So how many SDL owners have had or currently have a fairly loud Injector knock ? How long has it been this way and or what can/have you done to reduce or eliminate it ? I am determined to have a Smooth and reasonably quiet (yeah I know its a diesel ) car,It is,after all,a Mercedes ! I will see this problem through to the end even if I have to start with new injectors and work back to the pump. This is NOT a lifter,you can plainly hear the noise from the injectors,especially # 3 and #4 .

I had an injector knock on my 87 300SDL. Figured since there were already about 250k miles on the original injectors, they served their useful life.

Installed new injectors, "heat shields", and return lines...the knock is gone.

__________________
Lance Allison
Lance@LanceAllison.com

Current:
11 MB S550 4Matic, 55k miles, Designo Black/Black
14 Ford F150 XLT Lariat Crew, 73k miles, 5.0
Coyote V8 4x4. Black/tan.
09 GMC Envoy Denali, 5.3 V8, 4x4 SWB. 38k miles,
Jewel Red/Med Gray.

Gone:
87 MB 300SDL, 320k miles, Astral Silver/Blue.
98 VW Jetta TDI, 488k miles, Classic Green/Gray.
85 Olds 98 Brougham FWD, 4.3 DIESEL V6, 80k
miles, 3x Gray.

MBCA Member, Chicago Region

Vlung

You didn't say the mileage on the car. Try something inexpensive first. I would recommend some Lubromoly Diesel Purge. I have seen it first hand eliminate injector knock.

Herb
'82 240D
'87 300SDL
'92 300D 2.5 Turbo

I have a 1987 300D which has the same engine.

It smokes unburnt diesel on cold startups for a minute or two.
It runs a little rough on cold startups for a minute or two.
It makes a nice diesel clacking sound when idling. (Been referred to as a "tractor")
Coolant system stays pressurized after cooldown - means I don't have any leaks. Do I have a micro-cracked head? Don't care.

It runs great on the road with lots of power.

I don't care about anything in the first paragraph - not worth fixing because its not broken yet....



Ken300D

Vlung,

Loosen the fuel lines attched to the injectors one at a time and see if the knock stops. If you find the knock stops on a certain cylinder, that cylinder has a bad injector.

You can try some additives but if the knock persists its time for new tips in the bad injectors. This should be done at a Diesel injection shop so they can set the opening pressure correctly. The cost should be about $50 per injector.

P E H

Ken300D,

Have you tested your glow plugs (GP)? The symptoms sound like a bad GP. Ths causes one or maybe 2 cylinders to missfire until the engine warms up enough to fire the cylinders with the bad GP.

The easiest way to do a GP check is to check the resistance. You need an ohmmeter with a low resisitance scale preferably a digital one.

Good GP should be less than 1 ohm.

I see you agree with my "if it ain't broken, don't fix it" policy. I do believe in testing something to determine if it is "broken", but only to replace if necessary.

P E H

Vlung,
I agree with airfoil, at the last fuel filter change I filled the filter with purge and it considerably quieted the knock.

'82 SD
'86 SDL

All new glow plugs here - tested visually (red hot) good.

Car starts perfectly. All cylinders hit, and no smoke. When the glow plugs have cooled down (maybe 5 seconds after start) then the smoke and roughness starts. Later diesels with aluminum heads solved the problem by keeping the glow plugs on for up to a minute (depending on ambient temperature) after the car starts.

It could be a bad, leaky injector. Don't care - car runs fine when warmed up two minutes. I suppose sooner or later the injectors will need replacement....



Ken300D

Ken300D,

I always wondered why MB designed the GP relay to turn off the GP as soon as the started is engaged.

The older series, manually operated GP stayed on when the starter was engaged. They would be turned on anytime the controller was pulled to the GP position, so you could keep them hot after the engine was running.

The newer engines that leave the GP on after starting the engine, sound like good idea. It was probably an antipolution mandate.

P E H

I've heard time and again that the afterglow does two things

1. Reduce emissions
2. Cut the life of glow plugs significantly

-brian

__________________
Brian Toscano