend you a known good ECU and save you a bit of time

classic kev said:

Injectors are earth switched by transistors in the ECU as far as I know. The trigger signal is from the coil negative so maybe check you have a good spark so you know the coil is switching. Check the connections to the coil and the ignition amplifier. Maybe a red herring but check the battery is good and strong, low voltage can cause injection problems. HTH.

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Are you using a 12v electronic ignition coil / distributor / amp?