turbo running lean ?? airleak
Turbo Mini Forums

hi gents

had this turbo motor in for over a year

done a few thousand miles on it, its properly tuned etc etc. it went well, as it should.

after a good couple of months lay up (over the winter) I came to use it again. it was running a little lean on cruise, this was corrected by using thicker dashpot oil.

I then added a larger intercooler, repositioned the air filter behind the grille and ran a bit more boost. the car was belting, fueling spot on etc etc.

it then sat for a few more weeks but now it felt different to drive. definitely down on power, slower to build boost up to the 16psi it is now running. found that one of the intercooler hoses was coming off so sorted this out.

however took it for a test drive today and its not too happy. let it warm up, went really well for a few mins. but has now decided it will run lean on boost.

so basically it now runs a little leaner on idle, and progressively leaner through the rev range once reved stationary (a little more lean than it used to).

when it sees any load (boost) it runs right up to 16 afr, and backfired/hesitates, quickly back off as its definitely far too lean and not at all happy.

there is also a high pitched whir when you rev it stationary.

so I topped up the dashpot oil (didn't really need doing), but my thoughts are that there is an airleak somewhere. checked all the hoses for lose connections / splits, cant see any. the inlet manifold nuts are tight.

am I overlooking anything that anyone can think of? thinking about taking the dashpot off and making sure that the piston/needle are moving freely, im also hoping to have to have a more thorough look for air leaks once it cools right down.

but it has me stumped right now.

I would appreciate it if anyone with experience of this or a simlular problem could give me some pointers, especially if im overlooking anything.

cheers, Dan

How's the fuel pressure doing when it's running lean? Have you got a blocked filter or something?

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

I don't have a fuel pressure gauge. maybe its something that I need to invest in. the filter is the original spi one, mounted to the back sub frame, with mpi fuel tank

I don't have a fuel pressure gauge. maybe its something that I need to invest in. the filter is the original spi one, mounted to the back sub frame, with mpi fuel tank

I don't have a fuel pressure gauge. maybe its something that I need to invest in. the filter is the original spi one, mounted to the back sub frame, with mpi fuel tank

Fuel pressure won't affect the mixture.

Check the part throttle pipe and the manifold fixings.

In the 13's at last!.. Just

Do the magic su fairys supply the carb with fuel via magic buckets in some kind of a chain gang?

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

Edited by Brett on 25th May, 2014.

Yes i moved to the darkside

Instagram @jdm_brett

Glad that's cleared up I was gonna suggest he needed to feed the fairys more or supply them with bigger buckets

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

Schrödinger's cat - so which one am I ???

you cant live in boost all the time

Yes i moved to the darkside

Instagram @jdm_brett

ok, so I whipped the dashpot off tonight and there was some wear to the float

know you aren't supposed to mix and match parts but whacked another float and dashpot on there just to see if this made a difference.

idle was back to normal.

however took it on a test run and the afr was 14 ish on cruise (usually 13 ish).

there is oil in the dashpot (thick transmission oil)

when I put my foot down and the engine was under any load it flew up to 16, 17, off the gauge, felt and sounded very lean also, this was before boost had been made.

so this week I plan on buying some clutch and brake cleaner and looking for a leak between the carb and head. if there is no air leak the issue has to be fueling in my mind.

I will swap the fpr (the one I have has only done a few thousand miles from new but I am cautious of the new stuff these days and thw quality).

then I will bypass the fuel filter. then will check the fuel pump (though it can be heard pumping as usual), before looking at swapping the carb

in my mind it has to be one of these components causing the issue, unless anyone can sugest anything else that I could be checking?

obviously will check fuel hoses for splits/kinks etc also but from what has been said here it seems that the consensus might be that the fpr.

if anyone else has any ideas please add!

cheers, dan

Schrödinger's cat - so which one am I ???

a fuel pump not providing enough pressure or a regulator not increasing the pressure enough would not manifest its self as 'running lean'
if the carb is set up correctly you would not even know the float bowl was not filling untill it cut out in boost

Yes i moved to the darkside

Instagram @jdm_brett

if it only runs lean under boost and fuel is coming through have you checked the boost pressure?

Masturbation is not a crime its a hobby

In the 13's at last!.. Just

Not sure on that one either. Thinking maybe the t piece trick may be worth a try too?

changing dash pot oil just changes the rate of change not the steady position the position is governed by vacuum after the bridge/ventury in the carb or how much wear/air gap its got
its likely when you filled it up you got some oil down the sides and made it seal better this would lift the needle and make it rich

id say the reg is having problems get a pressure gauge in the fuel line between reg and carb so as you can see what that is under different conditions should be 2-3 psi at idle and above boost

check the signal line to the reg is not restricted or leaking along with any leaks after the carb/butterfly
ie with the engine running use water to flood the gaskets/suspect places and if the rpm drop you have a leak
just for fun and to see how this works make a leak and flood it you will hear it

not sure about the noise it makes? have you checked the turbo shaft for play?

slow to get build boost perhaps the waste gate is not fully closed or something to that effect? leaky ex manifold? leaky boost lines or ic ?

usually more volume between turbo outlet and carb wont make it notably slow to build boost there was a guy on here with a turbo under the boot floor think he said it had next to no effect on lag

if its just flat out lean all the time try pulling the choke till its at the proper mixture see if that gets it back if so just adjust the jet down or lift the jet in the suction piston if its the fixed type

a vacuum leak will make it lean on idle but when wide open this has almost no effect

edit: needle position can also be change by the strength on the spring on the dash pot but this would be for an engine with more/less vacuum than normal id have thought ie more vacume will lift the piston/needle giveing rich as will low vacume have it sit low and cause lean threwout the rev range id thing may be wrong just how i understand it

Edited by Turbo This.. on 26th May, 2014.

spayed all of the inlet manifold connections with brake cleaner, there is no air leak there. have t piece parts coming later this week, will try that next. over the winter I found a mouse nest in the plenum! forgot about this but wondered if there is some crud from this blocking off the signal to the fpr, or affecting the carb float etc. will investigate and keep this updated!

Mouse nest in the plenum will now be my first suggestion if anyone has a fuelling issue. Lol

In the 13's at last!.. Just

sound advice there! I took my old intercooler off to mod and fit the new one/change planum/intercooler hosing etc. other things got in the way and it took a few months. when I came back to the car this is what I found! cheeky sods!

so I went out tonight and increased the fuel pressure by 1/4 turn. the car ran stupidly lean 16-17 psi as soon as the engine was put under any load. so turned it back and it stayed the same, so its back to how it was yesterday. seems the t piece trice did not work

so I am back to square one.

when it is floored in boost the afr is around 14 so far too lean (would have been 11-12 previous to this problem)

when the choke is out its far too rich on cruise as expected, trying to stall itself, when floored it flys as it should, afr 12. so this says to me that fuelling is still a problem.

i will get a new set of slightly colder plugs anyway and gap them just under 1mm.

i also noticed the crank sensor is crudded up, this has given me issues before but cant see how the car can run fine with the choke pulled out - surely if it was an ignition issue more fuel ie choke out wouldn't help the situation?

i think realistically the carb is at fault, i am going to remove, strip and rebuild.

the other components are mpi fuel tank, spi filter, spi fuel lines, turbo regulator, turbo carb, green heavy duty spring, 75/90 transmission oil in the dashpot, bbc needle. it ran fine until a few weeks ago on this setup

thinking that i will sort the plugs, clean the crank sensor and rebuild the carb.

any input, advice or options very welcome on this. its very frustrating, need to get this sorted so that i can get the car back on the rollers again

thanks, Dan

My car was intermittently leaning out under hard acceleration, and it could be rectified by lifting off and accelerating again. I suspected the dashpot piston was sticking but wheni took it off and checked it i could not find anything wrong. I was going to completely overhaul a spare carb and fit it, but time was tight so I tried just fitting the spare dashpot and piston on my carb. The problem never occured again.

thanks for the reply. this did cross my mind as a possibility - I did swap the dashpot and piston from another carb. fuelling issue remains.

intresting, i am having a very similar issue and have never got to the bottom of it, metroturbos post above describes exactly how mine reacts in correlation to lifting off and accelerating again! will be watching this thread.

Low boosting for now.