Hesitation from idle to ~1500 RPM with modest+ throttle

[DrFerry]

Originally Posted by Assimilator1

Thought I should update this thread, I recently replaced the plugs and injectors (@88.4k miles).
But before I put in the new injectors I tested for the hesitation, it pretty much disappeared after replacing just the plugs.
And since then I have driven it a bit too, I'd say at the least the hesitation is 95% gone, there's just maybe the occasional very slight hint of it left.

PS. Old plugs had done 27k miles.
Back of inlet valves were literally shiny clean

Thanks for the update. Mine’s also doing it a bit and the plugs are overdue. Mine is in need of quite a lot of maintenance items including carbon fiber roof restoration, headliner repair, valve covers, ICV, plugs, injectors etc. I can’t afford to do it all so will have to prioritize. I may have to DIY a lot of it with the help of this forum. Vision isn’t what it used to be. Sometimes the mind is willing but the body isn’t quite as cooperative. Hoping things improve over in your neck of the woods (the U.K.).

[Assimilator1]

Originally Posted by DrFerry

Thanks for the update. Mine’s also doing it a bit and the plugs are overdue. Mine is in need of quite a lot of maintenance items including carbon fiber roof restoration, headliner repair, valve covers, ICV, plugs, injectors etc. I can’t afford to do it all so will have to prioritize. I may have to DIY a lot of it with the help of this forum. Vision isn’t what it used to be. Sometimes the mind is willing but the body isn’t quite as cooperative. Hoping things improve over in your neck of the woods (the U.K.).

How many miles have your plugs done?

Re valve covers, don't be railroaded into thinking that new covers are the only answer, I nearly went that route but then simply decided to Google magnesium casing/wheels refurbishment. And I found a couple of places who did .One particular place (TPCS in the UK), (before I told them the size of the covers) estimated £95ea to refurb, much better than £1400 for a pair of ally covers!!

[DrFerry]

Originally Posted by Assimilator1

How many miles have your plugs done? Re valve covers, don't be railroaded into thinking that new covers are the only answer, I nearly went that route but then simply decided to Google magnesium casing/wheels refurbishment. And I found a couple of places who did . One particular place (TPCS in the UK), (before I told them the size of the covers) estimated £95ea to refurb, much better than £1400 for a pair of ally covers!!

Plugs have done 44.5K miles... Long overdue... Time with the vehicle off the road - in order to refurb the valve covers - would be another factor for me to consider, as well as the logistics of getting the old covers to a refurb shop, but thanks for the advice. Sounds like you saved a considerable amount of cash.

[Assimilator1]

Not done it yet, but will do

Yea those plugs are overdue!

[spammysammich]

What are we calling an acceptable service interval for the plugs? Mine have a little over 27k miles

[DrFerry]

Originally Posted by spammysammich

What are we calling an acceptable service interval for the plugs? Mine have a little over 27k miles

If I recall correctly the service interval is 36K miles or thereabouts.

[Assimilator1]

Originally Posted by DrFerry

If I recall correctly the service interval is 36K miles or thereabouts.

Yea, but mine and many others are getting ropey before that.
I think I'm going to 25k interval, or maybe 20k. I'll change before 25k if I get this problem again.
Evolve reckon 10-15k!

[DrFerry]

Originally Posted by Assimilator1

Yea, but mine and many others are getting ropey before that.
I think I'm going to 25k interval, or maybe 20k. I'll change before 25k if I get this problem again.
Evolve reckon 10-15k!

I understand. More power to you - and your S65 - if you have the skills, eye sight, patience, manual dexterity, tools and time to do the job more often. Here's some supplemental information for you showing how the ionic knock detection system depends on current (amperage) signal from the plugs. If they are worn then this system is affected. It means timing and retardation could be the cause of the hesitation phenomenon with worn plugs. The service value shown is 60,000km or 37.5K miles. I was close..
.

[Assimilator1]

Originally Posted by DrFerry

I understand. More power to you - and your S65 - if you have the skills, eye sight, patience, manual dexterity, tools and time to do the job more often. Here's some supplemental information for you showing how the ionic knock detection system depends on current (amperage) signal from the plugs. If they are worn then this system is affected. It means timing and retardation could be the cause of the hesitation phenomenon with worn plugs. The service value shown is 60,000km or 37.5K miles. I was close..
.

Yea I've got that doc, I think maybe I got it from you a few+ years ago .

I would've quite happily gone to the full service interval, but I suspected, then found that the plugs were the cause of my car's hesitation/occasional misfire from low revs with wide-ish throttle (think when pulling away in 1st, or low revs in 2nd gear). And it was getting worse each year (modest signs in 2024, slight the year before).

I only do 2-3k miles/year in my M3 (DD is a 330d), so even at 3k/yr that would last me 8 years for a 25k change interval.
If you're finding your plugs are lasting longer, happy days
Although it's also known their is a power loss as plugs get older, even without running problems.
As Evolve demonstrated with their before and after dyno run. They also show how far short the timing is at high revs with the old plugs (explaining the power loss). At 10min 30s you can see the before and after power graphs, from about 5500 - 8250 RPM it's about 10 hp up.

[DrFerry]

Originally Posted by Assimilator1

Yea I've got that doc, I think maybe I got it from you a few+ years ago .

I would've quite happily gone to the full service interval, but I suspected, then found that the plugs were the cause of my car's hesitation/occasional misfire from low revs with wide-ish throttle (think when pulling away in 1st, or low revs in 2nd gear). And it was getting worse each year (modest signs in 2024, slight the year before).

I only do 2-3k miles/year in my M3 (DD is a 330d), so even at 3k/yr that would last me 8 years for a 25k change interval.
If you're finding your plugs are lasting longer, happy days
Although it's also known their is a power loss as plugs get older, even without running problems.
As Evolve demonstrated with their before and after dyno run. They also show how far short the timing is at high revs with the old plugs (explaining the power loss). At 10min 30s you can see the before and after power graphs, from about 5500 - 8250 RPM it's about 10 hp up.

Thanks for your reply and for posting the video. I did not know Imran@Evolve had gone to the trouble of making their "before and after new spark plugs dyno condition" video. Imran@Evolve 's support of the E9X M3 chassis has been excellent over the years both from a product perspective and from and informational perspective. So kudos to Imran@Evolve for all their excellent hard work and efforts. Now that E9X M3s are selling for as much as $205K on BAT (https://bringatrailer.com/listing/20...-m3-coupe-113/) the platform will attract even more collectors and investors so videos like this one are - and will become - really useful as the years go by. Thanks again for posting this information. My car's plugs are overdue, and it's been my DD since 2008. I'll get around to doing them soon (this summer) as well as the valve covers, injectors, ICV, carbon fibre roof reburb and headliner refurb. $$$. I'll post about all of that work when it happens. P.S. I hope all is okay in the U.K. I hear retired military as old as 65 are now to be included in any draft (https://www.gov.uk/government/news/m...n-preparedness

[Assimilator1]

Originally Posted by DrFerry

Thanks for your reply and for posting the video. I did not know Imran@Evolve had gone to the trouble of making their "before and after new spark plugs dyno condition" video. Imran@Evolve 's support of the E9X M3 chassis has been excellent over the years both from a product perspective and from and informational perspective. So kudos to Imran@Evolve for all their excellent hard work and efforts. Now that E9X M3s are selling for as much as $205K on BAT (https://bringatrailer.com/listing/20...-m3-coupe-113/) the platform will attract even more collectors and investors so videos like this one are - and will become - really useful as the years go by. Thanks again for posting this information.
My car's plugs are overdue, and it's been my DD since 2008. I'll get around to doing them soon (this summer) as well as the valve covers, injectors, ICV, carbon fibre roof reburb and headliner refurb. $$$. I'll post about all of that work when it happens. P.S. I hope all is okay in the U.K. I hear retired military as old as 65 are now to be included in any draft (https://www.gov.uk/government/news/m...n-preparedness

Yea ok over here, aside from the high cost of many things, especially fuel!
Upto 65s is for the reservist. An effort to reverse (non combat side of) the shrinking army that's been happening for ~15 years.

Good luck with the car repairs this summer .

PS Just discovered something else this evening on my car which needs sorting, sounds like the RH exhaust manifold is blowing!

[RocketyMan]

Originally Posted by DrFerry

I understand. More power to you - and your S65 - if you have the skills, eye sight, patience, manual dexterity, tools and time to do the job more often. Here's some supplemental information for you showing how the ionic knock detection system depends on current (amperage) signal from the plugs. If they are worn then this system is affected. It means timing and retardation could be the cause of the hesitation phenomenon with worn plugs. The service value shown is 60,000km or 37.5K miles. I was close..
.

It would be awesome if someone could understand this ionic knock more in depth and tune for different spark plugs--like the NGK Ruthenium spark plugs. I think the design of the dual-prong platinum spark plugs have something to do with the characteristics of it and why we can't currently change them for anything else without misfires.

I learned that tuners that opt for the race spark plugs turn off part of the ionic sensing.

[Assimilator1]

Originally Posted by RocketyMan

It would be awesome if someone could understand this ionic knock more in depth and tune for different spark plugs--like the NGK Ruthenium spark plugs. I think the design of the dual-prong platinum spark plugs have something to do with the characteristics of it and why we can't currently change them for anything else without misfires.

I learned that tuners that opt for the race spark plugs turn off part of the ionic sensing.

I just don't understand why BMW didn't use normal knock sensors!

[rosemont83]

My plugs probably have 15K miles on them but I'm planning to change those along with the fuel tank breather valve. 49k miles on the car now and just had injectors changed- should have done these while they had the plenum off but didn't think about it lol

[RocketyMan]

Originally Posted by Assimilator1

I just don't understand why BMW didn't use normal knock sensors!

Well for one, you get exact combustion quality per cylinder with ion sensing vs the piezo style is "general" knock control. You can tap with a rubber mallet next to piezo style knock sensor and the timing will pull, vs ionic sensing can detect even inaudible knocking minus any "noise" like said mallet.


If we knew how to tune the coil, it could be a matter of adding a capacitor or resistor to accommodate the specific characteristics of said spark plug. Or better yet, if there is a specific spark table to tune in the DME for knock and misfire. That's why this two ground electrode spark plug looks the way it does. It in part has different capacitance vs say an iridium spark plug with only one ground electrode. When I mistakenly put iridiums in my car once, I could see this in the data how it looked different. The best route would be to adjust the knock and misfire tables to accomodate.

[Assimilator1]

Originally Posted by RocketyMan

Well for one, you get exact combustion quality per cylinder with ion sensing vs the piezo style is "general" knock control. You can tap with a rubber mallet next to piezo style knock sensor and the timing will pull, vs ionic sensing can detect even inaudible knocking minus any "noise" like said mallet.

.....

Good points, makes sense, but then it makes you wonder why they didn't use this with other high performance engines? (S85 aside).

[RocketyMan]

Originally Posted by Assimilator1

Good points, makes sense, but then it makes you wonder why they didn't use this with other high performance engines? (S85 aside).

Interesting question. I dunno. 12:1 compression ratio?

I'm not sure there are that many other production BMW engines with CR 12:1 or higher, barring diesels. S54 is 11.5:1, yet it's piezo knock sensing.