clanofwolves

Hey guys!
The other AM was cold, so I started my '01 (4.8L with 200K) and it idles rough for a minute until it calmed down and the 'choke' seemed to raise the RPMs and it was sounding smoother. However, when driving the "SERVICE ENGINE SOON" light was on and has been on constantly since; I have driven it three fairly short trips since; it is a rough under startup, but drives OK. I ran the codes via my Foxwell and got the following codes: PO171 System Too Lean Bank 1, and PO174 System Too Lean Bank 2.

Anyone had these codes and how did you test for or rectify these codes?

Thanks in advance!

David

mountainmanjoe

follow this troubleshooting
https://www.obd-codes.com/p0171

most common causes are poor fuel pressure (measure with gauge.), and vacuum leaks. (smoke test)

tech2

view the fuel trim data for both banks; at idle and 2500 rpm and post the result.

GM2550C01

I had the same problem with my 6.0 for years. I found my EGR tube was split on the intake side on the bottom of the pipe under the EGR. It's a common issue with these trucks, especially when the intake manifold is removed.
Use a mirror and flashlight to check it.

clanofwolves

Thanks for the info guys!

My reply is belated for two reasons: 1) life got real busy over the past days, and 2) the "service engine soon light" decided to stop illuminating.

Though I cannot currently measure the fuel pressure (measure with gauge.) mountainmanjoe, I can check for a) and vacuum leaks.(smoke test), and will also: b) view the fuel trim data for both banks; at idle and 2500 rpm and post the results tech2, as well as c) check the vacuum tube under the EGR GM2550C01. I'll reply when I get those done

Thanks again, you guys rock!

clanofwolves

Sorry it took a bit of time to get these, life simply gets messy sometimes 'eh? Anyway, I hope this helps you see what might be going on; I certainly hope so. Please note that I took these readings with the engine hot (and she doesn't like running smooth at startup when it's below 40 these days), and is as follows:

At Idle:
Short Term Fuel Trim 1: -3.9
Long Term Fuel Trim 1: 19.6
Short Term Fuel Trim 2: -3.1
Long Term Fuel Trim 2: 18.8

At 1876 RPM (65 mph):
Short Term Fuel Trim 1: -1.6
Long Term Fuel Trim 1: 9.4
Short Term Fuel Trim 2: -0.8
Long Term Fuel Trim 2: 10.2

mountainmanjoe

What?
So was it cold or warm?





I think tech2 meant 2500 RPM in Park.
If you're driving that puts a load on the engine.

clanofwolves

Warm. I guess my brain wasn't haha.

frank1

Is there a view option to look at alcohol/ ethanol content in the fuel ?

mountainmanjoe

there should be, if it's a "Flex Fuel" vehicle, and you have high end diagnostic tool