Sean S

Hi All,
My '99 3500 TD was doing that thing where it would hunt between lock and unlock... it was driving me crazy.
I did the battery disconnect trick "re-learn" thing a few times and sometimes it worked, but the problem would come back.

In any case, I finally heard from a Viper mech' that this was a TSB and the truck needed to be flashed.

I took the truck to be flashed and voila!, haven't had the problem since.

However, now it is having this "new" trouble...

I get uparound 70mph and after some time of driving, the truck *paritally* looses power. It's the weirdest feeling because the engine is still running at RPM and the truck just slowly starts slowing down. Giving it more pedal does nothing, but letting off the pedal completely lets the truck decelerate as it normally would (ie. faster) and then somewhere around 60mph it will again have the power to maintain speed or accelerate again. Once back up over 70, it takes a random amount of time for it to do it again... could be a minute, could be 10 seconds.
If the cruise is on, you don't even notice that the darned thing is floored and you have a parade behind you.

Perceptions....
The truck seems to do this after it's been running for awhile.

The truck seems to do this when it's warmer.

I didn't notice this before the "flash", but I also hadn't been driving the truck on long hauls as much before that.

It does kind of seem like it is related to the converter lockup, but that may be an illusion.

Any ideas?
Many Thanks

Sean

Stamey

Check fuel filter and fuel pressure. Sounds like you are running out of fuel.

Chris

Sean S

I'm trying to play the running out of fuel scenerio in my head, but my lack of experience in diagnosing diesels is likely holding me back.

OK,
Drive to an hour, everything is fine (or at least I haven't noticed anything strange).

Then, decide to pass or something and run it up from 70 to 80 and feel a little "bump" and the truck is no longer accelerating. It feels like I'm in neutral except that the RPM is still where it was (say 2200). The truck is coasting and but not decelerating the same as if I remove my foot from the pedal. It decelerating as if I'm still giving it fuel but not enough to maintain speed (yes, I hear myself).

Here's what I can't figure out...
If I keep going like this, the truck will keep slowing down, but if I totally let off the pedal even for 2 seconds, I feel another 'Bump" and off it goes....like the ignition cut back on.
Honestly, it almost feels like a speed regulator gone nuts where it starts cutting cylinders as you go too fast (except that is not the cause since it is not consistant at all and the truck will do 90 at other times without hesitation).

The other thing that makes me wonder about fuel is that as the truck slows, it wont find a speed where it re-catches.
If I continue to floor the truck (as the cruise has), the truck would likely slow down to a stop (at least it feels that way), and the only "cure" is to let go of the pedal completly and re-assert.

It also seems like it does this after quite a time of consistant speed driving. I don't know how or when the computer decides to lock up the converter, but it "feels" decidedly "intentional"

I don't drive this truck every day (about once a week), but I'm about ready to throw this tranny (and especially its computer) through the Dodge dealer's window.

I was hoping some others may have had this odd trouble.

Thanks
Sean

Stamey

I won't claim to be an expert on your problem, but I can tell you a little about the TC and stock lockup. When you let off the fuel the TC unlocks immediately. If you run out of fuel, the engine looses power and this may cause the TC to unlock. What happens when you floor it when it's doing this?
I'm not ready to blame the tranny yet.

Chris

Sean S

Well, the first thing that naturally happens during this "crisis" is to apply more fuel, so I can easily answer that....

When the power kicks out, it is as if the throttle pedal no longer exists *until* you back waaaay off.

I can sit and go from half way down (about where I was cruising at) to full floor and back, and tap my foot to a tune with zero change in *anything*. The engine RPM will stay the same, the engine will not change in sound. It's like being in a time warp where everything is frozen.
It takes backing the pedel off to about 1/4 or less before the engine will respond to the throttle at all.

Ok.. another example...
Sorry, this is such odd behavior that it's hard to discribe...

I'm doing 70 and I give it a little throttle to overtake a big rig.
I hit 77 and feel a subtle "bump". This bump is likely the same thing you would feel if you let off the fuel normally and wouldn't notice, but because it's not in harmony with that action, it becomes noticeable (or, it's the TC trying to kick on or off...not sure)
Let's say that the RPM was at 2200 when this occured...
Now the truck is slowly slowing down and the RPM is staying about the same. More pedal does zero change in any way. A little less pedal makes zero change in any way.
I usually cannot do this diagnostic for more than about 10 seconds because now I'm in the fast lane and the fingers are starting to fly. I cannot pass the truck and someone's behind me so I cannot pass behind the truck.
Now, if I quickly let off the pedal completely, the RPM will fall (as it normally would) and flooring it again will accelerate the truck. Usually I'm doing 60 or so by the time I let off and hit it again (due to the fact that the truck has been slowing during this process). Now I can zoom right up to whatever speed the truck decides to do it again. Sometimes it's right back at 70, sometimes I can hit 90. Sometimes it kicks out as soon as I'm back to 70, others it will let me run at 70 for a few minutes and then kick out. Loads and grades make a small difference (It will do it going downhill, but usually at higher speeds...hence fuel again).

The truck *does* feel like it is running out of fuel, no doubt, but it feels like it is doing it for an off reason...perhaps electronically.
For instance, I am basically talking about normal driving here. I'm sure it doesn't do this right when I get on the highway, it is after some time. If it were a bad pump or low pressure, you'd think it would do it at my first grade or venture into the passing lane, which it does not. It will cruise, pass, climb etc. for quite awhile and then out of the blue start this little tantrum. Once it starts, it seems to get worse.

Now, this all happens over the 70 mark. The truck will not get into this mode at 60, and I can cruise all day at that speed. However, the truck will drop below 60 once it starts this with the pedal floored. You'd think not enough fuel would mean that the condition of the truck would eventually mate back up with the available fuel...nope.

Since I don't know diesels well enough, I'd make guesses....

1. The fuel tempurature sensor is kicking off the lift pump because the fuel is too hot.

2. The speed govener (I think there is actually one of these for the RPM) is going nuts when it warms up.

3. Water in the fuel is vaporizing at a certain temp and causing vapor lock.

4. The program developers at Dodge were druck when the wrote the update that I just had my truck flashed with.

Another interesting note....
With the hunting problem that the flash took care of just before I made the trip where this new problem arrived, the truck would hunt on/off with that TC lock at 55-65mph so I'd *have* to run the truck over 70 to keep it from doing it.
It did indeed run along just fine at 70, for hundreds of miles at a time, and now starts causing trouble right around the same mark I had to stay above before. This would automatically point me to a bad program or flash, but if that were the case, I'd think others would be seeing the same trouble.
This was flashed 3 weeks ago.... maybe I'm the first victim.

Sean

Sean S

Oh... let me just add....

What you are saying about the TC unlocking immediatly if you release the pedal, and "may" unlock as you are slowing down kind of rings a familiarity bell with this problem.

TC locks, truck loses power, release pedal, unlocks, power back.

or

TC locks, truck loses power, don't release pedal, truck keeps losing power but you keep releasing before it would "normally" unlock to avoid an accident, thereby kicking the TC lock off and the power back on.

Call me crazy, but not knowing any better I'd swear that this TC lock up is not so simple in how it decideds. It seems like it analyzes your driving over time and if your pedal and speed have not changed in the programmed time, then it locks up.

If this is true, then it would account for the problem, because I've usually been driving for awhile before I kick on the cruise and maintain a very steady speed (like finally getting out of town and onto open highway).

I'll also add (although it may be illusion), that while it's doing this, if I am erratic with the pedal, it seems to wait, like it is trying to figure out if now is the time to lock up or if I'm still buzzing around the town. I've done this test intentionally to try to determine if the computer is causing this based on *steady* speeds and throttle positions...seems to help a bit.

Sean

Stamey

Another possibility is a bad TPS (Throttle Position Sensor). I don't know how to test it though. Once you have verified the fuel pressure and filter, that's when I'd go deeper, into the TPS and maybe even the ECM. You will likely have to take it to a dealer or a Cummins shop for the latter two. (try for a Cummins shop before a Dodge dealer)

Chris