Hi All,

I'm a bit baffled by an issue I can't seem to solve. Recently purchased a 2002 Fiesta with low mileage at 59,000 (genuine). Engine light was on with a P0351. The car was starting and driving when I bought it but Misfiring. When I had a look it looked like to HT leads and coil pack had been replaced fairly recently. When i removed leads 3 and 4 there was water in there so cleaned all of this up and replaced all 4 plugs. The original plugs seemed slightly too large so the lead covers weren't fitting snugly. I assume this is how the water got in. This seemed to solve the problem. Cleared the code and the engine seemed OK. Took it for MOT and it passed. Since then the issue has returned so I've replaced all 4 plugs and leads and fitted a new coil pack. I've tested the coil pack plug and it seems like its not getting any power when the ignition is on, only when I turn it over. Cylinders 1 and 3 seem to be sparking ok. I've swapped leads and plug from a good cylinder to a bad cylinder and the problem stays the same so leads and plugs are fine. The issue remains and I can't get the car to start now. I'm not an expert by any means as this is a little project for me so asking for any advice please as to what I can do next? It's a great little car if only I could get it running again. 

I've read that a faulty coil pack can damage the ECU, so checked continuity from the ecu wires to the coil pack plug and they look good. I've also read that getting the ECU sorted can be tricky because it could affect the mileage displayed on the dash, which is obviously low on my car, so I wouldn't want it showing higher mileage than it actually is. Does anybody have any advice please?

 

Many Thanks,

 

Steve

Did you clean the rust away from the spark plug holes before fitting new plugs?

Rust will stop the plug from earthing correctly

Then check with a slave plug, on each cylinder, to see if you are actually getting a spark.

If you are then you will need to do a compression test 

These use wasted spark.  I suspect both 2 & 4 both use the same coil and that coil is not being powered by the ECU.  I would check the wiring between that coil and the ECU plug before anything else.  If that's fine then it probably is the ECU.  Having your ECU repaired is a better option than fitting a donor ECU.

On 8/21/2025 at 9:24 AM, DaveT70 said:

Did you clean the rust away from the spark plug holes before fitting new plugs?

Rust will stop the plug from earthing correctly

Then check with a slave plug, on each cylinder, to see if you are actually getting a spark.

If you are then you will need to do a compression test 

I've removed the plugs and tested them without being fitted, still only getting sprk on 1 & 3. 

On 8/21/2025 at 12:22 PM, TomsFocus said:

These use wasted spark.  I suspect both 2 & 4 both use the same coil and that coil is not being powered by the ECU.  I would check the wiring between that coil and the ECU plug before anything else.  If that's fine then it probably is the ECU.  Having your ECU repaired is a better option than fitting a donor ECU.

Thanks, yes I've checked the wiring from ECU to coil and both are fine. My feeling is teh ECU must be at fault. Interestingly I can't sem to get a read from the constant 12V wire when the coil pack is unplugged with ignition on. Must be getting power when plugged in though to spark 1 & 3. Having my ECU cloned so will see if that works! Thanks for the reply.