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Thread: Puzzled

  1. #1
    Join Date
    Mar 2000
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    Geneva, IL
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    Default Puzzled

    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?
    Rich Phillips
    Member #27
    2019 K-2500 Crew Cab Z71
    Cedar Creek Silverback 33RL Fifth Wheel
    In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500

  2. #2
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Arrow

    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.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  3. #3
    Join Date
    Mar 2000
    Location
    Geneva, IL
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    Default

    Hi Dmaxmaverick,

    Thanks.

    Western civilization won't fall if I can't figure this out, but it does have me wondering...
    Rich Phillips
    Member #27
    2019 K-2500 Crew Cab Z71
    Cedar Creek Silverback 33RL Fifth Wheel
    In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500

  4. #4
    Join Date
    Mar 2000
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    Loyal WI US
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    Default

    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.

    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  5. #5
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
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    Default

    Quote Originally Posted by richp View Post

    ..... 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
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  6. #6
    Join Date
    Mar 2000
    Location
    Geneva, IL
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    Default

    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.
    Rich Phillips
    Member #27
    2019 K-2500 Crew Cab Z71
    Cedar Creek Silverback 33RL Fifth Wheel
    In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500

  7. #7
    Join Date
    Mar 2000
    Location
    Geneva, IL
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    Default

    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.
    Rich Phillips
    Member #27
    2019 K-2500 Crew Cab Z71
    Cedar Creek Silverback 33RL Fifth Wheel
    In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500

  8. #8
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
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    3,081

    Default

    Quote Originally Posted by richp View Post
    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
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  9. #9
    Join Date
    Mar 2000
    Location
    Loyal WI US
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    10,792

    Default

    Quote Originally Posted by richp View Post
    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.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  10. #10
    Join Date
    Mar 2000
    Location
    Geneva, IL
    Posts
    364

    Default

    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.
    Rich Phillips
    Member #27
    2019 K-2500 Crew Cab Z71
    Cedar Creek Silverback 33RL Fifth Wheel
    In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500

  11. #11
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    3,081

    Default

    Quote Originally Posted by richp View Post
    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
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

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