Question about 2002 GMC Yukon XL

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2002 GMC Yukon Problem

Normal 0 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} Here is my situation:
My girlfriend’s father has a 2002 GMC Yukon XL that isn’t running so great.

Characteristics: When you start it up, it will rev rather high (2500rpm or higher) then run rough and choppy until warmed up. After that specified time it goes away. More definite characteristics are seen the colder it is.

My Thoughts: I’m fairly knowledgeable with cars, and own a fairly heavily modified LS1 Trans Am. My first impression was an intake manifold gasket due to the fact that is runs fine when warm (my thought was the gasket would expand).

Before they contacted me, some other guy did a whole lot of expensive work and didn’t solve the problem. From my understanding, he swapped spark plugs, injectors, and a fuel pump. Granted my GF’s father lacks knowledge on vehicles and terminology (and his English isn’t very strong), so maybe I misunderstood him but by his descriptions that’s what I deciphered.

So all in all, here are my questions that I have.

1) Does my theory seem about right? If not, give me your input.

2) Since it is in “Yukon XL” trim it has a 6.0L engine correct? Are the intake manifold’s even different between the 5.3/6.0 engines?

3) When I researched I kept running across a “lower” and “upper” gasket. When buying a replacement is there something I should know? When I went to a dealership they told me it would run about $116, sound about right?

4) I’ve swapped intake manifolds on my LSX motor before, is there anything special to watch out for?

Sorry for my noobness in the GMC Yukon Category, thank you for your time.

-David


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You has a vacuum leak on the engine.


In order to troubleshoot this, you must start with a clean engine wipe down.


The major offender parts are


air intake gasket on the manifold

air tube after the mass air flow sensor

rubber seal under idle air control IAC motor

===

Warm up the engine for 15-20 minutes (LEAVE THE engine at idle) then spray a little Barmen carburetor clear on the potential air leak location (ONE AT A TIME) and listen for a surge in rpm.

If the engine speed go higher that's mean the carburetor cleaner (ADDITIONAL FUEL) got into your engine and that's the gasket you need to change.

There may be multiple leaky spots so take your time and check all rubber gaskets,sensor and hose that are lead into the intake manifold.

When you finish fill up with one tank of Chervon to clean out the injectors.


Try to get a toque wrench and tighten ever bolt on the valve cover back to specification. If you can not get hold of one then just give each bolt a gentle 1/6 turn.



Please post more information after your inspection.

Posted on Aug 31, 2009

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Replace the "knock sensors" under the intake manifold. They are water collectors and will corrode, then fail, and will cause the symptoms you described. Check to see if they have been replaced as they are not the easiest to get to. Hope this helps

Posted on Jul 06, 2009

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Do you have any engine lights on?if so have it tested with a code tester.it should tell you the trouble codes and what they mean.it may be the throttle positioning sensor.

Posted on May 17, 2009

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