[lathedog]

Hey guys ?I tried a search but so much different posts came up I figured I would try asking.
When truck is cold and I start off I get. Bad flat spot or stumble on acceleration.I cleaned the Maf sensor.This is a 07 2.9. My sensor didn't look like any Maf I have ever saw.it was a metal type enclosed case.I sprayed it down but that didn't help.I runs better when warmed up but I still get a jerk or mis at different times.I put in new Densos 4 months ago.It has 66000 miles.
Any advice? Thanks. Jim

 

[08Canyon]

Did you use MAF Sensor Cleaner?

You can try to clean your throttle body, it's common maintenance on our vehicles.
Get a can of spray Throttle Body Cleaner and follow the segment in this article for Throttle Body.
It's important to only use a rag and the spray or a soft bristle brush. Do not use anything abrasive and don ot try to scrape it clean with a scraper.

http://www.355nation.net/forum/how-...w-change-spark-plugs-clean-throttle-body.html

 

[Goros]

Yep.

Could also be a dying crank or cam position sensor. Both worth at least pulling to look at to see if they are gunked up/damaged.

 

[lathedog]

I cleaned the throttle body a year ago.or 6 thousand miles.it was fairly clean then.
Yes I bought a can of Maf cleaner.Didnt do squat.

Onc.e it's warmed up after 3 or so miles it doesn't act anywhere as bad as cold.
If it was a sensor why would it be better after warming up?

 

[FrEaK_aCcIdEnT]

When it is cold you are running open loop, when it is warm it is running closed loop. Might want to check O2 sensors as well.

 

[Goros]

Good call. Only the upstream/manifold o2 sensor does anything with the engine, replace every 60-80k miles for best MPG

 

[Fred T.]

I am hoping my cold stumble is caused by my bad valves. At 200k Compression not bad but 2 cyls. failed leakdown test on #s 2 and 5. Anybody know anything about milling head to up comp ratio? I am also hunting rebuildable I5 for 06 Colorado near Asheville NC

 

[lathedog]

I eliminated the manifold 02 sensor 2 years ago.put a scanner on it and shows a misfire but didn't say which cylinder.was told by a mechanic that it's probably a plug wire...It doesn't have a wire as we know but could one of the springs that join the cop to plug cause this?

 

[08Canyon]

A code for misfire will point to a particular cylinder, unless its a 'random' misfire code.

Commonly the code indicates which number then that coil pack is swapped to another cylinder then rescan for codes. If the code number moves with the coil then you know you have a faulty coil. If the same cylinder has a misfire then it's a cylinder or spark plug.

I THINK there is a random misfire code but I can't remember for sure because I'm not that smart.

 

[lathedog]

The guy that pulled code said it just showed a misfire. He said he would need to run it with the scanner on it to see which cylinder.

 

[08Canyon]

Take it to a parts store if you get a chance, they can usually tell. I THINK most of the hand held OBD scanners return the cylinder code.

Others will chime in if this is incorrect information-if not then I'd just swing by the parts store in the morning.

 

[Goros]

I am hoping my cold stumble is caused by my bad valves. At 200k Compression not bad but 2 cyls. failed leakdown test on #s 2 and 5. Anybody know anything about milling head to up comp ratio? I am also hunting rebuildable I5 for 06 Colorado near Asheville NC

Sounds like you may have gotten one of the rare 2006's with the head failure.

It was caused by valve seats not being hardened sufficiently for what the engine presents.

When my rebuild was done (under warranty) they replace the head, valve springs, timing chain and a couple other things I don't remember.

They did this on the 2004-2006 canyon/colorado as well has the h3's. 2006's with the problem were all built pre-feb 2006.

There were new part numbers issued for the heads and the old ones were supposed to be sent back to GM off everyone's shelves.

 

[Fred T.]

Sounds like you may have gotten one of the rare 2006's with the head failure.

It was caused by valve seats not being hardened sufficiently for what the engine presents.

When my rebuild was done (under warranty) they replace the head, valve springs, timing chain and a couple other things I don't remember.

They did this on the 2004-2006 canyon/colorado as well has the h3's. 2006's with the problem were all built pre-feb 2006.

There were new part numbers issued for the heads and the old ones were supposed to be sent back to GM off everyone's shelves.

So at 200k on my motor and me being the umpteenth owner I suppose GM can't help me.?

 

[Supermodulation]

Could be just a bad fan clutch.

 

[Fred T.]

How in the World could a bad fan clutch cause an engine to stumble??? Maybe I don't know what "stumble" means anymore, "back in the day" (he said with a wheeze) stumble meant bog, miss, chug, wanting to die when opening the throttle.

 

[chizzel]

A fully engaged fan clutch wouldn't let mine shift. Don't know about a "stumble"

 

[Supermodulation]

How in the World could a bad fan clutch cause an engine to stumble??? Maybe I don't know what "stumble" means anymore, "back in the day" (he said with a wheeze) stumble meant bog, miss, chug, wanting to die when opening the throttle.

I agree! :th_lurkingrr:

I really think he has a micro vacuum leak causing his truck to run stupid lean, enough not to throw a code. If he has the stock intake then more likely the valve cover to resonator vacuum hose is dry rotted.

 

[Fred T.]

Originally I just had a miss that caused a quiver at idle. I looked high and low for a vac leak on mine. Acetylene then LP gas probed around, "pressurized" (with vacuum cleaner) the intake and soaked it with bubbles, built a smoke machine and smoked the intake, compression test showed wear (200k) but was good. All the while the miss turned into code throwing stumble so I built a leak down tester (you tube) and sure enough I could hear an intake valve leaking on #5, and #2 was going somewhere. Shopping for a rebuildable motor and still hoping to find info on how much to mill the head for a comp ratio of about 11:1 and what happens to the valve timing and ignition timing. I get a few hints and hopefully good info but I suppose I'll have to resurrect my math skills, experiment, and spend a lot of money to get it right.

 

[Goros]

Stock on our trucks is 10:1.

 

[Fredzway54#]

I'm baaack! Engine running well with 0.050" milled off the head. Compression ratio of 11:1.
Still have a stumble on CNG when cold. Do Coils get weak or just die??