I don't know squat. But I recently had to diagnose an intermittent engine stumbling/hesitation/miss in my Bronco's 5.8L gasoline engine.

I employed my normal method of diagnosing intermittent problems, which is wait until a total failure and then look for the part that failed.* This weekend it had a no start issue. The engine would turn over briskly because of a new battery connected to a trickle charger when cranking the engine, but not one "catch" or other hint of trying to start.

rla2005 had me check for spark, fuel and air. To rule out spark he had me remove a sparkplug and hold it close to the valve cover and have my wife crank the engine. A spark clearly arc'd from the plug to the valve cover. So it wasn't a missing spark.

I determined that I could not hear the pump hum, so was concerned that the PCM signal to the pump may be screwed up, or the relay to the pump may be bad, or the pump may be bad. By using the forum's search function I found out how to diagnose the fuel pump in a "Fuel pump relay question" thread with posts by dustybumpers and subford.* Here is a short synopsis of what they recommended with a little editorial license, and what I found out by doing what they said.

When I did what subford recommended, I did not hear the fuel pump. So I assume that means that this test bypassed the PCM's ability to turn off the fuel pump (see "Enable Fuel Pump Output" in ECCIV DLC diagram below) and even with the PCM's off-function bypassed amd the pump enable to continuously run, I still couldn't hear the pump hum.

So on to what dustybumpers recommended:

There are other recommendations in the thread, like removing the fuel pump relays (my parts guy at the dealership recommended taking the tow relay out and putting it in the fuel pump relay position, but the thread recounts breaking relay connectors, etc. so I didn't want to do remove relays on a 20 year old truck unless I absolutely had to, so I didn't.

So what did I find when I did what rla2005, subford and dustybumpers recommended?

Starter fluid baby! My wife started it right up. And died as soon as the starter fluid was combusted. And since I still have not heard one hum from the pump, I am dropping the tank this weekend.


Thanks to rla2005, subford and dustybumpers !!!

I rep'd them and if you find this compilation of their posts in thread https://www.ford-trucks.com/forums/8...-question.html helpful, please rep them too!


* Warning: I don't recommend this method and, in fact, it is probably a dangerous way to diagnose issues. So don't do it.

**


*** BTW, I got my Innova 3145 trouble code reader today and hooked it up and got no codes whatsoever. But maybe I am using it wrong. But there are only three steps to using it: 1. turn engine to on; 2. turn code reader on; and 3. Press test/hold button and read codes. So is it possible that a failed fuel pump does not throw a code?

 

The codes for a bad fuel pump would be in the CM portion of the KOEO test after the electrical test is done and you get the space code.

Also why do you say it is dangerous to ground pin #6 and turn on the key? That is the way the Ford shop manuals say to do it too.

 

Clean the contacts on the data link connector. Sometimes contact cleaner works, other times you may need to use something like a small nail file to polish them up.

 

Subford: Sorry for the confusion! There was a missing " * ". I don't say it is dangerous to jump pin 6. What I meant was it is probably dangerous to wait for a complete component failure before diagnosing the problem. Thank you for the excellent advice about jumping pin 6 to ground and your other advice in the orginal fuel pump relay thread.


rla2005: That makes total sense to me. When I was doing pin #6 jump to ground test recommended by subford, I noticed how corroded the contacts were in the EECIV (OBD) Data Link Connector (DLC). I have some CRC brand electrical contact cleaner, but you are right, from the looks of it, it will also take some abrasive action to clean those contacts given how corroded they are. Thanks again.