Hello everyone, my E300 D 1995 just went through a complete engine overhaul, at idle it now knocks a lot and sounds like a tractor, as the rpm increases the knocking reduces. There is also a little shake (miss) at idle but no smoke at all. Please advise.

 

Start with the easy stuff first. Check your Belt Tensioner shock. When worn-out, it tends to create a hell of a knock at idle, which subsides when RPM increases. Its sound could easily be confused with an Engine, or injector knock. There are several ways to check it.

One way, with the engine OFF, is to pull up on the serpentine belt with your hand, and simultaneously push and pull the top of the belt tensioner shock sideways. If it moves, than its worn out. Typically the rubber bushing at the top of the shock wears out, allowing the shock to rattle and make a knocking noise. The shock mechanism itself is usually OK.

Another way, but more dangerous is with the engine running. Take a long stick, such as a broom stick. and push it against the top of the belt tensioner shock. If the knocking diminishes, or stops. you found the problem.

Mercedes dealers usually use the first procedure to identify a defective belt tensioner shock.


Phil

 

Thanks Phill, checked the schock, looks fine, the noise is definetly from the top ( injector area). Pls. advise

 

When you mention engine overhaul, what do you mean? That engine in that car should be good for 400K+ being naturally aspirated, and serviced properly!

Sounds like an injector nailing! I would try first by doing a diesel purge with (Lubromoly) If that doesn't help, maybe it's time for injector re balancing, and spray pattern adjusted. Or maybe you have a lazy hydraulic lifter too.

 

Dear Benzbob,

Thanks for taking the time to reply to my post, it so happens that when I start the car it sounds like a tractor, but if I leave it at idle for about an hour all the noise disappears and it starts purring like a cat. As for the hydraulic lifters, I changed all 24 at the overhaul. please reply as to what this noise could be which finishes after idling for an hour or so.

Thanks in advance.

 

Can you record and attach the audio file of the sound that you are referring to. This should eliminate much of the guess work.


Phil

 

it sound to me that the injection pump timing is off...it doesnt take much to make to knock..who did the over haul..?? its also posible that cam timing could be out to ..man if i could make house calls i would be rich...is the timing chain tensioner new...

 

thanks MB/Techman, the overhaul was done by a local mechanic who does only MB overhauls, yes the timing chain tensioner is new, I fail to understand that if the pump timing or cam timing is out why does it get ok when the car warms up. Experts here say that it is the injector nozzles as I had put new ones and they will take some time to settle down.

could that be true, also what is injector nailing??

Thanks in advance.

 

well new injector are noisy for awhie....they make a system purge that you can run though your car ,,,like straight..system flush as be be run with out the fuel lines going to the car ,,,you got to stick the return line in the flush can ,,and the in line going to motor in the same flush can ,,,so it only runs off the system flush ..we use lubeamoly purge,,the motor will run about 10 min. on the can ...very the idle i bit when doing this ...helps more....let the can almost run out ,,,nut not all the way ,,,for you might know it will be hard to start ...its diffacut to make a clear dienoisis over web ..that might be worht a try ..

 

One thing that ought to be mentioned is the injectors. If unless they are genuine brand new Bosch, as from the dealership, they are almost always re-manufactured Bosch injectors. Most all suppliers sell re-manufactured injectors. The problem of late with the re-manufactured Bosch injector is the nozzle. It is about the only part within the injector that is replaced with a new part. The new nozzles are made in India, and are manufactured using inferior materials and craftsmanship. Those who have bought these re-manufactured Bosch/India injectors and installed into their MB cars have complained loudly. This is not an isolated problem with Bosch injectors, it's across the board. Your chance of getting a Bosch/India injector that has a good spray pattern is 1 in 5, according to Colorado Biodiesel, a small firm who specializes in rebuilding Bosch injectors for MB diesel cars. Time to settle down for good injectors, properly pop balanced, (each injector must match equally in your set of 6 injectors, hence a balanced set) with good spray patterns, should not need time to settle out, except if they are inferior India nozzles, and they may never settle out! You would need to take an injector apart to see if the nozzle inside says, Made In India, to know for sure, but try that diesel purge and see if it quiets down. If it does, you may have found your problem. But diesel purge is not going to eliminate crappy Indian nozzles, so the noise will likely return, if this is the issue, which it sounds to me it is!