A real head-scratcher

[ccurran]

I have a 2005 2500HD DMax with ~38k on it. A little more than year ago (May/07) it started what I can best describe as a "rough idle" problem. What I'm calling a "rough idle" is this: Sitting in PARK, the engine is running real rough - as if a plug wire or two is missing from a gas engine. The truck is physically shaking/rocking from side to side. To visualize, the tip of the radio antenna is moving back/forth six to eight inches. If you go back to the exhaust, it sounds like it's under water (those of you who visit boat ramps will know the sound - glug-blub-glug-blub - it's not how a normal running engine sounds). No obvious black/blue smoke.

Conditions:

1. Cold start: sometimes the truck would start/run fine on cold startup, other times it would start, but idle real rough (as above).

2. After driving at hwy speeds (~60mph) when pulling my travel trailer (~6k lbs). I would pull off the interstate and once I stopped at the ramp the truck would start jumping/bumping as above.

These two conditions started off as rarely happening, progressing to darn near all the time by Nov/07. The dealer first replaced the fuel filter (at my cost), when that didn't fix it flush injectors (at my cost), then they did some wiring harnesses work, egr swapped, new flash to the truck computer, injectors swapped, etc (all warranty). None of this fixed it. Note that all this time misfire codes were being thrown.

By Sept/Oct 07 the truck would fall into this rough idle problem after normal in-town driving with no load. Drive around until it warmed up, pull up to a stop sign/light and hang on - it felt like you were on a bucking bronco. One issue that has compounded this is that (of course) the truck never exhibited this problem at the dealer. I do understand that it's darn near impossible to diagnose a problem you can't witness...

By Nov/07 I had found a condition that I could repeat at will: drive around a little until the truck warmed up and it would develop a very slight rough idle when at a stop light or in park. If I "gunned" the engine at that time, it would kick the truck into the violent shaking/jumping as described above. With this new found knowledge I went to the dealer, sat in the service bay and repeat the problem. The darn truck was about to walk away sitting in park it was running so rough.

I grabbed the (one) diesel tech they had and brought him out to the truck (while in the rough idle state). To paraphrase, he didn't know what the problem was, he'd already changed out whatever parts GM would allow him to, and further speculated that it was my motor mounts. I've seen broken motor mounts - no freaking way. He wouldn't hook any device to the truck to help determine what was going on - come back next week I was told. Having purchased three trucks and a Tahoe from this dealer, I was very disappointed that I was turned away with an obvious and serious problem.

Later that day I'm driving through a parking lot and the truck shuts down. DEAD. It'll crank, but no start. Fuel is pouring on the ground. I'm not a mechanic, but even I know that's not good. I have the truck towed to the nearest dealer (not the one I've been going to) and they find that the fuel filter gasket has been blown out. They put on a new filter, replace a water in fuel sensor, and send me on my way.

The truck runs fine for about a week, then the faint rumblings of that rough idle start to show up. Very slight and rare at first, but it has progressed along the same lines as above. It's getting worse, and more frequent. I very much suspect that whatever blew that fuel filter out last time is coming back at me and I can't afford to have it happen when I'm 300 miles from help.

Someone else tells me that the water separator is leaking air, the leak got so bad that it finally blew the fuel filter out. But it's all greek to me...

I could use help with 1) what the heck this problem might be, but more importantly, 2) a diesel tech in the Tampa/Brandon FL area that I can take this creature to. I've lost faith in the local dealer, and need a mechanic that will do more than plug up a computer to my truck. I need a mechanic that will go looking for a vacuum leak, or a manifold leak, or whatever the heck is going on here.

tia,
Chris Curran

BTW: 100% stock.

[madmatt]

exactly what codes are being set????

[ccurran]

exactly what codes are being set????

P0300, P0302, P0305 (wiring harness fixed)
P0401, P0403 (replaced egr)

There is various other chatter during this time about fuel rail pressure, injector flow rates etc. The description of work by the dealer who fixed it after the break down:

"Fractured water in fuel indicator separator sensor"

It ran exceptionally well right after the above part was replaced/fixed. It took about week, maybe two before the ghost started showing back up.

Also, if it means anything, I don't run any fuel additives and always buy from the local Hess station (~8 year old station).

EDIT: Oh, and I'm religious about oil/fuel filter changes. Oil at 50% (via DIC) and fuel filter every 10k - always at the dealer. All work/service has been by the dealer. Even tire rotation. *Everything*.

[Mark Rinker]

Where do you get your fuel?

[ccurran]

Where do you get your fuel?

Local Hess station.

[Mark Rinker]

I'd switch stations - it sounds like you are getting water in your fuel.

[Jake99Z71]

Have you tried running any fuel treatment?

Did the dealer replace the FPR? This is what it sounds like to me. I've replaced a few on the LB7, have not heard of many going bad on the LLY.

[Hook_'em_Horns!]

I too have had the similar issue, on occasion (today actually), maybe a half a dozen times over the last 6 months. (LLY)

It was not as violent as you described, nevertheless it was a shock to have the truck rocking left and right, similar to a Big-Block gasser with bad sparkplug wires, just firing on a few cylinders. Most times it is on first start in the morning (70+*), but at other times the engine was warm.

Only in PARK and at idle, it goes away and the rest of the day is spent pulling heavy, on grades, in traffic, on up to and past 100* out, on the same tank of fuel with no other issues or occurrences.

I pulled the Dip Stick this morning after warm-up (20 miles pulling), and it looks like my oil level (2200 miles since changed) is on the high side. INJECTORS??

No warnings are showing but I’m going to check with my GM Diesel guy to see if they can pull any codes quick, no reason to drop it off without a consistent showing. I'm lucky here, we have some quick, on the ball techs with in and out service in half a day, no appointments.

[ccurran]

It was not as violent as you described, nevertheless it was a shock to have the truck rocking left and right, similar to a Big-Block gasser with bad sparkplug wires, just firing on a few cylinders. Most times it is on first start in the morning (70+*), but at other times the engine was warm.

Only in PARK and at idle, it goes away and the rest of the day is spent pulling heavy, on grades, in traffic, on up to and past 100* out, on the same tank of fuel with no other issues or occurrences.

Mine acted the EXACT same way - right before it blew the fuel filter gasket out. Let us know if you find out anything...

In the FWIW, category: A friend who sells to industrial diesel groups suggested I try a bottle of Stanadyne Jr. I did, and WOW. BIG improvement. It still "chuggles" a bit, but I'm starting to think it can't be a leak or vacuum related if this stuff improves the situation....

cheers & beers....

[ccurran]

Have you tried running any fuel treatment?

Did the dealer replace the FPR? This is what it sounds like to me. I've replaced a few on the LB7, have not heard of many going bad on the LLY.

Only recently - Stanadyne Jr, and it's vastly improved my problems with rough idle....

[ccurran]

I've come across an interesting new "condition": the clock is resetting to 12:00 when I start the truck....

This has been happening intermittently for a few months, progressively getting more and more frequent. One thing I couldn't remember to do at startup was to turn the key on, check the clock, then start the truck - I always did it in one motion so I never kinew if the clock was buggers (again) or is the voltage dropping due to the engine crank.

Well, I remembered this morning. Turned the key to "on" and the clock correctly read 8:29. Crank the engine and the clock resets to 12:00.

I'm guessing that I have a weak (or bad) battery or two. I'll have them checked later today. The question is this: Could a weak battery cause the rough idle problems I've detailed above? I know that in a gas engine a weak electrical system can cause spark problems, but I got no spark, so.... but could low voltage cause other problems in other subsystems of this hitech complicated diesel beast? The rough idle problem has been getting worse - is there a correlation here, or two separate problems?

[Johnny Cetane]

I would say you have 1 or 2 battery issues for sure or possibly an ignition switch going south. Get the batts load tested and check all power and ground cable connections from the batts to the motor/frame.

With the amount of electronics on these engines I could see a battery causing an issue. I doubt it's your cause but it's possible. I've seen low batts and loose battery cables raise holy hell with the GM gassers. PCMs and BCMs need good continuity.

[ccurran]

Well, well, well. I changed my batteries out three weeks ago and now the truck runs like new...


I would say you have 1 or 2 battery issues for sure or possibly an ignition switch going south. Get the batts load tested and check all power and ground cable connections from the batts to the motor/frame.

With the amount of electronics on these engines I could see a battery causing an issue. I doubt it's your cause but it's possible. I've seen low batts and loose battery cables raise holy hell with the GM gassers. PCMs and BCMs need good continuity.

[More Power]

I'm glad you finally found the cause of the problem. Generally, it's recommended to solve whatever problems you can identify (such as clock/battery/cable issues) before troubleshooting the more mysterious ones. Because these trucks are all electronic, any electrical problems could result in a wide variety of wierd symptoms.

Jim