My 300D has developed a rather scary intermittent knock that sounds like a gasser spark knock. It does it occasionally on acceleration, occasionally on deceleration, I never hear it while cruising or at idle. If I punch the accelerator at idle sometimes I can hear it "crack" but not every time.

Could someone please tell me how to diagnose this knock whether it is injector related or internal (piston, rod, wrist pin). Other than hearing this ominous sounding intermittent knock the car runs smooth and has lots & lots of power. No smoke.

I just recently set the IP timing. It was at 15deg BTDC and now she is at 23deg BTDC. I never heard this knock until I set the IP timing. Also, the chain is only two months old so I guess that could be ruled out. I have replaced the delivery valve seals in the IP and torqued them to specs. The car started this on Friday while in route to the ATL airport. I left it sitting in the parking garage for four days. It fired up just fine when I returned, no smoke, no knocking. I had her towed home just to be safe but I am a tad bit leary of driving her until I know how to narrow down what the noise MIGHT be. Any suggestions?

1980 300D

Kevin

I also have a knock that sounds like yours. It happens at every rpm and load and came without warning. I just pulled into a rest stop to get a drink and i noticed an odd sound. I have replaced such things as the injectors, precombustion chamber, delivery valve (Big performance boost ), and set cam/IP timing.

To date, only the delivery valve has made ANY difference in the knock and performance. I have not checked the main/crank bearings yet, I'll be doing that on my next oil change in March.

Have you "cracked open" an injection line to see if it goes away? Swap injectors with a cylinder across from the problem cylinder (I.E. #1 swap wth #5, #4 swap with #1, etc.). If it follows the injector, just replace it. If it dosen't, you're in for some "fun."

I forgot to add this. My knocking started in May and I have been driving it like normal without any problems other than the noise. I have been lucky that it hasn't thrown a rod or blown up, yet...

You would be best off to park it until you know what the cause is.

I just took my 6 year old daughter to school this morning and I noticed that this "knock" stays constant in its sound whether accelerating or decelerating. It doesn't speed up or slow down it just knocks. It sounds just like a spark knock, a rather sharp spark knock.

On the positive side- since I set the IP timing the engine doesn't miss and hiccup when started in the mornings. I may set the the IP back some maybe to 21deg BTDC to see if the knocking subsides. Like I said, I never noticed this until I set the IP timimng to specs. It didn't do this at 15deg BTDC. It just smoked tremendously at initial start-up.

Kevin

So the knock beats at the same rate, independent_of engine RPM and vehicle speed?

All you touched was the IP?

Could be the AC compressor switching on/off for some strange reason. Just a guess.

Use a mechanic's stethoscope to see if you can pin point the knock.

Check your chain tendioner too.

__________________
You can get farther with a smile and a gun than you can with just a smile.

1984 300D
1985 300CD
1980 300SD
1993 SL500

We can rule out the A/C compressor. I don't have one!

I am beginning to think that this is more or less an injector knock. I have driven this thing very hard today trying to get it to throw a rod. I have floored it while parked. I have romped it numerous times. It will not make this noise unless it's under load accelerating and at speeds of 50 to 55. It is not a constant rattle or knock. It is intermittent, rather sporadic. Sometimes when I take off it is never heard. Other times it is heard for a few seconds, goes away, returns but never gets any louder. I do not hear it at highway speeds. At idle it sounds so nice and smooth. It has got to be something about the timing. I will find out tomorrow because I am going to set it back close to where it was before I messed with it.

As far as a stethescope- It only knocks while driving. It will not knock at idle. My wife refused to ride on the hood to help me diagnose the knock!

I have tried to throw a rod today just to see if it is a rod knocking. The bottom end seems rather tight. I have slammed it into passing gear many times today and revved it to the max but cannot throw a rod.

I did remove the # 1 prechamber today just out of curiousity. It was fine, at least I think it was. Nothing broken in there.

Kevin

Double check that the IP timing is at the correct 22-24* BTDC. 15* is waaaay to late for injecting fuel without any combustion problems. That late, the fuel won't have enough time to leave the PC and burn properly.

Let the questions start:
While you had the precombustion chamber out, did you have a look at the pison top?

Hows it's performance? Is it worse than, dare I say, your 240D at highway speeds before/after IP timing was adjusted?

Hows the camshaft timing?
Last valve adjustment?
Ever had a compression check?
Did you use the drip tool to check timing?

I used a drip tool for the timing adjust.
THe cam timing is dead on- new chain.
THe piston top looked black best I could see- carbon, soot.
THe valves were adjusted last week.

I really believe that it is the IP timing. I am going out in a few minutes to reset the IP timing. Wish me luck!

82-300td,

I got your PM about the parts. The man will not return my calls and I have been traveling a lot here lately (4 weeks vacation) so I haven't been to his shop in several weeks. I am still trying but it seems that I am very unsuccessful at it.

Kevin

I readjusted the IP timing and viola! No more knock although the IP is timed at 20deg BTDC now. Works for me!


Kevin