[06colorado2.8]

Does anyone happen to know what the normal operating fuel trims should be at. I have a scanner and the ability to view them, but don't know where they should be. I believe i have a vacuum leak but before i search for it i want to know if i am looking for the right thing.

 

[08Canyon]

I don't mean to question your mechanical ability - but why are you jumping right to fuel trims?

Instead of sensors, or fuel pressure, or anything like that??

 

[Goros]

There's a TSB for the PCM to address erratic low idle.

Get it flashed, then worry about the rest.

 

[06colorado2.8]

I initially thought sensors also. However, i have checked and replaced all according sensors with no resolution. The only sensors that could be the issue are the O2 which i realize would be likely, but i have unplugged them one at a time and the truck ran no different. It is my understanding that the truck would go rich without the O2 input, and might not run well.....but would run. The head was replaced about a month ago and i believe that during the reassembly something wasn't snugged up correctly, hence my vacuum leak. If i knew where my fuel trims should be i should be able to verify my assumptions. Also fuel pressure is at 60 lbs, and injectors were checked when the head was off.
I appreciate any input from you guys.
Thanks

 

[06colorado2.8]

Also, is the PCM flash a dealer ordeal, and do you happen to know the parameters for the TSB for it. I just forked out $1100 for the new head because GM refused to cover it under the TSB for the valve seats. I was less than 2 months outside the 7 year coverage for the TSB, and only at 78,000 miles, but they refused to cover it (after escalating my claim 3 times.) I'm just a bit leery of anything Dealer related right now.
Thanks

 

[RickD]

I fought a idle drop an a very rare stall for maybe a year until I found a discussion like tis here at the nation.
Went to the dealer with a list of PCM updates, one of which was for idle. That morning, with the truck warmed up, it would drop to 400 +/- rpms then settle back to just about 600rpm. When the update was done, I would settle to 675-690 rpm per my Scan Gauge.

Just looked at my work order, this is what the note says for the idle update:

"install available updates for PCM Program Code 1061F"

I'm assuming the PC 1061F was an update name or an address inside the PCM.

 

[RickD]

Part 2 , too quick on the submit button: After the update was installed and the idle was basically stable, never has dropped below 675 that I've seen and it's as smooth as silk.
The updates were done Jan 24 so it's been a couple of months of smooth stops. Can't tell you how many times I searched for a vacuum leak or cleaned the TB, etc etc.

 

[06colorado2.8]

Well i think i will give that a try, at least it's a place to start. The only dealer i still trust is about an hour away so i might not get to it till the weekend, but i guess that will give me more time to chase my tail. I appreciate the replies from all as i would like this to get this figured out as soon as possible, but also would still like to know those fuel trims if anyone has any info.
Thanks in advance

 

[Goros]

I'd also inspect the pcv tube and the brake booster hose for leaks or failure, and verify that all your QD electrical connections on engine related devices are good, as are your grounds. You never know what they may have knocked loose or what might have a corroded connection that was exposed from disassembly/reassembly.

Plus, those are free.

 

[06colorado2.8]

I know the coupler between the throttle body and resonator, the pcv hose, as well as the brake booster hose are all good as they were the first things i checked. There is one ground on the passenger side behind the air box that is corroded. I highly doubt it is the problem, but i might as well get the wire wheel out and make it shiny to rule it out. I'll post back.

 

[Goros]

Also cleaning the connections from the harness to the coils doesn't hurt either. Should be on the annual maintenance list.

 

[06colorado2.8]

Those connections were checked and re-checked, and then i applied di-electric grease so i know they are good. Also i don't have any misfire codes, just the lean code.

 

[RickD]

OK Guys, am I leaving myself open for a problem?

Over the 10 years I've had the Colorado, I have never cleaned the ground box with anything other than compressed air. Not that I do it all that regularly, enough that I can find it easily tho. cleaned it maybe 3-4 times in the 10 years.
Never brushed the contacts or used Dielectric grease to seal it back up.
Last time I used dielectric grease was on my old 64 Nova for the spark plug boots and to insulate the dual points and condenser. Still got the original tube I bought back in 1974 or 5.

 

[06colorado2.8]

If it's not broke, don't fix it....just my thoughts

 

[06colorado2.8]

Ok i figured since i wasn't hearing any more idea i would put in some new info:

Engine Cold:
-Short term fuel trim: -2.3 to 2.3
Long term fuel trim: 6.2
Map: 32
Rpm: 790 to 810 (that is where it has always been)
Timing Advance: 9.5 to 13.5
Air Flow Rate: 4.96 to 5.21
Absolute Throttle Position: 18.4
O2 sensor 1: .08 to .80
O2 sensor 2: .725 to .735


Numbers at operating temp before it dies:
Short term fuel trim: -1.5 to 2.3
Long term fuel trim: 3.9
Map: 31-33 (dies at 27)
Rpm: 800
Timing advance: 6.0 to 10.5
Air flow rate: 4.38
Absolute throttle position: 17.6
O2 sensor 1: .745 to .110
O2 sensor 2: .786 to 2.33


What i have done: checked for vacuum leaks, checked MAF sensor, replaced cam and crank position sensors, crank relearn, replaced cam actuator solenoid, checked coils ( no miss and no codes)

The truck will not even throw a code now, it will just die....but only at operating temp, but then will fire right back up. It has a stored lean code, but will not throw it on the dash.
The last thing i can deduce is i have a bad O2, or a bad cat, but i don't want to throw money at it until i can be sure. If anyone has any input i would appreciate it, or other ideas. Thanks in advance.

 

[RickD]

Sorry, you are above my skill level.

 

[Goros]

Unless debris from a failing cat is blocking your exhaust, you shouldn't be stalling, and if it was the cause, you shouldn't just be able to start right back up.

Also, we need to change our upstream o2 sensors every 80-100k miles just for gas mileage sake, but I don't see that helping.

Is there any possibility it could be a bad electrical connection to your fuel pump/failing fuel pump? I can't see how that would only happen at operating temps, but anything is possible. Also maybe check your PCM connections for loose wires? If it's got a bad connection it may be interrupting signals which operate the engine (really a stretch on that one).

At this point it may be something as simple as a bad ground or positive terminal connection interrupting power flow as the connector warms and expands, or it could be as bad as a damaged PCM.

Not enough personal experience to say either way.

Sorry

 

[06colorado2.8]

Well fuel pressures have been checked twice and they have been steady and appropriate both times. I had the pcm wires off when i did the head so i guess that's a place to look. Getting tired of fighting this thing ha.

 

[06colorado2.8]

Checked all connections and grounds today, including the pcm harness to pcm. All connections are good and snug. All grounds are checked and wire wheeled clean then covered in di-grease. Truck ran ok at idle today for about 10 minutes at opreating temp, died once, started back up, ran for another 10. I goosed the throttle to about 4000 and let it drop. The rpm dropped to about 550 before it caught itself, came back up to 800, then died. Started back up, ran for 5 mins fine, goosed it again, same deal dropped to 550 before it caught itself, jumped to 800 then died. I will need to put a fuel pressure gauge on it during this to see if it drops off or something because it seems likely that is the cause. However, i have 60 pounds at idle which is right where it should be, and it seems odd that it would, but who knows. I'm running out of ideas and starting to hate this truck. It's almost walleye season and my boat doesn't pull itself!

 

[Goros]

Did you ever get the PCM flashed to the latest update that fixes the erratic idle speed and low idle problem?