Very Short Spark Plug Life - 2.4 Duratec Engine

[27Dave]

Hi all,

I run a 2.4 Duratec engine in a Mk2 Escort, and I'm going through spark plugs for a past time as they black up/ soot up and begin to mis-fire, typically within a few hours of running or maybe 4-5 tarmac stages (40-45 miles).

The engine is circa 300bhp, and runs coil on plug ignition without a coil pack. The engine runs on fuel injection with a lambda sensor in the exhaust manifold downpipe... The problem is slightly exaggerated if the engine has a number of cold starts without a longer run, but that said the problem can occur when the engine is hot or cold with brand new plugs.

I have used 'special' Bosch plugs at £100 per plug as specified by the engine builder; I've tried NGK Racing plugs at £40 per plug and Denso plugs at £20 per piece, and I have the same issue with all of the plugs - so I think it's fair to say the plugs are not the root cause of the problem. That said, when the last set of plugs were removed 3 were black and one was a consistent beige colour, as I would expect to see on a healthy plug.

So my other possible theories are...

- the fuelling map in the ECU and possible over-fuelling?? But then why only 3 out of the 4 plugs affected last time out??

- or is it the exhaust manifold which is possibly too small for the engine to fully exhaust, at 1 7/8" primaries into 2" secondaries (was used previously on a 2.0l engine}?? I think ideally this needs to be 1/4" larger on both primaries and secondaries, but will this cure the problem??

- or is it some combination of the above maybe....

Anyone had any similar engine/ spark plug issues or thoughts on possible root cause of this problem please??

[GreenV8S]

Seems to me either the engine is over-fuelling or the plugs are the wrong grade.

Have you checked the actual AFRs, or tried running a grade hotter plugs?

[TooMany2cvs]

27Dave said:

The engine runs on fuel injection with a lambda sensor in the exhaust manifold downpipe...

Can you get any information from the ECU on whether the lambda's flagging up a rich mix, and trying to lean it down but simply not having enough scope to do so?

Have you looked at it with a wide-band and some kind of AFR read-out?

How was it mapped?

27Dave said:

That said, when the last set of plugs were removed 3 were black and one was a consistent beige colour, as I would expect to see on a healthy plug.

So my other possible theories are...

- the fuelling map in the ECU and possible over-fuelling?? But then why only 3 out of the 4 plugs affected last time out??

<shrug> Iffy fuel supply to that pot? Partially blocked injector? Air leak at the manifold-head joint, leaning it out?

[stevieturbo]

£100 a plug ?? Are you f****** nuts ?

Set fire to whatever moron told you to do that !

And get a competent tuner to look at it to ensure mixtures and tuning are all ok, as it sounds like it's a mile off.

And while you list different brands of plugs, you never mention what heat range you are using.

And no, the exhaust is fine, you're only making 300hp, not 600hp

Edited by stevieturbo on Saturday 22 September 20:37

[27Dave]

Thanks guys,

The engine was initially mapped on a dyno following a full overhaul (at which point I bought it), and then it was further mapped in the car on the road - it hasn't been mapped in the car on a rolling road as yet, though it has been on a rolling road for a power run...

I haven't checked actual AFRs yet but do intend to see what info is being captured on the ECU as the next step.

Denso plugs are heat range 8; NGK are 9, not sure about Bosch but I know others are using identical Denso and NGK plugs in virtually the same engine and set up, and not having an issue - so, I think plugs are out of the mix, and not totally nuts but a tad pee'd off with the cost of changing plugs now!!

[GreenV8S]

27Dave said:

I think plugs are out of the mix

Hopefully 'just' over fueling. That might be because the map is wrong, or because you've got some other problem such as bad coolant temp sensing or wrong fuel pressure. Should be relatively easy for anyone who can talk to the ECU to figure that out. Leave it too long like this and you could find aggravated engine wear from bore washing.

Meanwhile, until you sort that out, go a grade hotter next time you replace the plugs.

[Mignon]

Manifold sizing info is in my technical article here.

https://web.archive.org/web/20110918115047/http://...

Primaries are fine. Secondaries seem small. Depends somewhat if it is 4-2-1 or 4 into 1 but you don't say. It is however not your plug issue. Most likely that is an inadequate ignition system or fuelling problem. A compression test would be a good place to start though.

[27Dave]

Morning, thanks for your reply and thoughts. I’ll take a look at your article now. For info, the manifold is 4-2-1.

[27Dave]

Ah ha, I’ve seen your article before, and have read and used it several times.

So, the exhaust size is not the issue but out of interest and based on your article I understand that a manifold with 2” primaries and 2 1/4” secondaries into a 2 1/2 system would most likely be a better bet for my engine... is that a fair conclusion to reach??

[stevieturbo]

27Dave said:

Thanks guys,

The engine was initially mapped on a dyno following a full overhaul (at which point I bought it), and then it was further mapped in the car on the road - it hasn't been mapped in the car on a rolling road as yet, though it has been on a rolling road for a power run...

I haven't checked actual AFRs yet but do intend to see what info is being captured on the ECU as the next step.

Denso plugs are heat range 8; NGK are 9, not sure about Bosch but I know others are using identical Denso and NGK plugs in virtually the same engine and set up, and not having an issue - so, I think plugs are out of the mix, and not totally nuts but a tad pee'd off with the cost of changing plugs now!!

Why on earth are you running such cold plugs ? I wouldnt even run a 9 on an engine making 800+ let alone only 300hp.

And why a different heat range in Denso and NGK ( and Denso do not number "8" so I can only assume you mean equivalent ?

It would seem something in the NGK 7 range would be a more sensible choice. And surely when on the rolling road they also checked mixtures and recorded them ? If not, what was the point in going there in the first place ?

Really...there is no reason to be using anything other than regular copper plugs on that engine, £2-3 each. Whoever told you to spend £100 per plug really is a complete and utter idiot and never listen to a word they say !

[steveo3002]

didnt know you could get plugs for £100 each....did the tuner happen to sell them to you?

[27Dave]

Yes the Denso plugs were equivalent heat ratings, the Denso rating is 24

[P924]

sounds like it's too rich. as others have said.

If its only on 3 cylinders, are the injectors ok?

[stevieturbo]

steveo3002 said:

didnt know you could get plugs for £100 each....did the tuner happen to sell them to you?

Even these arent £100 ea !


http://kalecoauto.com/index.php?main_page=product_...

[27Dave]

Maybe not, but these do &#128563;

[stevieturbo]

And clearly a complete and utter waste of money

Put a set of normal cheap copper NGK's in a 7 heat range into it and around 30-35thou gap providing you're running the coils correctly.

[27Dave]

I’m not really sure it’s a plug issue, but when you say assuming I’m using the coils correctly, what do you mean?? How could I be using them incorrectly??

[stevieturbo]

27Dave said:

I’m not really sure it’s a plug issue, but when you say assuming I’m using the coils correctly, what do you mean?? How could I be using them incorrectly??

Incorrect dwell

[99hjhm]

Is the fuel pressure correct for how the engine was mapped?

As said chuck those plugs and buy a basic set in the 7/8 heat range.

[Mignon]

27Dave said:

Ah ha, I’ve seen your article before, and have read and used it several times.

So, the exhaust size is not the issue but out of interest and based on your article I understand that a manifold with 2” primaries and 2 1/4” secondaries into a 2 1/2 system would most likely be a better bet for my engine... is that a fair conclusion to reach??

Only if you think your engine has the potential to produce significantly more than 300 bhp. I have no idea if this is a valid assumption but I suspect it is unlikely.