No fuel boost from alda - PeachParts Mercedes-Benz Forum

Tasma · #1 05-31-2003, 01:13 PM

I have a 1991 300D with low power. I have narrowed it down the injector pump. If I run a new line directly from the manifold to the alda there is still no fuel enrichment. I even used the my air compressor to simulate turbo boost and nothing happens. The diaphragm is not leaking. Is there anyone here that has dealt with this before? I suspect the previous owner was told that it would be expensive to fix. I bought it figuring it was just a plugged line. The car is perfect in all other areas.
I posted a thread earlier stating the 0-60 times were low (17 seconds) and it should be 12.

CJ · #2 06-01-2003, 01:09 AM

If you find out, let me know.

bgoodeve · #3 06-02-2003, 06:12 AM

Before you go too deep into the injection pump be sure it isn't something else with the ALDA. Do a search on ALDA. Try some of the (sometimes controversial) adjustments. I found that a half turn adjustment made a lot of improvment on my 225+K 2.5. Since you appear to have no fuel increase at all, you might try something more extreme. In any event, the vacuum may be fine but the mechanicals of the ALDA the culprit (collapsed spring). I'd want to be very sure the ALDA was truly functioning as it should before going deeper into the pump.

gsxr · #4 06-02-2003, 03:22 PM

Your ALDA may be leaking or have a failed internal capsule. It's easy to test for leakdown with a MityVac, but harder to check shaft travel unless you have something to compare to. The other possibility is that your injection pump needs calibration and the ALDA is fine. This is not uncommon after 100-200kmi, the IP's don't stay "in tune" forever you know.

Simple ALDA test: Disconnect it entirely and test 0-60 again. If the power drops even more, the ALDA is doing *something* and is either partially failed, or the IP is bad. If the power is the same with the ALDA disconnected, most likely the ALDA is not functioning at all. You can't buy a new one from Mercedes but you can buy one from Bosch if you try hard enough (they're NOT cheap though.)

I have rebuilt the old style ALDA, used on turbo diesels up through 1987. The 1990-up type are difference and I have never seen one.

Good luck,

Tasma · #5 06-02-2003, 04:14 PM

I disconnected it and my 0-60 increased to 22 seconds.

The ALDA does not leak, so now it looks like maybe it just needs to be adjusted. It looks like you have to take off the intake manifold to do that.....not much fun and no way to make simple adjustments and try it out.

I am starting to miss the old 240D!!!

What next!!

bgoodeve · #6 06-02-2003, 04:31 PM

It's tight but you shouldn't have to remove the intake manifold. I had success modifying a couple of bicycle headset spanners, which are thin) into "special" tools to deal with the cramped quarters. Large channellocks can be used to hold the top of the unit if getting two wrenches in there is just not working. You will probably have to modify at least one wrench to the size of the bottom nut (28mm? I don't remember)When the ALDA unit is out you will need to remove (destroy) the sealing cap on top to reveal the adjustment screw. Mark the current setting in case you end up wanting to go back to where it was. Start with 1/4 turn counter-clockwise and replace the unit. If you notice some improvement and want to try for more, take it back out (it will be much easier this time around) and go to a 1/2 or 3/4 CCW. I've read that some have adjusted as much as 1 1/2 turn, which seems extreme to me. In any event, you may lose a little gpm, but you'll have a more responsive car.

gsxr · #7 06-02-2003, 05:22 PM

To test leakage you need a MityVac to pump it up to 15psi. It should hold 15psi and not leak down. A bad (leaky) ALDA will either leak very fast or won't let you build pressure at all. If yours really is OK, the next stop is probably an ALDA adjustment, but I doubt that will cure your problem. Next item is to adjust the internal full-load fuel stop but that is HARD to do, may require removal of the injection pump. And at that point you might as well just take it to a Bosch shop for a full calibration. or your problem could be something totally different like a clogged air filter, low boot pressure, clogged exhaust catalyst, etc... you really need to do more dianosis first.

For ALDA adjustment, doing it with the ALDA in place and the manifold installed is a nightmare. On the 86/87 turbo diesels, it is MUCH easier to simply remove the ALDA from the IP, adjust it in hand, then re-install. I think that applies to the 1990-up turbos as well. It just unscrews from the IP (the nut underneath turns), but you may need to disconnect a couple metal injection lines for clearance (my one car doesn't require that, my sister's car does).

CJ · #8 06-02-2003, 08:18 PM

Lots of good info!!!

Tasma · #9 06-02-2003, 09:47 PM

Looks like this weekend I will try removing the ALDA. What would happen if I ran the engine without it installed?

Different subject but...this car shifts very hard when cold. It sometimes feels like someone hit the rear of the car when it shifts to second. This is only happens under light acceleration.

gsxr · #10 06-02-2003, 09:59 PM

If you drive the car without the ALDA installed, it will have full fuel enrichment at all times. On some cars this makes it undrivable. Or put another way, if the IP is good, the car *should* be undriveable. If it's OK with no ALDA, the IP is probably way out of calibration. (Note that I am not positive about this.)

On the tranny - when was the last time you changed the fluid & filter? It is required every 30kmi, or sooner if city driven. My cars would exhibit similar symptoms near 30kmi and after the fluid/filter change, it was perfect. Using synthetic ATF helps this drastically. If your fluid/filter is ok, you probably have a problem with the vacuum signal to the transmission. The 1986/87 models have a temp switch that softens the shifts until the engine temp gets over 50C. I don't know if the 1990-93 diesel 124's have this or not.

CJ · #11 06-02-2003, 10:01 PM

GSXR,

Can you post some pics of the ALDA, internals, adjustment, etc??? I have seen some fantastic pics from you in the past of your cars and the work you have done.

coachgeo · #12 06-03-2003, 12:22 AM

ahhhhh???, have you made sure the pressure lines to the aldo are all clear? I hear it is not uncomon for the one connected to the Banjo bolt to clog with soot and reduce the amount of fuel correction by the alda as booste increases.

Make sure you exhaust the dumb little things before you get into the big stuff.

bgoodeve · #13 06-03-2003, 06:05 AM

Coachgeo is right, and one project at a time. Be sure ALL your vaccum lines are clear and secure (look for cracking at the splices). Since you think you're having shifting problems also, pay special attention to the line(s) running to the vacum amplifier and from there to the transmission. Then tweak your ALDA (it's not that bad a job once you figure out a good way to deal with the nuts.) If there's no improvement, you're on to deeper and harder things. However, if you can get to a good state after dealing with the integrity of the vaccuum system and the the ALDA you may find your shifting improves. When an automatic transmission is dealing with an engine that isn't behaving as expected at various speeds and rpms it gets confused itself and may shift hard and poorly. In any event, start by keeping it simple. It often is.

CJ · #14 06-03-2003, 08:07 PM

Good info!

Tasma · #15 06-03-2003, 08:44 PM

I found this web page with photos of a ALDA

http://engine.articles.mbz.org/diesel/alda/

The vacuum system is most likely not the problem because I ran a hose directly from the manifold to the ALDA and drove the car and it was exactly the same.