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  #1  
Old 07-30-2018, 08:11 PM
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Location: Jackson Michigan
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1987 190D advice needed in troubleshooting the ALDA circuit

[IMG][/IMG]

2.5 Turbo diesel or OM602

I'm a noob to the Mercedes world and this car is a welcome challenge.

So far I have tracked down and repaired all vacuum leaks in the engine compartment. I have disabled the EGR and have done both an oil and fuel system service.

The ALDA plumbing circuit was cleaned and all the hose ends were replaced.

The trouble I'm having is the car will start to surge right about 3000 RPM the surging will continue until I ease off the accelerator.

I temporally bypassed Y29 and Y30 and ran the manifold pressure directly to the ALDA (103) and the car ran great. The surging was gone and the transmission shifted a little better.

I went ahead and removed the bypass and put Y29 and Y30 back in the plumbing circuit.

This time around I swapped the electrical connectors to Y29 and Y30 and that made a big difference.

The PO had curious fingers and he may have mixed these connectors up or ???

Anyway, would anyone know the color code for the wires that go to Y29 and Y30?


Last edited by Doc Brown; 07-30-2018 at 09:00 PM.
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Old 07-30-2018, 10:00 PM
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Y29 is a switchover valve to control a shift delay on the transmission when cold. Y30 is the overboost protection switchover valve. If the sensor on the manifold trips from an overboost condition it is supposed to vent to atmosphere to prevent fuel enrichment (essentially cutting boost due to no ALDA enrichment).

If you have a copy of the service manual, it should have the wire colors noted for each plug.

For what it's worth, I run neither of those valves on my car. The shift delay is supposed to help warm up the catalytic converter faster. Federal diesels have no cat, so it is a pointless item, it just made the 1-2 shift excessively high/late/sloppy when cold.

The overboost valve is one that's a bit more controversial. A lot of people feel that it's important for safety of the engine should the wastegate fail. Clearly it was installed for a reason, however given the inefficiency of the engines lacking an intercooler and the IP already being pretty well maxed out on a stock tune at 14PSI boost, I don't lose sleep at night without mine in the circuit. My switchover valve was seized up, so it was never going to vent to atmosphere anyway.
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Old 07-30-2018, 10:15 PM
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Thanks for the informative reply. Unfortunately I do not have a service manual for the car. I have been pretty much just using google. Most of my searches bring me to this site so I figured I would join.

Anyway it sounds like these solenoids are pretty much useless if they are not working right. I'm thinking about stripping them out and wiring the overboost switch to a buzzer alarm. That should keep me out of trouble...
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Old 07-30-2018, 11:03 PM
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This should help you out a bit for service manual:

https://www.startekinfo.com/StarTek/outside/11832/?requestedDocId=11832

You're interested in the Electrical Troubleshooting Manual (be patient, it takes a bit to load). Look at drawing 112. It shows the wiring for both the transmission valve and the overboost valve.
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Old 07-31-2018, 07:39 AM
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Thanks for the link! The drawing on 112 is exactly what I needed. I'll post an update this evening on whether or not the swapping of the connectors makes any sense.
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Old 07-31-2018, 05:50 PM
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Ok, so according to the electrical drawing the solenoid valves were connected correctly before I swapped the connections. For the time being, Y29 and Y30 will be bypassed. I may never connect them back up, but I think I will try and find out why they are not working as intended.

The solenoid valves do work when energized on the bench, so that isn't the issue.

Also, in case anyone cares, the wastgate moves freely and the actuator works as expected.

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