OM606 Nailing under 1200 rpm - PeachParts Mercedes-Benz Forum

#1 05-17-2007, 11:44 AM

Hi

Got my injectors re-balanced for £25 each, the performance has greatly improved, a lot more pull on hills and is overall a lot more responsive -BUT - It's started nailing (pinking) under 1200 revs. The guy who did them said he had set the pop pressure at 160 because after ca 1000 miles the springs will settle back down and allow pop at 130-140 lbs of pressure which is optimal, which could cause nailing.

After a lot of reading and brain picking it seems that having the injectors balanced has highlighted the off timing of the fuel pump and valves, which is a common cause of nailing.

The easy (!!??) thing to do would be to reset the pump and valve timing to compensate for the optimal setting of the injectors. A MB mechanic (over 50 who lends me tools) said that given the age and mileage of my car the chain would have some stretch and renewing the timing chain and tensioner should pull everything back together again. So I ordered a chain, tensioner + seal, sliding rail and three sprocket bolts for £200 and will set about it next week.

Any thoughts or tips on this undertaking

Cheers

Adrian

vstech · #2 05-17-2007, 11:51 AM

http://www.dieselgiant.com/replacetimingchain.htm
a good read before doing this repair.
John

777funk · #3 05-17-2007, 11:52 AM

Hi there,
www.Dieselgiant.com has a very good Mercedes Service tips section with a pictorial on how to do it. Same as the Haynes manual but you can actually use Russell's pictures on the diesel giant site.
thanks,
Nick

777funk · #4 05-17-2007, 11:53 AM

looks like me and vstech thought the same thing at the same time!

TMAllison · #5 05-17-2007, 12:02 PM

Unless you've previously confirmed chain stretch I might run 2 cans of Liqui Molly Diesel Purge through it and then give it some time before tearing things apart.

vstech · #6 05-17-2007, 12:09 PM

I would not put DP through the new injectors, I would pull the injectors, spray some DP in the Prechambers, let is soak for a day or so with the block heater plugged in. then spin the motor over with the injectors still out, to blast any liquid out of the cylinder. and put it all together and start it up. sorry your intake manifold is in the way of doing all this easily, but it's what I would do.
John

#7 05-17-2007, 01:20 PM

Cheers guys
I already have that "how to" on my desktop.
I have wanted to change the timing chain for a while as I bought the car with no history and I suspect it has been clocked at some point so now seem as good a time as any. I wanted a multivalve 124 and could see through the problems I would run into with this car - BUT it will be sweet again...... once everything is sorted

Is there anything lopsided with my diagnostic (un)logic thinking that if the chain is stretched a new one would pull everything back where it should be.
Or do you think that cos the guy set the pop pressure a little higher to compensate for spring wear that maybe overtime the injectors would run in and settle down. The guy who did them guarantees that they are pop balanced and the spray patten is how it should be.
I really have noticed a change in performance and response since having the injectors serviced it's just that at low revs it now sounds like rabbits screwing on a tin roof, with clogs on.
One thing - when holding at say 2000 rpm it is quiet, no knocks. When I let it drop it stays quiet until it picks up idle speed and starts nailing again which tells me it's not a mechanical knock.........??
Anyway cheers
Adrian

Parrot of Doom · #8 05-17-2007, 01:43 PM

Give it a few hundred miles to settle down before you have a go at the timing chain.

I have heard some horror stories about the tensioner and the correct method of installation, can I recommend you ask around about that?

Alastair · #9 05-17-2007, 01:44 PM

Quote:

Originally Posted by iamamanc

Hi

Got my injectors re-balanced for £25 each, the performance has greatly improved, a lot more pull on hills and is overall a lot more responsive -BUT - It's started nailing (pinking) under 1200 revs. The guy who did them said he had set the pop pressure at 160 because after ca 1000 miles the springs will settle back down and allow pop at 130-140 lbs of pressure which is optimal, which could cause nailing.

After a lot of reading and brain picking it seems that having the injectors balanced has highlighted the off timing of the fuel pump and valves, which is a common cause of nailing.

The easy (!!??) thing to do would be to reset the pump and valve timing to compensate for the optimal setting of the injectors. A MB mechanic (over 50 who lends me tools) said that given the age and mileage of my car the chain would have some stretch and renewing the timing chain and tensioner should pull everything back together again. So I ordered a chain, tensioner + seal, sliding rail and three sprocket bolts for £200 and will set about it next week.

Any thoughts or tips on this undertaking

Cheers

Adrian

Hate to say it, but it sounds like you were done.....

UNLESS he replaced the injection-nozzles for New.....(BUT at That price, they probably some cheap chinese crap if they were replaced with new--IF he didnt replace the nozzles, he Definately stuffed you!....)

30 BAR OVER---IS YOUR 'DIESEL-EXPERT' MAD!!!

He has set up the pressures WAY too high for a start, even allowing for New Nozzles,-The Maker,- Bosch- recommend only a 10 bar over quoted pressure to allow for 'bedding-in' of NEW nozzles only, and never for used ones-Used ones are supposed to be set to quoted pressures....

Setting too high like this will seriously affect the fuel delivery Rate (Slower) and point of injection timing, (retarded). Both could and does cause your troubles...

Injectors dont need 'Ballancing' as a service job, unless extremely high milages have been covered-'Pop' pressures seldom alter much after initial 'bed-in' even after 100-200K miles. If there is an issue, they should be cleaned or better still have new nozzles fitted -Correctly- and at the 10 bar above correct pressures.

I REALLY HATE to hear these stories of these incompetants ripping genuine guys like yourself off, Just because you like your car.....

vstech · #10 05-17-2007, 01:49 PM

Quote:

Originally Posted by iamamanc

Cheers guys
it's just that at low revs it now sounds like rabbits screwing on a tin roof, with clogs on.
Adrian

AWESOME!
I love hearing new quotes describing things. that one really tells a tale!
(anybody that has not raised rabbits just really can't appreciate the visual!)
brrrrr...POW!
John

vstech · #11 05-17-2007, 01:50 PM

NOW we know where the term "Nailing" came from!
John

Alastair · #12 05-17-2007, 01:57 PM

Quote:

Originally Posted by vstech

NOW we know where the term "Nailing" came from!
John

#13 05-17-2007, 02:20 PM

Alastair
I asked the MB mechanic if setting the pressures higher was ok and he said it should be. I assure you the guy who did the injectors knows his stuff, It's all he has done for years - Injectors and pumps. They were cleaned sonically, the nozzles were not replaced as the spay pattens were ok. Three of them were showing low pressure.

Does anyone else have any input on pressures, no offence Alister, you say it's wrong - he says it's ok. I can see how the pressure could effect the timing issue though

I admit that as far as injectors go this is the first time I have had any out so I'm a bit of a Manuel (I know nothing).
So what do you do, ask around and trust people wont rip you off, hey I'm a builder - ask me about trust

Hi Parrot
My eyes are bleeding from all the reading - but questions will be asked

Vstech

#14 05-18-2007, 08:51 AM

On the advice of Alistair I had a word with the guy who redid the injectors. It seem that the twat who picked them up for me didn't listen to what he was told.
They had new Bosch nozzles fitted
The pop pressures were set at ca 6bar above middle tolerance as per Bosch spec.
I think that the six is where the dummy who picked them up got the 160 from, well there is a six in it.
Anyway just thought I would clear that one up. It's amazing what you can learn from a cock up!!!!!

Cheers
Adrian
PS thanks again Alistair for taking the time out

vstech · #15 05-18-2007, 09:12 AM

again with the colloquialisms, I love it! the man who picked them up... did you misspell your nickname? if not, I would love to hear the explanation for that one.
John