Running on just five cylinders

DJ29316

MEMBER
2002 FORD ESCAPE
3.0L
6 CYL
4WD
AUTOMATIC
200,000 MILES

My daughter was driving back to college and called and said her car was not running properly. I hooked it up to the code reader and had a misfire on cylinder six. I drove it home and it ran rough, but only under a strain. I replaced the spark plugs and the coil on cylinder six. After investigating the plug, it was flooded with gas. I though that maybe the injector was stuck open so I replaces it. Now, The car will not start. I pulled the coil and plug to ensure there was fire and there is spark there. Will I was turning it over to check the spark, the engine fired up and ran great on five cylinders. I put the plug back in and it will not start again. Pull the plug out and it starts right up. I have checked the wear pattern on the cam and they appear to be in line. What can be causing this issue?

5 Replies

KENW1

MECHANIC
213 POSTS

Thanks for visiting 2CarPros.

It sounds like this coil being plugged in is disabling the coil drivers in the computer that ground each coil to fire it. It could be due to a coil that's faulty, (it does happen with new parts) or an ECM that is starting to go bad. I would swap a coil from another cylinder in and place the new one where it came from and see if it does the same thing.

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Monday, February 4th, 2019 AT 3:39 PM

DJ29316

MEMBER
3 POSTS

Thanks for the reply. Could it be grounding out even though the coil is firing the plug when the engine is turning over? When the plug is removed, it is drowned in gas. The plug is firing when out of the head, but put it back in and it does not fire.

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Monday, February 4th, 2019 AT 4:02 PM

KENW1

MECHANIC
213 POSTS

I think what may be happening is the ECM is not grounding the coil long enough to produce enough dwell time to fire hot enough to ignite the gas. I'll try to explain it.

Each coil on this vehicle receives 12 volts from a shared source. Then each coil has it's own wire going to the ECM to ground it. When the coil is grounded by the ECM it produces spark. The length of time of the grounding is called dwell. When the dwell is too short the coil does not produce enough voltage to adequately fire the spark plug to burn the compressed air/fuel mixture.

On the diagram below the pink wire is 12 volts to each coil. A poor solder joint at the splice could also cause issues. Check voltage with key on at the pink wire of number six.

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Monday, February 4th, 2019 AT 4:07 PM

DJ29316

MEMBER
3 POSTS

I will have a look into that. I know we checked the voltage at the plug, just not sure if it was traced back to the ECM.

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Monday, February 4th, 2019 AT 4:39 PM

STEVE W.

MECHANIC
13,017 POSTS

Easy way to test if it's a bad coil or plug. Swap them to different cylinders. I have seen a lot of junk in new boxes over the past few years. On these a simple way to check for the spark signal is to pull the connection off the coil and connect a cheap test light in it's place. Start the engine, if the light blinks the coil is getting both power and the ground trigger. Light green/yellow is the ground trigger from the ECM. White/violet is power. If no light then just leave the light connected to the Light green/yellow trigger wire and touch the light to the battery positive terminal. If it now flashes the power feed to the coil is bad, if it doesn't trace the trigger back to the ECM.