The early ('89-'90) LH 2.4 ECU (Bosch number ending in 561) sometimes fails to ground the Fuel Injection (aka Fuel Pump) relay. Until now, the only safe fix was to replace the ECU with an updated 951 version.

But Colin UK recently found and posted a fix that allows the "bad" 561 to be used safely by replacing the White LH Fuel relay with a K-Jet Fuel relay, which senses ignition pulses directly from the coil, or the coil wire at the Tach. This bypasses the ECU, while maintaining the safety requirement —no fuel pumping unless the ignition is working. Colin UK's post, describing the 740 relay wiring changes is here.

This post describes the 240 version (different wire colors). To verify that you have the ECU ground problem, use a meter to back-probe the BLUE/GREEN wire at the relay socket. If it stays at 12 volts while cranking, the ECU ground is probably failing. To retrofit the K-Jet relay, 3 relay socket wires are switched and 3 are replaced. So you will need 3 replacement wires (with tab-lock terminal ends) and a K-Jet Fuel relay. Wire and relay details are given below (•)

1 – Start by disconnecting the Battery Negative cable, then remove White LH relay from its harness socket.

2 – Remove each wire from the harness socket by going in from the front, using something like a narrow-bladed jeweler's screwdriver to depress the terminal's locking tab. With a bit of wiggling, the wire and terminal will pull out from the back.

3 - Familiarize yourself with the K-jet relay terminal numbers. Looking at the base, they should be like this:
30 - 15 - 87b
31b- 31 - 87

4 – Refer to the terminal numbers above and rewire the empty relay socket as follows:

30 - gets the RED wire (12 volt Relay Input from 25 amp blade fuse—or fuse 6 for '91 on)
15 - run a new wire (BLUE/RED if possible) from Hot Side of fuses 11—13 (Key-On, unfused 12V)
87b- gets the RED/BLACK wire (12 volt Relay Output to AMM, ECU, Injectors, etc.)
31b- run a new wire (R/W if possible) from the Tach R/W terminal, or Coil terminal #1
31 - run a new wire (BLACK) straight to any convenient ground point (chassis metal)
87 - gets the YELLOW/RED wire (12 volt Relay Output to Fuel Pumps)

5 – There should be 3 wires left over, a Yellow/Black, the Blue-Green (failing ground from the ECU), and a Red/Black (common to the one you plugged into 87b). After carefully taping each exposed terminal end, fold the wires back and tape them to the harness bundle.

(•) The added wires must have terminal ends with the locking tab. Try Autozone, Car Quest, NAPA etc., or get any color spare wires from a junker and splice in with insulated crimp connectors (Radio Shack).

(•) New K-Jet Relays (Green) are #3523639 for $24.50 at FCP Groton, or #1348600 for $46.00 at IDP (maybe better quality?). Older ones will also work — Gray 1 324 022 or Black 1 235 337 (or same # in the much-coveted antique aluminum). Check your favorite P & P yard.

As Colin says, "The above is a bit more work than fitting a new ECU but a hell of a lot cheaper, and it retains the original safety feature of cutting off the fuel supply if engine rotation ceases."

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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.