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blow of valve not working - Induction/Turbo/Chargecooler/Manifold/Exhaust - The Lotus Forums Jump to content
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Jimjitsu

blow of valve not working

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Anyone got any ideas why I cant get a blow off valve to work? plumbed into outlet for carbon canister as per instructions on lotus esprit world. Valve definitely works, when I bought the car it had been plumbed into where the map connects on other end of vacuum rail I have correct the vacuum lines as they were badly fitted and reinstalled BOV to where it should be fitted but the thing just wont blow off

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hello jimi i have a b.o.v. on my s4 but i fitted a recirculation one so that its much quiter, if you have one of these fitted then is very very quiet as is piped back into the air intake

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I have 2 that I have tried both are dumping to atmosphere and both work something seems to be wrong with the vacuum but I cant figure out what. I tried disconnecting the carbon canister vacuum line and fitting the one from the BOV direct to the vacuum line that serves the carbon canister still no dump

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Don't think the vac pump is part of this circuit bud looks to me like all that does is exhaust valve, throttle valve and interior vents could be wrong but that is all it looks like it does to me

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Correct the vacuum system has nothing to do with the dump valve in normal configuration.

The dump valve works by the piston being supplied air at boost pressure on both sides when boosting, however, when you let go of the throttle, the butterflies in the throttle bodies close the air flow down dramatically, and you then have lower pressure in the engine side than in the charge cooler / turbo side. This pressure imbalance becomes greater than the small spring in the BOV can cope with and thus the high pressure air on the CC/ turbo side pushes the valve open, and is then vented to atmosphere / ducted back to the air filter.

The small bore hose to the BOV is what supplies the air at engine side of the butterflies, thus if it's not in place you'll find the BOV dumps the boosted air nearly all the time (the spring can hold a small pressure). The small hose you are tapping into with the T piece is the bit with a one way valve to stop boosted air getting forced into the charcoal canister. The charcoal canister empties its vapour and some fresh air into the engine via this hose and is controlled by a small electrical solenoid.

You have got the one way valve on the canister side of the T piece haven't you?

You have got it black end facing the engine haven't you?

Now all that is out of the way.

Does the piston of the BOV move if you take it off the big CC/ turbo pipe and push it with your finger?

Yes = good

If it does. Put it back together but simply go from the one-way valve to the engine inlet connector and don't connect the small hose to the BOV. Drive the car a short distance and get just onto boost, did it audibly let air go (you will not get a whoosh, just a whistle)?

Yes= good

If both are Yes, and al is well with how it's installed, start swearing, because something is wrong, and I can't immediately think what.

Andy

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initiate swearing lol I have disconnected the pipe to the carbon canister completely and just fitted the BOV to the vacuum point so no chance of any interference from the carbon canisters vac line, also the BOV worked fine on the opposing connection on the vacuum rail the one that connects to the MAP sensor , Don't ask I didn't put it there that's how it was when I got it >< have corrected that now and replaced the craptastic blue silcone pipes that where there.

Thanks for all the info I'm gonna go and have a good look at it all again with your comments in mind :baby:

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I can't think of any reason why you cannot use that other connection on the other side, it's used for the MAP take off to the remote transducer, so I think it's mechanically the same point as the one for the fuel vapour.

I'd say swap it back, if it works there, leave it there.

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