300SD idle ping pongs, white smoke on startup

[tomas_maly]

I JUST fixed the mysterious oil leak on the passenger front side of the engine - seemed to be the timing chain tensioner's gasket.

Now first things first.... I have a 300TD that cranks like it's a hot summer day, no delay... but my 300SD takes a bit of coercing, even when it's 70 deg F out. I had my 300SD sit around for about 6 months when I noticed a major oil leak in the front of the engine (the crank seal and/or timing tensioner gasket), and didn't get it fixed until just now - it was half taken apart for all these months because I didn't have the right drill bits to remove the stripped crank pulley bolts.

But I got it all back together and the oil leak is gone.

I'm noticing now that the idle is really rough and ping pongs between 850rpm and 1000rpm, back and forth, back and forth. It just won't stay still. I don't think this is just a new issue, because I noticed it 9 months ago, there was a mild oscillating sound to the idle.

I also feel somewhat of a mild jerking sensation along with this, and looking at the engine from underneath does show a certain jerking motion with the same rhythm.

I swapped the timing chain tensioner with one from a parts car (one year younger, same otherwise), and I'm not sure if the tensioner's spring may have something to do with idle, smoke, etc. I took the cap off and put the old tensioner's spring in instead. Before that I was noticing white smoke from under the hood, somewhere around/under the turbo. It may be coincidental, or may be spilled oil, etc burning off the exhaust pipe or something, I dunno. I don't see anything under the hood anymore.

But I do notice white smoke from the exhaust at startup, even if it's 70+ deg F outside. The exhaust smells stronger than normal (at least stronger than my 300TD), more of a burning smell, like charcoal grill smell. I wasn't sure if the rough idle and the smoke were related.

Are there adjustments (that are out of whack) to stabilize the idle? I don't think it's just the idle screw since the idle bobs around +/- 150rpms with the distinct (mild) jerking to the engine.

I know there's a damper bolt that goes on the back of the IP. But I wasn't sure if there were other items worth checking as well.

[tomas_maly]

One thing that has changed in the last year with the car is that I replaced the injector tips and put the injectors back together. I used a torque wrench to tighten them (no leaking), but I didn't go to the lengths of testing/adjusting the spray pattern, etc.

I don't think this would explain the oscillating idle, though.

[vstech]

Originally Posted by tomas_maly

One thing that has changed in the last year with the car is that I replaced the injector tips and put the injectors back together. I used a torque wrench to tighten them (no leaking), but I didn't go to the lengths of testing/adjusting the spray pattern, etc.

I don't think this would explain the oscillating idle, though.

think again.
the pressures could be WAAAAY off between the injectors. easily cause this issue. also, one could be dumping fuel, or failing to open until very late.

[Diesel911]

Another Injector Issue. There is a part that is between the Injector Pintle and the Spring that if you assemble it backwards and torque the Injector Nut it often cracks off the end of the Pintle.

[tomas_maly]

I found a guy nearby who will pop test them for somewhere between $75 and $125. And mercedes source has a pre-built tester for $200.

But I've been thinking of wanting to make my own pop tester and save some money, and this seems to be the simplest version (the hand pumps can be purchased online from Home Depot):

How to build a diesel injector pop tester, big improvement! : 2 Tank veggie oil conversion and General discussion

[tomas_maly]

Seems that the white smoke under the hood was from a fuel leak. One of the return lines on an injector was loose and was dripping down under the engine.