Engine/Transmission (1998.5 - 2002) Intermittent drop/stumble @ idle ? ? ?

[Joe Mc]

Just started a few months ago. Has only happened 3 - 4 times that I recall. My drive is 16 miles with the first 6 or 7 at 35 - 50 mph having only an occasional stop for short traffic lights, then a 3 - 4 mile stretch at 50 - 60 mph, afterwards I'm in light to medium traffic 40 - 50 mph with frequent traffic lights, with 1 - 2 min wait times. Usually after the 1st or 2nd stop, while waiting for green, I'll hear a little drop/burble in the idle, which is cured by a slight increase of pressure on the go pedal - then smoothness returns? Then this doesn't happen again - until you've almost forgotten it ever happened at all. Keep in mind this only has happened 3 or 4 times in the last two months and usually when it's below 35 - 40*.

I'm wondering if it's the grids kicking in? My thoughts on this are: after running and up to operating temps, then coming to these 1 - 2 min wait times the incoming air + engine idling brings in cold air - then the IAT says "hey, that's too cold, time to heat things up a bit"? Does that sound possible?

Another possibility, fall 07 I had Smarty installed and removed by a fellow TDR member just to get the updated software, included the high idle / 3 cyl idle feature not in the 99 stock software. Prior to this (fall 07) I never had this drop/stumble, is it possible the high idle is trying to kick in and being overridden by ???.

Last possibility, VP trying to tell me something? To my knowledge it is original (bought truck w/75k, presently @ 173k) no power mods added until trans was DTT'ed around 139k.

Be reminded this drop / stumble never happened before and only has happened 3 - 4 times within the last 2 - 3 months.

Not overly concerned at this point, just looking for a possible answer to the big "why is this happening" question? I'm familiar with the "usual" VP antics when they fail; just dies, won't start, hard start, dead pedal, and etc. But, I've never heard anyone mention what I'm experiencing - ever?

I forgot to mention - no codes or check engine light.

Sorry so long, appreciate any reply/ideas.

 

[mhenon]

Joe, Take a peek at your battery voltage next time it happens. If it's the grid heaters. . voltage will drop noticably.

That little hiccup sounds like mine just before the VP went south. I didn't check for codes for a few months as it happened so seldom. Sound familiar?

Mike

ps: you might want to have your battery tested too.

intermittent low voltage to the ECU might do something weird like that

 

[blacksheepdiesel]

The ecm should keep the idle rpm at a set level regardless of any load on the engine from the alternator. The heater grids kicking in will cause a slight dip in rpm and then back to the preset level, you shouldn't have to press on the accelerator. I doubt the grids are kicking in when the engine temp is near normal operating temp.

The 3cyl/high idle feature will only work on the auto when the trans is in P and maybe N with the accelerator in idle position.

My vote is for an ailing APPS or VP, either one could be the culprit. With that many miles (if original) on the VP I would say it is time to find who you want to buy it from and be ready to pull the trigger. But who knows? It could last another year before exhibiting symptoms that become intolerable.

Godspeed,
Trent

 

[Joe Mc]

Thanks for the info, I'll start stashing some pennies . . .

 

[VolsFan]

my VP did the same thing when it was replaced the 2nd time. The 1st and original one was totally my fault, but the 2nd one was some flaw in the pump that was amzingly covered under the 1 yr warranty through the diesel shop I deal with, good bunch of guys. It started out with the symptoms you describe, very few and far between, then it got really bad where it would just misfire at idle and shut down while at a stoplight. One good thing about getting a VP today from what I understand is that they are being built more reliably, as in diaphragms and such that are not as prone to cracking, and they have come down a little in price.

 

[NavyDoc]

Ijust bought a used 01 2500 with only 36K on it. I have put 2K since I got it about a 3 weeks ago (1200 on trip back to NC from St Louis) and my truck has started doing this same type thing. Mine is running fine sometimes and others it does this sputter, idles down, and off. I wait a 5-10 seconds and it fires back up again and seems to run fine for a while. I changed the fuel filter - still doing it. Now more often and showing a 1693 code when I do the ignition switch thing that I learned about on here, then it says DONE, no other numbers. Going to try to pull into an Advance auto later this PM to see if they can read any other codes.

I did also notice some fluctuation in the voltage meter while running, so I am hoping all this may be is a bad set of battries and alternator, as the truck only got driven about 3K miles over the past 3 years.



Anybody got any further input for me, I'd be obliged as I am new to Cummins by only 3 weeks. Thanks a bunch.

I'll post when I get some more info later on tonght.

 

[blacksheepdiesel]

Hey Doc,

Glad ya got the truck! Hate it is acting up.

Definitely check those batts real good. Take them to a real battery shop and let them decide.

If that is not it you must put on a fuel psi gauge if it doesn't have one. If fuel reads above 5 psi at all times you are good there. Then we'll look at the APPS and then the VP.

Godspeed,
Trent

 

[NavyDoc]

Just ran an OBD checker and got a code from an earlier sputtering episode this evening and got an 0230 code, which said fuel pump malfunction - I was going 4 mph when the "freeze" code occured. The ECM records an event in this way (as I have learned tonight) which it can do without registering a CODE or check engine light. So any of you out there that are experiencing these type problems, you may have a "code" in there without an real indicator if all you do is do a code check with a basic reader. I got a good unit from Advance Auto Parts that can do real time readings and look at these "Freeze" episodes recorded in the ECM - my turck did not show a code or light a check engine light at any time - just FYI.

Blacksheep, thanks for lookin out for us new guys, will look forward to hearing your thoughts on some of my upcoming goodies - found a good diesel shop in SC that I am going to go to next week for some upgrades...

Thanks again.

 

[blacksheepdiesel]

Doc,

Good for you, a great diagnostic tool! You will need to compare the code you pull with the 24v code list as it is specific to our engine while the ones in your reader are generic. Go to the "24V code list" in the "24v engine and transmission FAQ" which is found at the top of the "24v engine and transmission forum".

The 0230 code shows the lift pump circuit is out of range. If you do not have a fuel psi gauge yet I would not drive the truck again until you do. The engine will run with a dead lift pump which will sooner than later kill the injection pump. If you find your pressures are low I strongly urge you to consider the AirDog which is a huge improvement over the factory POS. If your truck is still under warranty DO NOT let a dealer fix this problem because they will only make it worse by installing an in tank pump which is worse than the stock one. PM me for a dealer contact for AirDog.

Godspeed,
Trent

 

[Joe Mc]

To clarify what's going on w/mine: when this little change in idle happens placing my foot on the go pedal is more reactionary than anything else. I place my foot there a few seconds and when remove it all is well?

I checked the batteries Sunday, after the truck sat from Wed night, before starting both read 12. 3V. I started the truck and immediately checked then 14. 7V each, as the grid heater came on they would drop to 13. 4V and go back to 14. 7V after the grid went off. Checked both batteries w/grid cycling on then off. Also, plugged the OBDII in and no codes = passed. Saving money anyway . . .

 

[NavyDoc]

Joe MC,



I can tell you that when I ran the diag tool under a regular "code check mode" it also did not show any codes or record a significant event to trigger a check engine light, but there is a mode where you can look at the ecm which freezes info on a transient event that is still a "code" and will point you to a potential or real problem. Mine showed a lift pump malfunction after a sputtering episode, but to catch the "freeze" code info in the ecm, you have to look right after the driving trip in which it happened or without turnng off the ignition, or hook it up and let it read real time.

The ECM seems to store the most recent trip info, but only of the last drive. This seems to be the recording method if the ecm deems the hiccup not significant enough to register a true "code" or trigger the check engine light.

Just food for thought, as I was fooled this past week while trying to figure mine out and initially got NO CODES - but they were in there!

 

[Joe Mc]

Thanks for the tip Doc I'll stow the OBDII in the truck and the next time it happens I'll hook it up before shut-down once I get where I'm going. Interesting stuff.