'04 Ford Explorer Won't Start... P0172 and P0175


Asked by Dec 29, 2015 at 03:47 PM about the 2004 Ford Explorer Eddie Bauer V6 4WD

Question type: Maintenance & Repair

I'm usually the one answering questions, but here I am asking! My aunt has a 2004 Ford Explorer Eddie Bauer, 4.0L V6, that won't start. I scanned it and it's showing P0172 and P0175, codes for rich mixture on banks 1 and 2.
I checked for spark on all 6 wires from the distributor/coil pack, and all 6 sparked. I am thinking this could be a fuel pump, but I'd like some insight here before I tell my cousin (who takes care of the truck) to do anything.
The engine cranks, but won't start. We got it started once, but it ran horribly at around 500 rpm for a couple seconds, then died. The fuel pressure regulator was just recently replaced to fix an issue of the truck stalling out, and my cousin tells me that he read somewhere that running it on a bad regulator for too long will foul up the spark plugs, which are also relatively new, probably a year old. I have yet to check the spark plugs, because my dad and uncle are telling me that it can't be, but you don't know until you check, right?
I do hear the fuel pump going when I turn the ignition on. At least I think it's the fuel pump, as it's more of an electronic sound than I'm used to with my cars.
So, am I on the right track here? Maybe a fuel pump or a clogged/bad injector? Or does this sound more along the lines of spark plugs or wires? Or even the coil pack?

5 Answers

Guy Outland

Rich is generally speaking too much fuel or not enough metered air, check the pressure and the mass air flow sensor for obstructions. Verify that the throttle body is clean and functioning properly.

3 out of 3 people think this is helpful.

Your right about rich mixture fouling the plugs, I would check them before going anywhere else first, then go on to checking the MAF and all the fresh air intake hoses for leaks and too high fuel pump pressures. It is possible that the regulator could have went bye bye even though it was recently replaced. HTH

2 out of 2 people think this is helpful.

I'll take a look tomorrow, hopefully. There was an issue with the MAF sensor before, and I cleaned it. Maybe it's shot now!

2 out of 2 people think this is helpful.

Just an update here... I pulled and replaced all 6 plugs. The ones in there smelled horribly of gasoline, and they were burned on the electrode pretty dark. It appeared that there was fuel in the grooves of the threaded part. I used a spark checker tool, and the engine is getting spark. I double checked, and I DID hear the fuel pump upon turning the ignition on. Not sure if this tells me anything, but when I unplugged the MAF sensor, I got the same results as before, with it plugged in. So, I'm going to assume the shop that did the FPR did something wrong, or the part is giving the incorrect pressure, giving the engine too much fuel, and flooding it. Also, I had to jump is because the battery had died after several failed start attempts, and got codes 9352 and 9318 on the on board computer. I looked these up, and they appear to be power/battery codes, and not related to my issue. Just figured I'd mention it just in case. After re-reading the misfire codes' common related issues, I've narrowed it down to the fuel pressure being too high or fouled up injectors. I'm leaning towards the fuel pressure.


I'm very happy to say I fixed it! The PCM relay had gone out, and I had tested it using the method I saw online (switching the blower motor relay with the PCM relay) and, lo and behold, it started! Ran horribly, and poured smoke out of the exhaust, but it started! I added a bottle of Lucas fuel treatment and drove it a little, and the truck runs great now! So, what would have been a lot of money at the dealer turned out to be a $9 relay. Never overlook the fuses/relays!

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