... because you're my last hope[1].
The problem child is a '96 F250 Powerstroke with a slush box, and it occasionally cuts out while driving. The engine comes back within a few seconds - well, so far - and usually after I mash the pedal and hold it. This is sometimes accompanied by a check engine light, but not always, and according to the two shops that have tried to diagnose this issue, does not result in any stored codes.
Based on the symptoms - it only ever cuts out when I fully close the throttle while coasting, usually downhill - Internet "wisdom" suggests that it's an issue with a bad throttle pedal assembly, either the throttle closed switch or the throttle sensor. Based on that I replaced the throttle pedal assembly with an OEM Ford one. That made the issue less likely to occur, but not go away. Especially not if you're trying to two a trailer across the mountains from Morgantown WV like I did last night.
The issue does not happen when driving normally or if you don't fully close the throttle, which is why I was left foot braking my way home from picking up the Maxton. That (to me) mostly rules out the usual suspect for having the engine cut out, namely the cam angle sensor.
Anybody have any good ideas what to look for? I guess starting by checking all the connections to the ECU and cleaning them might be a good start, but other than that I'm a bit out of ideas.
Oh, and after it happened in the middle of rush hour traffic in Columbus OH, I've got this funny feeling that I really should do something about this, and ideally not something that would require the purchase of a different vehicle.
[1] Before I have to wade into Ford truck forums or similar entertaining places.
The cam position sensor is low hanging fruit. Just replace it and go from there. True, it’s not the typical failure mode of the CPM, but stranger things have happened.
I do have a brand new OEM CAS sensor, so I guess it would make sense to fit that first and see if it helps.
It sure seems to me, coming from the process controls side of things, that sensors with high failure rates also tend to exhibit multiple failure modes. The internet seems to only focus on the most predominant one and discounts the others. Start there first. It might have nothing to do with the CPS but it’s easy enough to eliminate.
That makes sense. Especially as the problem seems to mostly occur at higher rpm where I would expect a CPS issue to be more prominent. Plus it doesn't take that long to change the sensor anyway...
Anything else on when it happens?
I ask because my zx2 has developed an annoying stalling habit with the a/c on and out of gear while coasting. Of course since it's a manual it's easy to rectify but I'll be tracking it down this winter
There is a cheap stamped metal nut on the ipr to the drivers side of the fuel bowl. It's it's dying at a stop when accelerating or on a hill it could be that. Easy enough to check and see if it's worked loose- although it does seem like it's the opposite of your problem. Have you changed your fuel filter lately or drained water out of it?
In reply to Antihero (Forum Supporter) :
Doesn't matter if the a/c is on or not. The only common factor I've been able to determine is that I take my foot of the gas completely and trigger the idle switch, and the likelihood of it occurring is higher if I take my foot off the pedal at 65mph+, but I've had it occur at lower speeds (and thus engine speeds), too.
In reply to grover :
It does appear to be the opposite of my problem. In my case it never dies when it's idling or at a stop, only on deceleration. Plus it kinda feels like it's dropping down to idle, although the "restart plume" doesn't seem to agree when it catches again.
Fuel filter is new (just had the truck serviced), don't recall draining any water out of it. That said, it's been doing this for a couple of years now and I'm starting to get fed up with it.
Cam position sensor is usually the answer, but I'll throw a few other things out there to check.
Rig up a test light to the ECM power wire. The one that comes on when the key is on. If the test light goes out when you have your stalling problem, replace the ignition switch. It's a relatively common failure. Not sure why it's showing up on decel.
The returning to idle on decel is a pretty common trait for diesels. The torque converter isn't locked on decel, and the significant levels of compression and fortitude of the engine means that the transmission can't "push" the engine like on a gas vehicle. The tendency for the engine to return to idle is stronger than the force from the transmission side of the torque converter.
Describe the "restart plume." White? Grey? Black?
Curtis73 (Forum Supporter) said:
Cam position sensor is usually the answer, but I'll throw a few other things out there to check.
Rig up a test light to the ECM power wire. The one that comes on when the key is on. If the test light goes out when you have your stalling problem, replace the ignition switch. It's a relatively common failure. Not sure why it's showing up on decel.
That's a good idea, I'll try to do that. That said, wouldn't I also notice the radio et al cutting out?
The returning to idle on decel is a pretty common trait for diesels. The torque converter isn't locked on decel, and the significant levels of compression and fortitude of the engine means that the transmission can't "push" the engine like on a gas vehicle. The tendency for the engine to return to idle is stronger than the force from the transmission side of the torque converter.
That makes sense. One thing I described badly is that it sounds like it's trying to idle, but the tachometer is still reading what it would at those road speeds. It's almost like it had a fuel cut but the engine is still turning over. So it's not dropping RPM to idle as per the tach.
Describe the "restart plume." White? Grey? Black?
Grey, like the one it emits when I started it without running the glow plugs for long enough or when it has sat for quite a while.
BoxheadTim (Forum Supporter) said:
Curtis73 (Forum Supporter) said:
Cam position sensor is usually the answer, but I'll throw a few other things out there to check.
Rig up a test light to the ECM power wire. The one that comes on when the key is on. If the test light goes out when you have your stalling problem, replace the ignition switch. It's a relatively common failure. Not sure why it's showing up on decel.
That's a good idea, I'll try to do that. That said, wouldn't I also notice the radio et al cutting out?
Not necessarily. The ignition switch has separate wires. One leads to a relay fo power the acc side of the fuse panel, the other goes straight to the ECM through the switch from a hot fuse in the panel.... I think I'm remembering that correctly.
Describe the "restart plume." White? Grey? Black?
Grey, like the one it emits when I started it without running the glow plugs for long enough or when it has sat for quite a while.
Gotcha. That points to something other than CPS. When the CPS fails, the ECM doesn't know when to inject, so it doesn't inject at all. Raw fuel out the exhaust means it's still injecting. Possibly something about the reluctor for the CPS?
You also mentioned that the tach still works. The tach works off the CPS, so if you're still having correct tach readings, that is another point away from a CPS problem. Sometimes the tach can still work with a failing CPS, but I think that was only the 2002-later gray-colored CPS, not the black one you should have in yours. Let me ruminate on this for a bit.
One other blip just hit my brain.... don't they have a separate processor box for the pedal? Kinda like a drive-by-wire LS? If I recall, they might have a processor for the pedal and IT sends the signal to the ECM. Maybe good pedal, bad pedal box?
Ooooooo.... another one popped in.
Does it crank longer or shorter when the engine is hot? Does your problem ever happen when the engine is cold?
If the answers are "longer" and "no" it could be the HPOP pressure regulator or associated O-rings. Officially called the IPR (injection pressure regulator) and it's on the HPOP. Another similar symptom could be had with an ICP sensor (injector control pressure). If you pull it out and there is oil in it, it's toast. Replace the pigtail too because the oil will push into the strands of copper.
In reply to Curtis73 (Forum Supporter) :
It cranks shorter when it's hot. I had the HPOP rebuilt in Nevada, that was maybe about 7k miles ago.
The Pedal brain is interesting- I wasn't aware that it has one, but that would make sense given that the failure feels "electronic" to me.
Since the tach works during failure it's unlikely to be CPS. If the check engine light is coming on then it should be setting a code. Generic code readers, and even some expensive ones don't work on those trucks. You need one that'll read the Ford enhanced codes.
Is your third brake light fried? I'm embarrassed to say that the wiring has something to do with the transmission. May want to check it out and make sure it's not doing weird things or shorting.
In reply to APEowner :
One issue with the check engine light is that it doesn't stay on, it comes on for 5-10 mi utes and then goes out again. I can take it to a Ford dealer and see if there are any stored codes, however at least one of the shops was adamant they had the right code reader and couldn't find any codes.
In reply to grover :
I don't think this truck has a third brake light. Should it have one?
Edit: Doh, forgot that it should have one at the top of the cab, which is obscured by the camper shell.
I'd check it. They like to get water in there. My 96 had some corrosion, I siliconed my 97 and it's been fine. I'd love a camper top.
Mine was an early 95, so OBD1, but the only thing the brake light circuit controlled was telling the ECM to unlock the torque converter. 96 is OBD2 so it may do something else as well?
grover said:
. I'd love a camper top.
You silly folks. It's a cap. A camper is one of these:
In reply to Curtis73 (Forum Supporter) :
I'll take either.
Curtis73 (Forum Supporter) said:
Mine was an early 95, so OBD1, but the only thing the brake light circuit controlled was telling the ECM to unlock the torque converter. 96 is OBD2 so it may do something else as well?
Wouldn't that cause his issue? I admit to being fuzzy about TC's outside of stall speeds.
My only 2 cents right now is to comment that the OP was correct to bring his diesel problem here instead of the diesel truck forums. I’m fairly confident that the collective here knows more about diesels and can communicate that knowledge much more coherently than the coal-rolling, knuckle dragging forums. Those forums tend to choke my iPad down with nonsense ads to boot.
I just wish we had a dedicated diesel / tow-pig sub-forum.
