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Old 02-19-2021, 04:34 PM   #1
Join Date: Jul 2018
Default ECU not earthing injectors

I've converted a 1991 940GL from an LH2.4 B200F & M47 to a 1995 B230FK with M90 gearbox.

The car was running when it came in and I drove it around the block so I know it was all okay.

I have fitted T5 blue injectors (no ballast resistor as the loom is N/A).

I have cut the MAF plug and extended the loom to the other side of the car so it can go in the original turbo position.

It cranks happily but the injectors will not fire!!! It is doing my head in now.

If I run a wire from the grey terminal of an injector across to the strut tower, crank the car and make and break the earth connection it runs. However the moment I stop earthing the injectors it stops running.

There is 12V at the green and grey terminals on the injectors when the plug is connected to the injector.

I have 12V at the blue yellow feed wire for the suppression relay and the relay works fine, I even fitted a known working relay just to make sure and it still doesn't start.

The fuel pumps prime once ignition is turned on and after "running" the engine they prime again.

I have checked the loom from the grey wire to ECU pin 18 and there is continuity with no resistance.

So what on earth should I be checking? It is like the ECU isn't earthing the injectors, I have tried two different ECU's and it won't start on either one unless I manually make and break the earth.

I've tried the 1995 ECU and a 1998 940 ECU that I know works as the car was running when I broke it for parts.
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Old 02-19-2021, 11:23 PM   #2
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Join Date: Aug 2014
Location: Boulder CO

The ECU needs to detect cranking before it will fire the injectors. Cranking is detected via the RPM signal from the EZK ignition box, EZK pin17 to ECU pin 1. After failing to start, check the diag codes (hole 2 and hole 6) to see if there's a clue. Also check the fuses for corrosion.

Being able to run briefly while manually firing the injectors means that the EZK is working. Hearing the fuel pumps prime means that the ECU is at least somewhat working.
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Old 02-20-2021, 04:14 AM   #3
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Join Date: Apr 2016
Location: Austria

The blue wire is connected to the right terminal on the coil?
Grounds are connected on the intake?
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Old 02-20-2021, 06:50 PM   #4
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Join Date: Jun 2009
Location: Sydney, Australia

LH 2.4 grounds the injectors through the radio supression relay

Check all four wires are fully inserted inside the relay otherwise your injectors will not ground
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Old 02-20-2021, 07:32 PM   #5
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Join Date: Nov 2002
Location: California

No ^

The ECU grounds the injectors. The "radio interference" relay POWERS the injectors.

I don't really follow what is going on here....
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