View Full Version : vacumm leak?

04-11-2012, 11:14 AM
i have a 2001 Z28, when i bought the car it did not have cats or rear o2 sensors and it was throwing engine codes p10171 and p10174. i replaced the cats and o2 sensors, but still have the same codes. i was told that it was a vacumm leak by one of the guys at the store that scanned my car. and someone else told me it could be a map sensor??? has anyone had similar issues that can help?

also, it has ls6 stage 2.5 heads, its the only mod it has. could that be a issue as well? Thanks.

04-12-2012, 12:12 PM
I assume you meant to post P0171 & P0174 fuel trim system lean bank 1 & 2?

Things that come to mind:
-plugs and wires (usually cause rich conditions, but it couldn't hurt)
-vacuum leak

04-12-2012, 02:16 PM
ok thanks, the spark plugs looked pretty good when i put them back in, the wires i had to buy because they were pretty messed up. as far as the maf, what would the car be doing if it had a bad maf?

04-12-2012, 05:27 PM
Have someone check out the fuel trims. Should be Between +10 -10

04-12-2012, 09:54 PM
P0171 and P0174 means both banks are lean, Your PCM is seeing long term fuel trims greater than 23 percent. Ideal fuel trims should be close to zero, You need to look at your HO2's with a scanner to see if they are fluctuating between 200mv and 800mv to rule out bad o2's. If they check out ok the next step would be too look for

- Vacuum leaks at the throttle body, injector o-rings or the intake manifold
- leaks on the exhaust system before the HO2S
- Leaks in the AIR System or malfunctioning shutoff valves
- Low fuel pressure due to weak fuel pump or restriction at the fuel filter.

04-13-2012, 10:19 AM
alright, ima take apart my car this weekend to see if i can find anything simple. i already know the p side exhaust manifold has a broken bolt on it. the air system i noticed is always on. as soon i turn the car on it kicks on. dont know if that is normal or not.

04-13-2012, 03:24 PM
Fuel pump

04-13-2012, 05:22 PM
Grab some carb cleaner and carefully spray around the intake manifold for any leaks. Also behind where the map sits and so on. Check all hoses and connections. Listen carefully for an idle change while doing this. Do this before you start to take things apart or start to throw parts at it randomly and waste money you don't have to.

04-13-2012, 11:30 PM
ok ill def try with the carb cleaner. do you guys think having the ls6 stage 2.5 heads would change anything on my car? or should i not worry about those? i would hate to swap them again.

04-14-2012, 12:38 AM
no, the heads most likely are not causing your lean condition. Its most likely gonna be a vacuum leak, do the carb cleaner thing manny suggested before you take it apart. Focus on the tb gasket, pcv lines, and manifold gaskets where it seals against the heads. The manifold gaskets are just cheezy o rings that often go flat and leak

04-17-2012, 10:03 AM
ok, so the check engine light is still on and the only thing i found that was unplugged was a small line that wasn't plugged in, not to sure what it was, it went towards the direction of the heater core. i went ahead and took everything off anyway, i resealed everything, the tb, manifold gaskets, the pcv valve was old and i noticed that there was alot of oil throughout the intake and spark plugs so i replaced that. i also tried the carb cleaner. and i wasnt able to find any leaks. i dont have a scanner, and kinda running out of ideas. any more thoughts?

04-17-2012, 07:25 PM
If the problem doesn't exist anymore the light will go away on it's own, not instantly but eventually it will. Find someone with a scanner and look at your long term trims

04-18-2012, 05:48 PM
the light went away yesterday, i had it scanned again and now it's throwing p0300 i think, random misfire. i already changed spark plugs and wires. not to sure what else can cause misfires.

04-18-2012, 05:51 PM
What type of plugs and wires?

04-18-2012, 05:57 PM
Make sure the spark plug wires are plugged in all the way and that you dont have a cracked spark plug.

04-19-2012, 09:02 AM
i have the ngk tr5ix? i think thats what there called. and as far as wires, they are oriellys stock replacement wires. as far as the wires, when i put them in all of them would click in but i'll double check to make sure.

04-19-2012, 11:42 AM
is there some kind of software compatible with my laptop that i can get to be able to read my car computer?