vacuum leak and missfire codes

**SgtMarshal** · 02-16-2013

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

**Bluemagic** · 02-16-2013

Vacuum should be 19-21 I believe.

**Fivefingerdeathpunch** · 02-16-2013

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.

**SgtMarshal** · 02-17-2013

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.

**Erik Adam Rodriguez** · 02-17-2013

get carb clener and spray aroung the lim

**mskram1** · 02-24-2013

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

**SgtMarshal** · 02-25-2013

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.

**mskram1** · 02-25-2013

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...

**Scottydoggs** · 02-25-2013

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

**SgtMarshal** · 02-27-2013

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?