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need help with gtp

S

Sergio Esparza

New member
I have a 2004 pontiac grand prix gtp , and just recently my car bogs out at like 32mph , new plugs wires coil pack low bank 1sensor replaced. Any advice or help? Only code thrown is p0420
 


Likely a Clogged Cat Converter but you would need to check and make sure before dropping the $$$ on a replacement.

[h=2]Causes[/h]A code P0420 may mean that one or more of the following has happened:

  • Leaded fuel was used where unleaded was called for
  • A damaged or failed oxygen sensor (HO2S)
  • Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
  • Leaking fuel injector or high fuel pressure
  • Cylinder misfire
  • Oil contamination
[h=2]Possible Solutions[/h]Some suggested steps for troubleshooting a P0420 error code include:

  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
  • Replace the catalytic converter
Click to expand...
 
Yeah thats what some are telling me, but if it was clogged wouldn't it not accelerate to 32mph .. I can push on the gas as hard as I want till 32mph then damn thing bogs out ... in park it only revs between 3000 and 4000 rpm.
 


In park there is a default rev limiter to keep people from revving it to destruction, you have to be rolling at 15+mph to go over that.

As far as driving I have seen them clogged to the point it would just die when started to being able to drive on the highway if you baby it but you get into the throttle and it would shudder and try to die no matter what speed. Depends on how it clogged up.

As said you can un-bolt the 02 sensor before the cat and see if it runs better, or my personal favorite annoyance to those around you, unbolt the downpipe and move it out of the way and support it and see if it drives better. It would be loud as crap (open headers) but if the converter is clogged to the point of causing the issue you will know quickly.

If not, search on and test more.
 
Or in neutral it still only revs to that range of rpm, but I'm going undo the front sensor to see it helps, someone was also telling me to cut off cat and run straight pipe (flex pipe)
 
Sergio Esparza said:
Or in neutral it still only revs to that range of rpm, but I'm going undo the front sensor to see it helps, someone was also telling me to cut off cat and run straight pipe (flex pipe)
Click to expand...

Same applies in Neutral or Park, computer controls the engine revving and it will cut the fuel to keep it from revving past 3800rmps if its not in gear and rolling.

I wouldn't suggest just removing the CAT unless you get the car tuned or try a "02 Simulator" (available at 3800 performance and other vendors). If you just remove it the 2nd 02 sensor will notice no change and keep the CEL on and would kill MPGs &/or performance. There are high-flow replacements that work well in place if you plan to mod, if you plan to keep stock just get a OEM replacement and keep on rolling.
 
Sergio Esparza said:
Couldn't I just disconnect the the front 02 or completely unbolt?
Click to expand...

Need to un-plug & un-screw it so that the hole it screws into is open to allow exhaust out. It basically allows a bypass so its not so restriced by the converter alone. Only other way is to unbolt the converter completely to remove the block.
 


soo i just got done driving with the o2 unscrewed and unplugged , no difference in accleration when trying to hit 32 mph. let me add some more info to this. this just started like 3 days ago, for some reason ever since this has occured, the indicator brake light stays on. the emergency brake is no where near being engaged . it works fine

the other day i was going over a very steep bridge, and the idicator light went off and the car acted normal.. then after i turned off and turned car back on . indicator light still on and car still did not accelerate . then i was driving it and the light would cut in and out and car would still act according to it. then yesterday i was going up a hill to reach a parking garage then i looked down and noticed light went off and car act normal and of course turn off turn on, light is still constant. i noticed when it first happen i could i feel and hear a small nudge on the break pedal.

really confused lol
 
the more pressure on gas pedal when hitting 32 mph+ , bogs out

soo i just got done driving with the o2 unscrewed and unplugged , no difference in accleration when trying to hit 32 mph. let me add some more info to this. this just started like 3 days ago, for some reason ever since this has occured, the indicator brake light stays on. the emergency brake is no where near being engaged . it works fine

the other day i was going over a very steep bridge, and the idicator light went off and the car acted normal.. then after i turned off and turned car back on . indicator light still on and car still did not accelerate when pressure applied after 32mph . then i was driving it and the light would cut in and out and car would still act according to it. then yesterday i was going up a hill to reach a parking garage then i looked down and noticed light went off and car acted normal and of course turn off turn on, light is still constant. i noticed when it first happen i could i feel and hear a small nudge on the break pedal.

really confused lol i changed coil packs, plugs & ​wires , 02 sensor

2004 grand prix gtp
 
Re: the more pressure on gas pedal when hitting 32 mph+ , bogs out

gas gauge is fine and always lets me know when low etc. i doubt its a pump?
 


Re: the more pressure on gas pedal when hitting 32 mph+ , bogs out

No, what he meant was that the pump may not be delivering the proper pressure to keep it running.

Have you checked the brake fluid level in the master cylinder? That would cause the brake light to come on as well.

Also, what brand and type of spark plug did you install? Hopefully a copper or irridium plug and NOT platinum.
 
Re: the more pressure on gas pedal when hitting 32 mph+ , bogs out

what about fuel filter? and no i havent checked it in the master cylinder, i dont know how lol :/

i installed irridium
 
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