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Discussion Starter #21
Ok, so after I posted this, I ran across an article on how the EEC in these trucks work and figured it out. Sorry for getting back on here late, and thank you for the suggestions. The O2 sensor was the problem, and I'll explain how I determined that;

I'll repost the big "take away" of the article I found in case someone else finds this post in a google search. So..on these vehicles, the EEC operates in closed loop only at warm idle, and steady cruise. All other states, acceleration, deceleration, WOT, start up, and warm up are open loop operations. I was a little surprised by this behavior, as I'm used to the EEC-IV on the fords, but, once I saw this I had a pretty solid feeling that the primary O2 sensor was the culprit. That's the one that's used to adjust the fuel trims, and if it's out of whack, the computer will be either throwing to much, or to little fuel into the mix once closed loop operating temp is reached (165 degrees I believe).

The reason I didn't suspect this immediately, was because on other vehicles, a bad O2 would have the truck bogging horribly under moderate acceleration, or leaning out..since that wasn't happening I was not sure about the O2 as the cause until I read what I posted above. The O2 is ignored under acceleration conditions. So I went about proving this. I unhooked the primary O2, reset the eec by unhooking the battery, and took it for a ride. Problem solved. I've been driving it everywhere for the last 2 days just to be sure, and haven't had a problem since (although the CEL is now on as a result).

Now the fun part will be removing that sensor...it's been in there since 1998, and it won't budge. I'm currently working out a date to get down to my buddies house so I can throw it on his lift and use a torch to get the thing out...because it is STUCK.

Anyway, thanks again guys...sorry it took me so long to post back up once I realized what the issue was.
 

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Just wanted to add something to Fishtails diagnosis. I too have been working on trying to trouble shoot a very similar problem. Come to find out, the Crank Position Sensor was part of my problem. Since replacing the CPS, my '96 B2500 w/318 has be able to idle great, no longer stalls after reaching normal operational temp, and no longer dies/shudders/stalls when coming to a stop while driving.

Again, just wanted to add this possible fix to an already great thread. Thanks.
 

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Discussion Starter #23
Just wanted to add something to Fishtails diagnosis. I too have been working on trying to trouble shoot a very similar problem. Come to find out, the Crank Position Sensor was part of my problem. Since replacing the CPS, my '96 B2500 w/318 has be able to idle great, no longer stalls after reaching normal operational temp, and no longer dies/shudders/stalls when coming to a stop while driving.

Again, just wanted to add this possible fix to an already great thread. Thanks.
So...it turns out my problem is back. It drove fine with the new O2 sensor for a while, but now it's back to stalling out again. Only, now that I've driven it a bit more, I've been able to better characterize exactly when it does it for the most part.

In my case, it doesn't do it until the truck is warm. Cold start, I can put the truck in forward or reverse, and drive all around, no problem. Once it's warm though, the truck will stall unless I drive with 2 feet to keep my foot on the gas while at a light in drive, and will just flat out stall when placed into reverse, unless I give it a bunch of gas and basically neutral bomb it. As soon as it sits for a while and cools off, it's fine again. CEL isn't on, and there are no codes present. This problem is driving me nuts. I replaced the IAC a couple days ago hoping that was the issue, but no dice. Let the truck warm up while shoveling the driveway after this snow storm, and it stalled the instant my wife put it in reverse to move it so we could shovel around it.

It even stalled in park on her once, and once it stalls it's now also becoming more difficult to restart. And it knocks/rattles after a restart for a second or two as well.

I'd love it if my problem were the CPS, but wouldn't that throw a code? Has anyone had one of those fail and not throw a code?
 

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Either cam (CMP) or crank (CKP) sensor can fail and not throw a code.
 

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Discussion Starter #25
Either cam (CMP) or crank (CKP) sensor can fail and not throw a code.
Good to know. As it happens, the car did have a code P0340, but my scanner didn't report it. It wasn't till I plugged it into torque that I got the code off. I'm just going to replace both the CMP and CKP, since I don't trust that code much. I can readily reproduce the stall, but the code doesn't always show up.
 

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Discussion Starter #26
Well, replace the cam position sensor today, truck has a more responsive throttle now, but still stalls. This time it took me a few minutes to even get it to restart. Still no code. Crank sensor came in this afternoon, so I'll replace that too, but I'd be surprised if that's the issue.

This only starts happening after the truck gets warm. I'm not sure when these things kick into closed loop, but I wouldn't be surprised if this was related to closed loop operation. The O2 sensor is new, so I suspect a faulty ground, or a bad ECM could be at play, since this problem was gone entirely when the sensor was unplugged. I doubt the new sensor has failed already, but I wonder now if the ECM is still getting a bad reading.

Does anyone here have torque or an OBDII scanner that can live stream pids? If so, and you have a healthy truck, could you let me know;
What your Throttle position % reads at idle
Timing at idle
RPM
Any pids from the O2 sensor. I haven't looked closely at this pids yet (so I'm not sure which are available), but I will tomorrow. I realize they won't be the same between vehicles, but I'm interested to see if mine are drastically different.
 

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Discussion Starter #27
Well, replace the cam position sensor today, truck has a more responsive throttle now, but still stalls. This time it took me a few minutes to even get it to restart. Still no code. Crank sensor came in this afternoon, so I'll replace that too, but I'd be surprised if that's the issue.

This only starts happening after the truck gets warm. I'm not sure when these things kick into closed loop, but I wouldn't be surprised if this was related to closed loop operation. The O2 sensor is new, so I suspect a faulty ground, or a bad ECM could be at play, since this problem was gone entirely when the sensor was unplugged. I doubt the new sensor has failed already, but I wonder now if the ECM is still getting a bad reading.

Does anyone here have torque or an OBDII scanner that can live stream pids? If so, and you have a healthy truck, could you let me know;
What your Throttle position % reads at idle
Timing at idle
RPM
Any pids from the O2 sensor. I haven't looked closely at this pids yet (so I'm not sure which are available), but I will tomorrow. I realize they won't be the same between vehicles, but I'm interested to see if mine are drastically different.

OK, so to update my own assumptions...I replaced the crank sensor yesterday. Truck did not stall after it was warm, and previously the stall would happen pretty much 100% of the time after the truck warmed up. I still don't trust it yet, but IF this fixed the problem then my best guess is the issue was due to heat soak of the crank sensor. That thing is in a really stupid spot. Right next to the head, and the header, conveniently where it's very difficult to reach, aside from an area where it will get hot. So I'm holding out some hope that the issue is fixed, but I'm far from convinced.
 

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Discussion Starter #28
Just a thread update for anyone that runs into this as part of a search;

It's been about a week, and while I don't DD the truck I've been driving it as much as possible since the last attempt at fixing the issue. So far, so good. It's unfortunate that this issue didn't trip a light, but perhaps the sensor was still within tolerance, and that tolerance is set to wide. As a result, timing isn't where the ECM thought it was, and the extra load from putting the truck in reverse caused a stall. If I don't post in here again, that means the sensor replacement resolved this issue. That's speculation of course, but that is all I have to go on at this time anyway.
 
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