Worrisome engine symptoms 617.952 - Page 2 - PeachParts Mercedes-Benz Forum

t walgamuth · #16 07-21-2005, 10:41 PM

was your knock intermittant? it would be fantastic (not good, just amazing) if your problem was duplicated!

LJ DERBY · #17 07-22-2005, 01:26 PM

My knock was very noticable at idle, but not intermittant, and seemed to diminish at higher rpm's. I say that because the other noises from the engine increase and might be masking the knock. Although the knock level did not increase with higher rpm's. It ran and accelerated better than my 300D, which has the same engine, even though the D is lighter.

boneheaddoctor · #18 07-22-2005, 01:30 PM

Quote:

Originally Posted by LJ DERBY

My knock was very noticable at idle, but not intermittant, and seemed to diminish at higher rpm's. I say that because the other noises from the engine increase and might be masking the knock. Although the knock level did not increase with higher rpm's. It ran and accelerated better than my 300D, which has the same engine, even though the D is lighter.

Sloppy bearings and a weak oil pump can do that......at higher rpms the pump volume and pressure is enough to quite it down....Have seen that situation more than once. But thats a consistant problem..not intermittant.

83mercedes · #19 07-22-2005, 04:46 PM

Drove the car maybe 20 miles today in city traffic and ran beautifully (other than shaking), no knock.

My game plan for now is to rebuild the vacuum pump as a preventative measure (hell, it is 20some years old anyways, right?), and hopefully this will eliminate the knock. Also will get a compression test gauge and adapter and then see if my results reveal anything. Quite possible that one cylinder may just be messed up and this is causing my rough idle.

boneheaddoctor · #20 07-22-2005, 08:49 PM

Quote:

Originally Posted by 83mercedes

Drove the car maybe 20 miles today in city traffic and ran beautifully (other than shaking), no knock.

My game plan for now is to rebuild the vacuum pump as a preventative measure (hell, it is 20some years old anyways, right?), and hopefully this will eliminate the knock. Also will get a compression test gauge and adapter and then see if my results reveal anything. Quite possible that one cylinder may just be messed up and this is causing my rough idle.

If you get numbers that are within 10% of each other then you know the motor is basicly sound...until then everyone is just guessing.

t walgamuth · #21 07-23-2005, 01:41 AM

of good even compression bad mechanical noises are to be ignored at great risk. ask me how i know...no don't... see above post.

83mercedes · #22 07-23-2005, 02:55 AM

I'm going to try rebuilding the vac. pump, but I find two repair kits, one specified as "valve" for $77.13 and one as "rocker arm" for $268.60. I'm assuming that the "valve" one is the commonly mentioned rebuild kit, and the one I should purchase to attempt to cure this knocking noise. Awaiting reply to purchase and proceed.

boneheaddoctor · #23 07-23-2005, 07:49 AM

Quote:

Originally Posted by t walgamuth

of good even compression bad mechanical noises are to be ignored at great risk. ask me how i know...no don't... see above post.

Heh, heh, haven't we all been there before once or twice....

t walgamuth · #24 07-23-2005, 09:18 AM

the seals only fail and make it not work well. it is the rocker that is the dangerous thing. it has a large roller bearing that fails and binds and breaks the rocker and it all more or less falls into the abiss below and jams the cam chain.

btw the appearance of this device when disassembled is just outrageous. you look at it and wonder how and who ever imagined it and made it work at all. it is completely ani -intuitive.

83mercedes · #25 07-23-2005, 09:40 AM

So you're saying I've got to buy the $300 one?!!

That's obscene.....I don't have that kind of money right now....

Or should I remove and open up the pump and look around to see if I find anything amiss? Only problem with that is the car is incapacitated until I get the pump back on...and it's my only vehicle. Good thing it's summer, I guess

.

pmckechnie · #26 07-23-2005, 10:39 AM

I also had a knocking (nailing) noise in my 91 300D. I cracked open each injector line at the injectors and found that the noise went away when #3 was cracked. It also had had the injectors replaced (before I got it). The problem was the injector. I proved it before I replaced it by swaping it with #4 and the problem moved to #4. Replaced the injector and all was well. My car didn't run rough, it only made noise. I would try to find the rough running problem before I started replacing parts as it could be the same problem and the vacuum pump probably wouldn't cause a running problem. Opening the injector lines will also help find the cylender that is missing. Go back and read post #15 by LJDerby. He used the same procedure to help find his problem.

t walgamuth · #27 07-23-2005, 01:32 PM

i dont know if visual inspection is effective or not. of course gross problems will be visible, like broken rocker but i dont know if that is enough. perhaps a used one is a good temp solution. i should think you could get one used for $20 or so.

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