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Vacuum advance- what happened? Posted by Saana88 [Email]  (#207)  [Profile/Gallery]
(more from Saana88) on Sat, 30 Dec 2006 18:55:58
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Two weeks ago I was working on my happy '88 900 exautomatic and decided to test the vacuum advance on the distributor. It didn't hold any vacuum or suction whatsoever.
Mike: And Bobby's hopelessly inbred synapses slowly begin to fire.
Last thursday, I disconnected the vac advance and put a golf tee in the line to cure the vacuum leak.
This weekend I took another 200-mile trip down the Thruway to visit my folks and celebrate the new year as I always have. I drove this time.
Along the way I noticed a few things. First, the car had a little more low end kick, undoubtedly because the vacuum leak is now fixed. The second I noticed as the numbers on the trip odometer advanced, mile after mile. Even though the temperature has not been over 40 Fahrenheit (the old CI injection on the 8 valve cannot compensate for cold temperatures as well) this car is getting even-better-than-average mileage. Normally, half a tank happens around 250-275 miles. This time it was around 310. Normally, the low fuel indicator light is lit continuously around 390-410. This time it was around 435-445.
Half a tank at 310? Does this mean I'm going to get 600 miles on this tank of gas? Apparently not. With the indicator on, I have 50-65 miles to go until I start getting nervous, and I have a habit of putting 17 gallons in my 16.6 gallon tank when I refuel. So 445 plus 50 or so is a solid 500-mile tank of gas. That works out to around 30 MPG in cold weather. That's a bit better than the average of 27 from before. I'm a happy camper.
Is this improvement because the vacuum leak is fixed? All of it? What exactly does vacuum advance accomplish? Does it help mileage, or does the advance hinder it a bit? I know it isn't working now, but do I want to bother to fix it now or should I wait until things get warmer?
Anything else special going on? Should I limit the car to 3000 RPM? Does it matter?
I plan to fix it and reset the overall timing adjustment, check the idle speed, and then check the mixture, but can one hose have that much of a difference? The leak wasn't bad enough to keep the dash vents from working properly, just enough that the vacuum in the reservoir would bleed off within a minute of turning the car off.
If this car is back to 30 or so in the winter, I can't wait for summer!
(The previous record for this car was in 2003 when it got 36.4 on one tank and averaged well over 33 for the entire month of July.)
This is why it pays to tune up your car, clean the throttle bore, and change your oxygen sensor.
So, fix now or fix later? (It's pretty obvious I don't drive very hard at all.)
213K today, only significant because it's the sixth anniversary of my last accident. RIP, Sus...
Sappy Haabing!
, Sat, 30 Dec 2006 18:55:58 <-- Viewing This Message, Mon, 1 Jan 2007 10:13:15, Tue, 2 Jan 2007 20:31:05
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