3800Pro Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
Good day I am pulling my hair out on this one. It is my daughters car 2005 Pontiac Grandprix it has 199000 miles on it. Started to miss and had a p0171 code and p0300 code. Plugs had never been replaced so wee replaced plugs and wires also replaced both 02 sensors as a maintaince item. Checked and cleaned the maf sensor. Before replacing the post 02 it was slow but within spec. after replacing all components listed the 0171 code is gone but still have the 0300 code and post 02 is at .89 volts. also the short term fuel trim is at 99% on the post cat 02 pre cat fuel trim is fluctuating between +6 and 0. checked for vacuum leaks with carb cleaner nothing apparent. I am going to put the original 02 sensor in after the cat to see if that changes anything. might have gotten a bad sensor.any ideas would be great. Car was running great then just started this problem.
 

·
Registered
Joined
·
33 Posts
Hi Turk. Do you have any noises at startup like a mild leaking exhaust manifold. That caused my P0300. How is the fuel pressure? If you are at a fuel trim of -1% that is great. However, an old fuel pump could intermittently change that.. Have you ever changed the fuel pump? Have you sprayed the wires at night to see if the spark is jumping. I bought new wires for my old '77 chevy truck and they spark jumped out of the box. They were not OEM.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #3
Hi Turk. Do you have any noises at startup like a mild leaking exhaust manifold. That caused my P0300. How is the fuel pressure? If you are at a fuel trim of -1% that is great. However, an old fuel pump could intermittently change that.. Have you ever changed the fuel pump? Have you sprayed the wires at night to see if the spark is jumping. I bought new wires for my old '77 chevy truck and they spark jumped out of the box. They were not OEM.
I have checked fuel pressure and it is steady at 60 psi with the car running. And yes it does sound like a small exhaust leak at start up. The most concerning issue is the high fuel trim on the post cat sensor. I reinstalled the old sensor and it reads the same as new one. I am leaning towards the cat being plugged. I set plug gap at oe recommended .60
 

·
Registered
Joined
·
33 Posts
I have checked fuel pressure and it is steady at 60 psi with the car running. And yes it does sound like a small exhaust leak at start up. The most concerning issue is the high fuel trim on the post cat sensor. I reinstalled the old sensor and it reads the same as new one. I am leaning towards the cat being plugged. I set plug gap at oe recommended .60
When you get on the freeway does it intermittently stutter at speeds of 50+? No noises at engine start up? My LT Fuel Trim is usually about 1.5 to 2 but I thought most mechanics started worrying at about 10% or more. Is the LTFT at higher RPM's? Have you checked the EGR pipes and EGR gasket for leaks? Are you going to unbutton the exhaust to see if the cat converter is the culprit? Good luck!
 

·
Registered
Joined
·
3 Posts
Discussion Starter #5
Just wanted to post the fix for this issue. After more testing, Checked the cat and it is ok. then pulled each cylinder up on my tester. I am using the auto ingenuity scan tool and it is a great setup for the price not as good as Snap-On but for what I need it is good. Testing miss fire on each cylinder found number 2 and 4 miss firing check compression and had 150 so the checked spark. No spark swap one of the coils and no change. Replaced the ignition control module and all good now.
 

·
Registered
Joined
·
33 Posts
Just wanted to post the fix for this issue. After more testing, Checked the cat and it is ok. then pulled each cylinder up on my tester. I am using the auto ingenuity scan tool and it is a great setup for the price not as good as Snap-On but for what I need it is good. Testing miss fire on each cylinder found number 2 and 4 miss firing check compression and had 150 so the checked spark. No spark swap one of the coils and no change. Replaced the ignition control module and all good now.
I am so happy for you. If you get a chance there was a south main auto video that included Ivan (Pine Hollow Diagnostics the had the ignition module of a gm 3800 running on only the first and last cylinders. If think you you will really appreciate that now:
 
1 - 6 of 6 Posts
Top