Hello all,
after 8.5 years of ownership, i’m finally taking my BBR Turbo onto the track at Bedford Autodrome on 19th December.
However, i seem to have developed a misfire under full throttle and was wondering if anyone could help me. Otherwise, the car seems to run fine. idles perfectly, uses no oil etc. Just don’t want to ruin my day by my car not accelerating properly.
I had something similar around 2002 which turned out to be the car over-boosting (the previous owner had tweaked the actuator boost to 7psi), but had the car rolling-roaded where they diagnosed this and set the boost at standard 5.5psi, so the BBR auxilliary ECU was no longer seeing too much boost and “rev limiting”. Problem solved.
My car has done 128k miles, running with Optimax, 98 RON switch setting (get misfire on 95 RON setting too) and the spark plugs (correct ngk BKR 7E11 long reach jobs) were last changed less than 2 years ago i think, but i’ve lost my spark plug gap gauge. I have a leak on the cam gasket cover so get oil on my spark plug wells, therefore threads & tips 1 and 4 when i took them out to have a look-see. My car has magnecor KV85 ht leads, which are probably around 9 years old. Prob need a new/to clean air filter. I don’t have a boost gauge. I have a spare coil pack which i got when trouble-shooting a few years ago. And the BBR ECU light is coming on.
I’m gonna be v short on time (ie. may only have one day) & funds to get this sorted in the next 2 weeks so my questions for people more knowledegable than me are:
1. i’m assuming there’s no way my actuator has turned back by itself so more boost is registering - seems pretty solid?
2. is it most likely that i just need to change the spark plugs & get the gap correct? They seem ok but i’m not sure.
3. do you think my magnecor kv85 leads have given up the ghost?
4. could there be a problem with my coil pack?
5. is it worth me putting some redex in my next fill-up?
as always, thanks in advance - any advice greatly appreciated…
LukeyBoy
I’ve had a similar problem with my BBR but unfortunately didn’t work out for sure what it was. My car cut out once on a track day and once backfired under full boost . I was running an electronic boost controller at the time and think this had something to do with it – Interestingly both of these occasions happened when the controller was turned off! The controller used to run at 8 psi and would spike at 8.5, the ecu never cut power and I maintained healthy AFR’s.<o:p></o:p>
To answer your questions:<o:p></o:p>
1. i’m assuming there’s no way my actuator has turned back by itself so more boost is registering - seems pretty solid? – The actuator won’t go out of adjustment but the spring can weaken which could result in larger boost spikes. Also the ‘signal’ pipe onto the actuator could have a split in it or have come off which would cause the turbo to over boost
2. is it most likely that i just need to change the spark plugs & get the gap correct? They seem ok but i’m not sure. – My car hasn’t misfired since I renewed my spark plugs, wouldn’t hurt to clean them and reset the gap if that’s something you want to do, even better to replace them.
3. do you think my magnecor kv85 leads have given up the ghost? – Likelly, they are renowned for getting a hammering on all MX5’s; because there’s only 2 coils the plugs fire twice per cycle. 9 years is a long time and I would recommend changing them.
4. could there be a problem with my coil pack? – I think this unlikely if it’s only happening under boost
5. is it worth me putting some redex in my next fill-up? – As a desperate measure it can’t hurt but I’d be amazed if this cured your problem!<o:p></o:p>
Hope this helps,
Andy “raw”
Thanks Andy, that’s very helpful.
I assume when you say ‘backfired’ you mean ‘misfiring’ under boost?
Well, my gut inclination is that the car is not revving as well as it should and not pulling as hard in the mid-range - when it’s normally so good - but i’ve driven the car so gently over the last couple of years that i haven’t really noticed. The impending track day has made me give it a bit of stick to test it. I remember when the car was over-boosting before, it could at times feel very quick, like a mini Impreza, and it doesn’t feel like that at the moment. Feels a tad flat. Interesting what you said about running at 8-8.5psi. i thought the standard injectors could only fuel enough for 7psi.
First step is to change the spark plugs. If that doesn’t work, i’ll get some new magnecor KV85s. If that doesn’t work, i’ll curse my car.
Is there a chance that the oil in wells 1 and 4 have contaminated spark plugs/magnecor leads/connections?
Point taken re the coil pack.
Like i said, i’m only running max 6psi (or should be) so the engine should be pretty unstressed for the track. fingers crossed.
thanks again Andy.
If you have a boost leak it’ll feel slow, and be massively overfueling and basically a bit rubbish.
Plumb in a boost gauge - just cable tie it to your wiper arm for a temporary install and check it has some boost. Boost gauges are cheap and easy to sell on.
cheers,
i was probably being a bit harsh. the car is very far from rubbish, still feels quick. is v economical etc, it’s just under full throttle that it stumbles.
car ‘seems’ to be boosting fine but it is stumbling in the mid-range and misfiring. The car won’t feel as quick as it used to at 7.5psi, so maybe it just feels a bit slow as it’s not sparking properly & i don’t want to rev that hard as it misfires. don’t have the time/intelligence to sort anything on the boost gauge at the moment…
A boost gauge is no more complicated than fitting a washer jet [:D] and they use the same size pipe too.
You’d only be making lots of boost under full throttle, and that’s where you have your problem.
I dunno though, it’s not like I work in a garage or something :shrug:
No, I actualy mean backfired! It was dark and I saw a flame in my rear view.
Ok, well i changed the spark plugs for brand new ones. no difference. Darn it!
Am probably going to order new magnecor KV85s and a K&N air filter today from mx5parts.
Before i do, i forgot to mention my MoT place said that i have a tiny exhaust manifold leak which is not worth worrying about and won’t affect the running of the car. If it did, i would assume it would affect idle etc etc. But the car is perfect when not under load…
cheers again,
LukeyBoy
I know this is an old thread but I wouldn’t risk my car on a track without confirming boost and A/F
ratios are always good. So I would suggest a boost gauge as well as a
wideband for your next track day.
Thanks for this.
The reason for the misfire was my old magnecor KV85s failing. Just a little aide memoire if anyone else has the same problem…