Some years ago I fitted NGK iridium IX BKR5EIX-11 spark plugs to my 1997 MK1 MX5.
Car has had very little use over the last couple of years as flirted with MK2 and Mini Cooper. Both these now sold so looking to spend more time driving the MK1.
I have been noticing the odd miss on acceleration and now the car flutters(misses) on aggressive acceleration from base idle(worse when warm). No problem once the car is under progressive acceleration so still drives very well with impressive power for the low BHP car.
The problem very surprisingly is the Iridium spark plugs. I fitted an old set of standard plugs and this problem went away. Iridium plugs look a perfect colour with no wear and probably only done 8000 miles. I thought these things were meant to last forever!!
No rogue plugs - it has this problem when any one of these is fitted.
I look at plugs as a replacement item when it comes to servicing time.
For the few quid they cost they give peace of mind.
Plugs like all items will wear out eventually, and as you say they were fitted a few years back so stick a nice new set in and give your engine a treat.
Ummh - 8000 miles for a set of Iridium plugs with no discernible wear and a good colour implies a problem with the plugs themselves. Read up on these - they are supposed to have a service life of up to 100.000 miles which is why they cost 5-6 times as much as standard plugs.
These have started to fail well within the service period of a standard plug(20,000 miles+)
I just wonder…more a hypothetical question than anything…if the Iridiums were either too “hot” or “cold” in specification no matter what it says on the box.
Are they designed to work best in higher compression engines for example?
For what it’s worth, I find Mx5Part’s Long Reach plugs are very good.
But then, it could be placebo. Mk1s are full of placebo effects.
If the older plugs hit the sweet spot…it thankfully eradicates horrid thoughts of a duff coilpack…or leads etc.
BKR7E-11 for MX5 MKI B6 Turbo/Supercharged 01/90 –>
MX5parts sell NGK and your long reach would be a good spec. the ‘R’ version has a resister in the plug to help stop interference with the radio so will probably go that route.
Girlfriend has Denso K16PR-U 11 fitted to her 1991 1.6 Eunos - they seem to work well.
You are correct re some relief that plugs were the problem as very easy to sort out. I have lots of MX5 spares but glad the issue has turned out to be very simple:-)
Suzuki Jimny on 60k miles and no problem, plugs due to be changed based on mileage.
2008 MX5 Mk3 at 34k miles no problem not due to be changed to 50k miles.
Impreza changed at 50k miles as per service schedule no problem and second set were fine last week when it went to it’s next owner at 86.5k miles.
Picked up 31k miles Impreza last week again Iridium plugs no issues not due to be changed until 50k miles.
Plenty reports on the Suzuki Jimny forum of Iridium plugs going at around 25k miles to 30k miles.
I think you have been unlucky.
In saying that I have flushed the brake fluid on say 15 cars in the last year with a Mityvac vacuum unit with no problem.
Flushed the fluid on of the Grampian Area guys MK3 today and managed to get some air in the drivers side rear caliper.
Just one of those things!!!
Don’t get me started about the Mk3 air filter after 20 minutes we found out that the marking of front and up on the element was wrong and should have been this side to the rear and up and then it fitted like a glove.