97 lesabre p0171 and won't start when hot - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-08-2015, 12:08 AM   #1
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Default 97 lesabre p0171 and won't start when hot

Hello everyone, been a viewer of the forums for awhile. My 97 lesabre, 155k, has had a system lean code (p0171) for awhile and recently began having a problem where if I let it run and get to operating temp then shut it off it won't run again until it'* cold. I am not sure if the two are related, so if anyone has input that'd be great. When warm I checked spark, have consistent spark out of all 6 coil terminals, new plugs and wires, I have gone over the vaccum lines, EGR tube, intake gaskets and MAP sensor with brake clean and no engine rpm variation, maf sensor functions well, moving smoothly throught the voltage scale. Fuel trims are reading high. STFT 26.6 and LTFT 16.4-16.6. At operating temp both O2 sensor readings show very lean conditions. When revved the engine will not pass 4000 rpms in park or neutral. Have not checked in moving gears. I have not been able to check exhaust back pressure or fuel rail pressure because it'* been too cold to work on the car outside. Any thoughts are appreciated, thanks in advance. -Rick
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Old 01-08-2015, 08:10 AM   #2
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lack of fuel pressure and air leaks are frequent causes of lean codes
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Old 01-08-2015, 09:54 AM   #3
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With this code, obviously your car is running LEAN(or "thinks" it is), and that is why your fuel trims are high....

Your car won't rev higher than 4K in Park, because the rev limiter built into the PCM won't allow you....

Since you have a scan tool, and your pre O2 sensor is reading lean, while the car is running and at normal operating temp, disconnect the MAF.....if your O2 sensor, no longer reads lean, it looks like a bad MAF......

could have an additional problem if you have been driving the vehicle like this for awhile......that pre O2 sensor could be carbonned up from the engine being commanded to run rich......

AS JW said, vac leak(at intake,PCV valve, exhaust donut, etc) or fuel pressure problem(bad/clogged injector, bad pump, plugged fuel filter, etc.), or bad MAF, or bad O2 sensor........

Also check your your ECT on startup, cold, to see if the reading matches your IAT, and then rises accordingly...

Also check that vac line to the fuel pressure regulator for any evidence of fuel.....

You are not losing any coolant?

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Old 01-08-2015, 11:51 AM   #4
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Quote:
Originally Posted by Tech II View Post
With this code, obviously your car is running LEAN(or "thinks" it is), and that is why your fuel trims are high....

Your car won't rev higher than 4K in Park, because the rev limiter built into the PCM won't allow you....

Since you have a scan tool, and your pre O2 sensor is reading lean, while the car is running and at normal operating temp, disconnect the MAF.....if your O2 sensor, no longer reads lean, it looks like a bad MAF......

could have an additional problem if you have been driving the vehicle like this for awhile......that pre O2 sensor could be carbonned up from the engine being commanded to run rich......

AS JW said, vac leak(at intake,PCV valve, exhaust donut, etc) or fuel pressure problem(bad/clogged injector, bad pump, plugged fuel filter, etc.), or bad MAF, or bad O2 sensor........

Also check your your ECT on startup, cold, to see if the reading matches your IAT, and then rises accordingly...

Also check that vac line to the fuel pressure regulator for any evidence of fuel.....

You are not losing any coolant?
ECT rises slowly with IAT, and fluctuates while driving for the thermostat operation. I have checked all the vacuum lines and none are leaking, no fuel is present at the fpr vacuum source. If the pre o2 is carbonized is there a way to test it with a DMM? No coolant loss since my elbow blew out last spring.just waitin for the paycheck to buy the fuel pressure gauge....
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Old 01-08-2015, 01:06 PM   #5
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Tried unplugging MAF, no change in o2 voltage and car died without it being plugged in
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Old 01-08-2015, 02:40 PM   #6
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Tried unplugging MAF, no change in o2 voltage and car died without it being plugged in
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Old 01-10-2015, 12:04 AM   #7
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Hooked up the new fuel pressure guage. Showing 5-8 psi ignition on engine off. 0 while cranking and 20-25 while running cold....
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Old 01-10-2015, 09:39 AM   #8
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shouldnt even start on that little
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Old 01-10-2015, 11:37 AM   #9
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Yep, it'* suprising to me, it'* been starting hard on me since I bought it November of 13. So curious as to how it'* been starting for me since. I have an acdelco filter for it, gonna try that and recheck pressure, and probably to a regulator too because it'* cheaper than a pump. But I'm leaning more towards the pump
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Old 01-10-2015, 02:32 PM   #10
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sounds like the pump to me. dont beat on the tank to see. they have weak baffles. and make extra sure its perfectly sealed after or you will get evap codes
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