LMM Will Not Regen

[richp]

Hi,

2009 LMM with about 128,000 miles on it. Past problems with dreaded P0087 code seem to have been cured by a mild ECM change and lift pump from John Kennedy.

I am now in Texas, having been towing my 12,000 pound fiver from Illinois in temps reaching 105 degrees. But my regeneration has gone haywire.

First, it went 750 miles without regenerating, and was stuck at 34 grams of soot. So I used my Edge Insight CTS2 to command a regen. No problem. Then, the next day, it built up to 34 grams again very quickly and stayed there. I tried a manual regen that evening, and it would not do it. Twice.

Today, I got to a total of about 750 miles stuck at 34 grams, stopped for the day, and when I restarted it in the campground, it gave me a dash message about servicing the exhaust filter, and the Edge showed 43 grams of soot -- the trigger amount as I understand it.

Tried a manual regen, it ran about 10 minutes, dropped the soot to 38, and stopped. A second attempt did not work at all. Two road runs without the trailer failed to start a passive regen, and soot stayed at 38.

I am at a loss to know what to do, and hope the expertise here can get me straightened out.

Thanks in advance.

[richp]

Hi,

Got it to fully regen just now, but it took three consecutive tries.

Any one have an idea why it would act this way?

[More Power]

Rich, Do you believe the truck should regen when towing heavy in hot weather? Has it regen'ed in similar conditions sometime in the past?

[richp]

Hi Jim,

I just installed the Edge Insight CTS2 a few months ago, so I don't have solid comparative data. Previous to its installation and the work John did, regens were totally transparent when towing. I rarely noticed the Banks analog EGT gauge jump up.

We had similar sustained heat in Page, AZ a few years ago, with no problems towing this trailer. I guess I assumed the elevated EGTs associated with towing kept it cleaned out. But watching the Insight, I sure got a different picture now.

To be clear, at this point, I don't associate this with the relatively slight ECM change John made to help with the P0087 issue. I trend in my thinking toward the truck's age and mileage.

But it is a puzzle. It surely is not normal to have soot build to 34 while towing 12,000 pounds on interstates, then stay there unchanged for hundreds of more miles. Neither can it be normal to have to manually command a regen three times to finally get to zero soot.

[richp]

Hi,

So here is the next data set.

Regenerated manually to zero soot yesterday. So today a no towing excursion.

I did 120 miles on mostly interstate this morning and soot went to one.

The next 115 miles was on essentially the same route returning, and soot goes to four.

EGT numbers were sub 900 the entire time. Pre DPF temps worked in and around the 550 to 600 range.

So a couple of days ago I go 750 miles while stuck on 34 soot for hundreds of miles towing. Today, with very low engine load, I do one third that distance and only accumulate a small fraction of that soot.

Is there somewhere I can get a complete explanation of how this DPF works on an LMM, and which might explain what I am experiencing?

[More Power]

… Is there somewhere I can get a complete explanation of how this DPF works on an LMM, and which might explain what I am experiencing?

Subscribers have access to the following link, which describes the operation of the emissions system.

https://www.thedieselpage.com/members/duramax/2007LMMEmissionsc.htm

[richp]

Hi Jim,

Thanks for pointing that out -- good read.

Now if I could just get to the second element of my question -- why it has been acting the way it has on this trip when towing. As of today, I am up to 400 miles of mostly high speed driving (not towing) here in the Austin area since that forced regen, and it is sitting at 9 grams of soot.

Seems fine, right? Plus, the P0087 problems from earlier in the year seem to be fixed. But this Sunday I am headed back north, and I sure would like some clues about any way to avoid the regen anomalies I experienced coming down.

[DmaxMaverick]

Just thinking out loud, but one tank of poor quality fuel can cause issues with the DPF. Fuel volume consumed compared with other sensory data may cause a logic issue with the PCM, in addition to excess soot.

Also, fouled or failing sensor(s) can cause similar issues. Once a regen is commanded (auto or manual), the PCM anticipates a specific response in sensory data. If a sensor is fouled or failing, it may cause the regen to abort, absent the correct sensory values. If the issue repeats X number of times, it may also force a default mode (warning, reduced power, then a countdown to shutdown). This happened with our 2014 Cruze Diesel when one EGT sensor failed. The sensor didn't fail entirely at first, but was sending erroneous values the PCM didn't see it as a fault until the math didn't add up. The sensor was replaced once, and the problem repeated some time later. A recall was issued and an updated sensor fixed it for good.

[cabletech]

I had a 2010 LMM that had the same issues. It turned out to be a problem with the diff pressure sensor. I replaced the sensor and the lines to it. I don't know if the sensor was bad but the soft line that hooked to the sensor were rotten. It fixed the problem.
FYI it should go into regen at a certain number of miles no mater what (not sure what it is for the LMM).
For me regens seem to be more often on summer fuel. My L5P goes over 800 miles between regens in the winter but only 500 to 550 in the summer. All of this is empty truck and about 80% highway at 75mph.

Also I have a good LMM diff pressure sensor you can have if you want it.

Jay

[richp]

Hi,

Thanks for the additional info folks. A lot more to ponder.

It did a spontaneous regen last nite in city traffic (between 440 and 450 miles since last regen), with only 9 grams of soot at the start.

I wondered about bad fuel and oddball sensor performance as well. Fuel from major truck stops on the way down; 5 percent bio here in Austin, according to the label on the pump.
.
I have the pressure differential reading available to me on my Edge Insight, and have been watching it every now and then. I will start paying attention to it when I start towing back north on Sunday. Anyone have thoughts about what numbers I should be seeing under load and no load conditions when soot is within normal range?

Jay, thanks for the offer. I may contact you separately about that after I get home.

[richp]

Hi,

OK, final trip report and some questions.

Got home after about 2,500 miles of towing the big fiver. The Kennedy changes seem to have worked pretty well -- only two quick sequential P0087 codes while towing up a long hill. Interestingly, they happened during a regen on one of the cooler days, but were cleared nicely on the fly by the Edge Insight. A great deal of the towing was in 95-105 degrees during the Texas heat wave, so I am pretty satisfied overall.

I am still puzzled by several hings.

1. What is the relationship between the PSI differential and regeneration?

2. The extra fuel is injected pre turbo in an LMM. Why is it I see pre DPF temperatures (way post turbo) that are higher than the pre turbo EGT readout?

3. Why is soot accumulation non linear? I can go 100 miles after a regen and accumulate only 2-3 grams of soot, in the next 100-150 miles see it grow to 30-35 grams, and on at least one occasion it stayed in the mid 30s up to 750 miles after the last regen.

Just trying to understand the operation of this thing a little better, so thanks in advance for any further commentary.

[DmaxMaverick]

Hi,

OK, final trip report and some questions.

Got home after about 2,500 miles of towing the big fiver. The Kennedy changes seem to have worked pretty well -- only two quick sequential P0087 codes while towing up a long hill. Interestingly, they happened during a regen on one of the cooler days, but were cleared nicely on the fly by the Edge Insight. A great deal of the towing was in 95-105 degrees during the Texas heat wave, so I am pretty satisfied overall.

I am still puzzled by several hings.

1. What is the relationship between the PSI differential and regeneration?

The DPF doesn't actually weigh the soot. It's calculated from the sensory values. Any variation in sensory input and physical conditions can skew it, but should only be slight in the grand scheme.


2. The extra fuel is injected pre turbo in an LMM. Why is it I see pre DPF temperatures (way post turbo) that are higher than the pre turbo EGT readout?The fuel is injected "post combustion", during the exhaust stroke. Meaning, the exhaust and additional fuel is sent downstream "wet", and is further burned progressively prior to the DPF. The fuel combustion in the exhaust stream is far different, and much slower, than the instantaneous event during cylinder combustion. The EGT may actually drop a little during the process, but may be so minimal it won't be measurable or noticeable at your gage resolution.


3. Why is soot accumulation non linear? I can go 100 miles after a regen and accumulate only 2-3 grams of soot, in the next 100-150 miles see it grow to 30-35 grams, and on at least one occasion it stayed in the mid 30s up to 750 miles after the last regen.

Just trying to understand the operation of this thing a little better, so thanks in advance for any further commentary.Soot accumulation isn't linear. Many factors change the rate, such as real-time EGT, load conditions, relative humidity, fuel quality, aftermarket programming, and general health of the system, although it should not swing so wildly as yours. I suspect you may have a sensor issue. Failing or fouled sensors, temp and/or pressure, can cause the issues you've seen. Common 02 sensor cleaning methods may be helpful. Cleaning kits and home/DIY methods are available. I suggest starting there if the issues continue.

[richp]

Hi Dmaxmaverick,

Thanks -- that is very helpful.

On the non linearity, I guess I was expecting that watching soot numbers during a full run of towing on all interstates would look different. But tank after tank, day after day, the pattern I described was the norm.

I also would have expected the psi differential readout would somehow track regen status, but it didn't seem to.

I will look into the sensor situation. Any suggestions on the most likely culprit, or should I just start at one end and work toward the other?

[DmaxMaverick]

I would start at one end and work all the way through. If some sensors are soot-fouled, it's likely they all, or most are. Don't use high pressure/velocity fluid or air on the sensors, such as blasting them out with 150 PSI shop air. If you use the aerosol O2 sensor cleaner, let them drip/air dry after a thorough flushing. Some DIY methods suggest using a solvent sprayer (that uses shop air), but I think it's too much. Air brush sprayers work well, though.

[richp]

Hi Dmaxmaverick,

Got it. Thanks very much.

[Kennedy]

I would bet money that this is programming related. I am working on an ECM core buy that should have me in very good shape on LMM's. I can whip up a test file and send you an ECM or two to test once I've secured the shipment.

[richp]

Hi John,

Sign me up.

Your lift pump and program changes to date have been a great improvement. Anything more will be icing on the cake. If you want more detail, give me a call and I can go over some of the numbers I jotted down as I went along.