Greetings! I just got back from a trip to College Station, Texas. I noticed that my car's engine ran quieter overall and started better when cold while at lower elevations. I assumed it was running a bit quieter due to the small amount of biodiesel Texas adds to the fuel. However, on the way home, still running a tank of Texas fuel, I noticed the same old noises I hear once I got back up into higher elevations (over 5000 feet above sea level).

Here in New Mexico my car's engine does a couple things I've not figured out but have gotten used to. For one, on a cold morning, below about +50F, my car starts well enough but when the afterglow cuts out it runs like crap until it's warmed up. It acts like it's getting too much fuel, runs rough and blows grey fuel smelling smoke. I can work around this problem by using the block heater for a couple hours before starting it up. Works fine when I do that.

The other thing I notice when at higher speeds and elevations is that the engine makes more noise at some power levels, a noise that sounds almost like nailing or clacking. It's a "crinkly" noise, if that makes sense. This does not occur when cruising on flat ground, or when the pedal is all the way down. I hear it between those conditions, like when going up grades or accelerating without flooring it.

The engine runs pretty good overall, plenty of power, decent fuel economy. I have had the injectors rebuilt and balanced. I have replaced the delivery valves with brand new parts. I have cleaned out the intake. I have not checked injection or cam timing. The engine burns zero oil.

We had some cool mornings while I was in CS, in the 40s, and the car started and ran fine. So what I'm wondering is if these cars have altitude compensation as part of the electronic governing system. If so perhaps my car's compensation is not working properly.

What should I be looking at here? Temp or barometric pressure sensor problem? Something else? Feedback appreciated.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

The injection pump on your car is more or less just an electronically actuated mechanical injection pump. It's not really sophisticated enough to trim fuel like a gas car or the later CDI type engines with full O2 feedback control loops. At 5000 feet elevation, there's considerably less air for the N/A engine to work with, you'll always be running a little rich compared to running at sea level.

The noise you're hearing could be injector related. Considering that you had the injectors rebuilt, it would be worth checking pop pressure and spray pattern. You could have an injector that's dribbling or spraying funky. Another possibility is EGR function. The altitude capsule on the 603 based cars is to help tune the EGR operation more than anything else, and I'd expect it's not much different on the 606. Given that EGR dilutes the fresh air charge with exhaust gasses, you can expect a bit more "clattery" noises, especially since you're already down on power from the lack of air due to altitude.

__________________
Current stable:
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In a diesel engine the amount of fuel = throttle.

So you can't be getting too much fuel at idle.

I would start by checking the injector spray pattern/pop pressure. And then check the ip timing

The altitude compensator is on top of the ip

Thanks fellas. I appreciate the replies. It appears that I should take a look at IP timing. Seems like an easy thing to check on these engines, and I have the simple tool for locating the reference tooth through the access on the side of the IP. I trust the injectors, and I trust the guy who built them for me. If IP timing were to check out then I would pull the injectors for inspection of spray pattern and pop pressures. Easy stuff first.

The IP in this car is mechanical but the governor is completely electronic, as noted by Diseasel300. There is no diaphragm pod on top if the IP like there is on earlier cars. Here's what it looks like:



And here are the guts inside the governor housing:


And on the IP side:


I lifted those two photos off the WWW but can't remember where. This car's accelerator is drive-by-wire, and because the governor is completely electronic I was wondering if the system has some form of altitude compensation that's not obvious to the eye.

Diseasel300, the crinkly noises I hear do not seem to be associated with one cylinder. Sounds random, but that could be hard to tell at higher RPMs.

Christuna, when cold and the engine is running poorly it's not just at idle. It's bad when moving, too, blowing smoke, bucking.

As an aside, I verified that this car will go faster than 100 MPH. Big rig traffic on I-40 was awful between Santa Rosa and ABQ, and in moment of frustration I floored it to get away from a gaggle that was clogging things up. When I looked at the speedo it indicated 105!

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__________________
- Greg -
1973 220D, The Prodigal Benz
1974 240D