engine cranks, won't start.

[meir]

hello guys. need some help with diagnosing an issue.

was working the other day on my truck, adjusting timing on the distributor.

engine was running fine, and i know that in order to adjust timing, i need to disconnect the tan/white wire that goes from the distributor to the ECM.

So, I turned ignition off, disconnected the wire, and try to start the engine.

Engine will not start.

I have spark, the distributer the plugs and the wires are brand new.

Checking the fuel, I have no fuel top the injectors. Fuel relay will not click when I turn the ignition on.

Tested the relay, relay is fine (and so all fuses)

Looking at the circuit diagram, it looks like the ECM is supposed to supply 12 volts to the relay when ignition turned on. Doesn’t happen.

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So before I pull the trigger on a replacement ECM, can someone tell me what can Couse the ECM not to provide power to the relay?

Thanks in advance.

Meir.

Edit: 89 350 5.7 TBI

 

[grampadirt]

Not sure on a 350 but on a 454 the ECM must see oil pressure from the oil pressure sensor,I'd check the wires going to it.

 

[someotherguy]

Tan/white? The timing bypass wire is tan/black. You sure you disconnected the right wire?

ECM's in these trucks hardly ever fail, so exhaust other troubleshooting options first.

Richard

 

[meir]

Tan/white? The timing bypass wire is tan/black. You sure you disconnected the right wire?

ECM's in these trucks hardly ever fail, so exhaust other troubleshooting options first.

Richard

thanks Richard. you are correct. it's the tan black (the only wire with a 1 pin connector).

I’ve done this procedure in the past with no issue. i also think it's not the ECU, but i want to make sure is receives all the inputs.

there is a "fuel pump oil pressure switch", located behind the distributor. reading about it, it's supposed to back up the fuel pump in case of relay failure.

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looking at the schematic again, it is also sending signal to the ECM. last night when i look at it, the connection seemed a bit corroded. i cleaned it a plugged it back.

i will try to jumper it tonight and see if it helps.

thanks for the reply guys.

 

[someotherguy]

I have read just a few cases where that oil pressure switch was bad but it generally caused the pump to stay running instead of preventing it from running.

When you're checking for power to the relay, are you doing this by turning the key on then getting out to go check under the hood? Because the ECM will only power it for a few seconds, then shut off. What you want is to already be on it with your meter and have a helper turn the key on so there's no time lapse.

Richard

 

[meir]

What you want is to already be on it with your meter and have a helper turn the key on so there's no time lapse.

that is exactly what i did. wife was not really into it, but had no choice

 

[7thdarkangel]

Have you checked the Fuse?

 

[magimerlin]

that is exactly what i did. wife was not really into it, but had no choice

Well your suppose to have the wife turning the key not doing the work under the hood....lol..

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[magimerlin]

You didn't knock one of the plugs in the back of the distributor loose when messing with the timing did you?

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[meir]

yes. the fuse is fine.
regardless,l the fuse is located on the output of the relay. i'm missing the signal from the ECU that activates the relay.
in other words, even if the fuse is blown, the relay should still click.
that is at least how i get it from the schematics.
what i need to better understand, is what signals the ECU is monitoring in order to supply power to the relay.

i found this document online, and i will follow the steps again.

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Have you checked the Fuse?

so far it leads me to believe that the issue is with the ECM, but there are few things i need to test again.
hopefully this weekend.