turbo running lean ?? airleak
Turbo Mini Forums

It seams like fuel to me
Get a contaner and mesure the flow rate at 3-5 also at full boost + 3-5 psi

You say choke out its rich on cruse and perfict full boost
Also say choke in its perfict on cruse and lean on boost
thiss tells me the needle needs to be thinner on the lower part where it is when on boost
Look for a needle that is thinner on the pointy bit or file it if you dont mind possibly trashing it

I think a carb rebuild is in order. the needle is one that I have used for a good few miles....

full throttle and when it hit boost the afr would drop straight to 11-12. this problem has just developed using this same needle so cant see the needle being at fault?

I believe the bbc that I use is the richest off the shelf needle available? cheers, dan

BCA is very very rich. Gave us good fuelling for 2bar of boost in the upside down skip.

bbc was what my rr operator suggested. he said he usually fits them to tuned v8s. with the bbc fuelling was perfect, it ran VERY well with this setup, just a bit rich on idle which I can live with. I had covered around 1500 miles with this setup, so something has changed intermittently since then. give the engine any load now and it goes lean so something is definitely amiss

cheers, dan

right, the plug onto the crank sensor seemed to be loose last night. I have had issues in the past with it running like shite when this has happened before.

so I thought that maybe the weak signal was not able to cope/ give a strong enough spark when the engine was under load.

sorted this out this morning. fresh fuel. car runs like an absolute dream again, afrs are again spot on.

so it looks like maybe I wasn't getting a decent spark causing the afr reading to show lean, and the engine to backfire/miss/hesitate.

I will see how it goes, may take it out again later for another test run.

also the misfire/hesitation in fourth after a accelerating through the gears hard persists (after around 15 seconds of hard acceleration). afr looks fine at this stage when this happens. however the problem is gone when the choke is half way out. so I think the fuel pressure might be a tad too low? I will increase this a slight bit and see how it goes.

hopefully this has it sorted? though im not banking on it just yet!!

dan

It should be, its an mpi one, only running 16psi of boost. One thing I have never checked is the fuel pressure. Set my new reg the same as an old used one I had. As a baseline to get it running. Seemed ok but left it there...

I'd get a remote pressure gauge and trap it under your windscreen wiper, then you can see what's happening as you drive without risking high pressure fuel in the cabin.

what fuel are you using?

Yes I ought to invest in a pressure gauge. Fuel is high octane forecourt stuff. Compression ratio 8:1

Edited by Brett on 30th May, 2014.

Yes i moved to the darkside

Instagram @jdm_brett

I have no idea what the fuel pressure is at. I guess I ought to buy a gauge but will have a play about first. over the next few days I plan to

increase the fuel pressure
increase the enrichment screw
get a set of colder plugs, gap them slightly less than 1mm

will try things in that order, hopefully can get this sorted soon. the car is belting when its going right, needs a bit more boost then a power run!

cheers, dan

any progress on this mate? also which dashpot oil are you using? might be worth trying different viscosity oils?

Low boosting for now.

Hi, not had chance to look at this until today. tried some colder plugs bpr8es, also closed the gaps a bit, this improved things somewhat. however the problem was still there a bit.

but as I have been busy for the last few weeks I took the car for an extended test run. after about 20 mins of varied driving the car felt much much quicker. also the hesitation had stopped.

in the past I had always thoroughly warmed the engine up before giving it any.

maybe the engine just runs better at warmer temps? once everything has warmed up etc, it is still a fairly new build with maybe only 2-3k on the clock.

or maybe the fuel atomises better with higher under bonnet temps? I am really not sure but it goes well again once its properly warmed up.

cheers, dan

it has been a few months - had a busy summer so not really used the car. to summarise looking back at this

-fuelling was ok with smaller intercooler, air filter next to the rad and less boost
-the changes were putting the filter behind the grille, larger more efficeient ic, more boost.

the car runs lean on boost.

plug gaps I have closed up.

car runs perfectly on boost with the choke out.

so really the mods I have done have all contributed to leaner running on wot, under boost.

I took the dashpot off today. that's all in good order and working as it should do.

I have ordered a bca needle. also going to run 2 green springs. if that doesn't work I may consider a bcg needle.

the problem definitely seems to be fuelling related ie choke open, more fuel, perfect running under boost.

if the above doesn't work I will change the carb itself.

don't think its the fpr or fuel pump (using mpi tank) at this stage based upon the above info.

has been a long while since I looked at this but plan on pulling my finger out and getting the car sorted.

dan

If it's lean on boost but pulling the choke makes it run okay, turn up the fuelling until it runs as it should under boost, and see what it's like on part throttle and idle

That bigger intercooler means that you would always have to recalibrate the fuelling.
(cooler charge, more oxygen therefore more fuel required and more POWER

True Dave. Also repositioning the air filter behind the grille as opposed to next to the rad will have a big effect on induction charge temps.

going to have a look at it later this week when the parts arrive.

Strange thing was on the old setup (smaller cooler, air intake not behind grille, 13psi,), full chat was around 11-12 afr.

Now when you put your foot down it can go to 16! obviously not holding it there but that's what happens. Choke out, afr on full throttle/boost back to 11-12.

Going to try some different needles and will report back.

Cheers, Dan

have tried a bca, x2 green springs, problem now sorted. it has never driven better.

it used to hesitate/ lean out at certain off boost throttle positions before, now drives perfectly. the occasional top end misfire has also gone.

the old bbc needle looked to be ever so slightly bent too?

the car has been transformed with regards to how it drives. cheers all for your input on this, dan