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Missing injector pulses - How to narrow down the problem? 700 1990

posted by  Will740turbo on  Sat Jun 14 14:01 CST 2014
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last visit: Wed Oct 22 16:09 CST 2014
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Hrm. I'm beginning to wonder about it being from a 92. I guess I should forget the year and go with the -560 designation with a red label. The -561 I know had both white and pink label versions. It's been running without problems for about 14 years, so I don't think the injectors are to blame, but I'll check their resistance and color. They might be greentops, I don't really remember. Are those resistor types?

I found a wiring diagram at And it shows the main/fuel pump relay being energized through pin 20 and then going on to power the injectors, the IAC valve, the AMM, and pins 9 and 21 on the ECU. I'm not sure what those do, but so far, I've had false codes thrown for a bad AMM, a code thrown for too-rich/lean at idle while cruising down the highway, and I'm losing injector pulses. As far as I can tell, the IAC is working fine.

Next to check:
Injector/ballast resistor supply power when running and losing injector pulses.
Main (fuel pump) Relay, pins, and wires into the back of the relay tray are secure and fiddling with them doesn't cause problems.

ECU ground again for the heck of it.
ECU ground pin to body has 0 ohms resistance.
That ECU pin 20 has power at all times while engine is running.
AMM pin (not sure which one) has power during missing pulses.
That pin 18 has power and that the wire feeding pin 18 has power in the engine bay.





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