Vacuum delay valve
Discussion
Hi, my car had this fitted when I bought her and can't decide is it really necessary on a tiv? It keeps my idle revs on 1100-1200 rpm for a couple of secs when stopping as it slowly releases the vacuum.
Here's an ebay link to the valve: this one...]
Tell me I don't need it
Here's an ebay link to the valve: this one...]
Tell me I don't need it
Thanks, now I need a longer vacuum pipe, this bleep is just sitting in the middle... 
How I love the full TVR service history the car came with... I had to change a camshaft with followers, rockers and shafts, timing gear and chain, distributor, leads, plugs (they put some denso in), fuel pipes, clutch, headlights. All these on a 62k car with sh up to 60k...
At least its quite sorted now and what a blast to drive
How I love the full TVR service history the car came with... I had to change a camshaft with followers, rockers and shafts, timing gear and chain, distributor, leads, plugs (they put some denso in), fuel pipes, clutch, headlights. All these on a 62k car with sh up to 60k...
At least its quite sorted now and what a blast to drive
walkie said:
How I love the full TVR service history the car came with... I had to change a camshaft with followers, rockers and shafts, timing gear and chain, distributor, leads, plugs (they put some denso in), fuel pipes, clutch, headlights. All these on a 62k car with sh up to 60k...
At least its quite sorted now and what a blast to drive
Not saying you but.... Some people say home servicing/looked after properly devalues a Griff At least its quite sorted now and what a blast to drive
Hope its all sorted now
Oh yeah, took all winter to sort them all out, but since then the car hasn't skipped a beat and I started to think these tivs are reliable
It's a bit overkill to use a 500 for daily commute, but the jag xjr can sit in the garage until next winter...
Oh, forgot to say, one of the precats was broken and blocked the exhaust so I've removed them both, nice deeper exhaust note is the reward. Also fitted a hot start kit therefore I dont need to pretend I'm checking the fluids after filling her up with gas
It's a bit overkill to use a 500 for daily commute, but the jag xjr can sit in the garage until next winter...
Oh, forgot to say, one of the precats was broken and blocked the exhaust so I've removed them both, nice deeper exhaust note is the reward. Also fitted a hot start kit therefore I dont need to pretend I'm checking the fluids after filling her up with gas
The vacuum delay valve won't hold the revs up, unless there's something very funny going on.
What it should do is allow the vacuum advance release quickly, but make it slow to engage. This was to cope with the ported vacuum that the EFI throttle body provides. (As far as I can tell, this was originally intended to work with a particular ignition setup to provide massively retarded ignition at idle (to improve emissions) and since the associated dizzy is no longer used the whole ported vacuum thing is utterly pointless and these systems really should have manifold vacuum. But since they do use ported vacuum, they need the delay valve to prevent transient glitches open the throttle quickly from idle.
Having said all that, the valve itself is routinely fitted back to front by people who misunderstand it, and can block or fail open or closed, messing up the vacuum advance. So if in doubt you're best to remove the valve and replace it with a straight tube connecting the two hoses together.
What it should do is allow the vacuum advance release quickly, but make it slow to engage. This was to cope with the ported vacuum that the EFI throttle body provides. (As far as I can tell, this was originally intended to work with a particular ignition setup to provide massively retarded ignition at idle (to improve emissions) and since the associated dizzy is no longer used the whole ported vacuum thing is utterly pointless and these systems really should have manifold vacuum. But since they do use ported vacuum, they need the delay valve to prevent transient glitches open the throttle quickly from idle.
Having said all that, the valve itself is routinely fitted back to front by people who misunderstand it, and can block or fail open or closed, messing up the vacuum advance. So if in doubt you're best to remove the valve and replace it with a straight tube connecting the two hoses together.
Useful info from GreenV8S here.
"The vac advance is connected to a throttle edge tapping. This means that when the throttle is closed there's no vacuum and hence no vacuum advance. Cruising with the throttle open a crack there's lots of vacuum and lots of advance. Full throttle there's no vacuum and no advance.
The problem with this setup is that as you slam the throttle open it goes through a brief period when there is full vacuum applied, and this causes the timing to jump as you go from no advance to full advance to no advance in a fraction of a second.
The point of the slow return valve is to prevent the vacuum from reaching the dizzy unless it is sustained for a second or so. So you don't get any advance whejn you slam the throttle open, but you do under cruise conditions.
The problem is that the valve can easily become blocked making the vac advance stay on or off at the wrong time, and it's frequently misunderstood and connected the wrong way round. These problems are far worse than the minor problem the valve was intended to fix and if in doubt I suggest you get rid and just connect a pipe straight from the throttle body to the dizzy."
I just binned mine in the end.
Andy
"The vac advance is connected to a throttle edge tapping. This means that when the throttle is closed there's no vacuum and hence no vacuum advance. Cruising with the throttle open a crack there's lots of vacuum and lots of advance. Full throttle there's no vacuum and no advance.
The problem with this setup is that as you slam the throttle open it goes through a brief period when there is full vacuum applied, and this causes the timing to jump as you go from no advance to full advance to no advance in a fraction of a second.
The point of the slow return valve is to prevent the vacuum from reaching the dizzy unless it is sustained for a second or so. So you don't get any advance whejn you slam the throttle open, but you do under cruise conditions.
The problem is that the valve can easily become blocked making the vac advance stay on or off at the wrong time, and it's frequently misunderstood and connected the wrong way round. These problems are far worse than the minor problem the valve was intended to fix and if in doubt I suggest you get rid and just connect a pipe straight from the throttle body to the dizzy."
I just binned mine in the end.
Andy
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