1987 300TD Lacking power in cold weather
 

Hello,

I have a 1987 300TD wagon that has been lacking power all winter (I'm in Michigan) It is most noticeable between 50 mph and 80 mph, and things improve when the car is warmed up, but even at operating temperature it's not great. If the outside temp is above 45F I don't notice the issue as much, accept on hills. It feels like the turbo is cutting in and out...sometimes the car is peppy and turbo charged, other times I feel like I've been downgraded to N/A diesel. I used to be able to drive as fast as I wanted on the highway, now it struggles to get past 75mph or 78mph

It's also been a little hard to start in the cold and requires 2 glow plug key-on cycles to avoid holding the key cranking indefinitely until the motor overtakes the starter.

I replaced all the glow plugs last August with Bosch after experiencing what seemed like hard morning starts in weather that should make a diesel happy. I also replaced the fuel filter and used 2 bottles of liquid moly diesel purge (one in the tank and one to prime the filter).

The drivability issues only came about with freezing temperatures this season. However, my door locks stopped working in September. I recently took it to a shop that specializes in german cars, and the guy was pretty good...he got all of my locks working again with replacement of the little electric vacuum pump, but his hunch was this vacuum leak would cure my drivability issues, and it did not. After three weeks at his shop he never addressed the performance issues, and I'm hesitant to bring it back there before hearing from the forum on possible issues.

Please help!

Thanks,
Marc

1987 Mercedes 300TD
1981 Volkswagen Caddy 1.6NA
1988 Subaru Justy 4WD
1972 BMW 2002
1987 Vixen 21TD

Need to try to test for turbo boost to see if it is happening like it should be.

I would check that the waste gate is not stuck open and also look for obvious places in the intake where it could be losing pressure. I think there is also a pressure line that goes to the injection pump from intake manifold. You should check that hose for leaks and make sure the hose and also the port in the intake is not clogged.

Molly diesel purge
 

Have you run diesel purge in a while? If not....make it happen. Do a direct dose of it by disconnecting the incoming and outgoing fuel line directly into a bottle of that. Also are all your 3 filters clean? Fuel tank mesh filter, pre-filter, and main filter? What about the air filter?

There is one thing you can try if you are handy. Remove the exhaust from the turbo, only 3 nuts but not easy to get to. My experience with my wagon is that the exhaust was plugged. Bypass the exhaust and see what happens.

You need a new mechanic. The door lock vacuum is not the same as the transmission vacuum. His hunch is just hunch, it ain't going to work.

Good luck.