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vacuum leak and missfire codes

SgtMarshal

SgtMarshal

Active member
my gtp has been hesitating under heavy acceleration. yesterday it tripped two codes P0171 P0300. how do I know how much vacuum I should have? I have an aeroforce scan guage that I can scan with but im not sure what it should be showing. any other help is appreciated
 


Setup the aeroforce to read MAP in/hgs, and see where its at. Should read around -19 to -20.6 at warmed up idle.

I would do a spark plugs and wire change if you never have aswell, would be easy things to do, to try and get rid of the misfire code.
 
I ran the engine until the coolent tempurture was showing 180 to make sure it was warmed up and at idle it was showing -14.2. I did the gen 5 swap 3 weeks ago so im wondering if it has something to do with that.
 
check the t fitting under the sc snout and the egr valve metal tube that goes to the lim... those are the most common and could also cause p0300 but i would also listen to fivefinger about the plugs and wires
 


I confirmed it is a vacuum issue. the fitting on the supercharger that you are supposed to run a vacuum line to the throttle body had a cap on it. so the supercharger had increased crank case pressure. I took the cap off and cleared the code and it hasnt come back, so if I understand it correctly the fitting is acting like a breather for the supercharger until I run the vacuum line.
 
ok you lost me there??? did you just uncap the fitting and leave it open or did you add the necessary vac line to the throttle body??? because uncapping a vaccuum fitting will not act as a breather and if its after the maf sensor itll cause issues...
 
i think hes talking about the pcv valve was capped off, and not ran to the TB like it should be. its a gen 5 swap deal.

and trust me i had to re read it 2 times to come to that conclution lol
 
the fitting im talking about is on the backside of the supercharger and im pretty sure that its the one I need to run a vacuum line from and connect to the throttle body. I just havent gotten around to taking the throttle body off to drill out the brass plug and install a fitting so I can install the vacuum line.

does that make more sense?
 


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