Low idle air

[Shoudabaughtsomthnelse]

Hello all , been reading these threads obsessively for some time looking for a solution I've been unsuccessful so here goes , 05 explorer xlt non flex. Just bought 3 weeks ago from craigs on the trip home on purchase day engine light came on, but no change in performance so went with it next morning went to start it snd terrible shaking no power, vibration on rpm increase, borrowed a scanner got p0506 code pulled and cleaned the extremely filthy throttle body,maf sensor and replaced air filter start up again same issue noticed spark arching across the plug wires routed on the left bank replaced plugs wires problem went away for 4 days engine light went out cool right ..no came back same issues. The truck seems to start out shaking and after a few restarts and engine temp comes up it goes away but always comes back so I've pulled the egr out cleaned checked for vac leaks ,none. Cleaned the pcv pulled the intake off replaced the o rings , verified fuel to all injection ports by removing plug wires and watching fuel spray into the intake ports with the intake off and I've verified spark to all plugs so I'm still stuck with this extremely frustrating issue I've pulled plug wires off of the coil while it's running to see which cylinders wo ignition it starts out missing on 2,5,and 6. But 2 starts firing again and I'm left with 5 and 6 dead and heavy fuel smell at the exhaust and now a cat that has been well over heated (BRIGHT RED) and spitting molten metal out. Its got 114,000 on it. Besides setting fire to it I'm not sure what to do .

 

[Drewmcg]

... verified fuel to all injection ports by removing plug wires and watching fuel spray into the intake ports with the intake off ....

Can you really run the engine w/o the intake on? Wow, that's a mind-bender to me! The PCM just goes to default mode?

This year is drive-by-wire (no throttle cable), right?

 

[Drewmcg]

This is the 4.0 SOHC, right? Hopefully, @ 114k miles, its not a timing chain issue/jumped tooth. Any rattles?

Other than possible timing issue, you say you have spark and no vacuum leak. Have you checked fuel pressure? See here for a recent thread: http://www.explorerforum.com/forums...-the-hell-stalls-no-dtcs.465676/#post-3645373.

What are your O2 sensors telling you (OBDII reader)? Does this truck have two or three cats? Blocked cat could cause back-pressure and even misfires.

 

[TechGuru]

You can't be disconnecting spark plugs with the wasted spark ignition system on these.

Disconnecting 1 spark plug disconnects TWO spark plugs.

So you've probably totally killed your CAT's now blowing gas from two cylinders into them.

 

[Drewmcg]

You can't be disconnecting spark plugs with the wasted spark ignition system on these.

Disconnecting 1 spark plug disconnects TWO spark plugs.

So you've probably totally killed your CAT's now blowing gas from two cylinders into them.

This does NOT sound correct to me.

 

[TechGuru]

This does NOT sound correct to me.

Which part? The part about the 4.0 V6's having wasted spark ignitions is FACT and can not be disputed.

The part about two cylinders blowing gas into the CAT's with a single spark plug disconnected is also FACT and can not be disputed (unless the wire going to the disconnected spark plug is grounded out to allow the sister spark plug to function).

The parts about not disconnecting a spark plug and killing the CATs are my opinion...so is that what does not sound correct to you? It may or may not kill the CATs depending on how long it was allowed to occur, but if molten metal was coming out of the tail pipe most likely the CATs are going to need replacement.

 

[Drewmcg]

I'm no expert, so please take what I say here with a grain of salt.

In my understanding, "wasted spark" refers to the fact that a coil is firing (sparking) two cylinders at once (so, on a V-6, its like having three coils instead of six). One spark is timed to ignite one cylinder in the TDC/compression stroke (or just before/after, depending on conditions/spark advance parameters set by the PCM).

The other spark is "wasted" in the sense that it is firing into a cylinder without gasoline vapor or compression (exhaust stroke), and so is not really accomplishing anything. See: https://en.wikipedia.org/wiki/Wasted_spark

If this is correct (I concede that it *might* not be), then disconnecting a spark plug wire to one cylinder will not cause the paired (coil) cylinder to stop firing. Hence, no raw gas going into that cylinder, as you fear.

Moreover, there is at least the possibility (here I am well beyond my comfort zone, however) that the PCM is smart enough to know that a spark plug wire is disconnected from the first cylinder (or that the wire failed somehow), and stop the fuel injector from firing on that cylinder. If so, then no raw gas going into either cylinder by pulling a wire. At the very least, I would expect the PCM to pick up on the fact that there was raw gas hitting the O2 sensors on the bank you pulled the wire on, and try through adjusting short/long term fuel trims to diminish the amount of raw gas going through.

"Waste spark" systems have been common for many years. I'm surprised that I've not heard before now this concern about trashing cats by pulling a spark plug wire to test for spark if it is really such a threat. But I'm all ears!

 

[TechGuru]

 

[Drewmcg]

this all appears consistent with my understanding. thanks.