Author Topic: Low mpg w/ a 4-speed? (Read 4272 times)

lacolocho · « **on:** March 04, 2007, 07:16:10 pm »

I just got an '81 Dasher 3 months ago with the standard 1.6L NA motor and 4-speed manual transmission.
I drove it down to San Francisco a month ago with three other people in the car and got about 38mpg going kind of slow (60-65mph) most of the way.
I thought that was pretty low, and I got the injectors tested when I got back and was told that they were spraying wide and down to 105 bar.
I had them rebuilt, and then in the meantime blew a headgasket, fixed that, and then got a superior fuel pump from 2manVR6 that he had used for about 10k miles, and timed it to .96 (the previous one was working fine and timed to .95) and then drove down to San Francisco again, this time driving 70-78mph (partially b/c I could), again with three people in the car.
I expected my mileage to go up a little or stay the same, with my rebuilt injectors, but it went DOWN to about 33mpg.

I usually run a biodiesel blend, so I had replaced the injector return lines with viton ones, but haven't replaced the other lines yet. So, I'm going to do that, but can that result in a loss of fuel efficency?

What else could be going wrong? Is it just from driving so fast with 4 people plus luggage in the car with a 4-speed?
Everyone I've heard from has said that their mileage has stayed the same when switching to these pumps. What do they have them timed to?
I'm thinking about turning the timing down to .88 or something.

A 5-speed is definitely in my plans for the next 6 months.

What kind of mileage do other people see with a 4-speed?

burn_your_money · « **Reply #1 on:** March 05, 2007, 06:14:31 am »

I think you will want to advance the timing rather then retard it. It will give the fuel more time to burn resulting in more complete combustion. What tranny do you have? If it's a 4A I'd leave it in there, they are great trannys.

I don't recall exactly but I think I was getting closer to 50 mpg when I was driving my rabbit (with a 4A), even with 1 person and a weekends supply of camping gear (worth about 2 people)

If you have a short ratio tranny (GC etc) then driving at the increased speeds will definitly kill your mileage because you engine will be at some ridiculous RPM

jtanguay · « **Reply #2 on:** March 05, 2007, 11:10:33 am »

70-78mph hmmm.... you definitely won't get 50 mpg driving at that speed! remember that with increasing speed, your MPG decreases more and more my guess is that 78 mph is getting you about 25-30 mpg (which is still pretty damn good vs. those new gassers :lol: )

hipifreq · « **Reply #3 on:** March 05, 2007, 01:27:53 pm »

I'd say the same about consumption, it's the speed more than anything else. Those cars were made to go around 60 mph, and much over that you're really pushing it pretty hard.

As for the tranny swap, I personally CAN'T WAIT to get my hands on a 5-speed. My '80 Dasher drives 55 highway, 65 if I really push it to the screaming point. I'd love the same ratios all the way to 4th, with that little bit of extra to get to 65-70 without pushing to RPMs. I don't care how good the tranny I have is, the 4-speed just kills me.

AdAm84 · « **Reply #4 on:** March 05, 2007, 07:05:18 pm »

I'm pretty happy with my 3+E. i get 40mpg with a half turn on the fuel screw. the timing is at whatever it was at from the factory. as far as i know, no one messed with it, the injectors are also original as far as i know. the biggest problem with mine was the lonkage bushind=gs and lack of lol. btw from what i've found, my tranny has one of the highest overdrives used on VW's.

hipifreq · « **Reply #5 on:** March 05, 2007, 08:08:59 pm »

Quote from: "AdAm84"

the biggest problem with mine was the ... lack of lol.

:shock: WHAT!? No LOL? :shock:
Straight to the compactor with that car! :wink:

AdAm84 · « **Reply #6 on:** March 09, 2007, 06:56:51 pm »

Whoops! :oops: lack of bushings. sorry that post was pretty FUBAR. i guess thats what the preview is for lol

Turbinepowered · « **Reply #7 on:** March 09, 2007, 08:04:43 pm »

Quote from: "burn_your_money"

I think you will want to advance the timing rather then retard it. It will give the fuel more time to burn resulting in more complete combustion. What tranny do you have? If it's a 4A I'd leave it in there, they are great trannys.

I don't recall exactly but I think I was getting closer to 50 mpg when I was driving my rabbit (with a 4A), even with 1 person and a weekends supply of camping gear (worth about 2 people)

If you have a short ratio tranny (GC etc) then driving at the increased speeds will definitly kill your mileage because you engine will be at some ridiculous RPM

The Dasher is a longitudinal engine setup, rather than the Rabbit's transverse. So I doubt he has the same transmission that your Rabbit did.

With the manual sitting right in front of me, I could tell you what his gear ratios are if they're the four speed; as I recall, they seem pretty dang reasonable, angling for low-RPMs. That was a selling point of the 1.5 diesel, according to the book, the low-RPM high speed cruising ability.

Alas, the manual is outside and it's a little chilly, I'm tired and there's forty feet of gravel for my bare feet to cross after a garage of unfinished concrete to chill them. I'll go out and get it out of the wagon later.