OM603 alda adjustment needed?
 

I have an 86 300sdl with 75k on it, when accelerating I have to give it a good amount of throttle to get going if I want to accelerate quickly, but once the rpms go over around 2000 it starts to pull hard and I have to back off the throttle. It seems to me that this would indicate that the alda is out of adjustment? The only smoke that is visible is a haze at idle and upon acceleration at night in the headlights of another car. In the day I can only see smoke if I floor the pedal.

Simplest thing is to remove the ALDA and see how it responds. If it improves and you prefer to have the ALDA installed, just back the set screw all the way out. If it were mine, I would just leave it off.

Your situation seems normal. At idle there's no boost. Off the line there's no boost either so you essentially have NA power until the turbocharger spools up and comes into play. The 3.5 liter 603 engine was made to have more oomph off the line as an improvement to the 3.0.

The ALDA adds fueling ability to the injection pump as boost pressure increases. When working properly, the ALDA won't be a hindrance. It witholds the fuel until there is proper air available to burn it all. A lean ALDA setting will decrease max power output. A rich ALDA setting will cause smoke when accelerating and high EGTs. The sweet spot is barely visible smoke during acceleration. If you remove the ALDA completely, you must be careful with your foot and placing the engine at full load without enough boost to burn the fuel.

When you adjust the ALDA be careful not to damage the screw or turn it too far in either direction.

I agree that the turbo takes a bit of time to spool up. But before you tinker with the Alda, check that the sense port on the side of the intake manifold is clear. If you look on the left side of your intake manifold, you should find a hose fitting just below the boost sensor. Remove the hose and unscrew the fitting. Clean it with solvent, and replace. This port is what allows the Alda to sense boost. If it's clogged, you can wait all day for the power train, but it won't pull into the station.

Please do not remove the ALDA, unless the OP would like to decrease MPG, increase smoke and engine wear, and remove a safety device.

Guys, this really drives me nuts, no offense intended, but the ALDA was put there for a reason by BOSCH engineers who know far more about diesel injection than we ever will.

ALDA's tend to lean out with age. Many have found that normal performance is restored if the screw is backed out about 1/2 to 1 turn.

I have never owned a 602/603 turbo engine that did not need ALDA service or adjustment at some point in the first 150k miles (and thereafter). There is an adjustment procedure in the FSM, which in simple terms tells you to back the screw out until there is just visible smoke off-boost at full-throttle acceleration.

With proper adjustment and tune, your car should jump off the line.

As mentioned above, there are three common issues with the boost and boost enrichment, two of which take less than 10minutes to test and correct.

1) Boost fitting, boost line from intake plenum to switchover valve plugged or broken, line from switchover valve to ALDA plugged or broken, orifice or switchover valve plugged or broken.

The hose from the intake plenum on the 603 comes from a fitting threaded into the driver's side around #4 cylinder IIRC, crosses over to the switchover valve, through a restriction (orifice), and over to the ALDA. You should be able to disconnect this at the plenum and ALDA and blow air through it. Even if you can, disconnect it and shoot some cleaner through it (I have used MAF cleaner, and WD-40, either one works). This will once cleared, shoot black crap all over and stain your garage floor. You should also be able to blow into the intake through that fitting, if not then clean it (if you shoot anything flammable into the intake, it can cause the engine to run-away or damage glow-plugs, best to remove the fitting if this is necessary, ... I just stick a paperclip through and give a quick squirt of WD-40).

2) The switchover valve has three connections, top is vent (should have a cap) and vents the ALDA when the switchover valve closes (overboost protection). Bottom connects to the intake plenum, middle goes to ALDA. The diagram should be on the car, and I believe that I did not confuse the bottom and middle.

3) Alda condition. If the ALDA leaks air pressure, it will not work. You will need to reseal: https://www.youtube.com/watch?v=i6TZ2bnlAjI

If it does hold air pressure (remember we're only talking about 1bar), then it might need adjustment, but this should only follow 1 and 2 above. It can be adjusted on the 602 and 603 with the intake plenum in place, I've done it on a couple of my cars, ... but it is painful. Your better method is to remove the intake (especially if the seal and cap are still installed) to do this. The post above is correct, 3/4 to 1-1/2 turns CCW is all I've ever needed and usually goes a little over the original off-boost enrichment to give a little black puff and lots of off the line acceleration improvement.

True that Bosch Engineers put this there for a reason, mostly emissions and Mercedes did not want smoky un-refined cars. These cars had emissions standards to meet. The ALDA compensates for atmospheric pressure (lose 3% of your air every 1,000' of altitude increase for example), and also for boost. However, giving the engine a shot of rich fuel at the drop of the pedal does increase initial heat out of your exhaust, and guess what spins your turbo, ... yep, faster spool-up and better acceleration.

Thanks for the info, btw I never had any intention of removing the alda completely, my car is 99.9% original and I have no interest in modifying a car that came off the line during the golden years of Mercedes engineering. It sounds like everything may be working the way it should then? If I floor the pedal from a stop, the car pulls hard from a stop, the only time I notice a lag is with part throttle, if thats they way these cars were from the factory I have no problem with that, I just want it to be correct. If the alda adjustment calls for rich enough to just see smoke on full throttle then it doesn't seem like its adjusted lean, as there is a fair bit of smoke with the pedal floored.

I removed mine... removed the antitamper cap, backed it fully out, and reinstalled. Car has been this way since 2005ish when I bought it. I have a light whisp of smoke from a dead stop until the turbocharger lights. Lean off boost makes for a dog of a car.

Been off the road for about four years now, car drove fine. Fuel economy was acceptable for it... 28-30mpg freeway (depends on wind, winter/summer fuel, speed around 65-70mph usually) and mid to low 20s city.

The car should not be a slug until boost builds. Do you really thing purchasers would have put up with that when these were new?



Lastly, I agree with Babymog 100%

Same or similar for 603.971 ? ?

I do not see why not.

Was the same on the 350SD/L which is the .970 Peek on top of the IP and look for this square device, around the No 2/3 intake plenum runner.


Oh also, the '86/87 CA cars (I believe) and the '87 Federal SDL had that trap oxidizer removed under the MB service campaign and tossed under the car. I have gutted three that were severely plugged up.

That typically results in higher exhaust backpressure which hampers the ability of the turbocharger to do work as well as higher than normal operating temperatures.

Quote: I do not see why not.

Thought I'd ask. My .971 doesn't have a valve between the the intake plenum port and the ALDA - just the boost sensor teed in.

Similar, yes.

The .971 does not have a switchover valve between the intake and ALDA, runs direct, yours sounds correct.

On the .971 the overboost protection runs a different switchover valve behind the right headlamp which interrupts the vacuum line to the turbo wastegate and drops boost.

My .971 (W140) got the typical oil/carbon mist clog in the boost line, killed my boost enrichment and the line/fitting needed to be cleaned to restore power. Mine will spin the tires with the brake on (found out by accident when troubleshooting my boost issue) when all is working properly.

Also in the .971, the wastegate defaults to open. It is open when you start the car, and unless all of the stars align and everything is happy in the computer, it will stay open. I have also had a switchover valve in the 140 leak vacuum, which again killed my boost. If you're not familiar with this system look up vacuum wastegate here, you should find lots of frustrated stories troubleshooting this system on the '90-'93 300D.

Your refering to the line to the sensor and ALDA?

Thnx. I'm not there yet - I have a couple of other things to work out. I don't even know if the boost is or is not working- I don't have a reference - suppose I should get a gauge and tee it in.

Yes that's the line.

Try running vacuum directly to the wastegate to test, if it suddenly has lots of power then you know you've been running without boost.