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95.5-2004 Tacomas & 96-2002 4Runners 4th gen pickups and 3rd gen 4Runners

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Old 05-16-2005, 11:01 PM   #1
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Attention anybody w/vacuum advance

I have latley had some pinging issues under acceleration and decided to check the timing. The timing ended up being dead on. I decided to check the vacuum advance diaphram by sucking on both hoses independantly. The hose leading to the diaphram closest to the valve cover does not hold vacuum very well while the one closest to the radiator does. Is this normal? I would think that both diaphrams should hold vacuum. The factory service manual is vague in this area. Could anybody do a quick check on their vacuum advance to confirm the above? Thanks!!

Dan

1984 22re
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Old 05-17-2005, 06:02 PM   #2
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i think the one by the valve cover is called the "sub-advance", and i haven't had any luck really figuring out what it does either. i do know you can block it off and run the outer one, if say, you put a weber carb on the engine that only has provisions for a regular vacuum advance.
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Old 05-17-2005, 10:46 PM   #3
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Do you know if your "sub adavance" diaphram holds vacuum or not? Mine seems to bleed it off. I've got EFI (non TCCS) so I'm not exactly sure what to bypass where. Thanks!
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Old 05-18-2005, 07:09 PM   #4
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is that factory? i wasn't aware that you could get an '84 4runner with an analog EFI system like the '83-84 celica -- all '84s i've seen had carbs...
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Old 05-18-2005, 11:07 PM   #5
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Yeah, it's factory....but not a 4runner, she's a 4X2 sr5 1/2 ton pickup. What is really strange is that for a system that is considered "inadequate" to TCCS, I can consistently pull 35-40 mpg and it is peppier than TCCS based systems from 85-88. Oh well, no complaints here

Were you able to test your sub-advance diaphram to see if it holds vacuum? Thanks!
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Old 08-05-2007, 11:25 AM   #6
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I have an 85' with a 22R and HAC system. I had the same problem with the "sub-diaphragm" not doing anything. I ended up switching hoses from what I could see in the service manual. The only way things seem OK is when I set the timing to 0 BTDC, connect the hose with full vacuum to the port closest to the radiator. The timing goes from O BTDC to 12-14 when I do this. This also puts, at idle, vacuum on the HAC canister. The other hose, the one that increases the vacuum with RPM, I connected to the other port. I read somewhere that one port is the advancer, the other is a retarder. One thing I know, if you connect it like the manual, you get no vacuum at idle and no advance. I went to a junkyard, tested one, and it acted like mine. Did you ever get to the bottom of this?
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Old 08-05-2007, 11:25 AM
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