Puzzled

[richp]

Hi,

Setting the scene: Returning to Illinois from Quartzite towing about 13k of fifth wheel. Almost 114 k miles on truck. Limp mode outside Oklahoma City, with fuel filter message. Changed filters. Repeat limp and message hundreds of miles later, near Joplin, MO. Both times event started while pulling a hill. Got to dealer and they replaced collapsing fuel line. Problem solved.

But here is my question. For the thousand or so miles before the first problem, I had begun to notice my EGT was reading a bit high -- at times maybe 100-150 degrees more than normal. So I was babying it, at first thinking I had got some gas-contaminated fuel, and then becoming more and more puzzled as I looked at it.

Now here's the kicker -- after the fuel line was replaced, the EGTs returned to normal for the rest of the trip home, including quite a few big rolling hills in Missouri.

Which finally gets to the question. Since I am reluctant to believe in coincidences like this, what connection is there between these two conditions?

Any thoughts?

[DmaxMaverick]

That is puzzling. There may be 2 possibilities. One is the PCM adjusting other parameters to manage the perceived "filter" issue, which may cause the EGT's to rise with timing, volume and dwell adjustments. The other is more simple: Air. A collapsed line may allow (more) outgasing of the fuel. Air in the fuel will delay/retard combustion timing and combustion dwell, despite the PCM's actions. The PCM doesn't directly compensate for air in the system (as there should be none).

This doesn't take into account natural possibilities, such as the climate. Temperature, air density, and/or humidity can effect efficiency and performance. A greater level of personal attention can also lend to a perceived change, as well.

[richp]

Hi Dmaxmaverick,

Thanks.

Western civilization won't fall if I can't figure this out, but it does have me wondering...

[Kennedy]

The ECM sees that it is having difficulty maintaining target fuel pressures and tells you to change fuel filter. The filter(s) may or may not be bad. It could also be mechanical or a combination of the two In the meantime pressures are running below target so the ECM extends the pulse to deliver requested amount of fuel in a longer injection event.

This is why fresh filters and lift pumps are so important.

Knowing the before and after restriction numbers would also be telling.

http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest1.gif

[arveetek]

..... hundreds of miles later, near Joplin, MO....

You were in my neighborhood! I assume you were traveling down I-44. I live just a short distance from Joplin, and work in Carthage, just off exit 18B on I-44. Glad you got it fixed and made it home safely.

Casey

[richp]

Hi Casey,

It limped out on me on the Interstate, about 25 miles south of town. I hobbled north, got on 44, and dropped the trailer at the KOA at exit 4. The next day I had Roper dig in on the problem. A very good dealer experience, I might add.

Best part of the whole thing was the excellent Mexican meal at El Vaquero!!!

Have a good one.

[richp]

Hi John,

The off-spec vacuum numbers they got pointed in the direction of a fatigued hose, which made sense given the age of the truck. And replacing it sure cured the problem.

This business of the elevated EGTs normalizing after the change was what caught my eye. The longer injection event scenario seems a plausible explanation for them.

Thanks.

[arveetek]

Hi Casey,

It limped out on me on the Interstate, about 25 miles south of town. I hobbled north, got on 44, and dropped the trailer at the KOA at exit 4. The next day I had Roper dig in on the problem. A very good dealer experience, I might add.

Best part of the whole thing was the excellent Mexican meal at El Vaquero!!!

Have a good one.


I've never eaten there! I suppose I should probably try it out. I'm glad you had a good experience with Roper. They have several dealerships and town, and have a good reputation.

Casey

[Kennedy]

Hi John,

The off-spec vacuum numbers they got pointed in the direction of a fatigued hose, which made sense given the age of the truck. And replacing it sure cured the problem.


Thanks.

For now. P0087 will return. I don't want to sound too negative, but I deal with this on a daily basis. 130-160k seems to be the most common range, but I get some as early as 70-90k and some as late as 200k+ but it seems it always comes a knocking.

I see all the collapsed hose comments but have never seen it first hand. That OE cloth braided junk is actually pretty firm until mechanically compromised. That and adding a lift pump increases the pressure inside to greater than atmosphere preventing collapse.

[richp]

Hi Casey,

I actually went to the other GMC dealer first, because it was close to the northbound interstate exit.

But I was treated so shabbily by the service writer -- ignored me when I first sat at his counter, grumpy, made remarks that made it sound like he was so busy that I was a nuisance, etc. -- that I walked out.

Roper treated me just the opposite, and I made a point of telling the service manager how satisfied I was.

FWIW.

[arveetek]

Hi Casey,

I actually went to the other GMC dealer first, because it was close to the northbound interstate exit.

But I was treated so shabbily by the service writer -- ignored me when I first sat at his counter, grumpy, made remarks that made it sound like he was so busy that I was a nuisance, etc. -- that I walked out.

Roper treated me just the opposite, and I made a point of telling the service manager how satisfied I was.

FWIW.

Thanks for the information!

Casey