4.0L OHV 93 4.0 OHV Cranks strong, spark on all 6, 35 psi at the rail, new coil/plugs/wires/CKP, and it won't fire with STARTING FLUID. Thoughts?


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Leave all the plugs out and crank it over to see if it's just dumping fuel. Long shot, but does it sound kike it's cranking even? If it's a non interference engine, maybe the timing chain broke on the failed cold start?
 
What fuel pump did you use for the replacement? A few years back I was stupid and used a China-cheap replacement pump on my '91 F-150. It lasted ~700 miles before leaving me stranded, but diagnosis was tougher than I expected. It was delivering the pressure but not the volume. Eventually I just replaced it with a Motorcraft pump and all has been fine since.

Other items to check are the TPS and ECT. As much as I hate to be a parts-swapper tech, I'd probably just swap in spares since it's easy. Check end-to-end resistance on those circuits. I had high-resistance on the TPS circuit recently, fixed by running a new wire.
 
Hey all.. an update. still crank no start here. Checked compression and I'm around 130. All spark plugs are sparking. I also checked the fuel system and wound up putting in new injectors, because why not throw parts at problems? Besides I had a hope that my new fuel pump in an aging fuel system created its own problem. I went through some electrical and backprobed and the throttle sensor is good, the coil is getting what it needs. I put in motorcraft spark plug wires on the outside chance my cheaper version was a problem. Running out of things to do. Starting fluid still not helpful.

The only thing I can say it is seems that the first attempt of the day is the closest to success. I get a pop now and then and the engine just sounds like it might turn over. I cleaned my old crank position sensor and will go back to it in case my after market part sucks the same way my aftermarket coil did.

Early on, I got a new to me ECU which did nothing, but I am also not sure why versus the original ECU I re-installed which also doesn't work, so I have some ambiguity if either works. Although I'm not sure how the ECU could stop a successful crank versus killing one off.

Anyway, while this has been a learning experience, I am tired of Ford Ranger school. Any suggestions short of the timing chain...would like to find something less drastic before going there. And if there are any folks reading this who live in the DC area, I would buy a grateful amount of beer for another set of eyeballs on this truck.
 
Maybe while swapping around the ECU's, a pin or 2 got messed up and with the plugs threaded in the heads, the spark is too weak with the cylinder pressure to fire? The failed cold start shook the motor enough to make some connection worse?
 

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