mpg

[ejust]

bump

[fspGTD]

If your engine is smoking, it is not burning all of its fuel.  Smoke is uncombusted fuel, after all.  To be more efficient you want to run it lean so that it does not smoke at all.  The most efficient torque for a factory motor is about 80% of factory max torque setting (it would be even less than 80%, if you've modded the pump to the point where you can get lots of smoke.)

Have you considered it could be the way you drive or the routes you are driving?  Using brakes a lot bleeds off kinetic energy which must be regained by burning fuel to get your car back up to speed.  So, driving in a way where you do not use your brakes as much, for example anticipating stop lights or allow traffic to cut you off and make you use brakes, will result in better fuel economy.

Also, it could be the way you or others are measuring their miles per gallon.  The method used to measure miles per gallon can also make mileages vary.  The most accurate way is to measure fuel consumed over a number of tanks and average the overall amount of fuel consumed over the total number of miles traveled - figures recorded over just one tank will not be highly accurate because the tank will not be refilled to the exact same level.  Furthermore, odometers are often miscalibrated, and can contribute additional inaccuracy to fuel mileage readings.

Bottom line - YMMV, or "your mileage may vary", applies when comparing fuel mileage numbers.  There is not necessarily anything wrong with what you've measured, especially if you drive in an area with traffic and frequent stops or frequently use high speeds on the freeway.

[vwmike]

I just filled up again today. Mileage is back up now that I turned the smoke screen off. 41 mpg in my 88 Jetta TD.

[Northboundtrain]

Do you have a lot of miles on your injectors?  Getting them rebuilt could certainly help.  This guy will do a superior job, and you can tell him that you want the injectors set up for maximum fuel economy.

http://www.coloradobiodiesel.com/injectors/index.html

[ejust]

the odometer on the car shows 222k mi (357k km). When i bought the car, the guy told me that at around 140 to 150k mi(225-241k Km), the dealership put a new timing belt on, but i guess timed the engine wrong so the valves contacted the pistons. he said the dealership had to replace parts. Which ones besides valves i dont know. So im not sure which engine parts are original and which one have about 75k on them.  My compression test last fall (engine cold at 50F (10C)) was as such
#1 - 445           #2 - 485                #3 - 465                #4 - 440
So compression seems to be ok. When i start the car cold, there is a hint a bluish smoke but its really faint which i figured is normal for diesels and it goes away in a couple minutes. It starts right up - almost faster than most gassers. Im thinking maybe the fuel system is original though so imagine the injectors and pump have the 222k on them.

[Northboundtrain]

Probably time for new injectors -- they can help out enormously.

[fillmore]

im getting 800kms per tank in city traffic in my 89 N/A

[ejust]

topped off again at the same point as last time....

124mi on 3.25 gal = 38.2MPG  
about the same as last time....
and the time before...
and before that.....

guess mine dont like 40mpg or better..and its not that zippy either :cry:

[chrissev]

53.6mpg recorded today (US gallons), after two weeks of city driving.  1988 jetta TD.  This car is AWSOME!

[ejust]

must be nice. dont understand whats going on. Even the bentley says i should be gettin 44 or above.  :cry:

[jtanguay]

ejust try getting your car re-timed.  Some people say changing the transmission oil to synthetic helps too.   You also have to watch the way you drive.. try to keep rpm's below 2000 and your mileage should be really good.  There is also some diesel additives such as cetane boosters.  Those help a lot .

[ejust]

im thinking there is something shot.  Has to be. Ive fixed up the car and made sure everything thats adjustable is basically to specs inc the timing is dead at .040 (1.01mm).

Ive noticed oily specs in my coolant. Ive done a couple flushes but it keeps coming back. Thinking the head gasket is going. And that might be my problem. How long before it totally goes?? I think injectors need redoing. So i guess ill have to just deal with it all inc the bad milage till i can afford to get all this done.

[fillmore]

it shouldnt be the head gasket, i drove mine whaile the geasket was shot and i still got 800+kms per tank

[jtanguay]

Just a thought... but could it be because the compression is so high, that it is actually creating parasitic drag on the engine at high rpm?  ie: the compression stroke is robbing the power stroke of energy?  Or would that even make a difference?  It might explain why oil is seeping into the coolant, mainly because of all that pressure.

If everything else is good like tire pressure, alignment, wheel bearings, no brake drag, and good suspension, then who knows...

[ejust]

first off..I wanna say thanks :wink:  to those who have helped me here on IDI. I know a ton of questions come in like i do about "my car" and ask specifics. I hope to gain the knowlege to be able to help someone else out someday!
This whole site is great and kuddos to the owner/designers/moderators!!

Ok..back to my dilemma LOL

high compression..im gonna rule that out  Reason being..at 23:1, the cylinder pressure is suppose to be between 400-500psi normally. Ive read so far that high boost can cause extra pressure which basically lifts the head off the gaskets microscopically and allows escaping gases. My head gasket could very well be doing that even though my setting are stock. Just a guess here.  Ive noticed its not as powerful as last summer, zippy when cold but loses power when it warms up, temp guage hovers around 1/4 (maybe 1/2 after lots of driving then sitting and idling), and milage is averaging around 38ish which is low. Bently says 44mpg(US) in mixed traffic above 32F (0C).  Going up a small hill i can step on it, itll smoke behind me but not real bad, but it the car hardly accelerates.  Losing power somewhere.  Ive tried setting the pump per the book for residule and idle settings.
Question..would a govenor mod kill milage?? I cracked open my pump 3 weeks ago and attempted fait. The govenor had like washers or something and springs. Dont know if it was tampered in the past but doesnt look stock or like a complete mod from what ive read. Intermediate and main springs look like it has 1/4" (6mm) of washers or something. What would that do to affect the car? Ive left it for now before either i put it back to stock or change it to complete mod and remove intermediate spring. Anyways, its back together and car is running the same so i must of not screwed anything up LOL What a pain the throttle springs are!
ive rambled enuf for now. Y'all can dissect this and hand me your opinions and expertise on this. Thanks again everyone!!

i wish i had a injector pressure tester. That would give me an idea here if those are good or not.