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rockaria's Avatar
 
Join Date: Apr 2002
Location: Southwest USA
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Quick Vacuum question 1.8 L-JET...

Hello,

I must have too much time on my hands. I keep taking stuff apart to see how it works. But here is my latest thing.

I have a 1975 1.8 L-jet with california plumbing. On my Throttle body I have Two Vacuum pipes. One that faces the front of the car and one to the rear. The front one has vacuum and goes to the Distributor on a pipe closest to the Dist. near the front of the car. The second hose Tees off to the EGR valve and to the Dist. on the pipe furthest from the Dist. pointing up and to the rear.

Here is my question. This second vacuum hose (to EGR with tee)has no vaccum (Even with hose off at the Throttle Body has no vacuum). Is this correct for the car?

Thanks,
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Christopher A. Landt
rockaria@rockaria.com

1979 911sc
1973 914 2.0
Old 08-01-2002, 09:50 AM
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That is correct. The second vacuum connection is a ported vacuum. That means that the opening for the vacuum connection is above the throttle plate. It won't see vacuum until the throttle has been opened slightly.
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Clay Perrine
74 914 1.8L (Frodrick)
73 914 /6 4.0L 964 motor (Igor)
70 914 /6 Factory Six. (Elwood)
95 BMW 540i (Inga)
Old 08-01-2002, 09:54 AM
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Cool! Thanks!
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Christopher A. Landt
rockaria@rockaria.com

1979 911sc
1973 914 2.0
Old 08-01-2002, 09:57 AM
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Yes, this is correct. This is called "ported vacuum" and originates above the throttle plate. If you rev the engine slightly you will find that you will have vacuum at that port, but very little to none at idle.

Also, FYI, this is the "advance" side of the distributor vacuum unit. The side closest to the distributor receives "manifold vacuum" and is the "retard" side of the vacuum canister. You will find quite a bit of low pressure (vacuum) on this line at idle.

Edit: Guess I'm a slow typist!
Old 08-01-2002, 09:59 AM
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So what is the best thing to do if you don't have the EGR valve installed anymore but you do have the second port on the throttle body?

Right now I've got that second port on the TB plugged and nothing on the vacuum pot (port facing up).
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Eric
'75 914 2.0L - Sold!
Old 08-01-2002, 11:57 AM
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I asked that question before about connecting to the ADVANCE side of the distributor vac advance, and was told that most (all?) of the 1.8s didn't have the advance hooked up. I think the car runs cleaner without as much advance, less NOx, (hence the temperature controlled advances on the US cars that would eliminate vac advance once the car reached temperature). I wonder if there is any performance advantage to connecting it, as long as you guard against pinging with higher octane fuel.
Old 08-01-2002, 12:59 PM
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I suggest hooking it up and driving. You may notice a bit better off-idle response. You may notice slightly better freeway gas mileage. A tailpipe sniffer might notice slightly higher emissions just off-idle.

I doubt you'll get pinging, even on regular-grade (87 AKI) gasoline.

--DD
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Old 08-01-2002, 01:33 PM
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