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TOPIC: No power to fuel injectors

No power to fuel injectors 23 Jul 2020 14:49 #21364

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  • CoreyJ's Avatar
  • CoreyJ
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We have an 86' 928 that won't start due to lack of fuel. The fuel injectors aren't pulsing - no power at the injectors. We have replaced the fuel injection module with a known good unit. What should we check next? Thanks!
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No power to fuel injectors 24 Jul 2020 08:21 #21365

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Hello Corey,

The fuel injectors are energized from the same circuit that powers the fuel pump.

There is 12V provided to the fuel injectors by the fuel pump relay XX pin 87 [via connector W13 at the fuse panel]. The LH fuel injection controller provides the switch to ground. The LH relay XXV pin 87 provides the voltage to the LH module pin 9 and MAF pin 2. The EZF relay XIV pin 87 provides voltage to the EZF module pin 25 and also LH module pin 18. If necessary, measure the resistance of each of these current paths to confirm that the circuit is good. [Note, 1987 and later model 928s are quite different in this respect!!].

My suggestion is:

a) remove the fuel pump relay XX
b) check for 12V at fuel pump relay XX position 30 (should always have 12V, direct wire to the battery). If no 12V, repair that circuit.
c) run a jumper wire fuel pump relay XX position from 30 to 87 position. The fuel pump should be running. If no fuel pump activation, check the circuit and fuel pump.
d) at this point, there should be 12V at the fuel injectors. An easy test is to put the positive volt meter probe lead on LH connector postion 13. If there is 12V, crank the engine and hopefully it will start. If no 12V at fuel injectors, repair that circuit.

I have a detailed overview of 1985 - 1986 no start suggestions. Please email me at info @ electronikrepair.com (remove spaces around @ symbol).
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