An idea for better mileage

[farkman]

I was wondering if it would be possible to put some sort of switch(ball valve or something similar) in the small hose running between the intake manifold and the boost enrichment (I think that's what it's called) part of the injection pump. The switch valve would be in the car close to the driver and a small hose would run from the intake manifold into the car to the switch. A second hose would run from the switch to the injection pump. The driver can then switch the valve on to accelerate or turn the valve off for cruising. Since there would be no boost pressure applied to the injection pump less fuel would be injected, hopefully increasing fuel mileage. Do any of you think it would work or would the car not have enough power to maintain its speed because too little fuel is being injected. Any input is very appreciated.  

Thanks.

[Dr. Diesel]

the LDA is load dependant. It only gives as much as the engine needs for things like passing, or going up a hill. No point in doing this mod.

[QuickTD]

or would the car not have enough power to maintain its speed because too little fuel is being injected.

Exactly. The pump is providing only as much fuel as is needed to maintain whatever engine speed is requested by the pedal position. The boost enrichment device (LDA) only controls the upper limit of the injected quantity based on boost pressure. It is not really limiting injected quantity unless the pedal is at or near the floor. Cutting off boost pressure to it will only result in very sluggish performance when floored and little fuel savings, unless of course you normally drive with the pedal on the floor.

[farkman]

Thanks for your input guys.

It looks like I'll have to think of something else to improve my mileage to hit that elusive 50 mpg mark .

[TDIMeister]

Drive slower.

[farkman]

TDIMeister

I already do. On the highway I drive at a VERY leisurely 95km/h.

Any other suggestions? .

I was thinking about making a new tubular exhaust header out of 1.5" stainless steel. You think that could yield another 1-2 mpg.

[Giles@PerformanceDiesel]

Just filled up our 84 rabbit tank today and it took 40.3 L and it
covered 573 KM.  that works out to 40 MPG. not bad for a car
that gets driven like it was stolen just in the city.

by the way i didn't get this good mileage when i had less power

before my mod pump that is.

who says more power equals less gas mileage.

Giles

[BlackTieTD]

longgg longg 5th gear. top speed on my diesel is somewhere around 170-180km/h so 100-120km/h is pretty leisurely. transmission code FF i believe... was the original 4speed + E that came in my 1982 1.6NA diesel.

[farkman]

Lanny

I don't know what type of transmission I have but it does have a long 5th gear. At 2400rpm I'm at about 97km/h. Theoretically I should have a top speed of about 210km/h at 5250rpm but my car stuggles to accelerate past 120km/h at 3000rpm.

Does anyone know if having the cold start accelerator pulled out while cruising will improve/hurt fuel economy? I definitely have more power with it pulled out, but if it uses more fuel then obviously I'd rather push it in while cruising.

Thanks

[TDIMeister]

The cold start knob advances the injection timing, nothing more, and as long as it's not advanced too far, WILL improve mileage slightly.

I was going to say that you should get a TDI .  I get 50 MPG (Imperial) effortlessly, and this in a heavy elephant Passat  

[farkman]

TDIMeister

My best tank so far was 45 miles per US gallon, so about 54 miles per imperial gallon. And that was 80% highway, 20% city. But I want to get 50 miles per US gallon so I can go to Florida (Pompano beach area, about 2500km away from what I've been told) with only one fillup along the way, somewhere in North Carolina probably.  

Although I would love to get a TDI, I don't have the money to buy one :lol: .  

Peter

[fspGTD]

What about some of those tires that they put on the Honda insight, to lower rolling resistance?  I don't see why they woulnd't work on a VW Diesel too!  They might be a bit hard though.  :lol:

[farkman]

fspGTD

I already have the hardest tires I could get for a reasonable price. They are 185/65R14 Michelin Destiny's. They have a wear rating of 680 and I have pumped to 42psi in the front and 40psi in the rear. I figured that a 185mm width tire would reduce the frontal area of the tire a little, which would reduce drag. I also chose a little taller aspect ratio than stock which would lower rpm's on the highway.

I'm beginning to think that there's very little I can do now to improve my mileage :x .

Peter

[VWRacer]

Peter,

I drove my diesel Rabbit very carefully for about 80,000 miles over 6 years, and only rarely got better than 45 MPG. The one time I got 51 MPG, I was following a U-Haul truck that was governed to 50 MPH.

Bottom line is that you are doing about as well as you can expect with that car.

One technique that I've been using recently with my TDI is to short-shift from 1st to 2nd and 3rd, then go directly to 5th at about 35 MPH (50 KPH). And any time I'm rolling at or above 30 MPH, I am in 5th gear. That has bumped my fuel mileage up a couple of MPG.

BTW, what is your target MPG?

Stan

[farkman]

Stan

My target is 50 miles per US gallon (80km per US gallon) all highway at around 95km/h. That would give me a range of about 1300 km on 62L(about 16.4 US gallons), or a VERY FULL tank of fuel   . As for short shifting 1st, 2nd, 3rd and shifting directly to fifth, I pretty much do the exact opposite. I accelerate quite spiritedly so I can get into fifth as fast as I can. I can only shift into fifth at around 60km/h (1600rpm)though. Below that the engine is lugging. I anticipate stops and roll in gear as much as I can to avoid braking and consequently re-accelerating. Of course, I only expect to get 50 mpg if I drive only on the highway at a fairly constant speed for the whole time. My car is a 1994 Golf TD with the AAZ engine so it's not a really light car. I think I need to focus much more on aerodynamics though, especially on the front end.

Peter