DiesalDummy

Hi, first post here.
I am a decent machanic but a diesel dummy as in my log-in name.
I have a 1991 300d 2.5 turbo that is having intermintant boost issues that seem to be and electronic based problem. I installed a boost gauge so I can track whats going on and half, some, most, or none of the time my car will boost and when it's not, I can get it to attain full boost just my activating the Accl. lever of the cruise control. Once it starts to boost it runs great and may go 1 min./day/week working correctly before the boost drops out again.
Whatever electrical device the Cruise Control circut is controling must be getting or not getting a signel from whatever is supposed to control it. What controls the boost system, is it the CPU or something else? What can I look at ?
thanks in advance!
kevin

Parrot of Doom

You sure its not the MAF?

DiesalDummy

I don't know, what would the MAF have to do with any of this?

Parrot of Doom

Well I'm just wondering, as I had a similar problem on my Audi 1.9Tdi, and it turned out to be a faulty MAF. The turbo didn't even kick in, and the car was taking forever to accelerate.

DslBnz

Strange. In all honesty, I am not quite as familiar with many Benzes 1990 and up. I'd suggest you make sure your fuel filters are clean, and your boost lines are clear to start. I assume the 1990 - 1992 300D's were much the same as the previous versions since the implementation of electronic engine management(ECU) didn't come into play until '93 for Mercedes.

I just can't make sense of the cruise control causing boost to be restored. All the cruise control stalk does is, upon engagement, sends a signal to be processed via the amplifier to the actuator. The cruise control actuator is a big metal box attached to the linkage underneath the intake manifold of the engine. The actuator is attached to the linkage via a lever, and electronically engages the linkage keeping the vehicle at a steady speed as it senses engine speed and drag conditions (hills, wind resistance, etc) to compensate.

If the EGR malfunctions on these engines, it will trigger a sensor that will cause boost to be dropped by half. Other than that, these cars can be run without any charge at all (dead alt, dead batt, doesn't matter).