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buckhunter#1
Novice
Feb 19, 2011, 12:55 PM
Post #1 of 11
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mysterious misfire 2.4 L
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alright guys, i need help. i have a 1997 cavalier Z24 with a 2.4L engine. it is running really rough while idling in park or gear. you can clearly hear the miss in the exhaust and see the engine shaking while its running. this miss is not so evident while driving. i still have pretty good acceleration, and dont hear or feel a miss while im on the gas. also, while deccelrating, once i get below 40 mph, which is around 1500 rpm, the tach starts jumping up and down ranging from 900 to 1400 rpm. it is jolting the engine while it does this. after a few seconds, once the car is slow enough, it levels out. it also occasionally acts as if its going to stall when shifting into drive after backing out. the only code that the engine has thrown is a injector #2 misfire, which i resolved by replacing the fuel injector.
Okay, here is what i have done so far:
i have replaced all four plugs. i then tested for spark, which was there.
i have tested the coils. they were fine. i have also swapped out the entire coil housing including the ICM with a different one with the same result. so it couldnt be the coils.
i have not replaced the wires as they are just little plastic connectors and show no evidence of being faulty.no cracks, the connectors inside are fine as well.
i have replaced one injector, and the rest are working fine. i disconnected the harness on each one while it was running to figure out the bad one initially. if an injector were bad, the engine would throw a code for that anyway. right ???
i have replaced a few of the vacuum lines that were in bad shape.
i really dont know where else to go with this. appreciate any advice you can give. thanks.
(buckhunter)
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re-tired
Veteran
/ Moderator
Feb 19, 2011, 7:29 PM
Post #2 of 11
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Re: mysterious misfire 2.4 L
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IM curious on how did you test coils . I think they are part of your problem .They can break down under a load . You say prob lessens as you get going . sounds like a vac leak also ... ckeck ciosely ariound pcv valve area.
LIFE'S SHORT GO FISH
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crh878
New User
Feb 19, 2011, 8:51 PM
Post #3 of 11
(7656 views)
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Re: mysterious misfire 2.4 L
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Sounds like you're not get either fuel or air to the engine especially when at low rpm's.
I'd start the car up and unplug each vacuum line individually and make sure there's plenty of suction from each.
This maybe a dumb question but how old are your air filter and fuel filter?
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buckhunter#1
Novice
Feb 19, 2011, 9:05 PM
Post #4 of 11
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Re: mysterious misfire 2.4 L
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i had the coils ohm tested at autozone. both coils tested fine according to their test. i also switched out the entire coil pack housing and icm with a buddies from his car and had the same problem. the switch made no difference in performance. i also am leaning toward a vacuum leak, just a matter of finding it. ive wiggled harnesses while running, and saw no apparent change in the idle. ill be trying to find an apparent vacuum leak tomorrow. any other ideas??
(buckhunter)
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re-tired
Veteran
/ Moderator
Feb 20, 2011, 7:24 PM
Post #5 of 11
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Re: mysterious misfire 2.4 L
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Heres an old tip. Alas , all my tips are old tips. Get a 2-3 ft lenght of hose . 3/8" vac or fuel hose is perfect and cheap from a parts house . Place one end at ear ,slowly pass other end near where you suspect a leak . As you pass over trhe vac leak it will sound like a tornado. Get an idea what to listen for by pulling a small vac hose off and passing hose over it.
LIFE'S SHORT GO FISH
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autojoe
User
Feb 21, 2011, 6:49 AM
Post #6 of 11
(7634 views)
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Re: mysterious misfire 2.4 L
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best way check for vacuum leaks is with smoke machine but next to that is with propane.propane is safer than carb cleaner.they make a special adapter I think thexton makes it that attaches to propane bottle.I would take a fitting used to sweat(solder)copper pipe available at hardware store and unscrew the end piece so all you have is the screw on piece that screws onto the portable propane tank with a short straight piece and attach the vacuum hose to that.only need a small propane tank and then start car and turn propane on and run along gaskets,hoses even the egr valve can cause a vacuum leak itself.if you notice a change in the idle you have found the vacuum leak.the vacuum hose gets real cold.I have used it before I got the one from thexton.Now I have a smoke machine.I also before hooked up a scan tool and looked at 02 sensors and ran propane and looked for a change to rich condition on scan tool.also try manually opening the egr valve with a hand vacuum pump at idle and see if you notice a rpm drop and engine stall....if not than egr may be leaking creating a vacuum leak.
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re-tired
Veteran
/ Moderator
Feb 22, 2011, 11:29 AM
Post #7 of 11
(7625 views)
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Re: mysterious misfire 2.4 L
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Smoke machines and propane enrichers are nice so would be a 4 gas analizyer . But none are practical for the homeowner diy type. A simple hose and an ear is safe ,simple and accurate . we are not deaing with shop techs. Just diy'ers looking for tips .
LIFE'S SHORT GO FISH
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 22, 2011, 3:09 PM
Post #8 of 11
(7624 views)
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Re: mysterious misfire 2.4 L
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I get your point RT but if that leak is not physically accessible, the hose isn't going to find it and he's going to assume he doesn't have one. We all know how thorough DIYers are in looking for leaks.......LOL
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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zmame
Veteran
/ Moderator
Feb 22, 2011, 4:06 PM
Post #9 of 11
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Re: mysterious misfire 2.4 L
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I know on those engines too the towers(from the coil to the plug) tend to go too. also ignition module since there are built in one unit makes it tricky to diag. My wifes car 01 sunfire 2.4L ended up being the towers. My friend had coil plenum i took one component off at a time and swapped it till it went away.
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Hammer Time
Ultimate Carjunky
/ Moderator
Feb 22, 2011, 4:24 PM
Post #10 of 11
(7618 views)
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Re: mysterious misfire 2.4 L
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I have fixed many of these with a new coil housing but he says he already changed that.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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1999Z24
User
Feb 26, 2011, 12:27 AM
Post #11 of 11
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Re: mysterious misfire 2.4 L
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O2 sensor? my old 1996 Cavi Z24 idled and bounced between 500-1500 RPM's. i was told it was probably vacuum leak or O2 sensor. just throwing out some suggestions. id hate to see you change the O2 sensor and that wasnt it. thats not easy to get off. lol.
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