HELP ME!!!

[theprovider]

2002 Tahoe Z71 5.3 176k miles

So I've been trying to figure out why my Tahoe is stumbling/surging between 40-60. I replaced all the usual suspects, fuel filter, pump, spark plugs, wires, cleaned the throttle body, cleaned the cone filter (k&n previous owner installed it...). I've had a CEL so I bought a scan tool. It said knock sensors, I cleared it, cel came back after a day and it said the same thing. So I looked into symptoms of bad knock sensors and one of them was surging under load (when my surging happens). So I spent the better half of today replacing those stupid sensors, all seemed good, then after a few minutes of driving I floor it up a bridge and it started surging again...

I really think its something to do with fuel/air and electronic related it seems to happen intermittently or after the truck is warmed up. My other thought was maybe torque converter but my transmission shifts really smooth. The TC went out on one of my old cars and it through a code and the trans shifted like doo doo.

I know there is still stuff to check..coil packs, maf, other sensors related to fuel and air. I'm posting to see if anyone else has had a similar issue and fixed it.

 

[theprovider]

Forgot to mention the first time I went to replace the knock sensors I bled the fuel system and a bunch of gas came out, like way more than I was expecting. The second time (after I got a tool to remove that stupid push connect fuel line) only a little squirt came out. Not sure what that means....

 

[Big Mama]

Do your rpms jump around during the surge? That’ll tell you if it’s trans related.

 

[Kraig]

What brand sensors did you use? Did you replace the knock sensor wiring harness too?

 

[SnowDrifter]

Could you provide a video of the problem?

 

[iamdub]

It's your fuel map, man. It's got a nasty hole.




My first suggestion at the moment is to clean the MAF, especially since you have a K&N cone filter.

 

[swathdiver]

2002 Tahoe Z71 5.3 176k miles

So I've been trying to figure out why my Tahoe is stumbling/surging between 40-60. I replaced all the usual suspects, fuel filter, pump, spark plugs, wires, cleaned the throttle body, cleaned the cone filter (k&n previous owner installed it...). I've had a CEL so I bought a scan tool. It said knock sensors, I cleared it, cel came back after a day and it said the same thing. So I looked into symptoms of bad knock sensors and one of them was surging under load (when my surging happens). So I spent the better half of today replacing those stupid sensors, all seemed good, then after a few minutes of driving I floor it up a bridge and it started surging again...

I really think its something to do with fuel/air and electronic related it seems to happen intermittently or after the truck is warmed up. My other thought was maybe torque converter but my transmission shifts really smooth. The TC went out on one of my old cars and it through a code and the trans shifted like doo doo.

I know there is still stuff to check..coil packs, maf, other sensors related to fuel and air. I'm posting to see if anyone else has had a similar issue and fixed it.

You need access to a good scan tool that can see what all the sensors are seeing and even graph them. Without one, you're flying blind and throwing parts at it.

 

[theprovider]

Thank you for all the responses! I cleaned the MAF when I did the throttle body. The rpms jump but nothing crazy. Not like the trans is slipping it’s more like a lack of power. I can try and get video today! I read about the MAP sensor. Definitely on my list but I thought a sensor would through codes....

 

[iamdub]

Definitely on my list but I thought a sensor would through codes....

If the MAF is clean then the next step, as @swathdiver mentioned, is to see what all the sensors are telling the PCM before you start throwing parts at it. A faulty sensor won't necessarily cause an SES light. The PCM will throw a code/SES light if a sensor is operating or reporting outside of expected parameters. A sensor could be faulty and telling the PCM misinformation and the PCM will adjust accordingly but not know that the sensor is faulty and "lying".

Acting up around a specific range as you mentioned tells me it's a load-based issue. The MAF, MAP and TPS are what the PCM uses to determine the load on the engine. Even if the MAF is clean, it could still be faulty. Unplug it and road test.

 

[theprovider]

All good points. I didn't mention I replaced the TPS. When I pulled the TB the TPS was super nasty, the TB probably was never cleaned. I'm also not a fan of the K&N cone filter...number one it doesn't fit very well and number two it collects dirt and crap. I'll check the MAF and MAP next.

Any thoughts on a coil pack issue? One of the related symptoms of a bad coil pack is an erratic gas gauge. When I first bought the truck every time I filled it up it would go full then empty when I started driving. It would bounce around for about 10-15 miles then go to full and work appropriately. After about a 3 months of me filling the tank when it was empty it kind of went away, very rarely does it do it now. Previous owner said "I never filled the tank" after I mention the gauge so that made me think it was the float in the tank.