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Discussion Starter #1
I just recently did a tune up on my car at 53k miles.

New plugs, GM Top engine cleaner, cleaned MAFS, cleaned IAC and throttle bodies, checked/cleaned PCV, cleaned PCV lines and ran a can of Gumout TB and Manifold Cleaner.

The PCV lines were actually very clean, as was the throttle body and IAC. However, the car still starts somewhat hard and runs very poorly when cold. When I say starts hard, the car would always catch at about the third revolution of cranking, and now it seems to take 5-6. At WOT at high rpms, I have seen and people report that I blow some smoke. I believe the smoke is fuel related because I would think that if it were a ring issue, I would see evidence in the PCV system. This weekend I was barely able to pull away from an old Formula 350 automatic in 3rd gear.

I am now suspecting the O2 sensor or an exhaust leak. There is definitely an exhaust leak going on, and it may be from the flange at the back of the header. I'm wondering if a leak before the O2 sensor could cause my problems? I was considering replacing the front O2 sensor and any gaskets in the exhaust system.

Any thoughts on the coils or injectors? The plugs had a very uniform appearance, so I don't suspect the injectors much. They all indicated a lean condition, but I have a CAI so I expected that.
 

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Jesse IL said:
I just recently did a tune up on my car at 53k miles.

New plugs, GM Top engine cleaner, cleaned MAFS, cleaned IAC and throttle bodies, checked/cleaned PCV, cleaned PCV lines and ran a can of Gumout TB and Manifold Cleaner.

The PCV lines were actually very clean, as was the throttle body and IAC. However, the car still starts somewhat hard and runs very poorly when cold. When I say starts hard, the car would always catch at about the third revolution of cranking, and now it seems to take 5-6. At WOT at high rpms, I have seen and people report that I blow some smoke. I believe the smoke is fuel related because I would think that if it were a ring issue, I would see evidence in the PCV system. This weekend I was barely able to pull away from an old Formula 350 automatic in 3rd gear.

I am now suspecting the O2 sensor or an exhaust leak. There is definitely an exhaust leak going on, and it may be from the flange at the back of the header. I'm wondering if a leak before the O2 sensor could cause my problems? I was considering replacing the front O2 sensor and any gaskets in the exhaust system.

Any thoughts on the coils or injectors? The plugs had a very uniform appearance, so I don't suspect the injectors much. They all indicated a lean condition, but I have a CAI so I expected that.
Yeah - a leak in front of the front O2 sensor can definitely screw with your fuel trims and cause a rich run. (can also set CELs actually) Thats kind of at odds with what your plugs looked like though.

Any chance you could hook up with someone with a scan tool that can read the OBD2 datastream and watch the long and short term fuel trims at idle, and cruise and whatnot - see if they are positive or negative and whatnot.

Also have you done a compression test lately?

And do you have a Power FC? If you are using it then its a whole nother ball game for diagnosis.



Anyways the most common causes of hard starts I see these days are as follows:

Fuel quality

Residual fuel pressure loss (pressure bleeding off due to pump/pressure regulator leak or injector leak) - will be worse after longer soaks

negative fuel trims due to faulty sensors (MAF or O2)

Carbon on valves

contaminated injectors


If you live in the northeast fuel quality and injector contamination are a definite possiblity. Its easy to check though - just pull a couple injectors and look at the tips around the spray nozzle - it should be clean and shiny. if there is brown or yellow or crusty build you have problems.
 

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Discussion Starter #3
I have not done a compression test in the past few years, but can easily get my hands on a gauge and test that. How warm would you suggest the engine be to do that? I worry about pulling plugs on hot aluminum.

Injectors, I'll check that.

MAF sensor I worry about because a few years ago, I cleaned it a couple times with a Q-Tip.


I am currently running the stock ECU but have a Power FC and Commander, so perhaps I can diagnose something there. I'll check into the OBDII scan tool, I might know someone who knows someone...

Also, is it possible that I'm seeing white smoke? Do gas engines blow white smoke under load when running lean like a diesel?
 

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Jesse IL said:
I have not done a compression test in the past few years, but can easily get my hands on a gauge and test that. How warm would you suggest the engine be to do that? I worry about pulling plugs on hot aluminum.

Injectors, I'll check that.

MAF sensor I worry about because a few years ago, I cleaned it a couple times with a Q-Tip.


I am currently running the stock ECU but have a Power FC and Commander, so perhaps I can diagnose something there. I'll check into the OBDII scan tool, I might know someone who knows someone...

Also, is it possible that I'm seeing white smoke? Do gas engines blow white smoke under load when running lean like a diesel?
Pure white smoke is normally coolant

as for compression it needn't be that hot - let her run for like 20 seconds and then check her.
 

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Discussion Starter #5
Alright I did the compression test. Here are the results from Cyl 1 -> 4, dry.

265 - 255 - 245 - 225

Unfortunately, my battery started dying during the test on cyl 3, and was cranking really slowly for cyl 4. The owner's manual suggests that the car needs to crank at 250 rpm or greater. Should I repeat the test on cyls 3 and 4?
 
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