99 Yukon Running Like Crap Intermittently

[FORKLIFTTECH]

Hey Guys,
Recently My 1999 Yukon 5.7L 4wd(102,000 miles), Started Intermittently Hesitating While At Light Throttle Or Shifting Between 1-2 And 2-3. It Only Does It Intermittently, And Does Not Matter If It Is Warm Or Cold. If You Floor It, It Comes Out Of It And Runs Good. But Then Goes Right Back To Running Like Crap. It Never Threw A Code Until Today Which I Have Not Yet Checked. Any Ideas?

Thanks
Todd
Bend, Oregon

 

[Sepiroth]

Have the code checked, then try back here with the code the PCM threw k.

 

[FORKLIFTTECH]

P300 Multiple Random Misfire

 

[73shark]

Check your fuel pressure.

 

[41racing]

Sounds to me like you need a tune up. Get yourself some new ac delco plugs, wires, cap, rotor, and pcv valve. Change your fuel filter also, and your air filter if it needs one. I like to do everything all at once, then you're good for another 100k miles.

 

[FORKLIFTTECH]

Just Tuned It Up 5k Ago.eplaced All Ignition Wear Parts.

 

[upstairsdave]

Hesitation

Yo,
I've got the same thing going on but mine happens after a warm up and I stop for grocery's or gas. It might be a Coolant temp sensor but the scan tool indicated that the engine temp was up to normal. Maybe it cools down enough and goes out of range. I should look up the ohm value of it and see how it compares to spec. It may also be the air temp sensor too. Mine runs lean and you'd think that a temp sensor that indicates it's colder or a CTS that indicates that the water temp is cold would run rich. This is definatley a lean misfire thing going on. I get a backfire - cough kinda thing out of the intake. Maybe the temp sensors are indicating Hot and the engine cools off enough that it needs a rich mixture and it's getting a command for lean. After a block or two the engine picks right up and has no power loss what so ever. That makes me think the fuel pump is OK. I already replaced the gas and fuel filter when I tuned it up. I have a K&N air filter element. You may have gotten an engine misfire code. I wish I had a code to go by. No codes here. I'm going to reset the record parameters on my Scan Tool and do another Record and see what it shows.
Let me know what code you get.
Dave

 

[73shark]

You'd be surprised how many different ways a failing fuel pump can affect an engine.

Check fuel pressure just to be sure.

 

[bowhunter22]

Have your throttle position sensor tested on a sweep scaner. It may have a dead spot or two. Affects both trans and engine