W123 1985 300D - Shaking at idle - PeachParts Mercedes-Benz Forum

marco5 · #1 09-25-2018, 04:13 PM

Hello all,

I've noticed in the morning car starts and runs fine, however, after the engine is warmed up and I've been driving for an hour or longer, the vehicle can no longer idle properly and shakes terribly. It idles fine for the first 30-40 minutes.

It's also getting worse by the week. I've been reading quite a bit that the lift pump can cause this, however, I don't want to just throw money at it. The vehicle is fine at highway speeds, I can go 140km/h-180km/h fine so this just affects idling. It also fires right up on the first crank in the morning. Some details are below on the vehicle. Let me know your thoughts before I start replacing parts and thanks for reading this.

Other notes: I noticed ticking at idle, almost like valve ticking from low fuel pressure in the middle number 3 cylinder. If I swap injectors, the tick does not go away or move with the injector, so my guess is that it's the pump? Perhaps due to lack of fuel pressure?

Mileage - 450,000-500,000KM

Rear Tank Filter - I doubt this is it as I have no issues at high speeds but I can try replacing, it is original.

Lift Pump - is original and not leaking. I don't see any air bubbles in the system at all

Fuel System - well maintained, only quality diesel used and filters replaced often

Valve Adjustment - just done and to spec

Timing - not much timing chain stretch at all. It is original.

Compression - 320-370 on all cylinders.

Overflow valve on injection pump - I've adjusted this spring to 27mm from 22 as per the factory manual

Rack Damper (Idle Stabilizer on injection Pump) - This is original. Yes I know. I will replace but there's no way this can cause this much of a idle issue. Right? lol

andrewjtx · #2 09-25-2018, 04:37 PM

Rack damper bolt absolutely can. But so can injector balance and spray pattern. Start with the bolt, it's the easiest.

vwnate1 · #3 09-25-2018, 05:09 PM

To see the various suggestions and solutions .

? Is there a specific method of adjusting the rack damper bolt ? . I just tweaked it until I got the best idle......

TIA,

Diseasel300 · #4 09-25-2018, 06:15 PM

It may sound stupid, but have you tried a diesel purge? If you have some crap buildup in the injection pump it can certainly cause idle quality issues. Do you have fuel coming back out the return line when the engine is idling? If so, the lift pump would be pretty low on the list of suspects.

Diesel911 · #5 09-25-2018, 07:01 PM

When I had the same issue when I first got the Car I bought a new Rack Damper Bolt. It did not help.

A valve adjustment and rebuilding the Injectors (new Monark Injector Nozzles and pop pressure adjusted properly) too away about 85% of the shaking.

New Motor and Transmission Mounts took away about 13% more. Note I damaged one of the hydraulic engine dampers and I had to replace that also.

Finally the no Rack Damper Bolt took away a little more shaking.

Also the Stock Bosch Nozzles have 2 tiny passages drilled in them that entirely plug solid with carbon and that effects the idle.

marco5 · #6 09-25-2018, 07:58 PM

Thanks guys. It's been 3 years since a diesel purge so about 100,000km. I'll try a diesel purge first and cleaning my injectors while also replacing the heat shields. I'll also do the rack damper bolt!

rocky raccoon · #7 09-25-2018, 09:29 PM

Be sure to do one at a time so you can pinpoint the source of your problem.

cho · #8 09-27-2018, 09:48 AM

I've tried everything from the book.
small but not significant improvements after all actions.

In my case the culprit was (worn) delivery valves (fuel IP) so I had to
change those. Pricey

.... for the US guys I recon it is easier/cheaper to swap IP ...

cheers
ChO

.

vwnate1 · #9 09-27-2018, 10:47 PM

? Where did you buy them and at what co$t ? .

Diesel911 · #10 09-27-2018, 11:57 PM

Quote:

Originally Posted by vwnate1

? Where did you buy them and at what co$t ? .

You need the information off of the Plate that is on the Fuel Injection Pump in order to get the right Bosch ones. Once you have the part number for them you can shop for Chinese ones if that is what you want.

On MW Fuel Injection Pumps the Hose from the Filter blocks the view of the ID Plate.

If you go to one of those part sites that has the exploded views of parts you could find out if Mercedes has a part number for them look for a seller with that or reference it to a bosch part number. However, I believe you still need the stuff on the ID Plate to do that.

vwnate1 · #11 09-28-2018, 12:01 AM

According to Mercedes, all MW injection pumps use the same P/N delivery valve, they've been redesigned a little bit .

I'd still like to know where the OP got his and what price .

Not really interested in Chinese parts .

Diesel911 · #12 09-28-2018, 01:55 AM

Quote:

Originally Posted by marco5

Thanks guys. It's been 3 years since a diesel purge so about 100,000km. I'll try a diesel purge first and cleaning my injectors while also replacing the heat shields. I'll also do the rack damper bolt!

You can do that but if you have the stock nozzles (see the attached diagram) as mine did which have the tiny drilled passages which at 190 thousand miles were entirely plugged with carbon I believe the purge will not touch it.

If the former owners had done periodic purges I think that might have kept the passages open.

In the diagram 1 and 2 are the parts of the Injector Nozzle and the circled area at the bottom shown in an enlarged view to the right to show the drilled passages.
The Monark Nozzles and the Bosio Nozzle that people typically replace them with do not have those drilled passaes to get plugged.