Do new PCM still have open loop for WOT?

[MDavis0424]

I know the early engine computers would go into an open loop mode at wide open throttle where they would ignore some feedback from O2 sensors, etc. and just use some mapped fuel curves. Is this still true, or have the emissions tightened up to the point where they run closed loop all the time?

Here's the problem I'm having. I'll be sitting at a stoplight, and all of sudden the car starts idling rough. The light turns green, and the car will barely move - until you get the accelerator to about 3/4 pedal, then it takes off like a scalded dog. You let up on the pedal, and it starts sputtering again.

It's had codes for both too lean and too rich, also O2 sensor out of range. The dealer replaced the O2 sensor, and said they found a vacuum leak around the intake and replaced the manifold. Most of the time I get no codes, no CEL. My thought is that it runs fine as soon as you put the computer in open loop, but it has a sensor that is giving bad data in closed loop but not bad enough to code.

 

[Quik LS]

yes - all cars still use open loop in full throttle.

likely you still have a vacuum leak, which under WOT is hidden because of the lack of vacuum that is needed when the engine is under load.

v6 or v8, what year?

 

[beaups]

sounds like a vacuum leak or bad injector dumping fuel. neither of these would create too much of an issue @ wot. Seeing the too rich code I'd be looking for a bum injector. As I understand it, Problem with an injector is the pcm adjusts fuel trim by bank...so if an injector is dumping fuel causing rich readings the pcm will trim the whole bank to get it "in line"...which would then mean 3 lean cylinders...and all sorts of misfires

 

[MDavis0424]

2004 v8.

Would fuel injector or vacuum leak be very intermittent? Problem only happens once a month or so, it's the intermittent nature that makes me think electrical.

 

[beaups]

Hard to tell. Only sensors I think could cause your symptoms would be 02 or maf sensors. Since you have a drive by wire model, it "SHOULD" rule out the maf as when the pcm sees maf data inconsistent with throttle plate position it goes into ETC failsafe mode real quickly. I would also think a significant vaccum leak would cause ETC failsofe mode as well. And you have already replaced 02 sensors.

Does it happen more after a rainshower? It could be as simple as a misfire caused by water in the coil wells, etc....

 

[MDavis0424]

I saw the TSB on the water leaking into the coil covers, was one of my first thoughts too. The last time it happened was fairly soon after a car wash. I know at least one other time it was cold and damp cause I had to sit in it for 2 hours waiting for Lincoln's "premier roadside assistance" to show up. But that leaves at least four times I can't account to rain or a car wash.

There's an old post on it somewhere, but here's what they have done each time:

Replaced throttle position sensor
Replaced throttle body
Replaced MAF
Replaced PCM
Nothing - had codes for one bank lean, one bank rich. Cleared codes and could not duplicate problem.
Replaced one of the O2 sensors, not sure which one.
Replaced #2 coil
Replaced intake manifold

 

[beaups]

My car did that from time to time...but never while driving it..always when I first started it. A few months later I had to replace the PCM. Seems they've replaced about everything other than the other 7 coils and possibly the tsb for water in wells. One bank lean and one rich sounds maybe like a fuel pressure regulator or fuel rail as well? I can't imagine anything else that would cause one side to get so much more gas than the other since the pcm adjusts the banks separately. Just another thought.