I have had 2 new gas caps and am still getting the 455 code. I've also replaced the cat, O2 censors, plugs, and wires and am pulling a 420 code. What the hell? I have an 05 grand prix gtp and out of nowhere I've got this hesitation that is the worst at high speed acceleration and wide open throttle. Driving normally there isn't a problem....HELP
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Re: PO 420 and PO 455 codes
There are three things that can cause this that is unrelated to the cap, if the valve on the carbon canister is defective it would cause this it would also cause a vacuum leak making the car run lean so check the carbon canister check valve first. Next your EGR valve could be dirty or not functioning, depending on the model and engine size it may have two EGR valves one a mechanical and the other the digital EGR and it to may be dirty, if it's dirty it can be taken apart and cleaned with carburetor cleaner and clean the pintal. And lube the pintal valve. If you’re careful and not tear the gasket you can reuse it. If this does not seam to fix the problem then you have a vacuum leak or the device that pumps pressure into the gas tank may be defective.
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Hi, I know from my past experiances the spark plug wires at the boot ends than slide onto the sparkplugs usually over time short out due to the metal tubes that protect the sparkplugs from heat kind of ark across from the metal tube through the plug boot causing an error code. Sometimes in the dark you can actually see them arking at the tube on the engine, and also hear a crackling noise. As to the code for the O2 sensor that's a normal wear and tear item that may need replaced. As all vehicle age over time electrical connections, and things have issues develop and cause havick with sensors and computers in these vehicles too.
As with the 441 code and then the other code for the O2 sensor showing up may mean both O2 sensors are going bad if your system has 2 sensors in the exhaust, usually one before the cat converter and one behind it. A lot of this also is due to what gasoline you use in the vehicle over time. Lower octane gas may be what is causing things to act up.
I would want to see the actual codes, but if it is one or two cylinders you could have a failing injector and it not show up as a trouble code. If one of the injectors is failing it can have a high resistance and affect the other injectors in that circuit. The O2 sensors and cat would not affect a power loss in one or two cylinders, and the O2 sensor codes would be present. The knock sensor only measures vibration, so it was probably ok before you replaced it. There is a chance the cap is shorting out internally which would be tough to see, and the optic sensor in the bottom of the distributor could be causing problems too. Some of the cylinders may not be firing when you think they are.
Are you sure it's 02 sensors? Just because code says 02 sensors doesn't necessarily mean they're bad. Bad 02 sensor code can also indicate bad cat. converter. If 02 sensors read exact same reading before and after converter they will trigger OBC to "sensor fault" - they should be reading 2 different readings. (Pre CAT/POST cat) I'd suggest replacing cat converter before replacing sensors.
remove the spark plug and see if it is wet. See if it smells like gas. Put the plug in the plug wire and crank the car to see if it sparks. If so, get a compression gauge and screw it into the plug hole and crank the engine. Good compression 100lbs or better. If good suspect injector.
Sounds like the cpi injector assembly. The fuel pressure regulator may be leaking. Or the poppet valves on the injectors may be sticking or shot. I replaced almost every part on my truck and that is what it ended up being the whole time. It's a common problem on these models. Hope this helped