Need help diagnosing an issue with my 2003 suburban

[Jocko PDX]

I have a 2003 Z71 suburban with 297K miles on it. It still mostly runs very well. It started having an issue this weekend. The motor loses power and stalls out if it downshifts while going up hill. It seems like it mostly does it when I am trying to accelerate. If I pull over and turn it off then re-start it 2-4 times it will start up and be fine again.. Until I try and accelerate up a big hill and it tries to downshift.. Google AI says: A 2003 Chevy Suburban stalls during downshifts due to issues with its electronic throttle body, Idle Air Control (IAC) valve, or related sensors like the Throttle Position Sensor (TPS) or transmission components. To resolve this, first clean the throttle body and check for vacuum leaks, as carbon buildup is a common cause of rough idling and stalling. If the problem persists, you may need to inspect the IAC valve for function, test the TPS, or investigate potential issues with the transmission range sensor or torque converter clutch (TCC) solenoid

 

[Fless]

After an event like this it would be interesting to see if any codes are present.

How long since the throttle body was cleaned?

Do this if nothing else but to rule it out. Put a fuel pressure gauge on it with a long hose and tape it to the windshield. Suspect fuel pump or clogged fuel filter (if it has one). The typical running fuel pressure is about 43.5 psi.

You can also check the KOEO fuel pressure prior to starting, using the same setup. If it's a Flex Fuel engine this spec will be different from the gas engine.

What is the condition of the transmission fluid, and when was the transmission fluid last changed?

 

[Jocko PDX]

After an event like this it would be interesting to see if any codes are present.

How long since the throttle body was cleaned?

Do this if nothing else but to rule it out. Put a fuel pressure gauge on it with a long hose and tape it to the windshield. Suspect fuel pump or clogged fuel filter (if it has one). The typical running fuel pressure is about 43.5 psi.

You can also check the KOEO fuel pressure prior to starting, using the same setup. If it's a Flex Fuel engine this spec will be different from the gas engine.

What is the condition of the transmission fluid, and when was the transmission fluid last changed?

I am suspecting a fuel filter issue as well. The tranny fluid was changed recently.

 

[Jocko PDX]

Strange update. I went to take it to the shop last night to drop off and it’s not doing it any more. So I will cancel the appointment and maybe just change the fuel filter.

 

[Fless]

Does it have a fuel filter? I'm thinking they were only on the flex fuel systems, but I could be mistaken.

This could also be a failing fuel pump, so you may want to have a pressure gauge at the ready.

 

[Jocko PDX]

Does it have a fuel filter? I'm thinking they were only on the flex fuel systems, but I could be mistaken.

This could also be a failing fuel pump, so you may want to have a pressure gauge at the ready.

it does have a fuel filter. I am thinking I could replace that on my own

 

[Jocko PDX]

Does it have a fuel filter? I'm thinking they were only on the flex fuel systems, but I could be mistaken.

This could also be a failing fuel pump, so you may want to have a pressure gauge at the ready.

I do not own a pressure gauge

 

[Fless]

Many auto parts stores have a tool rental program, where you "buy" the tool, then return it within a certain amount of time and get a full refund.

 

[jfoj]

My 2005 6.0l does not have a fuel filter.

If you are still on the original fuel pump, it is WAY overdue for replacement, I would replace it just because. I am thinking I may want to replace the fuel pump again, or for the 2nd time given I am at 275k miles.

What codes are you seeing if any, I would assume there should be something?

Restricted exhaust/clogged catalytic converters come to mind as well.