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  #1  
Old 01-04-2019, 04:16 AM
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190DT 602 questions

Howdy all!

Was looking for a good commuter and a local gent had a 87 190D 2.5TD for sale - as luck would have it, we got on like a house on fire and I ended up taking the beauty home.

I'm fairly handy but have more experience with VW diesels than the Mercedes at present...

The car came with a huge stack of receipts (all the way back to 1990 or thereabouts) and has been well cared for as far as I can tell. It does however, exhibit an annoying behavior that I would relish the opportunity to vanquish.

A previous owner (but not the fellow I bought her from) installed a boost gauge, which may provide a clue (possibly trying to track down this behavior)? Basically the turbo is behaving like an on / off switch at the moment, with a very fine threshold based on throttle input. On partial throttle (35-50% maybe) it will make about 5-7psi, anymore than that and it will immediately go to 13-15psi. Once you're in to the boost it will stay there until you cross back over the threshold whereupon it immediately drops back down to 5-7psi. Unfortunately this magical threshold occurs right where your foot is to cruise at 65mph or so- treating all onlookers to taking off like a rocket ship, only to slow down, and so on...

I'm planning on looking for vacuum leaks and hoping that will clear some things up. I've also read that I should clean the switchover valve and pressure sensor? Anything else that would be of use?

Otherwise the car drives pretty well. The glow plug light acts a bit weird where it doesn't always turn on when you turn the key on, but turns on after the engine is started and then goes out a minute or so later... I'm going to check resistance on glow plugs etc and see where that gets me.

Many thanks!
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  #2  
Old 01-04-2019, 10:36 AM
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On the left side of the intake manifold, there are two ports. The upper port holds the overboost sensor. This is an electrical pressure switch that controls boost pressure to the Alda device. While this isn't causing your symptom, it's a good idea to remove the sensor and clean it with spray cleaner. There's a tiny hole in the face of the sensor that gets clogged with soot. The lower port is the actual boost sense port. This port is especially prone to soot clogging. You should get in the habit of removing the hose and undoing the nipple for inspection every so often. When it clogs, it reduces pressure at the Alda and prevents proper fueling. Soot can also blow through the lines and the switchover and cause problems. The switchovers for the boost system are on the left wheel well, and it's worthwhile to blow them out with carb spray.

If the Alda system is clear, then the only other thing that can cause this would be the turbo itself. The waste gate is pressure actuated on this car. Although it can stick, it would appear your actuator is working properly. That would only leave the impeller itself. Let's hope it's just the Alda plumbing.

You have a gem. Mine just turned 450K miles, and the drivetrain is still strong. Rust will probably finish it off soon, and I'll miss it when it's gone.
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Old 01-04-2019, 10:51 PM
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Might there be an added boot controller between the pressure signal and the wastegate actuator? Maybe one of those ball and spring deals?

Glow light behavior sounds like one or more glow plugs is bad. Check continuity to ground for all glow plugs. Shortcut is to test at the big connector at the glow relay. The connector pins are numbered according to cylinder number. Anything more than 1-ohm is toast. Or cut to the chase and replace them all. Do the records show when they were last replaced?

Sixto
98 E320s sedan and wagon
02 C320 wagon
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Old 01-04-2019, 11:20 PM
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Quote:
Originally Posted by sixto View Post
Might there be an added boot controller between the pressure signal and the wastegate actuator? Maybe one of those ball and spring deals?
In a word, NO. The pressure takeoff is on the side of the turbo, and connects directly by a hose to the actuator. The actuator holds the gate closed until the specified pressure, so even if the hose was open or blocked, there would be boost.

Quote:
Originally Posted by sixto View Post
Glow light behavior sounds like one or more glow plugs is bad.
Actually, it means that one glow plug is open. Replacing the glow plugs on this engine requires the cruise actuator, crossover and intake manifold need to be removed. For the trouble of removing all that, you'll be doing all five plugs, so there's no point in figuring out which one is bad. Trying to do it without removing all that stuff is like building a ship in a bottle. It's a lot for a first project.

It occurs to me that what you may be seeing isn't a boost problem at all, maybe the transmission is downshifting early. This can be caused by something as simple as an accumulation of dirt between the accelerator pedal and the kickdown switch. Are you sure this isn't the case?
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Old 01-05-2019, 12:19 AM
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smoke gets in your eyes
 
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I meant might someone have added a boost controller to squeeze more from the 602.

The plugs can be replaced with the manifold in place, crossover pipe and cruise actuator off. Whether this is the way you should do it is up to you.

Read up on how the injector lines are restrained. Renew any broken or missing clamps if you pull the manifold.

Sixto
98 E320s sedan and wagon
02 C320 wagon
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  #6  
Old 01-07-2019, 05:53 PM
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Thanks for all the replies and my apologies for not getting back to everyone sooner!

Had a look at the glow plugs, 1,3,5 are testing < 2ohm, 2 and 4 are testing way over (30ohms and 3,000ohms iirc) so I'm guessing that's the problem, and will go ahead and replace all of them.

As far as the boost problem goes, the vacuum line from wastegate to outlet side of turbo is not interrupted, so doesn't appear to have an MBC installed. Quite a few cracked vacuum hoses around the engine bay, so I'm guessing that's not helping... Will clean the sensors mentioned and refresh some vacuum hoses and reevaluate.
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