I looked/searched and couldn't find anything for this specific issue- feel free to redirect me if I missed it. I'm hoping someone has seen or heard of this before and can at least help me narrow down where to look so I can track it down. It's odd.

My 1991 300D, OM602, 130k, runs beautifully, but has a very precise, periodic tick that cycles at nearly perfect 18-second intervals. From the moment the tick becomes barely audible, it spends almost exactly 10 seconds building in volume/intensity, then goes silent for 8 seconds

Stick with me here, I know it's sometimes futile to describe sounds over 'net, but I'm giving it a go anyway: So it's not audible, becomes softly audible, then "tick-tick-tick-tick-Tick-Tick-Tick-Tick-TICK-TICK-TICK-TICK-TAK-TAK-TAK-TAK-TAK," then suddenly silent again for 8 seconds. The interval is about 3-per-second at idle. After the 8-second silence, the noise builds again for 10 seconds, goes silent, and so on. Happens cold or hot. I'm clueless

If it were an injector, or maybe valve noise, it would be pretty much constant, correct? What the heck would cause a periodic cycling knock/tick?

Sounds pretty much like my lifter tick on my 87 300d. Does the noise go away when you increase rpm with a warmed up engine?

Difficult to say with all the elevated noise at higher RPM. Seems to diminish, though, yes.

EDIT: If it were lifter noise- why would it be so precisely-timed? I mean, I can sit there with a stopwatch over a period of minutes and it doesn't change. 10-8, 10-8, etc.

The first thing I'd do is remove the serpentine belt. Start the engine and run it for a minute or so (don't worry, it will take awhile to overheat). If the noise goes away, it's related to the belt, tensioner, or rotating components.

If the noise is still present, then remove the two hoses from the vacuum pump and run the car again. If the noise goes away, replace the pump pronto.

If the noise is still present after removing the belt and vacuum fittings, then my money is on a lifter. Perhaps it's periodic because the lifter is rotating.

I like this, Mxfrank. It's logical and has a good process of elimination. Thanks!

The Vacuum pump had occurred to me. The noise, at least to my way of thinking (which is admittedly not always on-target) could be associated with something building--->releasing vacuum, maybe? Hopefully not, as it seems the rebuilt pumps or rebuild parts are becoming very hard to find. Seems like it's better to just throw $$$$ at a new pump if problems arise with the old one.

Will proceed this weekend and report back.

A video or sound clip of something like this would be VERY beneficial in trying to diagnose what and where to look for!

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Indeed. Just got back into town last night, and will probably record it while running Mxfrank's procedure today.

I plan on running a diesel purge today as well to see if that affects anything.

1991 300D 2.5 Turbo cars are covered by the TSB detailing the defective/sub-standard timing chains and the eventual premature sprocket wear. A careful examination of the chain and the cam sprocket would be in order particularly if no other obvious source of this noise is not readily identified.

If it persists after checking the hother belt drive, loosen the injector lines one at a time to see if you can isolate the ticking to a cylinder.

Sixto
83 300SD
98 E320 wagon

I don't think that's correct (unless there's a second TSB of which I'm unaware). The TSB on defective timing chains on that engine affected a certain range of serial numbers in 1993.

See posts 14 and 15 of this thread for details.

http://www.peachparts.com/shopforum/diesel-discussion/56836-93-2-5-turbo-timing-chain-replacement-interval.html

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I ran a can of Diesel Purge through it and changed the primary fuel filter. Seems to have dampened the noise maybe a bit, but that could just be psychological after the purge, etc.

Anyway, video of me noise is here.

You can hear it pretty clearly at starting at this timestamp.

Could be that I was incorrect remembering exactly what model years and range of individual cars that TSB covers. According to the post you've referencedit would be cars built in 92 and 93 July 92-July 93, not just 1993 cars.

But I would point out that the TSB info in that thread is at least 13 years old since it was posted on the forum so there might be another TSB that has come out in the intervening years since that was done.

I would also put forth the other pertinent info from a few posts earlier than the TSB info.

post # 5:

"I just today looked at a "'91 300D Turbo - Blue, 178K mi, 40K on reblt eng, CD, sunroof, maintd, all rec. $7500".
Nice car, but the reason for the engine rebuild was the timing chain broke. "

post # 8:

"I have a 91 300D 2.5 with only 77K original mileage. I checked the chain for stretch a couple of weeks ago and was astonished to find that it currently has 5 degrees of stretch. This measurment was taken using the factory procedure at 2mm of valve lift, not the old "line up the marks" approach. I'm really surprised at this amount of stretch since the car came with records indicating oil changes every 4-5K miles.

I did look up the factory recall on the 602 chains - it was in a Star issue a couple of years ago. As I recall it applied to early versions of the 602.962. My 91 model was NOT in the recall so I can say that maybe you should at least check the chain for stretch since it would appear that at least some examples of this engine DO seem to have chain stretch issues. I also agree with Sixto, I have heard (second and third hand) about some chain failures with 602 engines.

I'll be doing the chain in my car as soon as I can get the time.

Tim "

So I wouldn't put all too much faith that no cars except those covered by that TSB might experience such a problem!

My point was that these 602 engines in some cases have been known to exhibit timing chain problems, being that the original poster was looking for information about what could cause the noises he described it seemed prudent to mention the possibility of a timing chain issue.

You can get a cheap "Mechanic's Stethoscope" at Harbor Freight that will allow you to listen to individual engine components and isolate just where a particular noise is emanating from. You can touch the tubular probe to a particular component and hear the difference between that location and others.

You can do things like touch each injector and hear them to find a noisy one, place the probe against the intake and exhaust manifold openings and hear any difference between one and the other valves opening and closing.

You can use the same technique to listen to the various pulleys driven by the serpentine belt to find a noisy accessory's bearing noise such as an alternator or AC compressor, as well. The Stethoscope only cost 3 or 4$ last time I bought one.

well, my 93 had a tick like that, I can't remember how intermittent it was though, I think it was worse hot. But in the end it was lifter tick due to oil pressure to the head. I replaced all my lifters and it still ticked after that (I don't think they needed replaced). I kept driving it with the tick. Eventually my head gasket blew, the gaskets on theses engine will push over and block the oil port that feeds the head and block oil flow thus lowering oil pressure to hyd lifters. They push between the number 1 and oil galley. I would tend to bet it could be this. If this is indeed happening you want to catch it before it blows because it can damage the aluminum head by gouging it at that point, that's what happened to mine. Anyways if you think it is an internal knock like that and not a fueling knock I would just do a head gasket. I believe there are other post on this problem try searching it.

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Check out my Frybrid Vegtable Oil Conversion at http://1990300dfrybridconversion.shutterfly.com/

There was another case of OM602 noise on this forum years ago that was solved by changing the two o-rings on the oil filter tube. Very strange. I don't think that noise cycled like yours, however. Cheap and easy enough to try.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
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