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  #16  
Old 06-03-2003, 09:19 PM
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Quote:
Originally posted by Tasma
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.
Are you saying you ran a hose from the intake manifold? It's not under vacuum. That's why the car has a vacuum pump.
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  #17  
Old 06-03-2003, 09:50 PM
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I am assuming the ALDA runs on pressure, and that the pressure from the turbo lifts the diaphragm. Please correct me if I am mistaken. My Dodge truck with the Cummins engine runs a line from the intake manifold directly to the pump.
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  #18  
Old 06-04-2003, 12:42 AM
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The ALDA requires a boost pressure signal, which it takes from the charge pipe (aka intake manifold). The pressure compresses two aneroid capsules inside, which allow the shaft on the IP to rise vertically upward as boost increases, adding additional fuel.

Vacuum is provided by the pump at the front of the engine. Vacuum is used for the climate control vent flaps, emissions junk, and signal to the transmission (via the VCV and other stuff on the way). The two are totally separate systems. They use the same 4mm OD Tecalan tubing and people often refer to it as "vacuum" lines, when in reality some are pressure lines, although they look the same... but the contents are different!

The test was valid, if you connect the intake directly to the ALDA you should have eliminated the overboost solenoid as the problem. HOWEVER until you have tested boost pressure with a gauge at full load, with a "T" at the ALDA, you still haven't fully diagnosed the problem. Low power could be from low boost, and testing that will help pinpoint the problem. Should be at least 9-10psi at full load, 3rd gear, 4000rpm.
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  #19  
Old 06-04-2003, 08:42 AM
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Oops, I had a brain fart. Sorry to confuse the issue by doing it in public.
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  #20  
Old 06-04-2003, 09:44 AM
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Is the 10 PSI valid even if the pump is not adding additional fuel?

Will it be 10 PSI at a steady 4000 or does the engine need to be producing maximum output?
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  #21  
Old 06-04-2003, 10:27 AM
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Is the 10 PSI valid even if the pump is not adding additional fuel?

That depends. If you are getting 10-14psi, your boost is fine. If you are getting less, say 7-9psi, the low boost *could* be due to low fuel - but not necessarily, it could also be the wastegate opening too soon (easy to test on a Garrett). If you are getting VERY low boost, say 2-4psi, I'd suspect a problem with the turbo. Let's hope boost is normal and then look elsewhere.



Will it be 10 PSI at a steady 4000 or does the engine need to be producing maximum output?

On a normal engine, max boost will arrive at much lower RPM, possibly as low as 2000. It will stay at max (or almost at max) to the redline. The test just makes sure you get a peak reading, which is why you want to be at full load in 3rd gear at 4000rpm. You need a LOAD - either full throttle accelleration, or climbing a steep hill, or better yet both. With the gauge hooked up so you can watch it while driving, you'll see what I mean. The needle will get to a certain point and not go past that, no matter what load you provide, IF the turbo wastegate is operating properly.

Note that low fuel delivery *can* cause a low boost situation, and I have heard of cases where people adjusted the ALDA and saw an increase in boost pressure. This will only occur if the previous boost pressure was below the wastegate opening point. Once the wastegate opens, all that extra fuel won't do squat for boost! Make sense?
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  #22  
Old 06-04-2003, 10:46 AM
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I understand now, Thanks.

Lets say there isnít much boost Ö.what could be the cause? I know the air cleaner is new and I can spin the turbo with my fingers.

Going to the hardware store to get a guage and fittings!
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  #23  
Old 06-04-2003, 10:57 AM
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VERY low boost (neart zero) is probably a wastegate jammed open or a failed impeller (not likely). Medium low boost could be lack of fuel or a wastegate opening too soon. Let's hope for normal boost. The turbocharger rarely fails other than some annoying oil leaks...
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  #24  
Old 06-05-2003, 09:26 AM
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I did the test today....glad that I did. The boost never got over 2 pounds with my foot on the floor going up hill in third.

I took the hose off the waste gate and it made no difference.

I am beginning to think the previous owner knew something that he didn't tell me!

Bad turbo? Banana in the tailpipe? Wasps make a nest in the muffler? Please help!!
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  #25  
Old 06-05-2003, 10:44 AM
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Uh-oh. At least now we know what's happening - it ain't the ALDA. I suspect either the turbo wastegate is stuck, OR the boost control valve in the intake charge pipe is malfunctioning. Could possibly be related to the EGR but I doubt it. The 2.5L engines are more complex than the 3.0's, and unfortunately I'm not positive what your problem is. I'd hate to pronounce your turbo (wastegate) bad only to have the problem be elsewhere! If nobody else has a good answer (remember folks, the 2.5L is VERY different from all other MB turbos!), try emailing the MBZ.org diesel email list... lots of techie folks over there that can help out.


Good luck,
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  #26  
Old 06-05-2003, 01:09 PM
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I took the air intake tube off the front of the turbo. Still no boost. I didnít hear the turbo spin like I can with my Cummins. I can spin the turbo with my fingers but it seems to turn a bit stiff and it doesnít coast at all. I would think after all this time it would turn very freely.

I could try taking the exhaust off the back side of the turbo and see what happens. The waste gate moves by hand and it chokes off the engine if I move it.

One of the people on the TDI VW forum had a turbo not work properly. It turned out that the air filter was bad and the turbo was sand blasted to the point the impellers were almost gone.

Waiting for words of wisdom.
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  #27  
Old 06-10-2003, 10:12 PM
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Might want to check the switch over valve. My 87 SDL was sluggish and the turbo wouldn't kick in either. After having changed the switch over valve the car is back to normal. Hope this helps.
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  #28  
Old 06-10-2003, 11:29 PM
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Keep us posted!!!!
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  #29  
Old 06-11-2003, 10:06 AM
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Tasma,

Based on past experience, I'd suggest you check the exhaust system for excessive back pressure.

ewstan
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