What did you do to your NBS GMT800 Tahoe/Yukon Today?

[MassHoe04]

This was a good explanation of what fuel trim is about...

 

[MassHoe04]

This was a really good write-up. Hope this helps!

Understanding Short Term and Long Term Fuel Trims

www.mechanic.com.au

Here are the key summary bullet points (see below)...


Below are some tips and tricks to diagnose the most common faults /defects / failures /malfunctions that cause rich air/fuel mixtures that result in high negative fuel trim values-

• Excessive fuel pressure; test fuel pressure with a dedicated fuel pressure gauge
• Leaking fuel injectors; test injector operation by performing a spray pattern and volume test
• Defective MAF sensors can under report the volume of air passing over them, thereby causing rich running conditions
• Exhaust leaks; repair all leaks found since exhaust gas contaminates the ambient air that oxygen sensors use for reference purposes
• Loss of some compression on one or more cylinders; loss of compression causes poor or incomplete combustion, which results in unburned hydrocarbons “fooling” oxygen sensors into reporting a rich mixture
• Marginal misfire; not all misfires are bad enough to set a misfire code, so check or replace suspect spark plugs, and check the operation of all ignition coils with an oscilloscope
• Marginally defective oxygen-, or air/fuel ratio sensor(s); sensors may be stuck at reading rich conditions as a result of not reacting to switching signals from the ECU, or may be slow to respond to switching signals

 

[iddqd]

I'd also added a leaking fuel pressure regulator

 

[Tonyrodz]

I'd also added a leaking fuel pressure regulator

What's a good way to test for this?

 

[TheAutumnWind]

Well

Conveniently

I've done both of those things

As well as an external filter, and second pan magnet as per TSB

Oh and a manual override for efans so I can get some flow through the thing even if coolant temps don't demand fan-on

I have yet to get around to an external fan filter. I wasnt aware of the TSB for another pan magnet. Thanks.

 

[TheAutumnWind]

Shouldn't take that much effort!!!

Grease the threads on the pulley tool

It certainly seemed like a lot.

 

[clandr1]

What's a good way to test for this?

Hook up a fuel pressure gauge. When you turn the key on (not starting), the fuel pump will prime the pressure. If the pressure starts to bleed off rapidly after the pump stops running, you have a bad FPR.

 

[SnowDrifter]

I have yet to get around to an external fan filter. I wasnt aware of the TSB for another pan magnet. Thanks.

I have a magnefine inline w/ my trans cooler

TSB:

https://ls1tech.com/forums/attachments/ls4-performance/377037d1350568544-new-turbo-gxp-service-bulletin-.pdf

 

[iddqd]

What's a good way to test for this?

Pull the vacuum hose off the regulator and check if fuel is leaking off it.

 

[Tonyrodz]

Pull the vacuum hose off the regulator and check if fuel is leaking off it.

Thx.