Coil on Plug ignition.

[Richmbutler]

Having experienced a failing coil and gone through the process of elimination to find the fault, I was prepared to change the coils on my new car when the same misfire occurred. That was as follows:- fine on hard acceleration but lumpy on idle and misfire when cold on part throttle.

It seems that the coils are a common fault. Often attributed to leaving the ignition on without the engine running, thereby heating the coils until they expand and cracking the insulation leading to faults when cool but fine when under load or when up to temperature. However, there seems to be another scenario....

Exactly the same symptoms as before and changing the coils will solve the problem but they are expensive. The fault maybe just in the rubber boot and spring! In the 'States the boots and springs are readily available and changed as regularly as the plugs but here in the UK we can only buy the coils.

I should be interested to know if I can buy just the boots and springs here and if anyone else has had the same experience.

Always open to suggestions as "Only a closed mind is certain"

Edited by Richmbutler on Sunday 27th September 14:01

[V8covin]

Buy them from American is the simple answer

[LimSlip]

Richmbutler said:

It seems that the coils are a common fault. Often attributed to leaving the ignition on without the engine running, thereby heating the coils until they expand and cracking the insulation leading to faults when cool but fine when under load or when up to temperature. However, there seems to be another scenario....

This was only a problem back in the day of a contact breakers and distributors. If the engine isn't running on a modern car (e.g. one with pencil coils) the coils will not be energized.

I have no idea where the separate parts of a pencil coil can be bought though, wasn't even aware they could be.

[Richmbutler]

LimSlip said:

This was only a problem back in the day of a contact breakers and distributors. If the engine isn't running on a modern car (e.g. one with pencil coils) the coils will not be energized.

I have no idea where the separate parts of a pencil coil can be bought though, wasn't even aware they could be.

Understood but this is with the engine running. The fault is between the coil and the plug. They are so expensive here £41 and only $5 each in the USA.
Pt No. NGK (CPB-FD007) Coil-On Plug Boot

Edited by Richmbutler on Sunday 27th September 14:10

Edited by Richmbutler on Sunday 27th September 14:11

[Richmbutler]

V8covin said:

Buy them from American is the simple answer

Of course, but us Brits should be able to buy these here. Opportunity for someone hey? $5 in the States, £41 here. My question was really asking if anyone else had similar symptoms and a pointer to a solution if they had.
Thank you for your reply.

[LimSlip]

Richmbutler said:

LimSlip said:

This was only a problem back in the day of a contact breakers and distributors. If the engine isn't running on a modern car (e.g. one with pencil coils) the coils will not be energized.

I have no idea where the separate parts of a pencil coil can be bought though, wasn't even aware they could be.

Understood but this is with the engine running. The fault is between the coil and the plug. They are so expensive here £41 and only $5 each in the USA.
Pt No. NGK (CPB-FD007) Coil-On Plug Boot

With the engine running the coils won't be overheating unless there is something wrong with the coil itself or the ECU (excessive dwell).

The Denso equivalent part is 671-4283, they are available on Amazon.co.uk though still pricey. It's another part number you can search for though.

[Richmbutler]

LimSlip said:

With the engine running the coils won't be overheating unless there is something wrong with the coil itself or the ECU (excessive dwell).

The Denso equivalent part is 671-4283, they are available on Amazon.co.uk though still pricey. It's another part number you can search for though.

Hello again, you must have spent sometime researching this, for which I thank you. They do seem to be the right part. Much better price too. Considering the genuine Cosworth coils are about £90 each, that would be a great saving. Cosworth use genuine standard Ford coils, strangely. Funny how we don't even get the parts offered to us.

My experience of this type of coil comes from an MX-5 NB which commonly burn up their coil packs if the ignition is turned on but the engine not started. I have often wondered why they would on a modern engine. Maybe the MX-5 coil pack used to overheat because of where it is placed; at the back of the cylinder head against the bulkhead...nice and toasty there.

I have found a set of four coils for the Duratec engine which are guaranteed for 5 yrs and only £50 the set. Worth a punt but wouldn't it be good if we could get the boots and springs for £5 each? It seems a weak point in the spark transfer, just a slim spring to take the current from coil to plug. I can understand how they could be damaged when doing a simply plug change or clean up.

Thank you once again.