The EFI "Case History"
Subaru Liberty 4WD 1989

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Leo's Team Talk
Courtesy of    BARTER'S AUTOMOTIVE SERVICE FORBES

Just a few days ago I received the result after my consultation into a very hard to find electrical problem which caused the Injector 1 not receiving an injector pulse.

Michael Barter faced a challenge to fix a problem no one else was able to fix.

DIAGNOSIS:

Basic fuel supply and engine component checks including harness connectors or plug and socket connection on the computer reveal no faults which may cause no pulse to the injector.

This is all I had to work on to pin point the most likely possible fault to advice Michael in what area to look first. Out of so many possibilities I come to the most 4 possible items to save on diagnostic time.

1. ECU Relay faulty ( Back probe for voltage supply to computer)
2. ECU faulty ( Swap computer to test improvement )
3. Broken or corroded wire in the loom. ( Check for continuity )
4. Bad earths. ( Clean and tighten all earth connections )

On the next Phone conversation it reviled that by swapping the ECU did not fix the problem. The Injector No 1 is not receiving the pulse signal from the computer even knowing that the test computer from another car is OK. It leaves then only the ECU Relay to be the prime suspect.

This last test excludes the Computer, bad earth or broken wire in the harness.

The relay which was a bit hard to find, was located by switching the ignition off and on to hear the clicking sound and to determine the direction and its location. Eventually it was found way up underneath the dashboard on the drivers side. After changing the relay with a new one the problem was still there, no pulse to Injector No. 1

This is a bid strange. ??

Michael swapped the computers again with the test one and off the Injector is operating away “Perfect”

Michael swapped then the relay (the suspected bad one) and the Injector did not work. The relay unfortunately is a sealed unit and by only destructively dismantling the relay housing, which is a last resort to see the evidence of the problem.

THE CAUSE:

One of the contact points is totally burned away which supplies power to the injector 1 amplifier module in the computer. This arcing contact left behind ash as insulation caused low voltage surge in the amplifier segment by destroying that amplifier in the computer. The reason that it did not show up in the first place when the test computer was used, is that there was no power coming from the faulty relay to energise the amplifier. The reason after replacing the relay with a new one and no solution to the fix of the problem was, that the newly replaced relay supplied now power to the amplifier but the amplifier died long before when the relay started to supply low voltage surges to the amplifier.

FINAL:

This Relay has damaged the Computer. After changing both items the problem was fixt.

IN the beginning; the reason the car run OK for few second, was that on the start up the fuel enrichment covered up the missing injector pulse.