OM603 Injector Replacement / Idle Speed Control Q's - PeachParts Mercedes-Benz Forum

Crazy_Nate · #1 09-01-2009, 02:44 PM

The car in question is a 1987 300D Turbo.

When the engine is running, there is a slight imbalance / shake. After looking at the injector lines, I think it's the 4th cylinder from the front. The injector line is pulsing a lot more than the others. I'd imagine that a partially clogged injector might behave like this.

I'm not sure about the age of the injectors, or if there's been any cleaning / balancing in the past, so, I'm thinking about just replacing all of the nozzles (the car does have 231k miles). What are the opinions about which nozzles to buy? Bosch or Bosio? Anything else that would need to be purchased besides the nozzles and heat shields?

Ok, the next question is about the idle speed control. The car starts up cold and idles around 700RPM and then drops to about 600RPM. Seems reasonable, however, when letting off the pedal after accelerating, the RPM's drop below 500 and the car shakes moderately.

After looking at the service manual (07.1-1100), I'd like to know if I can test and adjust things without the digital tester. It seems like the problem area is the bowden cable and / or the spring plate (or spring itself). If I change the idle stop position, will any of the other stops need to be adjusted as well? (Or should I just take it to a shop that can read the engine RPM better than me?)

babymog · #2 09-01-2009, 10:03 PM

Other than the injector and heat shield, you might need to replace some of the plastic fuel-line retainer clips as they are difficult to remove after years of heat embrittlement.

Idle speed should be controlled electronically, not by the mechanical stop. There is a round plug with numbers on it forward of the master-cylinder that can be unplugged, rotated to a higher number, and plugged back in to increase idle speed. If this has no effect, check the (blue?) unit on the rear of the IP to ensure it is plugged in, does the tachometer work properly?

Crazy_Nate · #3 09-02-2009, 01:15 PM

Thanks Jeff. I ended up taking out just a little slack in the Bowden cable (the spring wasn't resting fully against the stop. Very slight change, but still idling a bit low when the engine was warm (80C). After turning the knob (from 4 to 6) in front of the master cylinder, it idles a little above 600 (maybe 630 or so - as far as I can tell with the tach). It'll still drop below 500RPM if I let off the pedal really quickly while the car is stationary. Not noticeable while driving any more

I've attached some pictures in case anybody in the future wants to see what I did. The first picture is the nut you turn to adjust the bowden cable (you need to push the pedal a little bit to get access to it. The second is the electronic idle speed control knob.

babymog · #4 09-02-2009, 01:57 PM

A low or hunting idle during driving when first coming to a stop is one sign of fuel-starvation, check your fuel filters and check the fuel tank for vacuum by removing the fuel cap.

Crazy_Nate · #5 09-02-2009, 02:04 PM

The small clear inline filter looks fine. Only a small bubble at the top (I had the same thing with my 240D). When I took the fuel tank cap off, there's slight pressure. Not sure what this means...

I haven't noticed the low idle while driving after upping the idle speed back to the ballpark of where it should be. What about the shutoff valve at the IP? It feels slightly loose. Is this a common wear item?

carnut · #6 09-02-2009, 06:59 PM

The simplest way to confirm a faulty injector is, while the engine is running, crack open each hard line at each injector one at a time. Much like pulling a plug wire off a spark plug to locate a miss. If you crack open a line and the idle smoothness gets worse, that injector is OK. If, when you crack open no. 4, the idle barely changes, that confirms a faulty spray pattern and confirms the need to replace it. Watching a hard line vibrate is in no way a diagnosis. If you change an injector or all of them DO NOT bend the hard lines. Remove each one from both ends and then reinstall gently, hand tightening each fitting then snug it up. Make sure all hard line clamps are in place, dont leave them off.

Crazy_Nate · #7 09-03-2009, 05:48 PM

Ok, well, I cracked each of the injector lines one by one, and, sure enough, each time, the idle got worse...

I was under the assumption that these parts (injector nozzles) wear, no matter what, and usually need to be replaced or cleaned after a certain amount of mileage. Not that I need to be replacing things right now, but I'd like get some of these minor problems sorted. I can do a diesel purge, although, I'm not sure how much that'll help with anything.

Today I had to crank the engine for about a second and a half. I'm not sure if this indicates anything. There's usually a small puff of smoke when it first starts.

What else could contribute to a slight imbalance? If the valves are hydraulic, do those have any maintenance? Or do those just get replaced if a larger problem comes along?

I'll see if I can take a video of the idle and post it online. Maybe I'm off my rocker with the vibrations.

Diesel911 · #8 09-03-2009, 08:02 PM

If the Injectors are the origional one they I would expect that they need work with 231K on them.
Idle speed and idle roughness can be separate issues.

carnut · #9 09-04-2009, 03:28 PM

So, each injector felt the same cracked open. So the injectors are OK. A slight vibration could be collapsed engine mounts (very common) or an internal engine compression issue. Mileage has nothing to do with replacement of injectors. If they all spray correctly, they are good. One does not replace engine parts based on mileage, but based on a diagnosis to confirm necc replacement. A diesel purge is done when the diagnosis leads to a dirty fuel system not because it has a certain mileage.

Crazy_Nate · #10 09-04-2009, 04:18 PM

Ok, here's the video's.

First, starting and increasing the idle / letting off:
http://www.youtube.com/watch?v=GbeXKXAWMXk

Second, engine at idle and blowby (none):
http://www.youtube.com/watch?v=WcofDu6ooe8

Well, I agree that the injectors work...the only question is how well. To check the pop pressures and spray pattern, I'd have to take them out and send them to a shop. I might as well just have them change the nozzles if nothing has been done to them over the 231k miles the car has been driven. I can always have the old nozzles cleaned up and pass them on to another forum member...

Crazy_Nate · #11 09-07-2009, 12:50 PM

Well, I just put about 400 highway miles on the car. Drove great. 33.1 MPG and the coolant temp didn't exceed 90C. I guess something is still working correctly.

I'm not sure what to call this symptom, however, I could hear the engine slightly increasing and decreasing in speed when I was parking it. I couldn't notice any change on the tach, however, the oil pressure would move a little up and down (hovers around 2 bar idle, and then up and down maybe 1/8 bar or so). Not sure what to make of it.