3,9 Efi Range Rover problems.. again...

Lasse Kristensen · Post by **Lasse Kristensen** » Wed Jul 27, 2011 5:48 pm

Hello all.
My 3,9 Range Rover died on me recently, while driving. Engine spec : 3,9 Efi 1992 model.
As the symptom indicated lack of fuel, I checked the fuel pump relay. It turned out that it doesn't "click", and further investigation made clear, that the ECU isn't supplying the relay with ground connection. I checked the inertia switch and gave the pump direct positive feed, and it immediately began pumping.
I tried to fire up the engine, but it didn't fire up. I checked the spark with a sparkplug on the engine, and it was very weak.

I realise there's a number of reasons why the ECU won't start up the fuel pump, one of them being igniton feedback from the coil/rpm signal indicating the engine is running. At coil negative (which feeds the ECU with signal) I have some 7-8 volts.
In accordance with my Haynes, I checked the amplifier by measuring between battery positive + and coil negative -. According to Haynes the read-out with ignition off should be 0 volts. I have approx. 12 volts. The coil is almost new.

I recently changed the amplifier due to other problems which turned out to be defective ignition switch. I then installed the old amplifier, but still has a reading of approx. 12 volts. Is this progress of measuring correct?
The RR had a Cobra ignition cut-off module installed, which I have removed entirely, but no change.
What could cause these problems? I had ignition fall-outs when driving prior to the problems with the ignition switch and the current problems.
Could the distributorbe faulty or perhaps the ECU?

Any help or good advice is much appreciated!

Lasse Kristensen · Post by **Lasse Kristensen** » Thu Aug 04, 2011 9:27 pm

Hello.
Tried to change the coil, no difference.
The ECU does not turn on the fuel pump relay.
Anybody know what signals the ECU needs, and when they appear when turning ignition on and cranking the engine?
It's a 1992 EFi 3,9.

unstable load · Post by **unstable load** » Fri Aug 05, 2011 3:12 am

Isn't there a link between oil pressure and fuel pump switching? I seem to recall reading that on a thread here.

DaveEFI · Post by **DaveEFI** » Fri Aug 05, 2011 9:13 am

unstable load wrote:Isn't there a link between oil pressure and fuel pump switching? I seem to recall reading that on a thread here.

Don't think so. There was on some carb installations on the SD1, but not on EFI SD1s. So I'd guess RR was the same.

DaveEFI · Post by **DaveEFI** » Fri Aug 05, 2011 9:16 am

I'd first arrange a temporary independent supply to the fuel pump so it can be made to run continuously. If the engine now runs, that eliminates problems with the ignition and tach feed to the ECU.

DEVONMAN · Post by **DEVONMAN** » Fri Aug 05, 2011 9:26 am

You should be able to hear the fuel pump run for a couple of seconds after you turn the ignition key on. If not then It could be that it's the main relay or the fuel pump relay not switching properly.

You say the engine did not run with the direct feed to the fuel pump, so it may be a fault with the main relay which feeds the injectors. With the ignition on, test to see if you have 12v at the power resistor (Flapper type ignition) or 12v at the injectors (Hotwire type)( brown/orange wire).

Cheers Denis

Lasse Kristensen · Post by **Lasse Kristensen** » Sat Aug 06, 2011 10:59 pm

Hello.
Yes, I overran the fuel pump relay and made the pump run, but the engine didn't start. I'll try measuring for 12v at the injectors..
I only have one wire at my oilpump, guess it's just for oil pressure gauge.
Thx for input

DaveEFI · Post by **DaveEFI** » Sun Aug 07, 2011 9:22 am

Lasse Kristensen wrote:Hello.
Yes, I overran the fuel pump relay and made the pump run, but the engine didn't start. I'll try measuring for 12v at the injectors..
I only have one wire at my oilpump, guess it's just for oil pressure gauge.
Thx for input

The injectors have +12 volt all the time the ignition is on. The ground side is switched by the ECU. How long they are 'on' determines the amount of fuel injected.

I'd want to be certain the ECU is getting a signal from the ignition before checking anything else. A dwell meter can be handy to check the ignition primary circuit - it should read approx 30 degrees. If wildly out, likely a problem with the amp or VR sensor.