lousy mileage!

[Witt]

Lately I have been driving the car more frequently on longer trips and finally kept track of my milage. Last count: 77.5 miles to 33,236 Liter.....to my calculations that would be 26 Liter per 100 km !  
 I knew my milage was lousy but his is ridiculous !!!

The car starts, runs and idles fine, hot or cold. The CSV is not leaking, the additional air from the warm up regulator  shuts off after warm up....the linkage is adjusted according to specs....but, the plugs are black, the tailpipe black and full of sud and at full acceleration I lay a smoke screen.

On retrospec that problem seems to have started right after I got the car back from having a head-job done about a year ago.
Should I fiddle with the adjusting knobs on the IP to get better milage ? I seem to remember doing just that a few years back, probably need an refresher course! Any suggestions?

(not so cheerfull )
WITT !

[w113dude]

Hi Witt,

It could very well be your injectors, I just cleaned a set for a fellow forum member, after it was installed the idle went up 400rpm, this means that they were not providing the right amount of fuel for each cycle per cylinder, now he has gained a good 30% more per mpg.
Take it to a shop and have them checked, it's easy and inexpensive.

[Witt]

Thank you for the tip. I will make this part of the spring tune-up.

CHEERS !
WITT !

[jeffc280sl]

This is easy to try.  I assume linkage, csv and timing are okay.  What thickness shims do you have under the BC?  Start taking one out at a time.  If your feeling bold take them all out and wedge a piece of rubber hose against the  BC to hold it steady.  Put a piece of tape with an arrow on top of the BC and rotate it 1/4 to 1/2 turns and then go for a spin.  Clockwise rotation will lean the mixture. Use a feeler gauge to start where you shims currently have the BC.

[Witt]

Hey thanks'
Please excuse my ignorance, I am fairly familiar with my car by now but what is the part you are referring to as "BC".  Would that be the part that is called the "warm-up regulator" on other  fuel injection systems?
The procedure sounds pretty simple I and I love to try it. Please enlighten me.....

CHEERS !
WITT !

[jeffc280sl]

BC stands for barometric compensator.  It is located on top of the fuel injection pump next to the warm running device.  It adjusts fuel mixtures for altitude changes.  Since your car is very rich we want the fip to think you are at a higher altitude and lean your mixture.  This is accomplished by removing shims under the BC and turning it clock wise.  This will lean the mixture at all rpm ranges. You need a thin 19mm wrench to loosen the BC.   Here is a pic.  Let us know how you make out or if you have any questions.  Good luck!

[Witt]

Thank you Jeff, here is what I did today:
Removed BC and found three shims, 2 @ 1.92 mm and one @ 0.52 mm

1st try: installed one of the thick shims; cleaned one spark plug to monitor for rich or lean firring.
Result: hard starting, no idle. Increased idle mixture on IP, adjusted idle air, idle OK but no acceleration, no guts and lots of backfire and popping exhaust. To lean?

2ND try: installed on thick and one thin shim;
Result: a little better, but no good!

3rd try: installed both thick shims, idle to high, readjusted idle air screw.
Result: GREAT, just as good as before I started the adjustments. Sparkplug looks better after returning from "Italian Tuneup"But.....will removal of that thin shim have a great effect on my milage? I am thinking on getting some more thin shims to do some more experimenting after I determent if milage has changed at all.

Allow me one more question: You wrote:"...removing shims under the BC and TURNING IT CLOCKWISE" After I reinstalled the BC there is no more movement to turn it clockwise, or are you referring to screwing the BC back in a clockwise manner?
Please let me know if I missed something.

Thanks' again!

CHEERS !
WITT !
 

[stickandrudderman]

Why don't you simply adjust the fuel mixture at the adjustment knob?

[jeffc280sl]

Sounds like your making some good progress.  The BC directly effects the rack adjustment inside the pump so the slightest change can make a difference in air fuel mixtures and in turn mileage.  I think you are on the right track with thin shims and experimentation.  Ideally you would like to use a wide band O2 sensor and do some on road tests with an afr meter.

The mixture becomes leaner the lower the BC is moved in the fip.  It moves lower by turning it CW.  Put an arrow with tape on top of the BC and wedge a piece of rubber hose to hold it steady.  Turn it in 1/4 turn increments until you like the performance.  From there we can calculate the shim thickness using the BC threads.

[Witt]

Great advise, thanks'.......

CHEERS !
WITT !

[Witt]

Why don't you simply adjust the fuel mixture at the adjustment knob?

Good point, I will try that to, there must be a post about that somewhere on this site ?!

CHEERS !
WITT !

[jeffc280sl]

Never read about it before.  You can be the first.  I heard about this idea/practice from a very experienced MB expert.

[Witt]

There is a terrific writeup and pictures regarding the workings and adjusting of both the BC and the FIP right here in the Technical Manual.......it's all becoming much clearer now....thanks again....

CHEERS !
WITT !

[Witt]

Never read about it before.  You can be the first.  I heard about this idea/practice from a very experienced MB expert.

....sorry, you lost me....what procedure are you referring to, the adjustment of the BC or the adjusting of the FIP ?
So far I have also adjusted the mixture screw inside the pump. Future will tell if I am on the right track.....

CHEERS !
WITT !

[Witt]

In my ongoing quest to get better milage (now 10miles @ gallon) I finally decided to adjust the "full range adjustment " on the FIP.......but I can't find the darn thing on my pump. I just received the latest "Pagoda Notes" with a beautiful picture of all the adjustment screws. I also read the very comprehensive post in the Technical Forum.

 Here is the problem: When I unscrew the allen head screw on the tube like affair allowing access to that screw the L-shaped springloaded  bracket, pictured above said screw, is in the way and blocks the, what I belief to be the adjustment screw! I have another FIP sitting on the workbench, with only one solenoid, the access to the screw through the tube is unrestricted as described in the post.               

My pump used to have two solenoids, but I removed the top one and fabricated a cover for it. So, I removed the cover to have a better look and lo and behold when I insert a small screwdriver into the tube all I can do is push that darn bracket and can't reach the screw. However I can get to that screw ,sort of, after I remove said access cover, but I am not convinced that this is the correct adjustment screw?!

Am I doing something wrong, or do I have a screwy pump?

Help please ! 

PS:The fact that I broke the temp sender pipe in the process is a another story......

CHEERS !
WITT !

[jeffc280sl]

Sound to me like you have the correct screw.  You need a very thin shafted flat screw driver.  The shaft needs to be about 3.35 mm in diameter.  Also the flat part should be 3.35 mm wide.  On my spare pump I start to engage the slot of the rack screw at about 60 mm insertion.  If I look through the allen bolt shaft I can see the slotted screw head of the rack adjuster.  They are directly aligned and there is nothing blocking (L shaped bracket?) access.  You need to have a delicate touch with this.  You can push the rack forward.  The trick is the put a slight forward pressure on the screw driver to make contact with the rack screw.  Gently turn the screw driver until you feel it insert into the screw head.  At this point you will start to feel gentle detents/clicks as you carefully turn the screw driver CW or CCW.  Keep a very accurate count of the clicks.  Always double check yourself and notes and make sure you are turning in the direction (CW or CCW) you want to move.  This can be easlily messed up.  Something to consider is counting and turning the rack screw CW until it reaches its stop.  This way you always know how to get back to home base if you mess up.

I re-read your ealier post and I get the understanding that you have no shims under the BC and you are still rich.  This means that you are out of lean adjustment room using the BC.  Is this correct?

[Witt]

Thanks for the reply......I just removed one very thin shim on the BC and left the two thick ones in place......I may still fiddle with some thinner shims after I take another milage calculation.

As far as the adjustment screw on the FIP goes, the way you describe it works on my spare pump on the bench, but the on one the car has that upside down spring loaded bracket in the way. When I insert a thin screwdriver into the hole after removing the allen head screw all I can do is push that bracket in and it will return on its own.

If you look at the picture of the exposed FIP there is a nondescript knob on top of the "Full range adjustment screw" above and to the left of it is that upside down "L-shaped" bracket that is in obstructing the adjustment screw on my in car pump and not on my spare pump.

I have a strong suspicion that this pump is not the correct one, it was changed, unnecessarily as I found out later, shortly after I purchased the car and before I started to learn more about it through this site.

Just came back from a testdrive, car runs great  let's wait and see.

CHEERS !
WITT !

[jeffc280sl]

Adjusting the BC shims is equivalent to adjusting the rack and its a lot easier.  I don't know what to tell you about the bracket that is in the way of adjusting the rack.  Both of my pumps are the same and I suppose they are like your spare pump.  I would remove a thick shim and then use a feeler gauge of the same thickness to set a starting pint for the BC.  I would mark the top and turn it CW in 1/4 of a turn increments to lean the pump.  Wedge a piece of rubber hose against the BC and WRD to hold it steady while you drive.  Fill you car full of gas and go for a 20 minute ride while recording the distance with your odometer.  Fill you car up with gas again and do your mpg calculation.  Turn the BC 1/4CW turn and drive the same course again.  Go get a fill up and calculate mpg.  If improvement is too slow try turning the BC 1/2 a turn and then repeat the road course.  This is rough but it should get you in the ball park.  Some more tweeking and you will get there.  Record the number of 1/4 and 1/2 turns so we can determine the new shim thickness based on the thread pitch on the BC.   I hope this is clear enough.

[Witt]

Thank's, glad to hear that adjusting the shims at the BC has the same effect as adjusting the rack with the adjustment screw. I will continue to persue that line and follow your procedure.
Will get back with a progress report  on this post.

Thank's again
WITT !

[Witt]

.....seems all that fiddling is finally paying off, just returned from a testdrive and fill up: I AM NOW AT 15 MILES PER GALLON !!!! That would be an improvement of fifty percent.
I wold be interested what the average milage should be, am I getting close?

CHEERS !
WITT !   

[jeffc280sl]

Witt,

Nice to hear you're making progress.  I have only checked mileage on trips and I have a 3,27 ratio rear axle.  I get 20 mpg on the highway and I'd say me car is tuned pretty good at this point.  I used to get 24 mpg on the highway but my pump was too lean and I was robbed of some horsepower.

15 mpg for all around driving sounds like your in the ball park.   How does the power feel?  How do the plugs look?

[Witt]

Hi, power seems to be down just a bit, might be all in my head.......I certainly can live with that...............plugs look cleaner: electrode is clean, rim at the end of threads is
black.
I think I am going to leave it alone for a while and take another milage reading just to confirm, thanks for all the help everybody...

CHEERS !
WITT !