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97 GMC Suburban with power problem @ high altitude

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by alosier, Dec 2, 2011.

  1. alosier

    alosier New Member

    I am new to the GMTruckclub forum, and forums in general. I hope to gain insight from other GM/Chevy owners, and hopefully offer some as well!

    In July, I bought a 1997 GMC Suburban SLE with 152K miles. Love this truck. It was well cared for by the previous owner, but in need of some routine maintenance. I've spent nearly $2000 on updates and repairs--everything from tires to a water pump.

    Recently, I took it up to Vail--about a two hour drive from Denver. It performed perfectly going up but on my trip home, I could not get it to go above 45-50mph going up Vail pass, nor up to the Eisenhower tunnel. At times, it felt like a tranny issue. I'd accelerate and the RPMS went up to 3-4000 but the vehicle did not respond. Other times, it felt like it was starved for fuel. I floored it and there was nothing--no revving, no response from the vehicle. The 'service engine light' came on but as soon as I got past the tunnel and to lower elevations, it was fine. I should note, it "ran" fine the whole time too... there was no puttering, stalling, etc. Since then, the service light has gone off by itself and driving around town in Denver, I cannot get it to repeat the issue.

    A technician at Advanced Auto Parts as well as my mechanic ran a diagnostic and O2 senors (1 & 2) were the culprit. Problem is, both of these have been replaced since I bought the vehicle in July. My mechanic told me the codes showed that it was running lean, making him wonder if it was a fuel pump issue. Coincidently, it was running too rich back in July, which prevented it from passing emissions, which is when one of the O2 sensors was replaced to make it pass.

    Curious if anyone out there has experienced similar problems and has advice. I trust my mechanic but I cannot help but thing this has something to do with altitude given the locations where it started acting up.

  2. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    A fuel pump issue could be the cause here. The only way to really diagnose it would be to put a fuel pressure gauge on it when it is acting up and see what the fuel pressure is doing (which is kind of hard to do if it isn't acting up anymore). I might put a gauge on it anyway just to see what it is doing now, and see if there are any indications of fuel delivery problems.

    Your symptoms remind me a lot of what mine did when we were up around Yellowstone. when I finally tracked it down, the problem was as simple as a battery cable coming loose. I'm not entirely sure how, but that loose connection must have been enough disruption to the PCM's/fuel pumps/coils/or something in engine management to cause it to lose power in a similar way to what you are describing.

    Anyway, those are a couple of quick and easy things to check.
  3. Dantheman96

    Dantheman96 Member

    Mine did this last year on a road trip to Nashville. I had 8 people in it and tons of luggage. It hasn't done it since though. I didn't get a SES light. All I can figure is maybe the fuel pump gets over worked in certain conditions and cant keep up with the demand.
  4. TRPLXL2

    TRPLXL2 Epic Member 5+ Years 1000 Posts Platinum Contributor

    Okay this is going to sound retarded I know, but bear with me.

    I would suspect the MAP sensor, It is actually affected by barometric pressure outside. On my Firebird forum there was someone who drove there Firebird up into the mountains on vacation, and every time they would get to a high elevation the car would start doing all kinds of crazy crap. They hooked a scanner to it while up there, and the MAP sensor had took a crap. Weird I know, but I will never forget that story..

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