97 stumbles when cruising

[SUBURBAN5]

So got home from work today and started to investigate with my scan tool. Haven't been driving the Tahoe because of the issues and have a spare vehicle. The battery was dead so I hooked my battery charger up to it. As soon as the battery had power my scan tool turned on even though the key was off. If I'm not mistaken I shouldn't have power at the obd2 port unless the key is on. Could that be a bad ignition switch and could that explain the stumble on highway?

I doubt it. My scanner will hook up to the obd port and read active codes with the truck off..

 

[Kevin Callahan]

I doubt it. My scanner will hook up to the obd port and run test with the truck off..

I guess that's not one of its problems then. I'm at a loss at this point. Zero codes come up throttle position sensor tests fine. Everything looks good when monitoring on a scan tool

 

[SUBURBAN5]

I guess that's not one of its problems then. I'm at a loss at this point. Zero codes come up throttle position sensor tests fine. Everything looks good when monitoring on a scan tool

Your not the only one. I have a shudder as well . Different issue though. Still, I can't figure it out. As for you , put your truck on jack stands, chock the wheels and see if the shudder is coming from the drive train. I would think it's more of a vibration but could be mistake for a shudder? Nvm. I just reread about the RPM symptom. In that case check fuel pressure... also wouldn't be a bad idea to clean out your throttle body. Sometimes the iac or tps can play funny things

 

[Schurkey]

Zero codes come up throttle position sensor tests fine. Everything looks good when monitoring on a scan tool

Define "Everything".

What are the fuel trims at steady speed when it stumbles?
What are the upstream O2 sensors showing immediately before/during/after the stumbles?
What are the knock counts when it stumbles?
What is the spark advance when it stumbles?
Does the torque converter clutch lock or unlock immediately before/during/after the stumbles?
What are the individual cylinder knock counts immediately after it stumbles?

 

[Kevin Callahan]

Your not the only one. I have a shudder as well . Different issue though. Still, I can't figure it out. As for you , put your truck on jack stands, chock the wheels and see if the shudder is coming from the drive train. I would think it's more of a vibration but could be mistake for a shudder? Nvm. I just reread about the RPM symptom. In that case check fuel pressure... also wouldn't be a bad idea to clean out your throttle body. Sometimes the iac or tps can play funny things

I've checked pressure at idle but never at any kind of rpm. Pressure at idle is perfect. The throttle body was cleaned not that long ago as I had the lower intake gasket starting to leak but can't hurt to try it

 

[SUBURBAN5]

I've checked pressure at idle but never at any kind of rpm. Pressure at idle is perfect. The throttle body was cleaned not that long ago as I had the lower intake gasket starting to leak but can't hurt to try it

Well are the fuel injectors upgraded? Original?

 

[Kevin Callahan]

Define "Everything".

What are the fuel trims at steady speed when it stumbles?
What are the upstream O2 sensors showing immediately before/during/after the stumbles?
What are the knock counts when it stumbles?
What is the spark advance when it stumbles?
Does the torque converter clutch lock or unlock immediately before/during/after the stumbles?
What are the individual cylinder knock counts immediately after it stumbles?

I know I watched 02 sensor readings one of the last times I had it out and if I remember correctly there was no real change in them. As far as knock counts if my scan tool is able to tell me actual counts I haven't been able to find it on there. And I really wish I could monitor torque converter lock up because I'm not so sure that isn't the entire problem is the torque converter locking and unlocking

 

[Kevin Callahan]

Well are the fuel injectors upgraded? Original?

I upgraded them a couple of years ago because the stocks were starting to fail. At the time it made a massive difference in the way it ran

 

[SUBURBAN5]

How old your pump?

 

[Kevin Callahan]

How old your pump?

About the same age as the injectors. Was running rough and when I checked fuel pressure it was low enough that I was surprised it even started so I put a pump in. It helped but still wasn't right. Then i discovered the deal with the injectors