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Join Date: Dec 1969
Location: Bronx, New York
Posts: 102
1.7 Mpg

Hey Guys,
I'm getting about 10 miles per gallon, is this right for a 1.7? If it isn't what is needed to correct it?
Old 07-13-1998, 05:37 AM
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10 mpg is very wrong. Should be getting more like 25 or even 30 mpg, even on a 2.0 L.

To be this far off, I don't even know if running too rich could be the problem alone. I would certainly thoroughly check for fuel leaks. I you don't have anything on the driveway, under the car, you still need to check with the fuel pump working. These leaks can happen in a high pressure system (injection) after 25 years on the road. They can also be pretty dangerous and were, i believe, the cause of numerous fires.

As far as adjusting the injection system itself, I don't know much that you could do except fiddle with the knob on the computer, if you have one. Others will be better able to help you on that aspect. You don't say how well or how rough your engine runs either under power, at idle, cold, hot etc ...
Old 07-13-1998, 08:24 AM
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Is it FI or carbs. My 1.7L got 25+ MPG with a 2.0L/1.7L mixed (used parts from different cars) system. I have an old magazine ad that reads, "The 29 MPG Porsche". If you have a progressive carb you should get around (my guess) 15-20 MPG. With dual 48mm Webers then 10 sounds about right (once again I'm guessing). Your problem could be that you are jetted too rich or something is getting stuck inside the carb. Or it may be your odometer, test it or try a different one, I think Pelican has a article on how to test them. Also if the cam is not matched to the carb then it may also be affecting your MPG. If your car is faster than stock, you'll lose some MPG. Fuel=Power, or something like that.
Old 07-13-1998, 12:58 PM
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Hey Guys,
It's fuel injected. I think it idles pretty sound but thats after adjusting both the fuel regulator & pressure sensor by ear.
Old 07-13-1998, 01:45 PM
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I get about 20 MPG in my 2.0--and I have a VERY heavy foot, and the car is running rich at the moment. (Mileage drops to about 12-14 when I autocross.)

That's probably your problem, then. Adjusting by ear is fine for the idle mixture (lean it out until it hunts, richen it until it stops), but gets *very* tricky indeed when you start tweaking the other components.

Get thee over to Tim's 914 Fan Page, at http://www.estinc.com/porsche . Look into the Tech Refs section, and select Kjell Nelin's D-jet Guide. Read it, memorize it, then say ten Hail Ferry's. (heh heh)

Seriously, it's a good article. Buy yourself some good measuring equipment--fuel pressure and volt/ohm/ampere gauges at the very least. If you don't want to buy/can't afford the mixture gauge, then learn to love pulling your spark plugs to check the color of the insulators.

Racer's Wholesale, I'm told, sells fuel pressure gauges very cheap. And Radio Shack will carry the electrical multimeter.

Messing with the Manifold Pressure Sensor is a very tricky thing. Small adjustments apparently have large results.

I personally have so far only played with the fuel pressure and head temp sensor circuit. I have the equipment for measuring the quantity I am tweaking--a fuel pressure gauge and an ohmmeter respectively. And I still don't have it dialed in right.

--DD
Old 07-13-1998, 04:38 PM
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