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Old 01-06-2008, 01:05 AM   #11 (permalink)
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I wasn't aware that modern cars already used this fuel cut-off feature...its good that they do that.

My car has a manual tranny and manual steering, so no worries there...I just mentioned auto trannies and power steering so that maybe my idea could extend to other cars.

I'll have to do a little research on vacuum canisters. If anybody can offer some decent links that would be awesome. In the meantime I'll check the archives on this site. I'll also have to practice that handbraking technique in some low traffic areas, it sounds worthwhile.

By the way, here are the selenoid valves I was thinking of using:


Part # SV430. Its more of a general purpose valve and isn't automotive specific, but I think it should work. If anybody can think of a valve that would be better suited please let me know.

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Old 01-18-2008, 07:04 PM   #12 (permalink)
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Originally Posted by Dane-ger View Post
I'll have to do a little research on vacuum canisters. If anybody can offer some decent links that would be awesome. In the meantime I'll check the archives on this site. I'll also have to practice that handbraking technique in some low traffic areas, it sounds worthwhile.
Here ya go!

Summit Racing vacuum canister page

BTW, VW TDIs have speed sensitive fuel cutoff. For instance, in 5th gear if you take your foot off the "throttle" pedal (leaving the car in gear), injection stops completely until you slow to ~25 mph (actually 40 kph), whereupon it picks up smoothly.

Couple of interesting side notes. First, VWs also have a system to permit persons not comfortable with manual transmissions to drive them effectively. Simply start the car in neutral with the clutch depressed, shift into 1st gear and let the clutch out slowly and steadily. The ECU adds fuel and starts the car rolling without the driver having to coordinate power and clutch. You can go right up to 5th gear without touching the "gas" pedal, and the car will roll right along at 40 kph on the flat or even uphill. Press down on the go-pedal at any time to go even faster.

Second, there is some controversy in TDi circles about which is better, coasting in neutral or the automatic fuel cutoff feature. I used to use the automatic feature, but lately have been taking the gearbox out of gear for much longer coasting distances on the premise that since I can coast out of gear at least twice as far as with the engine engaged, I burn less fuel in idle than I do under power to cover half the distance. The jury is still out though, as I haven't collected a tank's worth of data for each case. I share this car daily with my wife, too, which complicates good data collection.
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Old 01-18-2008, 07:38 PM   #13 (permalink)
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Cool, Another fellow early Z car person!
Have you tried driving without the booster? My 260Z booster has been dead for about 10k miles and giving no effect. It isn't easy but defiitely live-able. My old calipers wouldn't even lock up while standing on the brake pedal to the floor. I went to bigger (yota 4x4 with solid rotor) brakes and now I have much better stopping power without the booster (Can lock up the tires... and stop MUCH better without locking them up. I.E. not scary)
Just an option...
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Old 01-18-2008, 10:44 PM   #14 (permalink)
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With the pre TDI I have a momentary switch right on the shift knob. Cuts power to the fuel injection pump. definitely helps brake when I come in too hot. Easy way to kill the engine without reaching, when I want to coast. The pre TDI's go to idle on decel not off. If trying to restart with the clutch always use high gear on a diesel. Or its hard on the clutch. On the little ladies van I want to put a momentary switch on the Idle Air Control (IAC), that thing really tics me off.
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Old 05-27-2008, 06:16 PM   #15 (permalink)
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look to see if there is a plastic "thing" inline in the hose that brings the vacuum from the intake manifold to the booster. If so, it is probably a check valve. These can get stuck in the "shut" position, and now you never get vacuum to the booster.
An easy test would be to pull off the hose right at the booster with the engine running, you should have vigorous suckage into the hose. Plus the engine may run poorly while the hose is off.
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Old 05-27-2008, 07:36 PM   #16 (permalink)
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If you just cut fuel going to the carburetor the carb still has fuel in the float bowl, enough to go maybe a quarter mile or more, then it will slowly lean out, at this point your engine is running really lean and this seems like a bad idea as an extremely lean burning engine tends to over heat the engine, this is why when honda started implementing this very idea in the mid 70's they put 4-5 solenoids on the carb, one on each supply to each jet, it added some complexity to the carb, but made the car use alot less gas.
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Old 09-12-2008, 02:08 AM   #17 (permalink)
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Down shifting is an easy way to take it easy while braking and also a great way not to waste so much gas. When your engien revs and the rmps increases, especially when you downshift, you're just using more gas than what is needed at the same speed.

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Old 09-13-2008, 11:22 AM   #18 (permalink)
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In terms of autos... my 1989 auto actually does care about the TC. When slowing down, it does fuel cut above 80km/h, but once the torque convertor lockup deactivates, it instantly starts using the same amount of fuel per engine cycle as it would at idle - which means it is better to put the transmission into neutral - so at least it 'idles' more slowly
Same goes for my 1989 auto. If Im going down a long steep hill in gear with foot off the gas, itll cut fuel after a few seconds, but then bring back the fuel for a few seconds, keep doing that till the car quits gaining speed. If I pop it into N then the idle speed will drop and itll pick up a lot of speed. But I dont like how it reengages when I shift back into D, I feel like Im hurting the trans, so I avoid doing that. But one thing I just figured out last night, is if I hold the throttle in just the right spot on a long downhill, itll keep the TCC locked but cut the fuel. The fuel will stay cut all the way to the bottom of the hill and Ill maintain speed. And no funny actions at the end since I dont have to shift back into D. Something I have thought about is a momentary switch to cut the fuel. Then with the fuel cut, the throttle can be really opened up, keeping the TCC locked and reducing restriction at the intake, maybe getting you farther down the road.

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Old 09-13-2008, 01:34 PM   #19 (permalink)
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When you have an SUV.... Power steering in traffic is a must...

In a geo... power steering is pretty much not required at all.

Thats what I've figured out heheh.

Yea.. I drive a Jeep and I'm on a fuel economy site, but you just wouldn't understand... "It's a Jeep thing!" *Jeep Wave*

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Old 09-13-2008, 02:06 PM   #20 (permalink)
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DifferentPointofView -

Originally Posted by DifferentPointofView View Post
When you have an SUV.... Power steering in traffic is a must...

In a geo... power steering is pretty much not required at all.

Thats what I've figured out heheh.
110% agreement. I am on the cusp, but I know it will work for me, so it's on the todo list (edit: convert to manual steering).



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Last edited by cfg83; 09-13-2008 at 02:41 PM..
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