Possible Vaccuum Leak
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Freshman User
Joined: Jun 2003
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Possible Vaccuum Leak
Hi,
I have a 99 F-150 4.2L and is giving off codes 171 & 174. I have about 150,000 miles on my truck. I have been experiencing some kind of jerky feeling when I accellerate faster at some times in the past month before the 171 and 174 codes ever showed up. I initially thought it was either my transmission skipping or my brakes rubbing against my rotors. My transmission was rebuilt about 15,000 miles ago and my brakes were replaced last month. I am thinking this could very well be a vaccuum leak that has been in existance before the pcm ever triggered the 171 and 174 codes. I am just wondering, based on my observations and conditions, Will vaccuum leaks happen without triggering a code for some time later? So far, I have replaced my PCV and the hose behind the intake. I have not replaced the hose under the intake or the hose from the pcv to the intake before the metal tube. I guess I will try those next. What else could there be that is causing a vaccuum leak?
Thanks,
Chris
I have a 99 F-150 4.2L and is giving off codes 171 & 174. I have about 150,000 miles on my truck. I have been experiencing some kind of jerky feeling when I accellerate faster at some times in the past month before the 171 and 174 codes ever showed up. I initially thought it was either my transmission skipping or my brakes rubbing against my rotors. My transmission was rebuilt about 15,000 miles ago and my brakes were replaced last month. I am thinking this could very well be a vaccuum leak that has been in existance before the pcm ever triggered the 171 and 174 codes. I am just wondering, based on my observations and conditions, Will vaccuum leaks happen without triggering a code for some time later? So far, I have replaced my PCV and the hose behind the intake. I have not replaced the hose under the intake or the hose from the pcv to the intake before the metal tube. I guess I will try those next. What else could there be that is causing a vaccuum leak?
Thanks,
Chris
Senior User
Joined: Feb 2005
Posts: 131
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There is a hose that runs against the LH side rear of the firewall and connects to the back of the throttle body that is bad about rubbing against the firewall and rubbing a hole in it.
The best way to find a vacuum leak, or leak(s), is to first off listen for one - then go buy you a couple cans of brake parts cleaner and just start spraying all around your engine - all vacuum compents, intake gasket and plenum, etc etc until you hear a change in the way the truck runs. When you hear a change in the way the truck runs, its sucking that brake cleaner in and there is your vacuum leak.
Also a possibiliy your mass air flow sensor could need to be cleaned or actually be bad. Also, make sure you change your fuel filter and clean your fuel injectors and never rule out your fuel pump as possibly being bad.
Good luck
The best way to find a vacuum leak, or leak(s), is to first off listen for one - then go buy you a couple cans of brake parts cleaner and just start spraying all around your engine - all vacuum compents, intake gasket and plenum, etc etc until you hear a change in the way the truck runs. When you hear a change in the way the truck runs, its sucking that brake cleaner in and there is your vacuum leak.
Also a possibiliy your mass air flow sensor could need to be cleaned or actually be bad. Also, make sure you change your fuel filter and clean your fuel injectors and never rule out your fuel pump as possibly being bad.
Good luck
