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Old 09-13-2013, 09:17 AM   #1
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Misfire

I have a misfire at idle and need to break down and try to find it. I've taken it to a shop and he said it could possibly be an intake mani leak. Then I changed my plugs ended up blew one out. Had to fix the threads and new cop and everything was good with that but I still has the misfire at idle. He said that its only at idle idk about that. I can feel it when I'm just barely cruising no problems at wot. This was addressed a while back but had the misfire since I've owned it. I'll post a video below. And I'm gonna scan it myself what should I be looking for?

http://youtu.be/dfG8yguxN5E
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1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-13-2013, 09:33 AM   #2
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Mine is doing the same thing now I did spark plugs, and my coils are good and my intake is good I'm Gona go new upstream oxygen sensors it's the only thing left, unless its a faulty injector but mine only does it at idle or at a steady rpm
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Old 09-13-2013, 09:35 AM   #3
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I think he said maybe an injector he putting some cleaner in it. Will that throw a code?
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Old 09-13-2013, 09:52 AM   #4
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Nope
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Old 09-13-2013, 10:06 AM   #5
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**** okay
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1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-14-2013, 12:56 AM   #6
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A bad egr valve could cause idle misfire
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Old 09-14-2013, 02:37 AM   #7
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Sounds like a vacuum leak. If u slowly increase throttle then almost suddenly the misfire goes away, the rpms jump a bit and it runs fine - thats usually a vacuum leak.
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Old 09-14-2013, 08:28 AM   #8
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It still misses when i slowly rev it up but not at wot.
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2003 GT - full bolts ons, suspension, and drag radials
1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-14-2013, 12:35 PM   #9
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That could be a really bad air leak.

Its like this, when not at wot there is too much air in the air to fuel ratio to fire properly, but at wot its sucking so much air it pretty much needs all it can get.

Get some hairspray or something flammable and sprayable and while running the engine (but not hot) spray around the intake manifold, vacuum lines, etc. if at any point you hear an fluctuation in rpm then you have found ur leak.
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Old 09-14-2013, 01:29 PM   #10
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Might try that tonight. I know these intakes are known for that
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1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-14-2013, 09:30 PM   #11
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I had a coil that was good at wot but it would random misfire at idle. I bought a cheap 15.00 coil from jegs to use as a tester. I would put the new coil on and drive it a bit and see if the misfire was still there. After moving the new coil to the third plug on the driver side the misfire stopped. Then I bought a new motorcraft coil and I keep the cheep coil in the trunk for emergencies.
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Old 09-15-2013, 01:57 AM   #12
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From my experience following a head swap from a 97 stock to a 2004 new head, I suffered the same with a bad injector because I was using remanned injectors. number 7 failed and cause the car to sound like a tug boat. The symptoms are as follows: When at idle it sounded through the exhaust at the connection of the manifold to the downpipe like a chugging sound on the driver side. While driving it operated fine till I dropped below 2000 RPMs. It lagged with a almost stalling or chugging sound at any speed anytime the RPMs fell below 2k. Pulling the spark plugs will reveal a fuel wet plug at most. At WOT all injectors are firing a near optimum and the offending injector will not be visible. I am certain you have an injector problem. Not sure how to fix with coil on plugs, I have standard ignition. however, 99-04 do develop the blow-the-plug-out problem regardless due to compression problems. I got a 2012 head set so I believe that wont happen to me pushing near 400 NA and all. Keep us posted when you figure it out.
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Old 09-15-2013, 02:28 AM   #13
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Quote:
Originally Posted by Mfore33 View Post
I had a coil that was good at wot but it would random misfire at idle. I bought a cheap 15.00 coil from jegs to use as a tester. I would put the new coil on and drive it a bit and see if the misfire was still there. After moving the new coil to the third plug on the driver side the misfire stopped. Then I bought a new motorcraft coil and I keep the cheep coil in the trunk for emergencies.
I do the same thing
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Old 09-15-2013, 02:35 AM   #14
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Both of the last posts are good, first thing u do though is see if there is a vacuum leak, then to see if it is a cylinder that is misfiring, see if u can read the code. That will help a lot. If you cant do that then while running the engine, pull one cop off at a time and the one that doesnt make ur engine run worse is the culprit.
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Old 09-15-2013, 09:48 AM   #15
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Gonna do this today. How do i pull the cop i know how but i wanna make sure before i get out and not be able to ask anyone. Isnt there screws to take it off
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2003 GT - full bolts ons, suspension, and drag radials
1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-15-2013, 01:49 PM   #16
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Should be just one bolt holding cop on the intake and one plug on the top if the COP. Then it just pulls off
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Old 09-15-2013, 05:07 PM   #17
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I don't have the tool to do this right now. Left my tools at home. damn
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2003 GT - full bolts ons, suspension, and drag radials
1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

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Old 09-16-2013, 03:57 PM   #18
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Another thing you should always have in ur trunk is an emergency tool kit.
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Old 09-16-2013, 07:52 PM   #19
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I have a tool box that i always keep in there but ii had my wheels in the trunk so had to take it out.
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2003 GT - full bolts ons, suspension, and drag radials
1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

Follow me on instagram @nicknold for car and truck pictures
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Old 09-16-2013, 09:00 PM   #20
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Haha sounds like my luck man
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Old 09-16-2013, 10:12 PM   #21
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I'm gonna have my car loaded down two wheels and four tires or whatever i can fit.
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2003 GT - full bolts ons, suspension, and drag radials
1998 cummins - 150hp injectors | FASS fuel kit | 4" straight pipe | 5" lift | BHAF | 20" wheels | edge juice w/ attitude | built auto trans with stall | closing in on 900tq | bigger turbo soon..

Follow me on instagram @nicknold for car and truck pictures
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