Fate of a tyre valve cap

[ligertigon]

I have a tyre valve cap stuck in the AAV hole to lower my startup idle to a nice 1200RPM. (hole drilled in it)

Started car today and it idled up to the more memorable 2500RPM.

The valve cap exists no more

It was a good tight fit how did it come out?

what will become of it in the engine.

suggestions

[un1eash]

It will be chewed up and spat out the exhaust, shouldnt really cause any damage.

[System-G]

Not the first time I've heard this happen. No real horror stories of damage either so I think you'll be OK there.

[IanClements]

I'v done at least three so far and no problems. The current one must be the first that fits properly coz it's been in a while now.

[classic mk1]

Hi, Where can i find the details for this mod. My car revs its self silly first thing in the morning which can attract some strange looks at the traffic lights just down the road.
Cheers Colin

[un1eash]

The mod is part of doing the manual choke conversion but instead you drill a hole in the tyre valve cap to reduce air flow and revs, the valve goes in the throttle body....



start with a small hole in the cap and increase to get the desired revs.

[ligertigon]

Did last for 8 months though, and probably saved on fuel, so time to fit another

[coverco]

I have always wondered how the valve cap gets into the engine? Surely it would end up in the TVIS

I used some silicone sealant on mine when I fitted it, and it has been in for 18 months, although I have a manual choke fitted so did not drill a hole in mine

[Tony jinxy froude]

Ive lost about 4 on mine & i have a woodsy choke kit on my mk1 & its been on there for years, all the valve caps go to valve cap heaven but only after kissing "saint piston" & going through the gates of "exhaust valve" first
Jinxy

[flippin'eck]

Sent a steel throttle butterfly screw through a TS50X once with no ill effects

[viperrr]

The mod is part of doing the manual choke conversion but instead you drill a hole in the tyre valve cap to reduce air flow and revs, the valve goes in the throttle body....

Image Replaced With URL For Quote http://i2.photobucket.com/albums/y17/un ... axstat.jpg

start with a small hole in the cap and increase to get the desired revs.

Hi guys

This might seem a VERY stupid question, but please bear with me

I can see that restricting the airflow with a hole in the valve cap will keep the revs low from cold... But surely as the engine warms up, and the car reduces the airflow itself and having the valve cap in their will restrict the airflow even more - dropping the revs substantially when warm?

Is this the case? Or is it a fact that the car will reduce the airflow a minimal amount, so the restriction of the valve cap has little effect.


Thanks!

[coverco]

Normally the start up revs are controlled by the AAV or waxstat, the hole where the valve cap is inserted allows air to pass thus decreasing the air to fuel ratio and increasing the revs. By inserting a valve cap with a hole you allow more air to enter the throttle body and so the revs decrease. When the engine gets up to temperature the AAV closes and so no air goes through the valve cap so you are back to normal

I think this is how it works anyway Hopefully the following drawing should explain it better, click on it to enlarge.

[ligertigon]

Normally the start up revs are controlled by the AAV or waxstat, the hole where the valve cap is inserted allows air to pass thus decreasing the air to fuel ratio and increasing the revs. By inserting a valve cap with a hole you allow more air to enter the throttle body and so the revs decrease. When the engine gets up to temperature the AAV closes and so no air goes through the valve cap so you are back to normal

I think this is how it works anyway Hopefully the following drawing should explain it better, click on it to enlarge.

QED

[viperrr]

Normally the start up revs are controlled by the AAV or waxstat, the hole where the valve cap is inserted allows air to pass thus decreasing the air to fuel ratio and increasing the revs. By inserting a valve cap with a hole you allow more air to enter the throttle body and so the revs decrease. When the engine gets up to temperature the AAV closes and so no air goes through the valve cap so you are back to normal

I think this is how it works anyway Hopefully the following drawing should explain it better, click on it to enlarge.

Image Replaced With URL For Quote http://i114.photobucket.com/albums/n266/coverco/AAV.jpg

Makes perfect sense now, I had no idea about that hole in the top too

Thanks!

I put a holey valve cap in the right place and it seems to have done the trick - I am most pleased.. and I'm sure my neighbours will be at 7:30 in the morning too!

[coverco]

Normally the start up revs are controlled by the AAV or waxstat, the hole where the valve cap is inserted allows air to pass thus decreasing the air to fuel ratio and increasing the revs. By inserting a valve cap with a hole you allow more air to enter the throttle body and so the revs decrease. When the engine gets up to temperature the AAV closes and so no air goes through the valve cap so you are back to normal

I think this is how it works anyway Hopefully the following drawing should explain it better, click on it to enlarge.

Image Replaced With URL For Quote http://i114.photobucket.com/albums/n266/coverco/AAV.jpg

Makes perfect sense now, I had no idea about that hole in the top too

Thanks!

I put a holey valve cap in the right place and it seems to have done the trick - I am most pleased.. and I'm sure my neighbours will be at 7:30 in the morning too!

And you don't look like a chav at traffic lights

I do recommend Mr Woods automatic choke though, as it completely does away with the AAV system (Please note I am not on commission)

[jimi]

Normally the start up revs are controlled by the AAV or waxstat, the hole where the valve cap is inserted allows air to pass thus decreasing the air to fuel ratio and increasing the revs. By inserting a valve cap with a hole you allow more air to enter the throttle body and so the revs decrease. When the engine gets up to temperature the AAV closes and so no air goes through the valve cap so you are back to normal

Not quite, the fuel/air ratio ( at idle ) is decided by the ECU acting on info from the MAP sensor. Without the cap a certain amount of air passes through the port, the MAP sensor sees this and tells the ECU which increases the fuel accordingly and the idle rpm rises to around 2000/2500. With the cap (with a hole in it ) fitted then the amount of air passed is less because the hole is smaller, the MAP sensor sees this and tells the ECU which increases the fuel accordingly and the idle rpm rises to a level which is decided by the amount of air passing, so bigger hole = higher cold idle rpm and smaller hole = lower cold idle rpm. If you go too small then your car won't idle properly when cold.
Paul has found an alternative solenoid for his choke kit which is adjustable (MR2 MK2 aircon idle up VSV) and allows you to set the cold idle to suit yourself, mine idles around 1200/1300 rpm with the manual choke on. You can achieve the same thing by fitting a restrictor in one of the pipes to the normal solenoid that Paul supplies with his kit.
I'd highly recommend Paul's kit, I fitted one about 3/4 years ago and wouldn't be without it.
Jimi

And I'm not on commission either

Paul very generously made all the info on his choke kit public for anyone who would like to try making their own there are a couple of articles with all the info available on "another forum" due to the NETIQUETTE rules I can't post a link as you will have to register to read them, but it's free and I'm sure you can guess where I mean

[coverco]

Not quite, the fuel/air ratio ( at idle ) is decided by the ECU acting on info from the MAP sensor. Without the cap a certain amount of air passes through the port, the MAP sensor sees this and tells the ECU which increases the fuel accordingly and the idle rpm rises to around 2000/2500. With the cap (with a hole in it ) fitted then the amount of air passed is less because the hole is smaller, the MAP sensor sees this and tells the ECU which increases the fuel accordingly and the idle rpm rises to a level which is decided by the amount of air passing, so bigger hole = higher cold idle rpm and smaller hole = lower cold idle rpm. If you go too small then your car won't idle properly when cold.

Assuming this is correct (I am sure it is) then why bother with a mechanical system like the AAV? Surely all that is required is a temperature sensor in the thermostat housing, as the engine gets up to temperature then the ECU could alter the fuel/air mix accordingly

[un1eash]

I made my own kit for about £5 from things lying around the garage. I have thort about extending my manual choke to include a temp swtich and diesel relay so its only active for 10-20 seconds which is all thats need.

[coverco]

I made my own kit for about £5 from things lying around the garage. I have thort about extending my manual choke to include a temp swtich and diesel relay so its only active for 10-20 seconds which is all thats need.

Have a word with Jimi, he has added a timer relay to his (and mine Thanks Jimi) . My choke turns itself off after a minute or so

[jimi]

Assuming this is correct (I am sure it is) then why bother with a mechanical system like the AAV? Surely all that is required is a temperature sensor in the thermostat housing, as the engine gets up to temperature then the ECU could alter the fuel/air mix accordingly

You would still require some method of increasing the airflow past the closed butterfly to raise the cold idle. It could have been done using a solenoid ( same method as Paul only directly controlled by the ECU )
Mr T chose to use a temperature controlled waxstat to operate a mechanical valve. He must have had good reasons for going this route, but I have no idea what they were