CEL came on yesterday, 2006 ODB trouble codes

[Fless]

I went on a drive (over highway 17 and back) and the temp. stayed steady. The temp. did drop a bit on 5-6 mile downhill but not much. I think filling and burping the cooling system did the trick. If that's it - the easiest fix I've ever completed. At this point the DIY gods owed me that.

No new codes are showing up. However, I do see my long term fuel trims are at +9% during idle. I don't think the fuel filter or fuel pump has ever been changed (180k miles). I'm considering doing a fuel pressure test to start with. Also I plan to rig up my scanner with long and short trims showing and drive around to see if the engine goes lean requiring more positive trim.

If the positive trims at idle is something that just started happening, re-check the intake plumbing. If the intake tube between the MAF and the throttle body has any leaks, that will cause unmetered air to enter the system (like a vacuum leak). What are the short term fuel trims looking like when the LTFTs are positive?

Agree to document the fuel pressure with the standard tests. Regulated fuel pressure should be around 43-45 psi at idle.

A couple other things to check with a warm engine:
- read the MAF g/s at idle, that should be approximately the same as the engine displacement in liters (e.g., 4.8, 5.3, etc.)
- read the short term fuel trims at idle, then at 1800 or 2000 rpm. If they're very positive at idle but go down with higher rpms, start looking for a vacuum leak.
- are the upstream O2 sensors reacting and voltages moving between 0.1 and 0.9v?

 

[2006Tahoe2WD]

If the positive trims at idle is something that just started happening, re-check the intake plumbing. If the intake tube between the MAF and the throttle body has any leaks, that will cause unmetered air to enter the system (like a vacuum leak). What are the short term fuel trims looking like when the LTFTs are positive?

Agree to document the fuel pressure with the standard tests. Regulated fuel pressure should be around 43-45 psi at idle.

A couple other things to check with a warm engine:
- read the MAF g/s at idle, that should be approximately the same as the engine displacement in liters (e.g., 4.8, 5.3, etc.)
- read the short term fuel trims at idle, then at 1800 or 2000 rpm. If they're very positive at idle but go down with higher rpms, start looking for a vacuum leak.
- are the upstream O2 sensors reacting and voltages moving between 0.1 and 0.9v?

Thanks much for this.
Yesterday I ran the engine in the driveway watching the LT and ST trims. The short term trims were bouncing around 0, e.g. up to the range of +/- 3% but mostly +/- 2%. The LT trims were +9 and +10 and then went to both at +9%.
I will retest per your instructions and borrow the fuel pressure test kit from Autozone. I have a fuel pressure gauge but I don't think I have the right adapter.

Thanks again.

 

[Fless]

Thanks much for this.
Yesterday I ran the engine in the driveway watching the LT and ST trims. The short term trims were bouncing around 0, e.g. up to the range of +/- 3% but mostly +/- 2%. The LT trims were +9 and +10 and then went to both at +9%.
I will retest per your instructions and borrow the fuel pressure test kit from Autozone. I have a fuel pressure gauge but I don't think I have the right adapter.

Thanks again.

The connection on the passenger fuel rail is a large Schrader valve. Like a bike tire valve (not Presta style) but bigger.

 

[2006Tahoe2WD]

This is funny. I looked at the Harbor Freight fuel pressure kit. I had a strange feeling like I've been in this place before. I went up into the attic looking at my seldom used tools collection - sure enough I have a HF fuel pressure test kit that is unopened. So I'm ready to dig in - tomorrow or the next day.

 

[2006Tahoe2WD]

At idle my scanner reads 0.01 lb./sec. and 2400 Hz. I don't see a grams/sec. option.
I went on a drive and watched the LTFTs. Nothing too crazy - some 4-5 and a couple times +10%. I need to dive in and take a fuel pressure reading.

 

[strutaeng]

At idle my scanner reads 0.01 lb./sec. and 2400 Hz. I don't see a grams/sec. option.
I went on a drive and watched the LTFTs. Nothing too crazy - some 4-5 and a couple times +10%. I need to dive in and take a fuel pressure reading.

On scanners where you can't change units, simply "Google" 0.01 lb/sec to grams/sec.

My google search says: 4.53 grams/second.

You could figure out conversion factors, but this easier. I think my Innova handheld scanner gives lb/minute units ...

 

[2006Tahoe2WD]

My error. I was able to change the units on my scanner. MAF reading 5.3-5.4 g/s.

 

[2006Tahoe2WD]

Major update re. fuel supply/trims.
I extend the fuel pressure gauge and taped it to the windshield. It held very steady 59-60psi all the time. Is this too high? I could not see a regulator. Is there one? I drove on a few steep grades and the pressure did not move. At the same time I watched the LT and ST trims. When I got onto a steady grade the LT trims might read 4-5 or maybe a bit higher - sometimes reading zero. The ST trims were up and down passing zero.
I also graphed the MAF and it went up and down according to my feeling on how much air should be going in. I think no worries at this point on the MAF functionality or signal.

 

[2006Tahoe2WD]

I read somewhere that the fuel spec. is 60 psi +/- 5 psi

 

[2006Tahoe2WD]

It looks like I have the non-return type fuel system and it is not a Flex engine. I think that helps limit what the fuel pressure should be.