Overrun switch/valve
Discussion
Most gratefull. on a pre hot-wire the overrun valve is on the rear end of the plenum. It allows metered air into the plenum if the vacuum exceeds a certain value.
If it is mal-adjusted then it can cause idle hunting and high revving.
I had to adjust mine to stop this but it produces a satisfying banging on the overrun.
Russ
If it is mal-adjusted then it can cause idle hunting and high revving.
I had to adjust mine to stop this but it produces a satisfying banging on the overrun.
Russ
I think there is a thermo switch that runs the cold start injector (the 9th injector that sprays straight into the plenum) but can't remember where it is located.
Maybe this is what they are talking about but I am pretty sure it runs the injector direct and not via the ecu.
I understand that there is no real need for this injector anyway and that if the auxiliary air valve (mounted on the front right hand side of the block) is working ok then you shouldn't have a problem when starting from cold. The valve is open when cold and closes slowly as it heats up, either from heat soak from the block or because of the internal electrical bi-metallic strip which I think shares the same feed as the injector. If this feed was missing it may take longer to warm up but still should close.
Are you having cold start/high idle/rough running problems ?
If not tell them not to worry about it !
Maybe this is what they are talking about but I am pretty sure it runs the injector direct and not via the ecu.
I understand that there is no real need for this injector anyway and that if the auxiliary air valve (mounted on the front right hand side of the block) is working ok then you shouldn't have a problem when starting from cold. The valve is open when cold and closes slowly as it heats up, either from heat soak from the block or because of the internal electrical bi-metallic strip which I think shares the same feed as the injector. If this feed was missing it may take longer to warm up but still should close.
Are you having cold start/high idle/rough running problems ?
If not tell them not to worry about it !
'Cold start issues' W, what have you been tinkering with?.
The cold start was always pretty good, a little lumpy for a few seconds then the engine would warm up to around 1k revs nicely.
The valve at the back of the plenum on the 350i would bleed air into the system to stop the car running on after switch off?.
The amount of air can be adjusted I believe by screwing in a bolt inside the unit. I remember hearing from someplace that the spring goes soft over time and may start to cause issues with stalling. I have seen a few cars missing the unit altogether and the hole blocked off.
The hotwire cars had the stepper motor positioned in the same place.
Air bleeding in here would probably cause issues with idling and cause the engine to die on you when out and about.
Correct me if i am wrong on this.
MikeB
The cold start was always pretty good, a little lumpy for a few seconds then the engine would warm up to around 1k revs nicely.
The valve at the back of the plenum on the 350i would bleed air into the system to stop the car running on after switch off?.
The amount of air can be adjusted I believe by screwing in a bolt inside the unit. I remember hearing from someplace that the spring goes soft over time and may start to cause issues with stalling. I have seen a few cars missing the unit altogether and the hole blocked off.
The hotwire cars had the stepper motor positioned in the same place.
Air bleeding in here would probably cause issues with idling and cause the engine to die on you when out and about.
Correct me if i am wrong on this.
MikeB
Havent touched a thing honest. I leave this kind of tinkering to the experts. It seems to have got worst with the weather. Theres a spares fellow in Northen Ireland who e-mailed me that he has one but I won't get it till next week.
So I'm having it back tomorrow (Wednesday). He's fitted a new coolant temp sensor, new plugs (they were sooted up a bit) and he's done the timing, so I can't wait to see how she goes. Sounds great with the new manifolds on too.
Hows the 450 coming along? We'll have to do a Wedge run sometime soon. Looking forward to meeting everyone.
So I'm having it back tomorrow (Wednesday). He's fitted a new coolant temp sensor, new plugs (they were sooted up a bit) and he's done the timing, so I can't wait to see how she goes. Sounds great with the new manifolds on too.
Hows the 450 coming along? We'll have to do a Wedge run sometime soon. Looking forward to meeting everyone.
mikeb said:
'Cold start issues' W, what have you been tinkering with?.
The cold start was always pretty good, a little lumpy for a few seconds then the engine would warm up to around 1k revs nicely.
The valve at the back of the plenum on the 350i would bleed air into the system to stop the car running on after switch off?.
The amount of air can be adjusted I believe by screwing in a bolt inside the unit. I remember hearing from someplace that the spring goes soft over time and may start to cause issues with stalling. I have seen a few cars missing the unit altogether and the hole blocked off.
The hotwire cars had the stepper motor positioned in the same place.
Air bleeding in here would probably cause issues with idling and cause the engine to die on you when out and about.
Correct me if i am wrong on this.
MikeB
The valve opens under manifold vacuum i.e. when the throttle is closed but the engine is still spinning fairly high (overrun), not after switching off. It allows air in to mix with any excess unburnt fuel. It's a fairly simple spring activated valve and if it was sticking open would give a high idle. The spring tension can be adjusted - described in the bible.
rus wood said:
The adjustment is a small M4? nylock nut which can loosen off. Make sure that you use a new one or lock it on - a small dab of paint or matching nail-varnish will do the trick.
What colour should the nail varnish match? The blue of the nylock insert, the grey of the casting, the colour of the body, the driver's eyes, or your girlfriends lipstick???
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