Is the ecu bad or would it be a relay?
1991 Ford F-150

Is the ecu bad or would it be a relay?

(1991 Ford F-150)
91 f150 5.0, sat for 3 years and I need to get it started. After fixing the no spark issue, due to failed hall sensor. It still will not start. I have fuel to the rail, however with key on I can hear the ejectors popin on and the fuel pump running constantly, I’m leaning towards the ecu due to the ejectors, a pressure sensor wouldn’t cause them to pop on. I have continuity on all my grounds and powers, I don’t have a break out box so anyone know a good way to test this with out damaging the pins on the ecu
Tags: ford, f 150
2 answers & 1 comment
Popular Answer
on March 19, 2019
Fuel pump not turning off .. I’d be inclined to suspect a relay problem..

Difficult to diagnose here online - as well as *hands-on* without proper schematic and diagnostic flow chart.

God luck!
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on March 20, 2019

Additionally - I don’t think you’re hearing the ‘injectors’ pulsing - can be confirmed using noid light.
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on March 19, 2019
Fuel pump not turning off .. I’d be inclined to suspect a relay problem..

Difficult to diagnose here online - as well as *hands-on* without proper schematic and diagnostic flow chart.

God luck!
Sign in to reply
on March 20, 2019

Additionally - I don’t think you’re hearing the ‘injectors’ pulsing - can be confirmed using noid light.
on March 19, 2019
Yes, understood, a break out box is the way to pursue testing -- and there is no other practical way to test directly at the PCM.

I do not feel like you have a PCM issue, mostly because unless there was some kind of trauma to it (electrical damage due to some kind of surge or water damage, for example), typically they do not need to be replaced.

Are you saying you have fuel to the rail but not to the cylinders?

Keep in mind you need fuel pressure and delivery, ignition spark with a properly timed engine, and the proper amount of air (cold engine -- basically choked of air). No vacuum leaks, no air intake leaks.

You are saying you have a properly set distributor and the TFI (Thick Film Ignition) module is working properly -- spark is getting to the plugs?

Certainly check for any issue with relays - there should be a PCM and a fuel pump relay in the box.
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