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High rpm engine problem

H

honkbox

New member
Good morning all. This is my first post, so thank you for providing this forum for all its wealth of information. I have a 2000 GTP. Under 1/2 and 3/4 throttle the car has no problems. Under WOT the car has no power and seems to miss. I immediately figured it was a fuel supply problem and changed the fuel filter. No help. I checked fuel pressure at the rail and it was within specs. The one interesting thing it did do though, was it wouldn't hold pressure after the key was turned off. I immediately figured it was an injector. The problem with that is there are no idle issues and it does not blow any smoke upon start-up. New plugs and wires, new air filter and no codes are being thrown. I know this car has a 2 speed fuel pump but I'm not sure how to test if that is working correctly. Could a bad fuel regulator cause this problem? As you all know parts are pretty expensive so I am hoping someone can steer me in the right direction before I just start replacing stuff. Let me know if there is any other information I can give to help you aid me with this problem. Any help you can send my way will be much appreciated.
 


An add on to anyone offering help. Just got it to throw a code. Went to O'Rilleys and scanned it. Code P0420. Do you think with the high flow cat I installed, the computer is trying to lean out the fuel because the oxygen sensor is bad? Just trying to give any info that might help. Thanks again.
 
working on car as I write this. pulled a couple of plugs and the engine is definitely running lean. any help would be great as to what to check next.
 
check for vac leaks a rich biased o2 sensor will force it to run rich lean aswell since the front o2 controls fueling
Check it with a multi meter should bounce around from 200-800 milivolts if it doesnt thats part or your issue

the highflow cat will through a code if the rear o2 code isnt taken care of and so on

Highflow cats arent as effective as factory ones so the rear o2 will trigger the 420 cat efficientcy code
 


update: found bad plug and wire and replaced both. engine ran worse and threw a blinking ses light. did some more reading on this forum and decided to change all the coils. running better and now no ses light but the wot hesitation is still there. I think i had two problems and fixed only one of them. The problem must be fuel related. Does AutoZone have a scanner that works when the car is on? O'Rilleys only had a passive scanner. By the way checked for vaccum leaks like instructed and none found.
 
I have the exact same issue. Car is running very lean I've replaced both o2 sensors and still a problem. Have a highflow cat in about a year ago. Wondering if my FPR is gone or if the really whiney fuel pump is the culprit. I have a tiny studder on idle almost like a miss and have replaced all the plugs and wires still there. Got no idea where to go hopefully someone can help before I start dumping un necessary money into this thing. The fuel filter was also changed about 5000kms ago that didn't help either. what is the best way to check for vac leaks all my lines seem fairly new I think they were replaced before I bought the car. Under WOT it seems like its missing something ..fuel or air Im assuming fuel sine i just put a brand new k&n in.
 


Still dealing with this problem thought i would throw it back and see if anyone has any new ideas. Replaced the pre cat O2 sensor but that didn't help. Seems like some others are dealing with the same problem and i was hoping they found a fix and can give some advice. Also, could any of you guys in the know, tell me if a slipping s/c belt might be the culprit. Would this cause the problems i am having? Thanks.
 
does it happen all the time, or does it get better when the car warms up, my car bogs down when my cars cold and im trying to figure out what it is. its not a bad MAF ive had that, youre car would be all over the place at idle and almost stall. and a slipping supercharger belt, you would hear it, look at the belt see if its torn at all
 
car runs like it should when it's cold. When it comes up to temperature is when the problems start. When the engine is cold isn't the computer put into a closed loop system till the car comes up to temp. Trying to figure out why this problem only seems to happens when car is warm. The only other thing I can think of is the fuel pump. Can anybody explain how the two speed pump works and how i can test it. Replacement is the last effort due to cost.
 
apply vacuum to the FPR.

if fuel comes out then the FPR needs replacing.

is the O2 wire touching any of your spark plugs?
 


hows youre fuel economy? code p0420m has nothing to do with youre car running this way, i had that issue for a long time before this happened to my car, its just the high flow cat flowing too much emissions, you can get that deleted if you know a guy with GM software. really seems like fuel pump, have you tried injector cleaner? and you might want to try a fuel system treatment too, i dont think its too much $.
 
Thanks for your input backinblack. When this whole thing started i put a new fuel filter on and put pour in fuel system cleaner. Guess I will try the fuel injector cleaner that you hook to the fuel rail. Can't imagine its a injector since there are no startup issues, no idle issues, no offline stumble, or any smoke upon startup. The car runs absolutely perfect and has no driveability issues except at WOT. 1/2 throttle and 3/4 throttle are just fine too, it's just when you smash it, the power goes away and you can smell it running hot. This weekend i am going to get elbow deep in the car and try to figure this out. I think i am going to get rid of the 9.00 a piece iridium plugs and see if that may be the problem too.
 
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