I have a 94 f150 5.8. The truck has 300,000+ kms. I just bought it a few weeks ago and its been running fine. On a recent road trip, I ran the rear fuel tank down and switched over to the front tank. Not too long afterwards (not sure if its related to switching tanks but thought I should mention it) I noticed the check engine light come on. After a while it went out, then came on again. Then I noticed I was spewing out big clouds of black smoke from the exhaust, especially under load. Fuel economy went in the toilet. Its been spewing black ever since.

Obviously there is a running rich issue. I bought a code reader and these are the codes that were stored (not sure how old any of these might be):

111
10
171
173
181
542
624
628


I've looked them up in my Haynes manual and I see that 171, 173, 181 are O2 sensor failures. Are these the cause of running rich or a result of it?
542 says Fuel pump secondary circuit failure - pcm to ground. Huh?
624 says EPC solenoid or driver circuit failure. Is this a transmission issue?
628 seems to be a torque converter fault.

Can anyone offer up an interpretation and possible diagnosis? TIA Todd

 

Since its easy to do, I would start by hooking a fuel pressure gauge up to the fuel rail, and record pressure from each fuel tank. A bad fuel pressure regulator can drown that motor in gas, make black smoke and foul O2 sensors and plugs. Should be around 40psi at the rail. About two weeks ago I saw a '93 F150 302, that was blowing black smoke and fouled the plugs within a minute. It had a bad fuel pressure regulator and had 90psi at the fuel rail. Code 173 says O2 sensor indicates rich, this could have set when the rich condition first happened, then once the O2 sensor was fouled by the excess fuel, it may always read a false lean condition and the computer will try to add even more fuel, setting code 171 and 181 (lean codes) If your fuel pressure is good, you could have an o2 sensor problem. They are about $50. You could try switching the left and right ones to see if your codes change 171, 173 and 181 are all codes for bank one (the passenger side of the engine, cylinders 1-4) If you clear the codes, swap the sensors and get codes 176, 177, or 175 (bank 2 codes), it would determine that your O2 sensor is bad. On some vehicles you can swap the O2 sensor connectors without removing the sensors. Anyway, hope this helps. Good luck.

 

Ok, put in a brand new O2 sensor, still pumping out the black exhaust under load.

 

You should check the fuel pressure like MintFord said.

 

No offense intended here, but you were given good advice, instead you ended up replacing a part that was doing its job. If you're spewing black smoke out the exhaust, that means the engine is running very rich, which is what your O2 sensor(s) was(were) telling you. With all the other codes you're getting, your problem is likely elsewhere, like the fuel pressure regulator. Check that first, then clean your plugs, clear your codes, then try again.

Jason

 

I think I would also look at & clean the elect system grounds. Check the underside of the fuel relay for corrosion & maybe the EEC main connector as well.

Does the pump/pumps prime, then shut off when the key is turned to "on", but not started? Or do they continue to run?

You seem to have way too many things going (code wise) on at once to be just one problem.

 

I wasn't ignoring the advice. I replaced the o2 before anyone had responded. Looking at it, it definitely needed to be replaced anyway. I will check the fuel pressure today (I don't have a pressure gauge). I will also check to see if the pump keeps priming.
I haven't used the rear tank since the problem started. I'm going to switch back over to the rear tank this morning and see if anything changes. The problem started when I switched tanks and I'm wondering if maybe that wasn't a coincidence. Reading through my Haynes manual, I'm wondering if the Fuel Delivery Module for the front tank might have a stuck closed shuttle valve. According to the manual, a stuck closed shuttle valve would cause a high pressure situation and therefore a rich condition. When I switched tanks, it was the first time I had tried the front tank.
But first things first, I will check if the pump stops priming, and I will check the fuel pressure.
Thanks for the feedback, it is appreciated.

 

Pull the vacuum line off the fuel pressure regulator, if you get any fuel out of this the FPR is shot.