Engine/Transmission (1998.5 - 2002) Engine cuts out at constant speed

[cerberusiam]

Working on an issue with a 99 3/4 4x4 auto with 158k. After cruising at a constant speed for 20 to x miles the power goes away and truck starts slowing. Has happend anywhere between 40 and 80 mph. If the throttle is worked it will sometimes pich up and run again for ???? miles/time. If the throttle is held and the speed drops under 50 mph it will pick back up and run right, sometimes, for ???? miles/time. Some days it will run with no problems. Take it to a dealer and it won't miss a beat. Tach does not drop to zero but slowly drops with rpm. The truck will not miss a beat accelerating or pulling unless the speed is held constant for a time and even then it is never a consistent amount nor any particular event to trigger it. Truck came out of OK where dealer claims they have problems with heat and humidity causing issues.



Injection pump has been replaced previously, no more info. No info on lift pump replacement or fuel pressure. Computer is showing no codes. Notation on dealer work order indicates APPS is out of spec. No info on when, where or how reading was obtained.



Following is what we are doing:



1. Pull negative battery cables, leave key on to discharge capacitors and clear computer.



2. Clean, grease, and reset all body and engine grounds, ECM & PCM & APPS & crank sensor connections. Load test batteries.



3. Reset APPS.





Ok, what have I missed and what else could be the problem. If the above doesn't cure it, it is on to checking fuel pressure and whatever else could be wrong. Replacing the APPS is an option but for $400 I would rather exhaust all other possibilities first.



Is there a quick cheap way to load the pump like a fueling box to see if it could be the problem? It really acts like the pump is TU but it will not throw a code.





Observations? Ideas? Experiences?

 

[cerberusiam]

TTT



28 views and no opinions????



This place has the greatest concentration of knowledge in the known universe and the silence is deafening... ... ...

 

[Gary - K7GLD]

HMMmmmm - didn't see any reference to checking/replacing the fuel filter - that's usually one of the first checkpoints...



And, without GUAGES, those of us WANTING to help are flying blind! You guys simply HAFTA help US help YOU with as much info as possible, and in cases like this, fuel PSI is a critical issue!



All the "combined knowledge" in the world is no better than the supplied info - not intending to pick on you, but we seem to be getting more of these long-distance guessing games all the time...

 

[SS]

The following is just an opinion:



I had a gasser several years ago that behaved similarly. It had a bad spot on the Throttle Position Sensor if it was held at a constant pedal position. The tests could never find it because it happened when warm and only in the one spot. TPS test said all was O. K. Replaced it anyway and it was immediately corrected. Good luck!



The previous message was just an opinion.

 

[Coonrod]

Had a 7. 3 Powerstroke do it to me. It would only do it every once and a while. It was the Throttle Position Sensor also.

 

[cerberusiam]

Fuel filter was presumed new as truck was serviced prior to buying. It is being changed to rule it out and fuel pressure gauge is being installed. I had ruled out a fuel problem as the truck would perform quite well except at inconsistent intervals.



After pulling the battery cables and dumping the computer and reseting the APPS the problem has temporarily disappeared.



I don't expect a complete diagnosis over the Internet, just a check to see if I missed something, speculate please.

 

[Sticks]

Might me the crank sensor as well.

 

[mhenon]

Just a guess!

Sounds like the APPS to me. Don't want to hijack the thread but does anyone know what a new APPS cost and how difficult it is to change out. I'm thinking of carrying a spare on our winter trips to Mexico.



Mike

 

[mhenon]

Opps!

Ok, I see that a new APPS is $400. 00 bucks

 

[Gary - K7GLD]

After pulling the battery cables and dumping the computer and reseting the APPS the problem has temporarily disappeared.



THERE ya go!



THAT tidbit of info is probably the most telling of all. MOST engine sensors run at constant levels without internal variables to lose momentary contact or go intermittant - they usually work, or DON'T... Sure, the crank/cam sensor might drift out of adjustment - but resetting the computer USUALLY would not have any significant effect - but a failing APPS MIGHT be temporarily "fixed" by a reset, until it again momentarily lost internal contact and integrity - causing what you describe. At this point, I'd also bet on the APPS or something in that circuit...



Keep us posted - we all learn from these little exercises!

 

[cerberusiam]

Crank sensor failure should be accompanied by tach dropping to zero and either staying there or bouncing back up. There should also be a code set for that but no codes.



I suspect what was causing the problem was the positive cable on the passenger side battery. At some time the threads had been stripped and it was not making firm contact. Tight enough that it wasn't flopping but loose enough it has started some oxidation between the pieces.



Ordered a new apps thru a Cummins dealer and got it for $380. Dealer wanted $500 and had no idea what the problem could be. Have it in case it is the problem. The Cummins mechanic felt it was a connection somewhere, possibly at the pump, that was failing. Claimed dielectric grease would draw water into the connector and make it fail. Huh???



If it was a bad spot in the APPS wouldn't the failure happen at about the same position every time? Considering the failure would happen anywhere between 40 and 80 mph that would mean about half the strip is messed up. I have not heard of a failure that bad on only 150k but I suppose its possible.



For now it is working and will see if it holds.

 

[cerberusiam]

Well, that worked for 3 days. Drive the snot out of it and couldn't make it fail. Hooked up to a load of hay and made it 20 miles and now the problem is back. No check engine lights or indication there is a problem. Guess will have to wait on the gauges and get some more info.

 

[libertyram]

I am battling the same thing. I replaced the apps and the problem went away for about 2 weeks and now is starting to show up again. I have done the battery and ground stuff to no avail.

 

[jebia]

I had both problems, both symptons.



My truck would cut out for a few seconds at a time and my truck would lose speed (10 to 15 mph), and then pick up again. Almost felt like I can out of gas (put my fuel pressure stayed up, gauge indication). I replace the APPs (throttle position sensor) and fixed it.



A few months later my truck would idle eratically (plus or minus a couple hundred rpm), and would buck (miss), especially under load. Not a cut out like the above problem, you could maintain any speed you wanted to, it just ran very rough (especially if you tried to use the curise control, this accentuated the problem). I replaced my crankshaft position sensor and it fixed it.



Jon

 

[cerberusiam]

Jon, did you see any bouncing with the tach? Every issue I have seen with the crank sensor has been accompanied by an erratic tach. Its possible the ECM is seeing something out of range and compensating but I would think there would be a code somewhere. Suppose better put a crank sensor on the list.

 

[jebia]

Yes I did have eratic idle (as seen by looking at the tach), that's what I meant when I said "plus or minus a couple hundred rpm". Looking at the tach it was subtle but you could see it, and more so feel it causing the engine to buck.



I checked codes and didn't see any, I read somewhere on this forum that the crank shaft sensor will fail intermittently at first and then eventually fail over hard. So I decided not to wait. I bought mine from mopar 4 less, I think I paid $35 or so for it (ask for your tdr discount).



Jon

 

[John - K5AWO]

Okie dokie,



I just read this thread from start to finish... . here is what I feel is going on. It seems that your problem occurs after the underhood temps stabilize and are at accelerated temps. IE, pulling that load of hay.



One of the components is expanding from the extra heat load. Since you already have that APPS now, I would put it on and rule that part of the system out (maybe if it is a good new one).



The ECM is just about a zero percent chance of being the problem. It will most likely be from things that move in normal service, IE, the APPS or another sensor strip.



You obviously need guages to verify you aren't loosing fuel pressure when the pump gets heat saturated (another moving part).



There is one other item that comes to mind. A vacuum in the fuel tank as fuel level is being pulled down. Easy test, loosen the cap and see what difference that makes. The tank is supposed to be vented, maybe it got stopped up. The truck is from my home state, and there are a lot of mud dobbers there



Luck,

John

 

[cerberusiam]

John, thank you that is just what I was looking for. Something I missed like a plugged fuel tank vent.



As Jeff Foxworthy says "Sometimes the simplest things..... ".

 

[cerberusiam]

Update, VP = dead.



After swapping trucks and driving the 99 around empty for 3 days no more failures except at the start. However, it has developed flat spots and stumbles in the acceleration curve. Tested the fuel pressure under load and never went below 10 psi with 15 psi at an idle. It is now throwing pump failure codes so new pump is next step.

 

[jpmutt]

Hey guys, I'm new to the site and just read through this and was thinking fuel pressure issue. I know everyone knows the transfer pumps are junk and fuel pressure is the first thing that comes to mind when a driveability issue arises. One thing many people dont instantly think of is volume. The transfer pump should flow a minimum of 45 fl. oz. in 25 sec. i. e. bump key and let transfer pump run and measure how much fuel it pumps. Lack of volume (not only pressure) is a key VP pump killer. Not trying to butt in, just my . 02 cents.