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Unread 04-12-2014, 04:24 PM   #1
qaiphyx
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1979 CJ7 
 
Join Date: Mar 2014
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Cylinder misfire, Idle and accelleration.

Have a cylinder misfiring and cant figure out the problem. New plugs, wires are good, timing is set, fuel mixture good. Misfires at idle and higher revolutions. Compression in all cylinders is good. Ideas?

1979 CJ 7 258 Carter Carb Electronic ignition.

Video of exhaust. Low idle

https://scontent-b.xx.fbcdn.net/hvid...cb&oe=5349DC50


Last edited by qaiphyx; 04-12-2014 at 04:38 PM..
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Unread 04-13-2014, 05:20 AM   #2
Mike Romain
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What kind of plugs? Bosch platinum will fast carbon up and cause a miss.

I do a test for leaky plug wires by spray misting them with water while the engine is running in a dark place. Sometimes there are amazing light shows from this.

I next check inside the distributor cap looking for carbon tracks or crud.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-13-2014, 07:49 AM   #3
Matt1981CJ7
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The video isn't working for me.

Assuming the ignition system is all good, the spark plugs are correct, and the timing is right, I'd be looking for a intake leak.

Matt
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Unread 04-13-2014, 07:49 AM   #4
qaiphyx
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Quote:
Originally Posted by Mike Romain View Post
What kind of plugs? Bosch platinum will fast carbon up and cause a miss.

I do a test for leaky plug wires by spray misting them with water while the engine is running in a dark place. Sometimes there are amazing light shows from this.

I next check inside the distributor cap looking for carbon tracks or crud.
It does it with both platinum and copper spark plugs, from what I can remember it also still had this problem when the dist and wires were brand new but ill do the spray test and see if I can find anything.

Any other ideas?

Could it be possible that the valves still need to be adjusted?
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Unread 04-13-2014, 07:51 AM   #5
qaiphyx
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Quote:
Originally Posted by Matt1981CJ7 View Post
The video isn't working for me.

Assuming the ignition system is all good, the spark plugs are correct, and the timing is right, I'd be looking for a intake leak.

Matt
Ill see if I can correct the issue.

Intake is good Ive already checked all the way through with leaks. Has new exhaust and intake gasket.
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Unread 04-13-2014, 08:15 AM   #6
qaiphyx
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basically it just goes mmmmPuhmmmPuhmPuhmmmPuh. doesn't run right seemingly either in the fact that it needs alot of rev to get going and well die out if I just slowly let the clutch out, maybe that's normal though?
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Unread 04-13-2014, 08:32 AM   #7
Mike Romain
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Quote:
Originally Posted by qaiphyx View Post
basically it just goes mmmmPuhmmmPuhmPuhmmmPuh. doesn't run right seemingly either in the fact that it needs alot of rev to get going and well die out if I just slowly let the clutch out, maybe that's normal though?
The valves are hydraulic, no adjustment other than tight.

I would be looking real close at the EGR valve too. A bad one that is sticky or a leaky one (had a foot rot off on mine so it was loose) can cause symptoms like you describe.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-13-2014, 10:02 AM   #8
qaiphyx
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Originally Posted by Mike Romain View Post
The valves are hydraulic, no adjustment other than tight.

I would be looking real close at the EGR valve too. A bad one that is sticky or a leaky one (had a foot rot off on mine so it was loose) can cause symptoms like you describe.
Im not currently running an EGR Valve.

Thanks for the information on the valves. I highly doubt that one is loose.
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Unread 04-13-2014, 10:22 AM   #9
Mike Romain
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Quote:
Originally Posted by qaiphyx View Post

Im not currently running an EGR Valve.

Thanks for the information on the valves. I highly doubt that one is loose.
Could the cover plate for the EGR be leaking or is that non existent?
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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Unread 04-13-2014, 11:33 AM   #10
qaiphyx
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spayed it with starter fluid, nothing. I opened a port in the manifold though and the idle went up, is this normal?
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Unread 04-13-2014, 11:34 AM   #11
Mike Romain
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Quote:
Originally Posted by qaiphyx View Post
spayed it with starter fluid, nothing. I opened a port in the manifold though and the idle went up, is this normal?
Yes
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
Some Canadian Bush Jeep Runs and Build Photos: http://mikeromainjeeptrips.shutterfly.com (10 new albums added Sept 16/10)
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