This is kind of a long post, but here goes.
6-5-2016
Last fall I had a problem with my 72k mile Cobra stumbling and missing in all gears around 1800-2100 RPM. The IMRCs were functioning fine (and they still are). I changed the fuel filter and had the ignition system tested on a scope by a local shop last fall. They found out later that the plug wire on cylinder 1 was bad. I replaced the whole set with genuine Motorcrafts and the problem went away … for 3000 miles. This morning, I noticed the car started doing almost exactly the same thing and not setting any kind of a code. I think I will change the plugs with a fresh set to see what that does. I am thinking that the misfire may have fouled the plug on cylinder 1 last year and maybe it is just now acting up because of that.
Update: 6-6-2016
I correctly gapped and changed the plugs and there was no change in the symptoms at all. All of the old Autolite plugs were fine and not fouled. Cylinder 3 did have very small amount of oil in the spark plug tube that coated the very bottom of the plug body. I know this is very symptomatic of a perished spark plug tube o-ring seal in the valve cover.
So now I am left with only a few possibilities now that the wires and plugs are new with no change in the symptoms.
Update: 6-7-2016
I looked at the spark plug tube on cylinder 3 again to see if it had oiled up again and it hadn’t. The spark plug boot was clean and dry so I am kind of ruling out that cylinder as the cause of the miss. I cleaned the MAF sensor with MAF cleaning spray and reseated all of the spark plug wires again. Took it for a test drive and there is no change at all. I will still change the passenger side valve cover gasket and spark plug tube seals as a maintenance item but I do not believe it is causing my current problem.
I think the only thing I can do is schedule it to be scoped again so it can be accurately diagnosed. I don’t want to guess and throw parts at it.
Update 6-8-2016
So, the car finally set a code P0301 Cylinder 1 misfire detected. The car is really running badly now. This is the same cylinder that was diagnosed as having a bad spark plug wire last year. As I stated, I replaced the spark plug wires at that time and the problem went away but came back this week after 3000 miles. I don’t get what is going on with that!
I put a spark tester on cylinder 1 and it seemed to give good spark. I checked the whole side and they all seemed to have a similar look to the spark. I was bummed because I had expected to get no spark on cylinder 1 which would have indicated a bad wire or coil tower. I had planned to swap wires between 1 and 5 (short cables) to see if the problem followed the wire thus telling me if it was the coil or the wire. With my luck I would switch them and the ECM wouldn't set a code.
I don’t know whether to think the 3000 mile wire is defective or not. Logic tells me the coil is bad but I am not often right when throwing parts at a problem.
The other option could be a bad fuel injector on that cylinder. Based on that, I tested the injector and it came back at 14.6 ohms, which seems within spec. I put a noid light on the harness and it lit fine with the injector pulse signal from the ECM.
Just curious what you all think and I appreciate any responses. This is getting frustrating. My vote is still for a bad coil but I just don't know. It is a non-returnable part so if it isn't the problem I will have wasted the money. I really expected to find I had no spark on cylinder 1 due to the wire or coil but found neither to be the case. The wire also showed a resistance of 8.65.
6-5-2016
Last fall I had a problem with my 72k mile Cobra stumbling and missing in all gears around 1800-2100 RPM. The IMRCs were functioning fine (and they still are). I changed the fuel filter and had the ignition system tested on a scope by a local shop last fall. They found out later that the plug wire on cylinder 1 was bad. I replaced the whole set with genuine Motorcrafts and the problem went away … for 3000 miles. This morning, I noticed the car started doing almost exactly the same thing and not setting any kind of a code. I think I will change the plugs with a fresh set to see what that does. I am thinking that the misfire may have fouled the plug on cylinder 1 last year and maybe it is just now acting up because of that.
Update: 6-6-2016
I correctly gapped and changed the plugs and there was no change in the symptoms at all. All of the old Autolite plugs were fine and not fouled. Cylinder 3 did have very small amount of oil in the spark plug tube that coated the very bottom of the plug body. I know this is very symptomatic of a perished spark plug tube o-ring seal in the valve cover.
So now I am left with only a few possibilities now that the wires and plugs are new with no change in the symptoms.
- A defective spark plug wire in the set I just put on to seemingly correct the problem 3000 miles ago. It could be shorting to the block somehow but I am not sure.
- A bad coil but these had tested fine on a scope by the shop when the problem originally surfaced 3000 miles ago. As soon as I got home from the shop that diagnosed the problem and changed the spark plug wires, it was corrected. The car ran perfectly fine for the 3000 miles since I thought I had corrected the problem with new wires. I don’t have an extra to test that theory with.
- The leaking o-ring in spark plug tube 3 allowed oil to seep in over that 3000 miles and ruined that spark plug wire. I don’t have an extra to test that theory with but the cable is clean and dry and like I said, it was a small amount.
- Bad fuel injector somewhere
Update: 6-7-2016
I looked at the spark plug tube on cylinder 3 again to see if it had oiled up again and it hadn’t. The spark plug boot was clean and dry so I am kind of ruling out that cylinder as the cause of the miss. I cleaned the MAF sensor with MAF cleaning spray and reseated all of the spark plug wires again. Took it for a test drive and there is no change at all. I will still change the passenger side valve cover gasket and spark plug tube seals as a maintenance item but I do not believe it is causing my current problem.
I think the only thing I can do is schedule it to be scoped again so it can be accurately diagnosed. I don’t want to guess and throw parts at it.
Update 6-8-2016
So, the car finally set a code P0301 Cylinder 1 misfire detected. The car is really running badly now. This is the same cylinder that was diagnosed as having a bad spark plug wire last year. As I stated, I replaced the spark plug wires at that time and the problem went away but came back this week after 3000 miles. I don’t get what is going on with that!
I put a spark tester on cylinder 1 and it seemed to give good spark. I checked the whole side and they all seemed to have a similar look to the spark. I was bummed because I had expected to get no spark on cylinder 1 which would have indicated a bad wire or coil tower. I had planned to swap wires between 1 and 5 (short cables) to see if the problem followed the wire thus telling me if it was the coil or the wire. With my luck I would switch them and the ECM wouldn't set a code.
I don’t know whether to think the 3000 mile wire is defective or not. Logic tells me the coil is bad but I am not often right when throwing parts at a problem.
The other option could be a bad fuel injector on that cylinder. Based on that, I tested the injector and it came back at 14.6 ohms, which seems within spec. I put a noid light on the harness and it lit fine with the injector pulse signal from the ECM.
Just curious what you all think and I appreciate any responses. This is getting frustrating. My vote is still for a bad coil but I just don't know. It is a non-returnable part so if it isn't the problem I will have wasted the money. I really expected to find I had no spark on cylinder 1 due to the wire or coil but found neither to be the case. The wire also showed a resistance of 8.65.
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I can't imagine it being compression or burned valves on a moderately driven 75k mile car but anything can happen with cars.
