EFI fault

Rangie · 26th April 2011, 12:15 PM

The EFI system from my 1986 Rangie has developed a hard to diagnose intermittent fault. I was hoping someone on this site might have an ECU for sale. I have checked and double checked all the sensors, fuel pressure and ignition. Just for good measure, I replaced the distributor rotor arm, coolant temperature sensor. Also checked the voltage signal coming from the airflow meter, throttle position sensor and cleaned up the ECU earth point behind the block, cleaned just about every other connector but have not found the fault. The annoying thing is that the vehicle will be perfectly fine all day and then the next morning the engine will fire up as normal but after about three minutes of driving, it will begin to loose power and then eventually stall and will not re-start. After an hour or so, it will start like nothing happened. I suspect the ECU is the problem and have checked it for dry joints so would like to swap it out to confirm or eliminate it as the culprit. I just want to fix the fault then upgrade to a newer Rangie or perhaps a diesel Disco.

Cheers,
Richard.

**PhilipA** · 26th April 2011, 01:10 PM

Ignition amplifier?
Regards Philip A

Rangie · 27th April 2011, 08:50 AM

Thanks for your suggestion. The ignition amplifier module was recently replaced. I always get a good spark and replaced the distributor rotor button with an original Lucas one as they often break down. I think my problem is in the ECU because when the engine will not start after lots of cranking, the spark plugs are still dry.
Cheers,
Richard.

**PhilipA** · 27th April 2011, 09:09 AM

I am not completely familiar with a 4CU. However I am with 14CUX and the earlier "Federal".

Does the 4CU still have the fuel pump controlled by a time delay relay or does the ECU do it? If so I would look at replacing the fuel pump relay.
Seeing the plugs are dry, the problem could be fuel pump related.

Have you checked the fuel pressure when it is stopped rather than when going? Seeing the rail does not have a Schrader valve that would be hard I guess. Maybe undo the return at the rail and see if fuel is coming out when stopped.
Maybe call Gary at CLR to see if he has an ECU.

**mechanic2you** · 27th April 2011, 11:08 AM

Richard

Just out of left feild do you have injector pulse whilst it doesn't go, if not try the over run relay (I think your model has one) situated at the rear drivers side of the inlet manifold

Rangie · 27th April 2011, 08:42 PM

Thanks for your suggestion. I was thinking of wiring up a LED indicator on each bank in an attempt to see if I can determine if the injectors are pulsing correctly when the engine dies. I guess a multimeter that can measure the injector pulse width would be the proper way to do it. Better still would be an oscilloscope but I don’t have those tools.
The vacuum over run switch is in a normally closed position and mine is electrically OK. However, I have shorted it out for good measure.

Cheers,
Richard.

Rangie · 27th April 2011, 09:50 PM

Good day PhilipA,
Thanks again for your input. The Lucas 4CU ECU is an ancient analog rather than a microprocessor ECU and does not have diagnostics capability. It uses a “flapper” airflow meter to determine the mass of air entering the engine.
The fuel pump is controlled by a relay via a switch in the airflow meter and by a vacuum controlled fuel pressure regulator to keep the fuel rail pressure at about 35psi which increases to 40psi under load when the vacuum drops off.
I fitted a pressure gauge to the fuel rail and saw that the fuel pressure dropped off quickly after the engine was turned off. I thought I had found the problem but it just turned out to be a small leak in one of the hoses attached to the fuel rail. The fuel pressure is still maintained at 35 psi even when the engine decides to die.
I will try CLR to see if they have an ECU.
Cheers,
Richard.

**PhilipA** · 28th April 2011, 09:47 AM

The fuel pump is controlled by a relay via a switch in the airflow meter

Yes I know.
BUT there is another control for it on starting. All Lucas injections have a timer for cranking which cuts fuel after 4 seconds. On the old "Federal" which is quite similar to the 4CU, this is via a timing relay. In a 14CUX it is via the ECU earthing the fuel relay after 4 seconds or whatever.
The timing relays were quite troublesome and caused some intermittent problems.
However this does not seem to be your problem.

I just looked at the USA 1987 manual but that is an earlier 14CU. However it did alert me to one thing. The inertia switch. Maybe bypass it to see if it is intermittent. It should be under the passenger seat..
Regards Philip A

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