# Vacuum leak



## speedy_240sx (Nov 6, 2003)

I have a vacuum leak that is causing a miss fire. Do any of you have an idea of which vacuum line that it might be and a pic would be helpful to help me locate if you have an idea. IT only misfires at low rpms at around 1250 all cylinders are firing. the misfire is so bad that it makes the whole car shake like there was a big cam in a big block V8.


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## rogoman (Dec 16, 2004)

speedy_240sx said:


> I have a vacuum leak that is causing a miss fire. Do any of you have an idea of which vacuum line that it might be and a pic would be helpful to help me locate if you have an idea. IT only misfires at low rpms at around 1250 all cylinders are firing. the misfire is so bad that it makes the whole car shake like there was a big cam in a big block V8.


How do you know the motor has a vacuum leak? Did you test it with a vacuum gauge?


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## speedy_240sx (Nov 6, 2003)

THe reason I know it is a vacuum leak is because you can hear the suction over the rumbling of the motor. I have change spark plugs and wires so thy are not the reason for a misfire.


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## rogoman (Dec 16, 2004)

speedy_240sx said:


> THe reason I know it is a vacuum leak is because you can hear the suction over the rumbling of the motor. I have change spark plugs and wires so thy are not the reason for a misfire.


If you can hear the hiss that loud, you should be able to easily pinpoint the source of the leak. Check the intake plenum bellows for cracks at both ends; next to the MAF and next to the throttle valve housing. Also check for loose intake manifold nuts.


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## James (Apr 29, 2002)

speedy_240sx said:


> THe reason I know it is a vacuum leak is because you can hear the suction over the rumbling of the motor. I have change spark plugs and wires so thy are not the reason for a misfire.


That's not a good way to know if it's a vacum leak. Get your hand on a vacum gauge and see how it is at idle. Hissing sounds can come from anything.


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## speedy_240sx (Nov 6, 2003)

I pinpointed it out today. it is the intake gasket between Cylinders 3 & 4. Right there there are many hoses that either are vacuum lines of fuel lines so it was hard to figure out just what it was but the guy that helped take my head off and put it back on showed me a trick to find the leak. We sprayed WD-40 around the area until we were able to pinpoint the problem. So the problem actually was a intake leak.


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## speedy_240sx (Nov 6, 2003)

The new gasket fixed the problem. it took about 3.5 hours to replace. runs like a champ again.


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