Engine/Transmission (1998.5 - 2002) Very bizzare "dead pedal" experience

[KATOOM]

Well I'm only hopping that what I just experienced isnt what I think it is but nonetheless.....this is what happened.

This last weekend I took my 14k lb 5th wheel trailer up in the mountains, as I've done many times before. As usual for the north state valley area, it was stinking hot outside and I was pulling hills in 100* weather. No fun either as everything just gets too darned hot when its like that, but surprisingly this truck does amazingly well in staying within the tolerable running gear temps.

The situation I'm posting about occurred when I crested the top of one longer grade. I was at about 5500 ft in altitude, running in 3rd gear at around 2300 RPM, and the engine was on the hotter side peaking out at around 215*-220*. Thats the HOTTEST it ever gets too and only for a few minutes at longest. Having reached the top of the grade I shifted into 4th gear to let everything cool back down but strangely the throttle was non-reactive to any further increase in pedal. Weird, so I shifted back to 3rd and all throttle was normal. Then I quickly tried 4th again but still the same thing happened where it seemed the throttle didn't react to any increase in pedal. But back to 3rd again would result in complete normal throttle. So after holding 3rd gear for a couple minutes more since I had lost some momentum, I tried 4th gear a third time and this time the throttle resumed normal action. I have no idea what happened and it didn't do it again throughout the towing trip. When I got home I checked for codes but nothing was there.

I cant tell you how much I go through to assure the VP is happy so why out of the blue I'd start to have issues, I dont know. Its 6 years old, I only shut it off when I NEED to, and I'd be surprised if I have 50,000 miles on it. I dug around the internet to see what others have experienced with dead pedal and found the same thing over and over again but of what everyone had experienced with dead pedal, the only thing I can say that would resembles was that it was hot and the engine was hot. I've driven in higher altitude enough to know that sometimes the throttle is less reactive in the thinner air but I dont remember it being like this. I almost thought the ECM was accounting somehow for the hot engine but that sounds like I'm reaching for something. Addressing the heat, I've had others suggest overly hot fuel but again, no codes and I'm not even sure if that code is something my $150 code reader will find. Can the VP get so hot during high load conditions that the fuel temp sender causes a temporary throttle shut down even though there's ample fuel pumped to the VP?

In saying all this, I do remember feeling the dead pedal running in the higher 6k-7k ft altitude about 8 years ago with the original VP on the truck, but if I remember right it was a complete and momentary loss of throttle control no matter gear or anything. What I felt the other day didn't seem to be like that but then again.....maybe I'm in denial.

If anyone has some input I'd appreciate it.

 

[RikDavis]

On my 99 somewhere around 350k I would get an occasional total loss of throttle and then it would recover in a few seconds.. In my case it was the throttle position sensor (APPS?). Not quite the same circumstances but it would be something to consider

 

[KATOOM]

Thank you and yes, I've considered the APPS as well but I've been researching and I understand correctly that if it was the APPS then there "should" be a code registered too. I know thats not always going to be the case either.

 

[DonFitzwater]

"should" Don't let that fool you. If it were my truck I'd drive it until a complete failure happened. Swap in a new VP44 and an APPS and roll on for another 6 years........

 

[KATOOM]

DFitzwater, its not the failure I'm afraid of. Its the failure with a 5th wheel connected to the back of the truck 300 miles from home. That would be immensely inconvenient since I'd have to find a place to park the 60 foot combo for a week, order the replacement VP, and come back with tools. Not the end of the world but certainly would end result in a lot more money and time than if I was closer to home and without the trailer. My original VP failed without any notice. Just kaput in the middle of the road.....in traffic.....on a bridge. So I'm a little gun shy.

 

[Road Dog]

I had a similar experience -- dead peddle and shifting down brought it back. The VP44 was going in and out of limp mode. There were codes. It turns out that a fuel line leak was introducing air bubbles that caused a timing fault. For whatever reason it was worse at lower rpm. It never left me stranded. It looked like a classic overheating injector pump but a new injector pump didn't fix the problem. It was the most expensive hose clamp I ever bought. At least the new upgraded pump should last a long time.

The shop that did the work brought in a Chrysler Diesel tech (and his Chrysler scan tool) to do a deep scan and analysis of the injector pump. Just a thought if you're looking for some assurance of what's going on.

 

[KATOOM]

I had a similar experience -- dead peddle and shifting down brought it back. The VP44 was going in and out of limp mode. There were codes. It turns out that a fuel line leak was introducing air bubbles that caused a timing fault. For whatever reason it was worse at lower rpm. It never left me stranded. It looked like a classic overheating injector pump but a new injector pump didn't fix the problem. It was the most expensive hose clamp I ever bought. At least the new upgraded pump should last a long time.

The shop that did the work brought in a Chrysler Diesel tech (and his Chrysler scan tool) to do a deep scan and analysis of the injector pump. Just a thought if you're looking for some assurance of what's going on.

Very good to know. I will scour the lines for any leaks. I'm not sure what to do about a "deep" scanning since I dont have access to such an expensive scanner and being in CA, I dont think anyone can legally do it unless the trucks on their racks.

 

[KATOOM]

In regards to electrical disturbances, I think its important to include that I was towing a 5th wheel whereby the truck is also technically plugged directly into the house batteries of the trailer so could the lower charged batteries of the trailer cause enough interfering draw from the alternator, and possibly truck batteries, that it threw a phantom issue with the VP? I know I'm reaching here but it sounds logical..... Any input?

And with that said, I'm going to test my batteries and alternator just to be sure they're on the up and up.

 

[JR]

In the event your truck does overheat the ecm will derate the engine but I "think" you were still below the coolant temp threshold. Can't remember for sure what the temperature cut off is but I believe you were still ok at 220. You would also get a P 0217 "Decreased Engine Performance due to engine overheat condition. Engine overheating, ECM will derate engine'performance"

 

[KATOOM]

I "think" I found the issue. After talking with a multitude of people regarding what I described on this thread, I happen to trip across a DDT noise filter website whereby it stated something I found very interesting. Here's what it said:

1996- 2007 with the 5.9
Symptoms : Transmission shifting in and out of gear or TC locking and unlocking under light to medium conditions between 40mph-60 mph. You can very often address many of the above symptoms by doing the following :

Look for any ground straps or electrical connections that may be loose or contaminated. Check battery terminals, look for bad chassis grounds, bad PCM connections , bad ECM connections.

This is a minor electrical glitch that is a pain in the butt and causes many transmission failures.

It can take a good 4- 5 hours to properly go over all the above I have mentioned.

In addition to the above we developed the DTT Noise Filter. We have been testing it for over a year in house and via our dealer base. It has addressed over 80% of the electrical noise we have encountered.

Here is what we found :

Testing has shown alternator noise spikes present in the TPS signal to the PCM. These noise spikes may be responsible for improper operation of the lockup circuit and/or the overdrive circuit. The more load on the alternator ( ie air conditioning , charging a low trailer battery etc.), the higher the amplitude of the spikes.

The main cause of this is the fact that Dodge has run the TPS harness wiring along with the alternator wires and noise is induced as a result. Testing has shown that the noise is not present in the TPS power supply from the PCM.

We were looking for an ecnomical filter system to try and address the electrical noise issues in these dodges. The DTT noise filter was a result of our testing.

I think I'll be investing in a DDT noise filter.....

 

[JR]

What the noise filter is addressing is AC noise from the altenator. The symptoms for that are generally shuttle shifting or repeated lock/unlock of the TC. The noise filter is really nothing more than a bandaid. Your scenario seems different but still possible it could be related. Checking all grounds and connections is a good place to start. Also pull out your DVM and check the altenator for any AC voltage. It should not be putting out anything over 0.1 VAC, if it is the symptoms described above are generally the result and the real fix is replacing the altenator with a quality unit. It is possible for a reman altenator to produce AC noise right out of the box, likely because the diodes were not replaced.

 

[KATOOM]

Honestly I ran across the filter when reading this information about proper grounding, how easily its done incorrectly, and some of the problems it can cause. And along those lines, "could" there be a connection with APPS sensor issues or VP issues resulting from alternator voltage? Supposedly its "heat" which harms the VP PSG but could interference overloading play a part? http://www.w8ji.com/negative_lead_to_battery.htm

 

[JR]

If you are asking about high or low altenater voltage, there are high and low voltage CEL's anytime your sensors aren't seeing the voltage they need to function properly. However nothing can detect AC voltage which interferes with the sensors operation. The only place you can possibly get any AC noise is from the altenater Which is what the band aid fix for the noise filter remedies. You could potentially have ground issues but the noise filter will not fix that so the best bet is check them over like you mentioned and then check for the AC noise coming from the altenater just to eliminate it from the equation.

 

[KATOOM]

At this point, I'm not sure how to test it since my local rebuilder who is a quality but small shop told me that he has no way to test for a specific level of AC noise coming from the alternator. How else would I test this?

 

[JR]

Any digital volt meter that has the ability to read AC voltage. Your altenator should put out 13.5 volts to 14.5 volts DC and no more than 0.1 volts AC.
From the problems you described I am a little skeptical that this is your problem but between checking the alt. out and going through all your grounds is as good a place to start as any.

How is your truck running lately? Any more episodes? Have you towed since where you had to work the engine and try to duplicate the problem?

 

[KATOOM]

JR, I havent had a chance until today to take the truck out for a drive. It seems to run fine and hasnt repeated the that strange issue. But with the advise and guidance of forum members, I checked the voltage and AC readings and this is what I found.

Voltage at the batteries while the engine was running was 13.6.
Voltage at the alternator output was 13.6.
Turned on the A/C and fan on high and the voltage was 13.7.

At the alternator output, AC voltage was .020-.021. It would fluctuate a lot if I moved the multimeter sensor at all while touching the alternator output but maybe thats completely normal as I was probably reading the connection jump around.

After reading those figures, I would have thought that the batteries and alternator output should be closer to 14 volts, and more like 14.5 volts but maybe I'm wrong. The dash gauge was reading a tick over 14 but I'm not sure that means as much as the multimeter I was using.

That said, if the ambient temps were around 100* and the engine was well over 200* and the RPM's were higher.....wouldnt you expect the overall voltage in the system to drop and potentially cause the amperage to increase overall?

 

[neslie]

Did you ever figure out the problem? Mine is doing something very similar.

 

[KATOOM]

No.....I never did find anything which pointed positively to why I felt what I thought I felt during that day. As far as I can tell at this point is that it maybe was merely a combination of heat from triple digit summer temps and towing a trailer with weak house batteries, potentially causing higher than normal AC noise from my alternator. If it does it again then I'll maybe understand more.