One of the cylinders not firing!?

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Model T Ford Forum: Forum 2016: One of the cylinders not firing!?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 02:55 am:

The 1919 Roadster's running rough. I decided to ground each plug to try to figure out which cylinder was giving me trouble. When grounding number 3, there was no difference how the engine ran. When I take the plug out and turn the engine, I see a spark. Also there is arc coming off of the top of coil that goes to cylinder 3. Am I not getting enough spark to the plug while it's in the cylinder to ignite the gas? What causes the arc?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Tuesday, October 04, 2016 - 04:34 am:

It certainly seems like there is a problem with that coil. Try shift the coils and move it to another position - does the problem move with the coil?

If so, it's settled. Try another coil and/or fix the offending one. I would expect a bad capacitor so it's probably rebuild time.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rod Barrett - Anderson, IN on Tuesday, October 04, 2016 - 05:23 am:

If coil swapping does not solve the problem then do a compression check on the cylinder.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 05:35 am:

Compression in all cylinders is in the 40s.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Tuesday, October 04, 2016 - 09:46 am:

Is the arcing coming from the coil contacts, or the contacts between the coil and the coilbox? If it's coming from the coil contacts then the coil needs a rebuild along with the other three coils. If the arcing is within the coilbox, then you need to replace the wood with something better ... and check that your plug wires are good too. If high voltage can't get to the plugs it will start looking for another path. Roger gave you the best advice for narrowing down the problem fast - move the offending coil to another position.

Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By Pat Kelly Montana on Tuesday, October 04, 2016 - 10:53 am:

We had a guy on our last tour that had the same problem. We pulled all the plugs and they all sparked. Nothing fixed the poor running. We then changed all four plugs and it ran like a champ. PK


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 12:55 pm:

Coming from the coil contacts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Zachary Dillinger - Charlotte, MI on Tuesday, October 04, 2016 - 02:20 pm:

I agree with what the others have said re: switching parts around. Do it in a controlled manner, i.e. switch one part at a time. First the coil since it is easiest, then the plug, then the wire. See if the miss follows any of those parts and then replace as necessary. I'd bet you $100 you'll find it quickly with this method.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 05:08 pm:

Swapped coils and now cylinder 3 is firing and the cylinder I put the suspect coil in is not firing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 06:49 pm:

I figured the cap is bad so I rigged one I found laying around (a 630v 150m .22uf cap not correct) to the outside of the coil (not the right way to do things I know)

and It now runs on all 4. Than I thought (afterword of course) will this damage anything?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Tuesday, October 04, 2016 - 07:30 pm:

Jonathan,

It will work fine until you can make permanent repairs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Tuesday, October 04, 2016 - 07:47 pm:

Yeah it was a spur of the moment thing. I just
wanted to hear it run on all 4 for the first time since I owned it.:-)!! Thank you
PS; I didn't eliminate the original cap inside, ok? Jon


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