[urq] suddenly lean - the saga continues
larichard at plguide.com
Wed Feb 14 15:43:32 EST 2007
Two or three things I can think of:
- something moves and let air in (oil fill cap, oil dipstick, rear main
crank seal, ) and then is replaced by vacuum
- have you tried to push on the air meter flap, to see if it sticks
down there as when you close the throttle rapidly ?
- check the air inlet of the turbo, the little 90 degree rubber elbow.
Mine was cracked and it was difficult to see because it is so deep in
- have you removed the air filter, to see if there's no paper sheet
that gets suck and blocks the air filter and then drop back ?
- is your throttle cable and throttle body OK ?
- finally, it could be ECU related, because the ECU controls the
ignition, and if the ECU is having strange inputs (engine revs,
throttle position, vacuum/boost signal), it can retard ignition quite a
And don't be so sorry, at least you're providing us some food for
thoughts in this real quiet period !
Le 07-02-14, à 14:57, SpotatAshleys a écrit :
> Yes,yes,I'm tired of this too. Very tired but once again I need help.
> The "suddenly lean" symptoms have returned. Just to recap they are:
> If I accellerate hard in any gear it pulls like a train and the air
> meter shows (as expected and desired) a rich mixture. When I lift off ,
> change up and re-apply the accellerator the power has gone and the
> has gone lean. If I were to keep my foot down this condition would
> If I lift off and then reapply the accellerator then the power returns,
> the mixture returns to rich and it would continue to pull until I ran
> out of
> revs. If I keep my foot down instead of changing up the mixture remains
> rich so it does not appear to be a case of fuel starvation. (The
> sediment trap
> upstream of the fuel filter is clear as can be anyway). I have removed
> "igloo" and looked at the airflow meter flap and there is no indication
> that this sticks in any way - seems to be free to move. The injectors
> were new
> about 2 years ago as were the injector seals. The injectors are held in
> place with a steel injector bracket from a non-turbo coupe quattro and
> not move. I have not found any holes or splits in any inlet hoses. The
> seems in fine condition, never a hint of smoke and was checked for end
> play when
> the engine was rebuilt about 3 years ago.
> It only ever happens when warm but this is probably because I never
> hard until it is properly warm.
> I have been looking hard in to possible causes and the finger points
> at 6 possible components.
> WOT switch
> Vacuum divert solenoid
> Thermo-pneumatic switch
> One way valve
> Metering head
> I have checked the WOT switch - it functions as it should, triggering
> the vacuum divert solenoid at just after 50% throttle.
> The solenoid works - I disconnected the pipes and with ignition on,
> the WOT triggers the solenoid and it diverts to purge the vacuum,
> causing the CPR to reduce control pressure and richen mixture. The
> diversion was checked by applying positive pressure and seeing if
> solenoid allowed the pressure to be diverted (in the right direction).
> It does.
> The CPR/WUR was checked for continuity and to ensure bi-metallic
> spring heater received power. I am sure this works OK because the
> mixture leans off as the engine warms - as it should do.
> The thermo-pneumatic switch works fine- tested.
> The one way valve was removed and tested - but I had already ruled
> this out because as I understand it,if this failed and allowed
> movement of air in both directions the mixture would be rich all the
> Finally I am confident there are no air leaks. (I re-set the basic
> mixture setting with the breathers disconnected and plugged. Upon
> reconnection no changes were needed to the basic setting which says to
> me "no leaks in the breather side of things".
> Which leaves the metering head - which is just what I don't want it to
> So before I set to and remove this and investigate - does anyone have
> any final thoughts as to a possible cause of these symptoms?
> Preferably a very simple and cheap solution.....
> Sorry for the epic posting - (if having trouble sleeping, read it a
> second time!!!)
> As always, any suggestions gratefully received.
> All the best
> '87 WR
> '63 Daimler V8
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