fuel mileage

[akrabbit]

just bought a 80 4 door rabbiit, and was pretty disappointed with the 35 mpg i got on the highway at 65mph. i am a diesel tech by trade but never dealt with the vw diesels before, what should i check first? i have read that my 4 speed has a lower 4th than later transmissions, will a GP code trans from a 81 bolt up to my 80 1.5? i feel like my pump may be out of time also since when i pull the cold start lever out there is almost no change in the sound of the engine, definitely no rattle from the advanced timing. any help would be appreciated.

[TylerDurden]

just bought a 80 4 door rabbiit, and was pretty disappointed with the 35 mpg i got on the highway at 65mph. i am a diesel tech by trade but never dealt with the vw diesels before, what should i check first? i have read that my 4 speed has a lower 4th than later transmissions, will a GP code trans from a 81 bolt up to my 80 1.5? i feel like my pump may be out of time also since when i pull the cold start lever out there is almost no change in the sound of the engine, definitely no rattle from the advanced timing. any help would be appreciated.

Greetings,

That engine in good tune should get ~45-50mpg at 65mph.

I would begin with a few simple procedures:

• Install clear fuel lines to/from the IP (injection pump), to verify no air is in the fuel supply and/or being drawn into the IP.
  Ensure the useless water-separator by the rear wheel (under the passenger side floor) is bypassed.
  Put a vacuum gauge into the IP supply line to verify no restrictions (search for the value here, I cant recall ATM)
  Ensure the return line to the tank is unobstructed using compressed air: listen for bubbling.
  Check the compression to verify adequate range: ~250psi - 400psi. ( even compression as low as 200psi can still get good economy)
  Spin each wheel to verify no brakes/hubs are dragging.
  Check tire inflation.

Many here will adjust timing by-ear, with the following technique:

• Mark the IP and the bracket with a scratch-awl. ( To see how much it moves and to have a baseline to return to if needed.)
  With the the engine warm, loosen the IP (4 bolts) and turn the top towards the engine until the cusp of where the clatter increases. Retighten bolts.
  Loosen and retighten rigid injector lines (at the IP end) to relieve the torque from turning the pump.
  Repeat/restore as needed to refine the tuning, moving the IP in small increments.
  Constant clatter is too advanced, white smoke and hard starting is too retarded.

A functional CS lever should make a noticeable difference in clatter and starting ease, when the engine is cold. The lever should have more resistance to pulling when the engine is stopped, compared to when the engine is running ~1500rpm. The guts of the IP should rotate a few degrees when the lever is pulled, but if the barrel is stuck, no change will occur in clatter or starting ease.

A Robert Bentley service manual is always recommended.

I'm not sure about the tranny, but others will comment.

[bscutt]

Yes a GP will bolt right up. If I recall the GP has the overdrive 4th gear which can make hills a little more challenging on the highway (you get off the torque curve) but less revs at highway speed. If you can find a good FF or FN 5 speed that will work better for you. I actually had a 7A in the 80 1.5 Rabbit and it was great but the 7A uses the multi pin backup light switch which is pretty expensive and they seem to go bad quickly. If you go with a 5 speed you need the 5 speed shifter parts from the shifter itself all the way to the transmission

My 80 never got mileage above 42 or so but in the DC area your foot is always in it to keep up with traffic so these Rabbits get run hard. Plus it's hilly with lots of stoplights.

Also with time you learn shift points better. The 1.5s run better wound up so don't lug them. Redline is 5500 rpm - running at 3000-4000 will make you deaf but they run good there and get better mileage. IN other words use rpm instead of trying to get low end torque. The 1.6 had much better torque but the 1.5 is still a good runner and will usually serve you well if you keep oil and coolant in it and don't overheat it.

[texcl]

My 80 dasher get 43 mpg at 65 and it is quite a bit bigger than a rabbit. I would check compression first, then your timing and your IP pump might be set too rich which would make the milage not so good. Also rebuilt injectors are like $35-$50ea so pretty cheap if all else fails.

[akrabbit]

thanks guys, the previous owner did install a relatively clear fuel line to the pump from the filter and i did notice a small drip of fuel from the front of the pump somewhere, not sure if its the shaft seal or not. and there were a few bubbles in the line on shut down. i havent had time to check the water separator or the compression yet. as far as advancing the pump timing, the pump is already nearly touching the injection lines on the head and i dont think it can rotate any farther. the timing belt had been replaced about 5000 miles ago according to the sticker under the hood, do you think maybe they could have timed everything with the pump turned too far on the bracket?

[Dakotakid]

I would honestly think that a 3 + E transmission would be an absolute nightmare behind a 1.5.

It certainly was for me behind a 1.6. I spent ALL my time with the footfeed smashed to the floor just attempting to get the car literally moving. I think that transmission actually made me burn more fuel simply trying to get up to any sort of speed. I was relieved the day I wrecked the car and used that engine in another body with 5 speed.

I don't think a wide-ratio 4 speed is going to make you happy in real world traffic.

[texcl]

I wonder if you don't have a slightly botched timing belt change. I don't think it should be that much advanced under normal circumstances, but you never know, it should be a simple matter for you to retime everything from scratch with a dial indicator and go from there. I would get a compression check since you have access to a tester(free where as filters and injectors arent), an it is good to get a base line anyway.

[akrabbit]

ive got a tester, i will need to check if i have the vw adapter. Do they use a glow plug adapter or an injector adapter for these engines?

[bscutt]

I use a injector adapter on my compression gauge. I believe you can get either but the glow plug holes are harder to get to. The injector adapter also fits the older Mercedes engines so they are relatively common.

[TylerDurden]

...do you think maybe they could have timed everything with the pump turned too far on the bracket?

Yes.

One can probably tell if that is the case by lining-up the TDC mark on the flywheel; the mark on the pump's pulley will be a bit CCW from the mark on the pump's bracket, and the holes for the locking pin will be similarly misaligned.

The top of pump can be rotated away from the head without altering timing, as long as the pulley is also moved the same direction and the same amount (one tooth increments).

It can be a bit tricky, as the pump pulley will often try to snap into the position where the internal cam-plate is at the lowest point.

Using advice from the members here, I prefer to clamp the timing belt to the cam and IM pulleys using spring-clips or clothespins- and mark the belt and pulleys with a white grease pencil to know exactly where I started.

[akrabbit]

ok today i have taken the cover off of the timing belt and lined up the flywheel mark, and have the cam locked in place. i stuck a socket that fits snugly in the pulley on the IP and it slides right into the hole on the bracket, so i assume the belt was installed properly am i right? How is the pump shaft attached to the pulley, is it a taper fit or keyed? If there is only one way to get the pulley on the shaft then am i correct in assuming the pump is just advanced too far on the bracket? like i was saying earlier the top of the pump is nearly rubbing on one of the injection lines. I have not had the chance to do a compression check yet as i still need to order some injector heat shields to replace the old ones once i am done. tried uploading some pictures but i dont know how to reduce the file size enough to post them here.

[TylerDurden]

The IP input shaft is keyed to the pulley.

Sounds like the belt may be on ok. Pix would help.

I upload my pix to a third-party picture host, Picasa. Other free picture hosting is easy to find. Once the picture is uploaded, the URL (address) of the picture can be place in the message composition textarea, highlight the URL and clicking the IMG button (above the text composition area) will put the IMG tags around the URL like this:

Code: Select all

[img]https://lh3.googleusercontent.com/-1OENe62VsQs/UEJrwXuDXSI/AAAAAAAAAtg/Ltx9tyeqlfk/s640/IMG_9068.JPG[/img]

The image will then be displayed in the message:



Picasa lets me chose what size to post, without using a local image editor program. Even if I upload a large image, I can post a medium or small version. Very large images (>1200 wide) can be annoying.

[akrabbit]

well after tweaking the pump timing, and an oil change im up to 39mpg doing 65-70. still thinking it should be higher, i made sure the return line was clear, and there was no restriction on the supply line according to my vacuum gauge. tire pressure was good and the car rolls very easily. also the fuel screw appears to be in its factory location as the metal sleeve is still crimped to the threads. im not quite where id like to be but things seem to be getting better.

[TylerDurden]

I find there is a >5mpg difference between a constant 65mph and 70mph. I would try a religious 65mph.

I might also check the internal pressure of the IP - some folks have had significant fuel economy improvements by tweeking. (see the sticky)

I ran taller tires on my Rabbit pickup to raise the mpg.

[bbob203]

big difference between 65 and 70 in mpg. I had my last car slightly more advanced than spec and it helped fuel mileage 2-3 mpgs I think no scientific method used really just counting my odometer over a few months with the same slightly advanced timing.