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Vacuum Issue?

 
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Old 07-21-2007, 03:38 PM
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Vacuum Issue?

Ok, so my check engine was throwing a "cylinder #1 misfire" code... so I did a compression test.

Cylinder 1 200
Cylinder 2 195
Cylinder 3 205
Cylinder 4 190

And they all held... no pressure drop.

So it doesn't look like my valves or pistons are shot... the block isn't cracked because there are no oil/water leaks... what could it be???

I noticed that there was a vacuum hiss coming from under the hood, so I'm thinking there may be a vacuum leak somewhere? Could a vacuum leak cause a cylinder to misfire? My sparkplugs all look good, gonna run some Fuel injector cleaner as soon as the gas gets closer to empty. Any thoughts??
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Old 07-21-2007, 03:41 PM
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change your plug and or plug wire

if your plug wire doesnt fall within the neccisary resistant requirement you will get a weak spark

also if that doesnt help you may want to look at your knock sensor
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Old 07-21-2007, 03:42 PM
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also if you are using anti-size on your plugs make sure to use only a bare minimun amount as the anti seize can cause the plug to foul out
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Old 07-21-2007, 06:15 PM
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A vacuum leak could be from a pinhole in a line somewhere. Or a vacuum line could've gotten disconnected. I had an injector line disconnected on an 300zx that was causing an irratic idle and poorly firing engine. Try to find all the wires/vacuum lines and check for connections. (especially at the fuel rail)

A couple of years back, I was referred to a product known as "Seafoam". It is a universal cleaner for an engine. READ THE DIRECTIONS! I would try it for the fuel injectors first. Worked like a charm for me. (it was and older car though)
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Old 07-21-2007, 07:02 PM
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Well let me give you a little more background about what happened. I bought the car a week ago today, and i noticed that it idled too low and wanted to stall out sometimes. The other night, I took it out and really opened it up on the highway, i accidentally shifted from 7k in 3rd gear, down to 2nd gear instead of 4th (ouch!) it scared the piss out of me. I instantly noticed it sounded like a mis-fire at the exhaust. The next morning I drove it to work and the CEL came on. Upon diagnostics I got the "Cylinder number 1 misfire" code (71). I thought I floated a valve and bent it up or something from the mis-shift. But like I said before, the compression test came back fine. Do you think the mis-shift could have damaged my spark plug?? or maybe the #1 fuel injector??
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Old 07-22-2007, 12:14 PM
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Bump... any thoughts guys?
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Old 07-23-2007, 12:54 AM
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Ok so I found this online tonight:

"If compression is ok and the miss goes away at higher engine speeds, suspect a vacuum leak. At idle, intake manifold
vacuum is high and each cylinder receives a rarified air\fuel charge. A vacuum leak will lean out the mixture to the point
where the nearby cylinders will skip and misfire, but run ok at wider throttle openings."

Found that on a random Dodge website, but I assume that it's probably a universal statement.

Any suggestions on techniques to find a vacuum leak? I've heard a couple different methods. Someone told me to get a can of carb cleaner and spray it around my vacuum lines until the engine speed starts to pick up, meaning that the vacuum leak is sucking in the carb cleaner in a specific area...

I've also heard of grabbing a 3 foot length of 3/16" vacuum line, and putting one end to your ear and with the other end probing around the vacuum lines until you actually hear the leak through the hose... Any better suggestions guys?
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Old 07-23-2007, 03:06 PM
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No one?
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Old 07-24-2007, 03:30 PM
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im thinking just replace the vacuum lines check every single one of them i think thats the safest way and probably the fastest way to do it
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Old 07-24-2007, 04:27 PM
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Originally Posted by JDMPitBull View Post
im thinking just replace the vacuum lines check every single one of them i think thats the safest way and probably the fastest way to do it
ditto
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