3.0 No Start

Hey all,

I've got an unmolested 3.0 4x4 with 55k miles that suddenly will not start. It cranks strong, but that's it.

Some details:

- I can hear the fuel injector relay near the ECM clicking with key turned to On

- I no longer hear the click/buzz from under the hood when turning the key to On and again back to Accessory. Is there a relay or component switching or self checking? My guess is the problem is connected to this. After letting it sit, I did hear the clicking and the truck tried to start, after that it's been nothing.

- Before not starting, the truck had a slightly rough idle and a bit of lope at certain throttle positions (I thought injectors, possibly fuel pump was the cause)

- I assume I have spark (newer cap, rotor, plugs, and wires) and the ECM was replaced by the PO.

The trucks parked away from my shop so I haven't dug into it yet, I'm terrible at diagnosing so any help is appreciated.

I would first go through and check all of the fuses and see if there is power going across them (a fuse is easy to fix and diagnose). Check spark. If the ICM in the distributor is gone, you will lose injector and spark. Look at the plugs after cranking and smell for fuel. If you can pull codes from the ECM, figure out if and what error codes you are getting. Might not tell you 'exactly' what has failed but it will guide you on where to look. If you are already digging around the electrical system, disconnect and thoroughly clean ground leads from the battery to the chassis and engine as bad grounds can cause all kinds of hard to trace faults (look at the overall condition of the ground and main positive power leads for damage/corrosion). Strong and consistent cranking is a good sign though.

Likely ECU, PTU, or Dizzy. Like above, check for spark and go from there.

Thanks for the suggestions.

I hooked up an oscilloscope to the diagnostic pins, but was just getting noise. Then magically after cycling the key a few times I heard the throttle body (I'm 99% sure that what it is) do it's whirring clicks and got the "normal" wave pattern. The truck started right up but the idle seems just a tad bit rougher than it's previous rough idle. It also has an additional roughness as revs drop after giving it some throttle.

I'm not sure what's going on, my guess is ground, key switch, or ecm. Not sure if the idle issue is related (but it's weird that it got worse) or if the injectors are just dirty, I did run a can of sea foam through it recently.

We had a customer with very similar symptoms. Ended up being a bad dizzy.