Today I was stopped at red light when my trucks idle went up to 2500 and black smoke started pouring out the exhaust. I pull over but the truck feels like it wont come out of 1st gear. So I put it Nuetral and open the hood and hit the throttle a couple of times and its still black smoke coming out. So I turn it off and back on and the problem disappered drive the rest of the way home just fine.

Any help is most wanted before I take it ford and have them look at it.

See sig for details of truck

 

Broken, will try again

 

High idle
- vacuum leak
- IAC
- through throttle commanded open (pedal, TAC, cruise)

Rich - warmed up idle
- fuel pressure problem
- - FPR stuck
- - FPR vacuum off
- - return line plugged
- injector problem
- - leaking
- - failure to close
- calculation problem
- - O2 sensor offset (warmed up, not at wide open throttle)
- - MAF failure (cold or at WOT) (dirty would enlean, not enrich)
- - Fallback to Alpha-N if open loop, failed MAF
- command problem
- - Drivers for injectors failed shut
- - wire from PCM driver to injector shorted to ground
- Other fuel sources
- - Gas in oil, circulated by PCV
- - ruptured FPR diaphram runs gas through FPR vacuum line
- - EVAP purging at idle

Start with the high idle. 2500 RPM is about the limit of what the IAC can command. Vacuum leaks wouldn't be fixed by stopping and restarting (long shot, brake booster diaphram changed by stopping). Throttle would have to increase, not just stick, by your description. Unless cruise control kicked in, no other mechanism for throttle to have opened. I'm going with IAC commanded open.

Now for black smoke, I'm assuming this is a rich condition. Of all the possibilities, the only one that I can see that corresponds to the high idle is the Alpha-N scenario. Two fueling modes, closed loop is used when O2 sensors warmed up and not at wide open throttle (WOT), open loop is used until O2 sensors heated up and at WOT. Open loop is also used in most failure modes (clue). In closed loop, the MAF is ignored and the O2 sensors are used to determine fuel required. In open loop, the MAF is used to measure air flow and the airflow is used to calculate the amount of fuel required. The failure mode (clue) for the MAF is to use the combination of throttle position and RPM (Alpha is the throttle angle and N is the RPM in Alpha-N) to determine the air flow instead of the MAF.

If the TPS indicates off idle, the IAC enters throttle following mode to allow a dashpot function to prevent stalls on throttle snapped shut. If the TPS incorrectly indicates full throttle, the IAC wi diaphram runs gas through FPR vacuum line
- - EVAP purging at idle

Start with the high idle. 2500 RPM is about the limit of what the IAC can command. Vacuum leaks wouldn't be fixed by stopping and restarting (long shot, brake booster diaphram changed by stopping). Throttle would have to increase, not just stick, by your description. Unless cruise control kicked in, no other mechanism for throttle to have opened. I'm going with IAC commanded open.

Now for black smoke, I'm assuming this is a rich condition. Of all the possibilities, the only one that I can see that corresponds to the high idle is the Alpha-N scenario. Two fueling modes, closed loop is used when O2 sensors warmed up and not at wide open throttle (WOT), open loop is used until O2 sensors heated up and at WOT. Open loop is also used in most failure modes (clue). In closed loop, the MAF is ignored and the O2 sensors are used to determine fuel required. In open loop, the MAF is used to measure air flow and the airflow is used to calculate the amount of fuel required. The failure mode (clue) for the MAF is to use the combination of throttle position and RPM (Alpha is the throttle angle and N is the RPM in Alpha-N) to determine the air flow instead of the MAF.

If the TPS indicates off idle, the IAC enters throttle following mode to allow a dashpot function to prevent stalls on throttle snapped shut. If the TPS incorrectly indicates full throttle, the IAC will follow it. There was an example of this just a few days ago on this forum, I can look it up if you want. TPS fixed this IAC chasing a bad TPS resulting in a runaway high idle.

In Alpha-N mode, the failure mode for open loop with a bad MAF, the amount of fuel commanded is proportional to the throttle position (clue) and the RPM. In this case where the throttle is closed but the IAC open (maybe 1/10th the amount of air the throttle can flow), a bad TPS could command WAY too much fuel. Black smoke.

Problem is how would we get into a condition where a (I'm presuming this) warmed up truck would be in open loop (MAF is ignored in closed loop which would be normal for warmed up truck at idle) and the MAF is bad causing the faulty TPS to command fuel (Alpha-N)? This is thin, very thin. Either the wiring harness carries both or the same driver is used for the MAF and TPS in the PCM. A wiring diagram and PCM logic diagram could verify this. If it were me, I'd put the truck in park, warmed up idle, and start wiggling wires from the MAF and TPS back to the PCM. That's my guess.

Was the truck warmed up at the red light? Did you already have the MIL (check engine light) on? Did it come on during this?

There is probably a much simpler explanation that will turn out to be the case.

 

I tried several times to edit the above post, including deleting it and adding it back in. The first few paragraphs repeat and I cannot make it right. I'm sorry for the errors.