'85 300TD Engine Help needed- new user - PeachParts Mercedes-Benz Forum

benzing · #1 08-10-2008, 10:56 AM

Hello. I have an '85 300TD 140k that has been a great car until as of late. I had a new a/c compressor installed about two months ago. As part of this install, the garage installed a relay to bypass the full-throttle compressor cut off switch (which they said was a source of frequent probs in these old cars). I can't say specific time, but for past couple months the car runs runs terrible at low throttle and barely idles (shakes bad) for about 15-20 mins when starting up. Smokes heavily while rough idling. I have run Red Line DFC through with no change. I don't know that this could be related to the a/c issue, but thought I'd mention.

Also, I have not heard the turbo "whine" that I used to hear in quite a long time. Last time I checked the banjo bolt, it was clean.

I would appreciate any input you guys can provide. This car is a daily driver and I need to make her last. There are know knowledeable old-school MB diesel guys that I know of here in Springfield MO. Thanks in advance!

vstech · #2 08-10-2008, 12:18 PM

have the valves been adjusted lately?
they will cause poor running, hard starting and rough idle, AND they can cause the motor to burn valves if left tight for too long.
ya got more info on what the mechanic did to your a/c to "bypass"?

the tenor man · #3 08-10-2008, 12:37 PM

I don't know much about the older turbo diesels, but if it were me, I'd pull the injectors and get them checked...maybe they are hanging open and pouring fuel into the cylinders...and while you are doing that (because you are now really dirty), check the valve settings.

Although I don't think this has anything to do with your trouble; if the air conditioning compressor belt is separate, pull it off...may the compressor is running all of the time and placing an additional load on the engine at start-up...just a guess...

You may want to check your motor mounts, they may be on the way out and amplifying the vibrations.

Lastly, BAD FUEL...try running some new fuel into the engine...I've had problems with fuel on my 1987 300D Turbo...I thought the engine was on its way out, so I connected the line to some fresh fuel and that solve the really rough idle....just another thought.

Keep searching the posts...I know, it can take a long time, but with time and the expertise offered here, I think you will solve your problem.

The Tenor Man

kerry · #4 08-10-2008, 12:41 PM

I'm guessing the Klima relay was bypassed on the AC.

OldPokey · #5 08-10-2008, 12:50 PM

Does it run rough when the A/C is on? If so, you get to do the job of the controller the mechanic so aptly bypassed, which is to disable the compressor when your idle is too low or when you want more power.

Stevo · #6 08-10-2008, 12:57 PM

New injector nozzles cured the "start up shakes" in my "85" 240D.

benzing · #7 08-10-2008, 02:44 PM

Quote:

Originally Posted by OldPokey

Does it run rough when the A/C is on? If so, you get to do the job of the controller the mechanic so aptly bypassed, which is to disable the compressor when your idle is too low or when you want more power.

The a/c definitely pulls down the engine, and sometimes when cold, I need to shut off the a/c to get the rpms up. I certainly understand the need to the factory switch. The tach has been intermittent for some time, and apparently is also needed to allow the a/c to run under "factory" setup. The relay bypass that was done apparently takes the tach requirement out of the picture too. A

Appreciate the input.

JimmyL · #8 08-10-2008, 03:31 PM

Pull your Klima relay out {right in front of the brake booster} and see if the underside looks like this:

When my tach was inop, that is how my Klima was bypassed to make the AC work.

BTW, I think the "full throttle compressor cutoff switch" is the one on the valve covers of the '85 model W123's.....

benzing · #9 08-11-2008, 09:14 PM

Quote:

Originally Posted by vstech

have the valves been adjusted lately?
they will cause poor running, hard starting and rough idle, AND they can cause the motor to burn valves if left tight for too long.
ya got more info on what the mechanic did to your a/c to "bypass"?

Valves have not been adjusted. Is this something that has a torque spec? or is it left to the mechanic with the "feel" for what is right? (that's how it used to be with the v-8s back in high school

I also should mention that when cold (and running poorly) it sounds like it has a real bad ignition knock when accelerating. After a certain rpm (or about 14-20 mins), this seems to subside. It does not make this noise when engine is hot. Does this sound like valves? or maybe fuel delivery issue? Thanks in advance for the input.

kerry · #10 08-11-2008, 10:00 PM

Valves are not hydraulic, they need to be set with feeler gauges every 15k or so. You are describing the sound of 'nailing'. Doing a diesel purge (see dieselgiants tutorial on this) can sometimes cure nailing.

benzing · #11 08-12-2008, 08:23 PM

Quote:

Originally Posted by kerry

Valves are not hydraulic, they need to be set with feeler gauges every 15k or so. You are describing the sound of 'nailing'. Doing a diesel purge (see dieselgiants tutorial on this) can sometimes cure nailing.

Kerry- thanks for the input. Dieselgiants has a pretty compelling and detailed procedure for doing the purge and also adjusting the valves. Sounds like it certainly worth a shot to do both. Jeff