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Misfire at idle to 1000rpm **UPDATE** 

 

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 Post subject: Misfire at idle to 1000rpm **UPDATE**
Posted: Thu Jan 04, 2007 9:25 pm 
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I have a misfire problem that is mainly evident at idle on my 4l EF. It is a miss on every stroke which gives the car a baby calming shake. The miss becomes less noticeable on part throttle applications and seems to disappear at 1000rpm.

I have done the following: replaced plugs, leads, compression test (all 180psi), new coolant and radiator flush (not related I know), spray tested for vacuum leaks, replace PCV, disconnect PCV (no difference), reset idle speed to factory spec, clean and test ISC, change LPG mixtures to full rich to see if lean miss, change LPG mixtures to full lean to see if rich miss.

By placing a timing light on all leads it seems that cylinders 4 and 5 are missing. This would discount coil pack as they are no on the same coil (it is 1,6-2,5-3,4 isn't it?).

Any ideas?

cheers
Scott

 

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Last edited by MacGyver on Sun Jan 21, 2007 1:48 pm, edited 1 time in total.

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Posted: Fri Jan 05, 2007 12:36 pm 
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exactly the same problem in my ef! just i dont run gas!!! anyone have any ideas???

 

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Posted: Fri Jan 05, 2007 1:18 pm 
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I think I have eliminated fuel as the problem as above. Compression is out as it is perfect. That only leaves ignition. I have a spare coil pack here so I will change it when the engine gets cool.

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Posted: Fri Jan 05, 2007 1:41 pm 
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there was a thread on how to fix poor idle on the i6 a few weeks back. it was some little things in the computer that needed replacing, cant remember what they were called but it didnt seem like a big job.

 

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Posted: Fri Jan 05, 2007 1:43 pm 
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No that would not apply. This is not a rough idle ramping up and down as the ECU tries to control the idle speed, this is a misfire on one maybe two cylinders.

cheers for the input though

Scott

 

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Posted: Fri Jan 05, 2007 1:47 pm 
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Is this only on LGP ?

 

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Posted: Fri Jan 05, 2007 1:50 pm 
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Do the crank angle sensor and harmonic balancer ok?

 

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Posted: Fri Jan 05, 2007 2:18 pm 
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Car is LPG only. As I mention it is not fuel related as I have adjusted the mixtures to very rich and very lean with no difference in the misfire.

cheers
Scott

 

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Posted: Fri Jan 05, 2007 10:03 pm 
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Just replaced the plugs again, tried a different coil pack and tested all the leads (they were new anyways). Still a miss. Maybe a little bit better.

I guess I should test the cam and crank angle sensors. Also should do a ECU diagnostic.

I'll let you know.....

cheers
Scott

 

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Posted: Sat Jan 06, 2007 1:47 am 
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Yeah, certainly seems ign related - you'd probably find if you were still running petrol, the condition probably wouldn't be noticeable.

Unfortunately with LPG, any little weakness in the ignition system will show up.
I can only suggest to give the coil pack plug terminals a quick wire brush to make sure they are absolutely clean - plug leads are new so nothing needed there.
The other thing I'm wondering maybe a couple of plugs are struggling with the plug gaps. IIRC plugs come set at 1.1mm - maybe try 1.0mm.
The crank sensor may need a good clean. Since a petrol EF motor will run fine without the cam angle sensor (only needed for injectors), I doubt checking it will have any bearing on LPG operation.
The other thing is maybe do a nighttime visual on the plug leads while the engine is running - might notice some crossfire, etc. You wouldn't think so with new components, but wouldn't hurt.

 

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Posted: Mon Jan 08, 2007 3:06 pm 
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Update. I have pulled engine codes....111 so no problem. I have tightened intake bolts and rechecked for air leaks and nothing. Next I will try and see if I can isolate to one cylinder only by pulling plugs.


I'm having lots of fun.... :-P

 

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Posted: Sun Jan 21, 2007 1:47 pm 
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I've done some more troubleshooting lately. All valve springs and rockers are ok. No spark jumping across leads. I hooked a timing light up just to see what the timing was doing (can't adjust because it's an EF) and at idle the timing is all over the place. There are really big movements that coincide with the miss. Like 10 degree jumps. When I raise the revs and the miss goes away the timing smooths out to be rock steady with nice smooth movements.

What could this be? Knock sensor? Cam or crank angle sensor?

cheers
Scott

 

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Posted: Sun Jan 21, 2007 2:13 pm 
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i am interested to find a solution

 

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Posted: Sun Jan 21, 2007 3:50 pm 
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i did an efi course recently. during this course matey talked about the ef and au having earthing problems for the tps. he said this would cause a flood miss on idle, as the tps tells the computer that the throttle has been opened. when it hasn't. try providing the tps with its own earth.

 

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Posted: Sun Jan 21, 2007 5:13 pm 
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Dunno if the tps would have much effect as it is dedicated lpg so no way the tps can cause a flood misfire. Thanks for the input though.

Just did some more messing around and number 6 has a quite regular miss while 4 and 5 are missing as well though irregular. Worked this out by using timing light on all leads and 1,2,3 are nice regular flashes, 4 and 5 are a bit messier and 6 is down right disgraceful.

I have tried another coil and the miss felt the same although I only had that coil sitting on top of the tappet cover. It is still running the original coil now. Coil has a condenser bolted to the front right. Didn't think EF's had one. I might change that over and see if it helps.

cheers
Scott

 

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