Good article! Still do not believe this is my specific problem. If you adjust from "Drive" to "N" on your transmission, and your rpms go up it has nothing to do with the IAC valve. The IAC valves job enters the equation when the "idle table" within the ECU/PCM gets triggered. I am familiar with IAC and how it controls the idle circuit. I have tried cleaning my original IAC and it didn't help. I replaced it with a brand new FORD IAC and problem still persists. IAC's usually hunt or search for RPM's on 90% of the cars I have worked on when they start to go bad. My truck contains none of the symptom's other than random stalling that can't be triggered or replicated consistently. The only thing that seems to stop the stalling in my scenerio is putting my transmission in "N". This basically takes the load off the engine that the converter is applying and my guess is taht the converter is failing to release when coming to a stop for whatever reason.

No Check Engine lights present, ever. Again, I have a scanner and that's the first thing I checked.

Krewat may be of some help here as to why the converter isn't releasing, but it stumbles much like a manual car when you dont press in the clutch pedal when rolling to a stop and the engine just dies.

I have tuned a few cars/trucks and most have an idle circuit that you can activate/deactive at an RPM. In HPTuners it's called the Target Idle Speed vs Coolant Temp vs Drive&Park A/C On & Off table.

This table allows you to set certian rpms per coolant temp. This would basically allow the truck at certian rpms and coolant temps to set the desired idle. Once that is triggered the IAC would come into play because the truck is now in the "idle circuit".

There is also another table to adjust "tip-in/tip-out". IE: Your deep in the throttle and all of a sudden you need to brake or let off the gas for whatever reason, this table controls how much or little fuel continues to get applied after releasing the gas pedal. Most tuners set this to 0 to increase fuel mileage, however in certain circumstances this can cause a stumble/stalling effect (usually with cam'd cars).

I just filled up my truck and my gas mileage was 12.345mpg. Tells me the truck is running pretty strong. My engine was rebuilt 6k miles ago with all new parts, not reman. I highly doubt my scenario is the IAC.

Sorry for the rant. My truck also did this same thing with the old engine. Thus why I replaced the IAC as that's the only sensor that existed on the old engine and swapped to the new engine besides the TPS. I can monitor the TPS sensor with a multimeter and my tuning software and it looks to be functioning properly and that's what led me down the converter path causing the stalling.

Bottom line, if your truck is exhibiting symptoms like mine and stalls randomly, if you can put your truck from Drive to N before it actually stalls out and it fixes the issue, I bet your converter is on its way out or you have some other issue not related to the engine.

Again, Hopefully Krewat can explain what might cause these type of symptoms where someone would suspect the engine and not the trans/converter, where it might actually be a sensor in the trans, wheel speed sensor, converter etc?

I know quite a bit about engines and have rebuilt a few, but I don't know enough about transmissions to stand my ground. So hopefully Krewat can chime in.

 

From one of Marks post:
He responded to a guy that had the same issue you have. Mark know more about our transmissions than most.

http://powerstrokearmy.com/forums/showthread.php?t=44461&showall=1

"Problem with a tuner can cause this. So can low trans fluid, internal pressure leaks, a worn pump, or a damaged internal filter."

Thread says wrong fluid can cause this too.

It's an intresting thread.
I would stop driving it if you want to save trans.
Hope it's not converter, but if it is a new one needs installed before it takes out trans.

 

Well, still not sure on the stalling. It does it when coming to a stop. Now that my y pipe doesn't rattle I can hear better (truck is super quiet now). It still wants to drop to around 200rpm and then acts like you turn the key and it runs back up to 800rpm. Some times it dies, some times it manages to go down to 200rpm and then "turn over" and idle fine.

Hard to describe what it's doing.. I tried the transmission trick for a few days now and it has died even when in neutral. So I am going to rule that out.

Tranmission has new fluids, new filter etc. I tore it apart as the 3 bolts that commonly back out happened on mine after I put the new engine back in and had to fix that.

Only non new parts on the engine that I can think of at this point is...

Alternator
TPS
Coil packs (some new, some not)
fuel rail
fuel regulator

I haven't replaced the fuel pump either, but I made a video not too long ago and fuel pressure was fine.

Does our trucks have the fuel relay inertia switch on the passenger side kickpanel? Maybe I can plug a noid light or similar and see if the light comes on when the truck stumbles... My truck always starts right back up after it dies, so really don't think its the inertia switch failing, but just throwing ideas out there.

Otherwise I will make an appointment with FORD tomorrow and see if they can figure it out if no one has any ideas.

 

Well, your situation has me stumped so I can only grasp at straws.

If motor uses oil maybe the lower intake is full of oil and smothering intake?

Are all pullies running smoothly? Maybe one is starting to lock up.

Is clutch fan stuck or sticking on dragging down motor?

 

Motor uses no oil, 8k miles on new engine.

Pullies are fine, new.
Clutch fan is fine.

Im leaning towards something coil pack related... Since the truck has 230k miles.

 

The inertia switch just cuts power to the fuel pump after an impact.
If it was affecting the fuel pump power the fuel pressure would drop, but your testing ruled that out.
If anything was affecting fuel pump power it would more likely be the fuel pump power relay.

 

What about AC compressor. Maybe it's going out and when the pump comes on its pulling motor down?

Sorry just grasping at straws.

 

Possible, but I don't hear the belt squeal... Usually when compressor starts going out it drags and the belt makes noise.

 

Yah, thats true but I think pcm is supposed to increase idle speed when AC is on. Maybe when you put new motor in the ac plug is not firmly attached and it's not telling pcm to bump up idle.

As pressure builds it loads motor more and drags it down causing it to die?

 

Have you pressurized your intake to see if you ain't got a vacuum leak? A cracked/warped intake manifold or bad gaskets can cause this specially if it's a 2 piece design.

 

A/C on? Hah, its 40 degrees here still... No A/C being turned on yet.

 

I haven't tested that... though when I put the new engine in, the intake got new gaskets and looked fine. Not going to rule it out though.

I did a smoke test on the intake a while ago before the new engine and there wasn't any leaks. The problem happened with the old motor, and is now happening with the new engine. So it's either coil pack related or some other component external of the engine itself or a wiring/ground issue etc that I haven't tracked down. I ran new wires to my battery, battery is new etc. I have way more new parts than old on this thing.

 

Ok, after driving the truck today and actually able to hear what the engine is doing (now that my exhaust is nice and secure and doesn't rattle at idle, stupid slip joints)... I don't think its the coil packs. It doesn't sound like a miss at all. When it wants to stall down to 200rpm or so before it dies, the engine actually runs pretty dang impressive at 200rpm. The engine then "cranks" over and starts running normal if it doesn't die.

Since I am pretty positive its not the TPS that hasn't been replaced as I explained earlier... However, I was trying to think of any other sensors on the truck that could cause my random stalling at idle...

Crank position sensor or cam sensor?! Those are not new, and never have seen one go bad before, but it fits my symptoms.

Im leaning towards Crank sensor at this point.

I am actually going to be fairly suprised if it's not the crank sensor... Because what led me to believe it was coil packs at first was it acted like it wasn't getting spark, started to die and then spark would re-ignite the fuel and engine "turn over". That's basically the function of the crank sensor and it can stop the signal to the coil packs to fire.

************EDIT***************

I went ahead and pulled the old camshaft sensor out and replaced it. I am going to wait until Friday to replace the crankshaft sensor as it's harder to get to, and so I can provide feedback here as to which sensor fixed the issue.

 

I would think that the cam or crank sensors would cause problems at all speeds. I lean towards a vacuum leak. Often unchecked is the brake booster. Shut the engine off, wait a moment then press the pedal to see if there's still assist. If not it's leaking and could be the culprit. Another possibility would be the EGR valve sticking, if yours has EGR.

 

No EGR. I have had the vacuum system smoke checked multiple times. No issues.

Cam sensor didn't help, still having the issue when coming to a stop. I plan to tackle the crank sensor tomorrow.