Question about 1999 GMC Yukon

1 Answer

Losing power I have a 99 GMC Yukon with 5.7L gas engine. No trouble codes as per my scanner. When engine is ran for about 30-35 minutes it slowly begins to cut out at 3000 +Rpms and if you keep driving it will eventually not run over an idle (800 rpm). You shut the motor off and wait 3-5 minutes, restart and it acts perfect. full strong acceleration through entire rpm range until you run it for another 30 minutes or so, it starts all over again. Plugs show it getting "flooded out". Fuel pressure is constant 60-65 psi at all times (verified with gauge attached as driven). Put tranny in neutral when it happpens and it makes no difference, not tranny (4L60E). O2 sensors are all good. new plugs, cap, rotor, wires. Acts like PCM thinks it is cold and holds injectors open too long. The temp gauge on dash does not fluctuate so I do not think coolant sensor temp is problem as it supplies the PCM as well as dash panel. Not pulling air anywhere but through MAS. Any ideas or suggestions?

Posted by on

  • lukegoubeaud Sep 12, 2008

    same exact problem even had a new transmission put in everything else is factory



1 Answer

  • Level 1:

    An expert who has achieved level 1.


    An expert whose answer got voted for 2 times.

    Problem Solver:

    An expert who has answered 5 questions.

  • Contributor
  • 5 Answers

The previous owner had removed the catalytic convertor system and installed a straight through exhaust system with "cherry Bombs" on it. I did not think this was a problem (other than noise) until I checked the codes and kept finding an O2 sensor problem on a brand new sensor. The straight exhaust was allowing the exhaust gas to flow by so quickly the O2 sensors heating element could not heat properly and maintain the temp so the motor would richen the mixture, flooding the plugs. You shut down the PCM for a few minutes and restart with a fresh set of paramaters again until the O2 sensors were called for. I installed a piece of 1.25" pipe by 12" long between the pre and post catayltic sensors to simulate the flow impedance of a convertor, reset the codes and the truck runs great. The backpressure allows the sensors to attain proper temp and stay there so the PCM can regulate the mixture as needed. I am currently waiting for the new converotors and stock muffler/pipe system to come in to my auto parts supplier so I can bring the unit back to design standards. I thought there were no new codes, but I was wrong. I did not wait long enough for the codes to go from "pending" to "set" position. I also found my scanner does not reveal "pending" codes. Time for a new(better) scanner.

Posted on Jul 18, 2008


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya Mechanic can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
click here to Talk to a Mechanic (only for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

What Does GMC trouble code 1258 signify?

Four digit codes are brand specific. For GM vehicles, code 1258 means the engine computer is in default mode for an engine overheat problem. Most performance options are limited to allow you to get the vehicle off the road or to a shop for repairs.
The engine could have been run hot, or the temp sensor may have failed.

Sep 04, 2014 | 2003 GMC Yukon XL 1500 Denali

1 Answer

Major freon leak, knock sensor codes, reduced engine power

I would say your a/c evaporator may be the culprit for your leak. What code did it give you for the knock sensor replacement? I would give it a tune up if it has been awhile.

Apr 23, 2013 | 2003 GMC Yukon XL

1 Answer

Cant locate ecm fuse

The fuses for the computer are in the box near the battery. Not sure why you need them, if you are trying to turn the check engine light off you have to clear the trouble codes with a scanner.

Feb 28, 2013 | 1999 GMC Yukon Denali

1 Answer

I have a 2002 GMC Yukon xl, every time you give gas it dies, and then wont start for a lil while, what can this be

Could be low on fuel pressure, or a problem with the throttle position sensor. But if the sensor was faulty you should have a trouble code in the computer and the check engine light should be on.

Dec 17, 2012 | 2003 GMC Yukon

1 Answer

I have a problem with my 2003 Yukon losing power and intermittent power to the radio. While driving it will just start decelerating and a light saying reduced power come on. It also hesitates to start but...

Check all fuses in your power box. Sounds like could be electrical short. Check connections and grounds to alternator and starter and battery. Also check coils, plugs etc.

Once resolved, try a can of SeaFoam from Canadian tire $12.00..put half in a full tank of gas and the other half in your oil. Do this when the engine is warm, not hot. Let it sit for 30 minutes then take it for a 10 minute drive and see the difference. Save hundreds in injector flushing. This should alleviate the hard starts.cheers.

Nov 01, 2017 | 2003 GMC Yukon XL

1 Answer

99 yukon tugs after exceding 60 mph what can it be

top gear going up hill and chuggin and losing power is usually ignition like spark plugs, wires, and or coil, rotor and cap, basic tune up stuff

Jun 27, 2010 | 1999 GMC Yukon

1 Answer


id start with a trouble code scan, if the CEl came on it logged a code, have it read and start there, on some models you can disconnect the neg batt terminal for 5 min to clear and reset the codes.

Jun 27, 2009 | 2001 GMC Yukon XL

1 Answer

Service engine light staying on

Hello tdamm...No...the service engine soon (SES) light on your yukon is not telling you to change the oil.
This is a warning light that is illuminated when there is a problem affecting the Emission system and the engines computer management (ECM) has detected it from a fault. It could be something as simple as a loose or defective gas cap. If the SES light is blinking, it's more serious....
The yukon needs to be connected to diagnostic equipment (scanner) for fault diagnosis.
You can go to autozone they will hook up an OBD II scanner to your vehicle and explain the codes to you.
Good luck...i hope this helps and will fixya up.

May 25, 2009 | 1999 GMC Yukon Denali

2 Answers

99 gmc wont start

check electric fuel pump operation ( located in the fuel tank ). Occasionally a fuel pump will burn out when running out of fuel, due to the fact the pump runs DRY for about 30 seconds till the fuel stops flowing out of the injectors, the engine quits, simultainously losing oil pressure which FINALLY shuts off the fuel pump. Sometimes TOO LATE. Hope this helps

May 01, 2009 | 1999 GMC Suburban

2 Answers

I have a 2002gmc sierra 2 wheel drive 5.3lit 8 cylinder

You need to have the computer scanned for trouble codes before you waste any more money.Good Luck.

Dec 25, 2008 | 2002 GMC Sierra 1500

Not finding what you are looking for?
1999 GMC Yukon Logo

229 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

77499 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22306 Answers

Ronny Bennett Sr.
Ronny Bennett Sr.

Level 3 Expert

6927 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides