Engine/Transmission (1998.5 - 2002) Rough idle and high idle and rough when warmed up

[21skippy13]

Ok I am new to the site, had a long member friend tell me I had to join cuz I could find help here.



So I have a 1998. 5 24valve with about 430,000+ miles. Starting around the beginning of winter I had a slight small skip, nothing major barely even noticeable, as winter went on and we are now pushing through spring it has gotten way worse and is a really rough idle, and NOW beginning about 2 weeks ago it wants to idle about 1300 rpms after it gets warm while still sounding rough. But when you put it into drive or reverse and put the load on it then it sounds fine, unless you go to coast then you can hear it running rough, and with the idle wanting to run high makes it hard to brake and slow the truck down.

Here is a quick low down to what i have done, I changed the injectors and checked the valve lash about a week and a half ago thinking that might have been it but didn't change the way it ran. The injection pump was changed about 2 years ago with 20,000-25,000 mile on it. It doesn't have any lack of power and pulls hard with the new injectors, I have check fuel pressure and its an all stock system with the in tank pump, just checked the pressure today, 7psi at idle, and 5. 5-6psi while cruising, and 3psi at wot, which I heard isn't great but still kinda okay. Also I run WMO, I have been running it since August of 2012, never run more than a 50/50 blend, in winter I switched to 70/30 blend 70%kero/30%wmo, and I have now switched back to a 60/40 blend 60%#2/40%wmo, I have even ran a few tanks of pump diesel to check and see if that makes a difference, and there is none, I also have NO codes, has a good friend mechanic use his Snap-on motus to check and make sure there was defiantly no codes, and nothing.

Oh also changed out the ECM with another buddies to check to make sure it wasnt ecm and still runs rough at idle so it can't be ecm.



Please I would like some more help or ideas, no one here local has an idea, mechanics don't know nothing unless its got a code... please help, thanks in advance

 

[21skippy13]

Also to add that it runs rough the minute you start the truck regardless if its cold or hot, only when it's hot with it instantly want to idle high on its own, and it doesn't start hard, starts very easy. Again thanks

 

[Sticks]

OK, first off, Paragraphs are your friend. Makes it easier to read and identify different issues.



Now, your fuel pressure is way to low, and I am surprised your VP is not toast yet. 3psi is not "kinda OK", that's bad, and sound about right for the in-tank pump. Dodge says it's OK, but it's not. 10psi minimum at WOT. Get that fixed first. Either after market transfer pump (FASS, Raptor... ), or the combination of the in tank dealer update in combination with the block mounted OEM transfer pump.



I take it that WMO is Bio Fuel. Bio fuel is the Devil. There are no standards to regulate the quality in the US, and the bio fuel is an extreme fuel system cleaner - READ - any build up in all of your fuel system gets removed and sent down stream. Bad juju since there are a lot of lines after your fuel filter, and I am not convinced of the lubrication qualities. Bad enough they pulled the Cetane levels down on plain old #2.



Your VP44 is electronically controlled for engine RPM. It should either be at 800ish at idle or give you what ever your throttle tells it to go to. I'd bet good hard earned money that your TPS/APPS is starting to go TU. Something is telling your VP to increase the RPMs, or giving it an erratic signal. Blue Chip Diesel has a link to testing the VP44 that separates it from the PCM. http://bluechipdiesel.com/vp44diagnostichelp.html. Read it and follow the directions for testing it. It is possible that your are getting oil into the cylinders - but I don't think that I have ever heard of that giving a constant RPM. If if was a constant even flow, the PCM/VP would try to correct by defueling to get back to idle RPM.



If you perform the tests from the link provided and everything checks out OK, then your TPS/APPS is likely the problem. I'll have to do some digging to see what the tests are for that.



The PCM mounted on the left side engine block controls all the engine functions. The ECM on the right side firewall controls everything else. Few scanners can read both modules, but if there was a code in one module, the P1693 code would be present in the other. Your buddy's scanner should show the TPS values or current RPM and RPM demand. Do a search on here for re-calibrating the APPS/TPS and see if that corrects it, or at least makes a difference for a brief period. If you have a buddy with a 98. 5 to 2002 Dodge/Cummins, try swapping the APPS with your buddy and see if that corrects the issue.

 

[DavidC]

ECM (Engine control module) mounted on block. PCM (power train control module) mounted on fire wall.

Dave

 

[21skippy13]

Sorry for the one huge paragraph, yes I read through blue chip before and tested the apps and it tested out okay with an analog volt meter, and yes I changed the cummins ECM on the block with another truck and that didn't change anything. I have very minimal smoke, barely nothing, so I am hard pressed to believe there is extra oil getting into the cylinders.

WMO is just waste motor oil that I filter down through a set of oil filters, fuel filter, then run it through a centrifuge that spins it up to 2000 time stronger than gravity and removes anything bad less than 1 micron, then blend it with diesel fuel.

Like I said before all of my issues are at an idle, under any load the truck works great, but at an idle it's rougher then hell and it has 7psi not 3psi, if it was at 3 at an idle i them would believe it to be that, and for the idling high, yes I have heard that it can be caused by some other electrical source, example the computer but I tried another computer and that didn't change anything.

I was wondering if yes the low fuel pressure could have done mechanical damage to the injection pump at high speeds and then shows its face at an idle. And if that could be why I have no codes?

This has been making me pull my hair, I do appreciate all advice and am willing to try anything. Thanks again from anyone that responds

 

[21skippy13]

Sorry for the one huge paragraph, yes I read through blue chip before and tested the apps and it tested out okay with an analog volt meter, and yes I changed the cummins ECM on the block with another truck and that didn't change anything. I have very minimal smoke, barely nothing, so I am hard pressed to believe there is extra oil getting into the cylinders.



WMO is just waste motor oil that I filter down through a set of oil filters, fuel filter, then run it through a centrifuge that spins it up to 2000 time stronger than gravity and removes anything bad less than 1 micron, then blend it with diesel fuel.



Like I said before all of my issues are at an idle, under any load the truck works great, but at an idle it's rougher then hell and it has 7psi not 3psi, if it was at 3 at an idle i them would believe it to be that, and for the idling high, yes I have heard that it can be caused by some other electrical source, example the computer but I tried another computer and that didn't change anything.



I was wondering if yes the low fuel pressure could have done mechanical damage to the injection pump at high speeds and then shows its face at an idle. And if that could be why I have no codes?



This has been making me pull my hair, I do appreciate all advice and am willing to try anything. Thanks again from anyone that responds

 

[Bob4x4]

WMO is not healthy for the injectors or pump. The high pressure system should be removed and tested by a qualified fuel shop

 

[Sticks]

ECM (Engine control module) mounted on block. PCM (power train control module) mounted on fire wall.

Dave

Thanks Dave. Early morning posts, got confused waiting for caffeine to hit.

 

[Sticks]

When you checked the APPS, was that with the engine running, or just pulled and tested it? They are flaky, and may ohm out OK, but as soon as they are hooked up is when they start showing the erratic output signals. That is why I suggested to have a scanner hooked up to see what the TPS values are when running. At idle, it should show a constant reading and not jumping around.

The scanner should also show demand RPM vs actual. That will help to narrow it down. If the demanded RPM is 1300, then something it telling the VP to increase fuel delivery. Try to get your buddy to hook up to it again and let us know.

Try a WOT test. From idle, mash the throttle and hold it. The engine should go to redline (Cummins refers to this as high idle, won't hurt the engine any) smoothly with no hesitation. Watch the tach, it should be a smooth sweep. Any coughing or hesitation first points to fuel supply pressure, then possibly a dieing VP. Repeat and watch the exhaust through the passenger mirror. No white or grey smoke. A little puff of black is OK, white or grey points back to fuel supply or VP.

There might be a problem with the fuel lines between the VP and the injectors, but that usually shows as a miss that does not go away. Try cracking open one injector line at the head at a time to see if the rough idle clears up a bit, or narrow it down to a particular cylinder. Wear safety glasses, you are going to get fuel everywhere.

To verify, when you ran the Blue Chip tests, with the VP isolated away from any vehicle electronics, you still had the 1300 rpm idle and it was rough? Sorry to bounce around here, just trying to put in my head all the testing that you have done and in what order.

If you have done all of this, short of pulling the VP to have it bench tested, the only other thing that I can think of is a restricted return line from the back of the head, or an injector that did not seat properly, and fuel is seeping past the injector into a cylinder... worst case a cracked head. Maybe do a cylinder compression and leakage test. This is the one I use http://www.tooltopia.com/mityvac-mv5535. aspx, and the cylinder leakage gauge I got from Harbor Freight.

Puling a VP to have it bench tested means down time and added expense. I try to exhaust all other possibilities first.

On Edit - you don't have a programmer or chip hooked up do you?

 

[Bob4x4]

The APPS has no affect on the idle with an automatic truck... .

 

[21skippy13]

When I try a WOT test, I am assuming to do this while the truck is in park and not moving????

I did the apps test on the truck while it was running, and there was no fluctuating voltage while in ran rough and no increase in voltage when it idled up on its own.

I called Blue Chip Diesel and talked to Doug and Chip there personally, they told me to try the other ecm again and this time pay attention only to if the truck will idle up on its own disregarding that it runs rough to narrow down the idling up issue.

then they told me to do the air in the fuel test and I did and in the end result no air, I was going to call them back on Monday to give them the results, STICKS, you have been much help along with them too.

also where is this return line that is at the back of the head? is it some thing I can check, I have a hard time believing that the injectors aren't seated right only because it ran rough before I replaced the injectors but I guess **** can happen, and maybe there is a cracked head, the truck is never over 190, but I will keep trying any possible idea.

I hope to get this fixed soon, when I do I will let everyone know what they might have to look forward to if they have similar symptoms, till then I will keep you all in the loop of my test and results

oh and sticks, I did do the hot wire test which just runs the pump off 12volts and ground with no communication to the ecm (which blue chip told me to try) and it ran at the appropriate rpm but it still ran rough but at the same time kinda smoother since the engine wasn't running away to 1300 rpms.

 

[DavidC]

Thanks Dave. Early morning posts, got confused waiting for caffeine to hit.

Know the feeling, at my age now it becomes a 2 pot before doing or saying anything :-laf

Dave

 

[Sticks]

The APPS has no affect on the idle with an automatic truck... .

It would if it was giving false signals (READ - sending a signal to increase engine RPM as if the throttle was being depressed, even though there was no input from the driver).

 

[Sticks]

I had a post then my computer went TU.

Anyhow - since you have tested the VP and verified that the idle is normal and the rough idle mostly goes away, that confirms that you are having an electrical problem, not necessarily mechanical.

I still think the APPS is part of the problem. Could also be your crank position sensor or tone ring on the crankshaft (not unheard of for it to come loose), or any number of other electrical problems (something backfeeding through the ECM on the VP44 control circuit).

Try disconnecting the APPS and starting the truck. Idle RPM normal or not? It's going to throw a code and put it in limp mode, hopefully it will return to normal after you reconnect it.

The WOT test is done in your case with the vehicle in park.

I am getting to the point that I would need to have the truck in front of me and access to a DRB III to isolate your issues.

 

[21skippy13]

Okay, last night after I posted I went up to my buddies that let me try the other ECM, this time I was only concerned with the high idle, swaped out the ECM with his and started the truck, ran very rough but it did not idle up, I let the truck run for about 10 mins or so to warm back up to see if the idle would increase and it didn't. I revved the truck up too, to see if the rpms would increase and stick at high idle but they didn't.

So I put my ECM back on and started the truck and it instinitly revved up to 1300 rpms. So I guess I will be purchasing a new ECM this week. Installing it in hopes that it fixes the high idle issue, and to see what happens with the rough idle and go from there.

Do you think the apps would be causing the rough idle and to try unplugging it for the rough idle reason?

 

[Sticks]

Since you double checked with the donor ECM, and your idle issue went away, then came back with your original, then that would seem to be your problem. A glitch in the programming. You can either replace or see if dodge will re-flash the programing to see if that corrects it.

The rough idle if present with both ECMs is likely mechanical. Flaky APPS usually is surging RPMs or erratic throttle response. You can try unplugging it, it won't hurt anything.

 

[Sticks]

Side thought, probably nothing. Is your cruise control electronic or vacuum controlled?

 

[21skippy13]

Side thought, probably nothing. Is your cruise control electronic or vacuum controlled?

Sorry been busy this week, new ECM will be here Monday, and the cruise control is vacuum I believe, it has a vacuum line going to the cruise control unit, what would that have anything to do with my issues, just wondering.

 

[Sticks]

If there was a slight leak in the valve that controls the vacuum settings for the cruise, it could be what is pulling the RPMs up at idle. Like I said, probably nothing, but there is a second influence on the apps that is not the driver. If you have not already tried running the truck with the APPS disconnected, try it. If by chance the idle issue goes away, disconnect the vacuum line going to the APPS, and see if your results are the same.

 

[Bob4x4]

If there was a slight leak in the valve that controls the vacuum settings for the cruise, it could be what is pulling the RPMs up at idle. Like I said, probably nothing, but there is a second influence on the apps that is not the driver. If you have not already tried running the truck with the APPS disconnected, try it. If by chance the idle issue goes away, disconnect the vacuum line going to the APPS, and see if your results are the same.

What????
A vacuum leak from the vacuum system has no effect on engine speed. There has never been a vacuum input to the apps. You have me lost lol