Stalling after downshift

[Creager]

Hello

I've had this problem for a while now, since before my motor rebuild. Originally I figured It was something that would magically get fixed with the new build, but it didnt hehe.

The problem occurs after downshifting while comming to a stop.

Example: Slowing from 45mph, Ill lightly hold the brakes, downshift from third to second, let the motor brake all the way down close to my stopping speed. Ill depress the clutch petal just before comming to a complete stop when it instantly just shuts off. No hesitation, struggle, or fight like the 4.0 would normally put up, it quietly shuts off like if i was turning the ignition off. Usually im still rolling when it stalls, rolling, but rolling slow: <5mph. Only time it ever does it is at this very slow speed, while comming to a stop.

Any opinions?

 

[BrooklynBay]

Check to see if you have a vacuum leak. It sounds like you have a manual transmission. If it would be an automatic, I would say that it is the TCC solenoid, but you don't have this on a manual. Clean the IAC, MAF, and throttle body too.

 

[Creager]

Yes manual transmission. Im pretty confident the vaccume is sealed, otherwise i'd probably have some bigger issues. Throttle, MAF, and IAC was cleaned during the rebuild, rebuilt motor has less then 1k on it.

Although im kind of suspecting the IAC now that you mention it, i dunno why, but its one of the only remaining factory parts on the truck!

Although i would probably have a problem with idling if it was the IAC, MAF or a vaccume leak, wouldn't I? Engine idles a consistant 750 rpm with a little loop from the overlap cam, this is where it idled stock. Idle doesn't flucutate very much if at all.

I was kind of wondering if something with the ignition-switch in the steering column might be at fault, its too weird for the 4.0 to stall without a fight.

 

[BrooklynBay]

If it would be an ignition switch related problem, then you wouldn't have any power in the truck when it stalls. You mentioned that everything was rebuilt 1K miles ago. What kind of plugs, and wires did you put in? Did you check the gap on the spark plugs before you installed them? What condition are the battery cables, and contacts on the battery? Check all of the ground connections. Scan the PCM for any stored codes.

 

[Creager]

Yes, when it stalls the CEL and the Battery light both illuminate, i think the RABS light does also... so yes i do have power in the truck when it stalls. When it does, everything appears exactly like it would when you turn the key on without cranking the engine over.

Motorcraft plugs and wires, plugs gapped to .54" I ended up replacing the positive terminal and starter cable due to a no-start condition. It could be good to go back and replace the negative. All the grounds along the starter circut were actually cleaned to bear metal and covered with grease or undercoating spray back when i was diagnosing the no-start.

I like the idea of replacing the negative battery terminal, but wouldnt I have problems starting or with any accessories if there was a contact issue at the battery?

I guess scanning for codes would be a good place to start! No CEL illuminated, but it doesnt need to be to have codes stored, correct?

 

[BrooklynBay]

There could still be a code stored. Since it's an intermittent issue, it won't always show up while cranking the engine. When everything was rebuilt, did you install new sensors, like the coolant temperature sensor, and the crankshaft position sensor? I think your OHV engine would have that part, not the camshaft position sensor. Please correct me if I'm wrong.

 

[dogfriend]

Although im kind of suspecting the IAC now that you mention it, i dunno why, but its one of the only remaining factory parts on the truck!
.

The IAC is supposed to act as a "dashpot" to keep the engine from stalling when you suddenly close the throttle. So maybe it isn't doing it all of the time.

 

[Creager]

The coolent temp sensor is new. The MassAir, Idlecontrol, Intake temp, throttle sensor, crank sensor, 02 sensor, coil pack, and fuel injectors which were all reused. I did replace one injector, and the 02 sensor is less then a year old. Thats all I can remember being there, except for the oil pressure light and low oil sensor which were on their own section of harness. Yes, there isn't a camshaft sensor, in its place is just the gear for the oil pump drive.

Probably wouldnt hurt to replace most these parts. I've cleanend the IAC a few times in the past, i know i sprayed it out again during the rebuild. Maybe it doesnt want to be cleaned anymore? hehe, with my 02 sensor only reading one side of the motor (long story) im probably running rich as it is, maybe I can remove the IAC let more air get in there, and ill run normal!

...right, ahha i can laugh at myself.