OM603 - Why does ALDA adjustment affect shifting so much?
 

the shutoff valve on my '87TD went bad and i replaced it. the ALDA came off in the process so i adjusted it 1.5 turns CCW. off the line acceleration was greatly improved and shifting was smoother too. the only issue was mileage went down drastically. i removed the ALDA again yesterday and set it back to the original spot. now i can't stand the way the car shifts, it is hard into second and worse into third. the car needs the diff carrier mounts replaced also, and this makes for a nice 'clunk' into third gear, depending on the throttle position when it shifts the 'clunk' is more or less pronounced.

so what exactly is going on? if the ALDA is controlling mixture, why does the richer mixture so drastically affect the shifting of the transmission? also, is it normal for mileage to take a nosedive when the ALDA is adjusted 1.5 turns CCW?

The only way "ALDA adjustment" can affect shifting is by affecting the vacuum to the transmission. Since "ALDA adjustment" does not normally affect vacuum, it probably means that there is a check valve or other component that is damaged or leaking.

There is a vacuum hose going to the ALDA as well as a boost signal hose. The vacuum hose is supposed to limit fuel enrichment until the car warms up by bleeding off the boost signal. I bet the hose or the 'Y' connector is cracked. I just removed my ALDA and my mpg stayed the same. You just have to get used to not sticking your foot past the floorboards like you used to have to do...

i understand what you are saying. when i was replacing the "stop unit" a few of the hard lines cracked just by moving things and working around the lines. i replaced 2 or 3 of the bad plastic vacuum hoses by pulling them out of the sheath and replacing the whole line with new (for some reason it was only the clear or milky clear ones that were brittle). i have also replaced some of the rubber connectors since i have owned the car and they should all be good. i will look them over again. i see on the vacuum diagram that there is a line off the ALDA rubber Y that goes the "vacuum amplifier switch-over valve automatic transmission", so this line may be a suspect.

i did a bit of searching on this forum and others have commented on shifting improvements after adjusting the ALDA.

The ALDA changes the throttle : power ratio. In other words, with the alda 1.5ccw you're using less throttle to accelerate the same so the transmission shifts more softly. With the alda back, youre using more throttle to accelerate so the tranny shifts harder.

that makes sense. i'm still not sure i understand the mileage drop. the car is driven mostly by my wife and she drives gently, but still the mileage went way down, maybe about 30%, with the ALDA 1.5 turns CCW.

You're pressing the throttle like youre used to which consumes more fuel to accelerate faster.

i guess it could be that simple.

When you play with ALDA and are getting more power for less pedal, adjust the Bowden cable going to the tranny and it will get engine and tranny talking the same language again. IIRC, Bowden sets the RPM shift points.

You can also adjust the blue UFO pod a little bit, there is a screw on its underside, this will affect tranny shift firmness. And so will any other vac mods you do in the area.

It is this simple: whenever you see black smoke blowing out the back, that's unburned fuel. Your mileage is going down the tubes the more/often you see black.

Anything that affects engine performance can affect transmission performance. Even a fresh fuel filter can improve transmission performance.

there was no black smoke at all with the ALDA 1.5 CCW, that's the odd thing and part of why i was so surprised to see the mileage dive. i suppose i might have been able to make it smoke with a very heavy foot but there was no smoke with normal driving.

If you are showing a measurable change in fuel mileage from ALDA adjustment, something else is at play. I'll spare you the speech about the inaccuracy of single-tank MPG comparisons as it seems that you're aware enough to know.

As the ALDA only increases off-boost fuel (actually limits it, the adjustment increased it) and that fuel flow even tripled wouldn't be enough of your total fuel useage to drop your average mileage 30%, seems unlikely.

There must be something else at play, I'd go with the 1-1/2 turn CCW adjustment or wherever you have good performance with just perceptable smoke at take-off, and leave it there for a while to see if there's something else affecting your mileage.

My right foot seems to be my biggest problem, only solution seems to be Cruise-Control. Which BTW is another point; on the highway you pretty much always have boost, so the ALDA won't affect the power or mileage there either.

OK, thanks for that input. when i researched making this adjustment i never saw any info that told me there would be a significant (or any) mileage hit so i agree that there must be something else factoring in.

i will do some work on the car over the weekend (in between olympic hockey games) and see what i can see.

Canada rocks, sent those Russians packing!

C'mon Germany!