2006 poor cold starting in cold weather, p0300 obc runs fine when warm

[cbduffeck]

Hello Guys,

Got a good one. we own a 2006 TB 4.2L with 145,000 miles. The vehicle has given out coeds of p0300 and p0171. I started by changing the Oxygen sensor on the first bank. The rsults never changed. When it is cold outside <32F the engine will start right up and idle at 1200. after a period of 10-15 seconds it starts to idle down. get to 800 RPM and it starts to misfire. Checked all coil packs, Appear to be good. Clean the Mass Air flow sensor. Changed plugs. Still no difference. Once the engine is warm the truck runs good. The characteristics makes it sound like the engine thinks that it has warmed up when it has not. I noticed that if the coolent temp is over 110 F it will start and run fine. What next, any leads?

 

[RayVoy]

Try some injector cleaner.

Check the compression.

You've checked the other common things.

 

[cbduffeck]

Hello,

Have tried the cleaner, no difference. I truly think that the electronics or sensor is causing the fuel to lean out too fast and causing the rough idle or stalling till the motor or outside temp is warm.

 

[The_Roadie]

Did you change the O2 sensor because you had real time data showing its output was faulty? Or was it a guess? What's the real time sensor data look like now?

How did you check the coils? By disconnecting one at a time while the misfiring is happening, or swapping a new one into each position in turn? A visual inspection is not useful unless you see gross cracks, a rare failure mode.

Do you have access to a high-end scan tool that will show real time data? Especially fuel trim? And the freeze frame data that's captured when you get a P0171 code?

Did you Google for "P0171" to find it means "excessively lean condition causing the fuel trim to go over 20%"?

I'm guessing (but you could help with more observations) you have a vacuum leak on the intake manifold side (hoses, cracks, loose manifold bolts), and a vacuum check would be illuminating.

 

[cbduffeck]

I changed the o2 sensor because the nuckleheads at Auto zone said it was the problem. Then when that did not fix it I purchase a OBDlink SX diognostic reader.
I also picked up a spare coil pack from a parts store. the check that i made on the coild was ohm readings on the coils and visual inpections. then I changed the plugs. Altough most of the plugs looked relatively good. I installed the replacement coil in the #6 cylinder because the plug looked the worst. Fired it back up and had several new codes P0306 and P0356. Which said the #6 coil was bad. put the old one back in and cleared the codes. started right back up and was fine. But by that time the motor was warm. So I let it cool down for 5 hrs outside and tried it again. Same issue. What does the computer read to sense the engine temp and when too lean out the fuel mix?
I will check the vacuum line in a couple of minutes. wouldn't a vacuum leak always be there and cause problems all the time?

 

[The_Roadie]

I changed the o2 sensor because the nuckleheads at Auto zone said it was the problem.

Man, I thought everybody got the memo about these goofs. Have them READ the code if you don't have a code reader. Don't have them INTERPRET the codes. If they were trained, competent technicians, they would be WORKING AS auto techs.

Then when that did not fix it I purchase a OBDlink SX diognostic reader.

Everybody needs one nowadays, or one person in a group of friends. Mandatory.

What does the computer read to sense the engine temp and when too lean out the fuel mix?

Coolant temp sensor. The scan tool should give you that data, unless all it does is read codes (I was too lazy to check out your features.) If it doesn't, you may have underbought it. If your dash gauge reads straight up 210 when hot, the sensor is probably OK.

I will check the vacuum line in a couple of minutes. wouldn't a vacuum leak always be there and cause problems all the time?

Not the ones caused by loose intake manifold bolts.

 

[cbduffeck]

Man, I thought everybody got the memo about these goofs. Have them READ the code if you don't have a code reader. Don't have them INTERPRET the codes. If they were trained, competent technicians, they would be WORKING AS auto techs. Everybody needs one nowadays, or one person in a group of friends. Mandatory. Coolant temp sensor. The scan tool should give you that data, unless all it does is read codes (I was too lazy to check out your features.) If it doesn't, you may have underbought it. If your dash gauge reads straight up 210 when hot, the sensor is probably OK.Not the ones caused by loose intake manifold bolts.

Hi roadie,

I can send you the recording of the sensors, I took the recording when I was having the problem. O2 sensor is fluxuating working normally. I think I need to make some more checks on some of these items and get back to you. Thanks

 

[cbduffeck]

I just looked the the in-take manifold. what a pain in the ass. and that is just looking at it. But I will snoop around some more.

 

[cbduffeck]

I just looked the the in-take manifold. what a pain in the ass. and that is just looking at it. But I will snoop around some more.

I think that Roadie may be onto something. I looked at the Intake PSI and it is all over the palce and then it goes straightlined, for a couple seconds. then it starts to go crazy again. I take it that it should remain relatively stable? correct?

 

[GM GUY]

I just looked the the in-take manifold. what a pain in the ass. and that is just looking at it. But I will snoop around some more.

This is an old trouble shooting method. With the engine running, use a little WD-40 or silicone spray where the manifold meets the head or where you suspect there is a vacuum loss, watch for changes. Do not use starting fluid or highly combustible fluids for obvious reasons. When you are done use a rag to wipe the engine of the spray used.

 

[CaptainXL]

I think that Roadie may be onto something. I looked at the Intake PSI and it is all over the palce and then it goes straightlined, for a couple seconds. then it starts to go crazy again. I take it that it should remain relatively stable? correct?

Yes it should remain stable at about 18.

Does the needle drift up and down along with rpm at the same time?

 

[cbduffeck]

Yes it should remain stable at about 18.

Does the needle drift up and down along with rpm at the same time?

The issue was actually a dirty Throttle Body. performed a really good cleaning of it and the truck is running great.

 

[CaptainXL]

The issue was actually a dirty Throttle Body. performed a really good cleaning of it and the truck is running great.

Hmm. I'm thinking that replacing all the other stuff actually fixed the issue. Cleaning the throttle and disconnecting the battery just reset the learned parameters. Keep an eye on it.

 

[cbduffeck]

Yeah, hard to believe. But all the readings from the sensor never changed with all that was replaced. I cleared the codes with every repair and parts replacement. The vehicle is running really good since tuesday morning. No old codes and no new ones, checked all the sensor via diagnostic tool, they look pretty good.
Thanks