98 E300TD - name that clack... - PeachParts Mercedes-Benz Forum

KarTek · #1 06-22-2007, 03:57 PM

OK, so I've been here for hours reading all the helpful info in the DIY section and I want to try to put some of that knowlege to use with a noise that just developed with my car.

This morning it was about 67 deg. When I started the car, it was missing, only running on 4 or 5 cyl and making a loud, intermittant clacking sound that seemed to be coming from the top of the engine rather than a lower, rod knock sound.

It seems to be only one cylinder and it really sounds much like the normal sound of my GF's TDI except that it's only doing it on one cyl. A kind of "raspy" clack. As the car warmed, the noise has gotten quieter and has settled down to what I would call a valve train click. It's noticable only at idle. At speed, the engine performs and runs perfectly aside from only delivering 27-29 MPG.

Could this be what I've heard referred to as "nailing"? I'm reluctant to do the ole' Italian Overhaul because I'm always suspicious of any knocking engine noise and I figure any stress will only make it worse. Aside from that, I'm getting an intermittant "oil level at minimum" warning and despite the fact that the dipstick is on full, I worry a little that something is up with the oil system. Again, I'm reluctant to run it hard. I've only had the car for a week so I'm not up on all the "normal" noises yet.

My Powerstroke Diesel did this one time I got bad fuel so I just filled up and I'll see if it makes a difference. Other than that, I figure I'll try the diesel purge procedure and I'll test the glow plugs to try to see if that's the root of the poor starting problem.

While I'm in there, should I do anything with the injectors? the car has 136,000 miles now and I've read that they should have new nozzles at 100K. I've also read about the trouble people have getting them balanced, etc... and I don't want to open any cans of worms.

Any comments are appreciated.

TMAllison · #2 06-22-2007, 04:15 PM

I inj's should only be replaced (with new nozzles) if they exhibit an incorrect pop pressure or spary pattern. Otherwise thay are fine. I've got 208K on the 606.962 and 311K on the 617; both OEM and never been pulled, adjusted, etc.

You first should get to the bottom of your GP issue as a cold cyl wont fire at the correct time until it heats up like the others. THAT is more than likely your problem.

After fixing the GP's if the nailing persists do a DP and see if that helps before pulling and testing inj's.

BioPOWER · #3 06-22-2007, 04:34 PM

It's glowplug time!

Fun, fun, fun on the 606!
First thing to do is to check each glowplug's resistance with an ohm-meter at the glowplug relay, located on the driver's-side fender by the ABS. Stick one terminal into one of the six sockets on the harness plug, and touch the other terminal to the intake, or another ground. Bad plugs will read infinity, indicating an open circuit.

It sounds like a bad GP, so you'll need to read up on how to remove them from a 606. With any luck, you won't have any stuck...I had (still have) one stuck, and mine were originals at 165k miles.
The story is here:
'99 E300 Glowplug Change-Only 1 Stuck
In the end, I decided I could live with one bad plug, rather than risking damaging the aluminum head trying to extract it. I'll get it out when I have the head off for a valve refreshing.

Good luck!

nhdoc · #4 06-22-2007, 05:41 PM

Does your glow plug light operate properly and do you wait for it to go out before starting the car?

The low oil level warning is commonly caused by a failing sensor...it's an easy fix and the part is about $50 IIRC. That is not foretelling of anything serious if the dipstick says it is full you can ignore the warning until you have the sensor replaced.

KarTek · #5 06-23-2007, 07:22 AM

OK, thanks guys.

Here's what I did so far:

The GP light works properly and I tested the GP relay and it functions normally. It energizes when it's supposed to and 12v appears on all output tabs. (of course now, the dang check engine light is on and the display is flashing an engine electronics alert. Anyone know how to clear these?

Also, all GP circuits test fine though, sometimes I'm getting a reading of .5 Ohm and other times I'm reading .8 though it's consistant across all six.

Could this be a bad engine ground?

Today, I'll go after the injectors and try the "crack" test. If I find the culprit, I'll go in search of a 27mm socket and switch it to another cylinder and see if the problem follows it.

I'll keep you posted.

TMAllison · #6 06-23-2007, 09:56 AM

You can go to autozone and they will supposedly pull the codes for you. You should probably invest in an OBDII scanner. You've got two newer cars and will need to know what the computer is telling you if you intend to work on them yourself. They are pretty inexpensive.

I wouldnt bother doing anything else untill you get the codes....your car is trying to help you now.

Save your money on the 27mm socket, thats for the old cars. Instead go to MB an buy the splined socket needed to do this job or you can find it above under the Special Tools tab.

KarTek · #7 06-23-2007, 10:54 AM

Thanks for the info Terry. Actually, a regular OBDII scanner won't work on the truck because of it's inability to dig deeper into the diesel specific controls. I'll have to invest in something like AutoEnginuity software to do a good job of it. I just haven't gotten the cojones' to pony up the $400 yet...

What I found out this morning is that in the past, some enterprising mechanic had gone to replace a glow plug in #6, snapped it off and proceded to wire another one to the side of the engine block so as to fool the computer. As a consequence, I guess that pot is always running cold and has carboned up the injector. While warming it up, I noticed smoke coming from the exhaust which I figure is from poor atomization.

When I cracked the line on that injector, sure enough, the knocking ceased.

The saga continues...

TMAllison · #8 06-23-2007, 11:32 AM

The OBDII scanner wont "dig deeper" into the MB codes such as trans, abs, srs, etc either but will provide you tons of info concerning the engine.

The turck should be the same as ALL vehicles after 96 are required to be OBDII compliant by law.

I'd be talking to whomever you bought it from concerning that GP. It is not a cheap or easy fix.

Some have sucessfully drilled and extracted them. Some have ruined thier head attempting to do so too. Some have left them in place. IMO there is danger of fouling the inj in that hole and developing a bad spray pattern that "could" damage the top of the piston if it is left there. I'd be reluctant to just leave it. Most give up and pull it and let a machine shop get it out. Is ~$2500 or so.....MB has a special extractor kit that some shops have bought. It very expensive and many dont have it. They charge a lot to use it and no guarantees.

You should still get those codes. Will prob be PO380 at the least (GP circut A malfunction) but may be others too.