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2001 Explorer 5.0 P0174 Code

The rest of the testing, on the correct wire, entailed continuity and resistance (good at first), then stray voltage, followed by testing for a ground, then resistance while wiggling the wiring harness - which revealed resistance variations when moving the coil connector. So, next step is to replace the connector and eliminate the break in the wire at that point. Connector in hand, will probably go in tomorrow. Cautiously optimistic that this repair will tie up this long, strange, series of failures and fixes. MTF.
 



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Great diagnostic work.

As these vehicles age, we are going to see more of this.
 






Good news and bad news... Good news is the coil 2 connector install went swimmingly. Tested the wire several times for resistance, checked movement, which indicated the coil end of the wire. Stripped back the wire and tested more, which indicated that I was past the problem area, though it wasn't apparent - see the picture, damage was supposed to be in the center of the stripped area. Test from the end of the wire, mucho resistance fluctuation; test near the insulation, next to nothing. Anyway, followed Ford procedure, stripped, soldered, folded back over, shrink wrap with the waxy goo in it (put over the wire before soldering :D ) - the end result looks great!

RD-LB.jpg


solder-1.jpg


solder-2.jpg


solder-3.jpg


solder-4.jpg


Coil-2-Connector.jpg
 






The bad news is it still runs like crap. But still some good news! I ran it through a 'drive cycle' as defined by the Ford manual - cruise at 40 mph for 10 min, 50mph for 10 min, accelerate at 3/4 throttle 3x, accelerate 45-60mph decelerate no brakes 3x, etc. - drove for 35-40 min. after all that, only 1 code, P0352. No misfires detected, no lean bank (which I think is odd). At any rate, I still think its the wire having a problem deeper in the harness. Where this batch comes out of the main run seems floppy, certainly a stress point, but didn't get any fluctuating resistance readings when moving it around. I forgot about load testing when I found what indicated as a break - pretty sure I fixed a valid problem, there's just a little more going on. Another round of testing is in order...
 






Do yourself a favor and replace the ground wires , to the engine and body sheet metal. Establish a very good ground.
 






Props to 1Neptune! I cleaned (didn't replace, yet) all the grounds I could find in the engine compartment. Two on the firewall near the PCM, one on the other side of the firewall that I think goes down to the engine. Five near the battery, three on the radiator support (1 battery ground, two from the wiring harness; two on the fender also from the wiring harness). I certainly seemed like it was running smoother, for having a miss. :p BUT, the code scanner did pick up the P0303 and P0305 along with the P0352, so the diagnostics improved! :D. Seriously though, they needed attention, something I hadn't considered.
 






Additional testing indicates the wiring harness to the coil is good, therefore the coil driver in the PCM is bad - was bad from the start, couldn't tell with all the other problems. Warranteed replacement arrives Tuesday. The corner mechanic will install as he needs to flash the new unit and register the keys. Fingers crossed.
 






looking over post. problem started with melted spark wires? that's not normal . but have you taken it to a mechanic that has the professional analizer not just a code reader . they can check all the sensors. and switching parts can get very expensive even dyi
been there spent a lot on old ltd 3.6 v6.. that scanner can also be checking when cars in use on test ride .
 






Problem Solved - Post Op Analysis (thankfully not a postmortem; additional details available higher in the thread). I think the initial problem that kicked this mess off was a failed EGR diaphragm. Theory is the EGR diaphragm failed, the control solenoid worked overtime to try and compensate, it failed and the shorted coil fried part of the PCM. I first replaced the spark plug wires thinking I had a ground (from a previous experience). Then MAF and TPS based on symptoms; chased vacuum leaks (found the EGR valve problem). Evap purge valve threw a code and I replaced it. Then the P0174 code popped – new O2 sensor went in. Still problems. Further testing revealed no vacuum to the EGR, exposing the lack of signal from the PCM to the EGR Control Solenoid. PCM was replaced... problems continued. Found a loose spark plug wire. Lean bank codes persist - start swapping out coils, no luck. Gave it to the mechanic for a week (he put in the new PCM), he put in a new fuel filter then threw up his hands thinking it was clogged fuel injectors (at 220K mi, its possible). So I break it down, replace the injectors and all the connectors, intake manifold gaskets, spark plugs (copper plugs were at life expectancy, put in Bosch double plats), and wires (one of which was bad [lesson learned: Ohm out your wires before you put them in ~1k Ohm/ft, (rookie mistake)] – problem persists. New crank and cam position sensors go in, no change. I get the Shop Manual DVD (PRO TIP – Get the Shop Manual DVD!! Available on Ebay, $45 cheap) and find a bona fide test procedure, buy a PCM safe test light, tests revealed bad wiring between the coil and the PCM. Identified the bad wire and replaced the drivers side coil connector. Still missing. Cleaned all the grounds. Problem persists, additional testing from the procedure then isolates to the PCM being bad (AutoZone replaced under warranty). A defective replacement PCM, now who would expect that! Between, winter weather, work, ordering parts, testing, and life in general, the whole ordeal took six months to work out. Now its running well, though the climate control had failed to DEF – no vacuum leak detected from the engine compartment, so THAT is a work in progress.

@allmyEXes I posted the ignition test procedure, might help with your rig, or anyone else's for that matter!

Thanks to everyone for the analysis and suggestions, this one was a real challenge! As mentioned earlier, didn't mind replacing engine sensors as most of them were original, but a no $#!+ test approach won out at the end of the day.
 

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Update - the 'climate control had failed to DEF – no vacuum leak detected from the engine compartment' turned out to be that the plastic vacuum line was pushed too far into the rubber boot connected to the 3/8" plenum tap (driver side; the double line boot where one line goes to the canister, the other to the fuel evap purge valve). The line was pushed up against the back of the boot, blocking the flow - pulled back 1/4' and could hear the vacuum take. All good, literally... dare I say it... no codes on the Scanner! :cool:
 






Mint great job
 






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