Hey guys wassup i have a 1998 pontiac bonneville ssei and i got it a couple weeks ago and been having problems since i got it the problems the dealership told me it had was a a/c problem which i fixed and a tune up well after tuning it up wit new plugs and wires i noticed it still ran rough so i ended up changing the 02 sensor the catallic converter the muffler the maf sensor the idc sensor the tps sensor the air filter oil change fuel regulator and fuel filter and getting a fuel injector cleanse from the dealership and now it runs ok but it still gives me the p171 code and still runs kinda rough so after all that i decided to take it to the shop since i couldnt figure it out and they said my cylinder 3 had bad compression and that it was the only cylinder misfiring so they checked the plugs and wired and coils and fuel injector plugs and said its probally my intake gasket cracked around that cylinder and needed to be changed but couldnt know for sure without taking it apart they said at the long shot it could be the injector but they dont think it is what do u guys think i need advice:(

P0171 is a lean code. And if cylinder is misfiring then it'* a good chance there'* a fuel problem in that cylinder. You would need to check the plug. I don't suspect a bad LIM gasket if it'* running lean. To test the injector you can switch that one with a different cylinder. If the problem follows then the injector is the problem. If it don't follow, the injector is good.

Bad compression in a cylinder shouldn't have anything to do with the injector or LIM gaskets because they are both before the valves that seal the cylinder as the piston comes up for the compression stroke.

Bad compression is usually caused by a chipped piston, bad rings, bad head gasket or bad valve to head seal.

it wasnt that it was real bad it was in the range of where it need to be just a little bit off imma try the injector today and see what happens

For the money...I would change the plugs & wires. I had a 2 year battle with po171 and it turned out to be plug wires. The terminal on one wire had actually rusted inside of the boot...not sure I would have even seen it if the boot hadn't tore removing it.

P0171 trips when the oxygen sensor senses excessive oxygen in the exhaust stream. Anything that interferes with proper combustion or what the oxygen sensor reads will cause it to trip

That said it can be caused by low fuel pressure/restrictions including fuel pumps, clogged fuel filters, sticky injectors etc. but it can also be triggered by incomplete combustion...in my case a weak spark on cylinder 6 caused by the rust Plug doesn't fire hot enough 02 sensor reads it .computer adjusts fuel trim thinking it needs a richer mix. when it has adjusted as far as it can and still reads too much 02 it pops the light on.

Also a possible concern is any type of vacuum leak at the intake manifold, or an exhaust leak at the EGR or the exhaust manifold. This one can drive you crazy I looked at all kinds of potential causes. There isn't much easier or cheaper than wires

Spit

In my case it would pop the SES light on once every 25-50 miles and the car seemed to run great most of the time.