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-   -   Diesel pre-ignition - causes? (http://www.peachparts.com/shopforum/diesel-discussion/191812-diesel-pre-ignition-causes.html)

WINGAS 06-20-2007 07:46 AM

Diesel pre-ignition - causes?
 
Folks, what causes pre-ignition in a diesel. No, its not nailing, the engine still has some subtle nailing here and there, its pre-ignition ( or maybe post-ignition??) at part throttle. Once above 4000 it runs like a champ, but at mid throttle acceleration, preignition and the engine bucks as it goes through incomplete combustion.

The good news is I;ve been driving it like grandma ( pretending its a 240d!)trying to keep it from rattling = 735 miles on a tank of fuel. BUT , that rattling has/is messing up the alum head for sure. ( hope not the slugs)

Cetane boost is in right now, to see if it helps. Might have to start brewing bio if it does.

Would low fuel pressure cause it?

I've reconnected the EGR as I think it will help mitigate it by upping the inlet air temps. ( backwards from a gasser)

Just trying to understand diesel pre-ignition as opposed to gasser, since gasser is usually bass-ackwards from compression engines. This is like throwing 87 octane in a 10.5:1 gasser.

BTW IP timing is spot on, injectors have been redone, engine has seen Purge.

THNX!

Kuhlrover 06-20-2007 05:11 PM

I don't think it is pre-ignition as you describe it. I suggest stop calling it pre-ignition. From what you descibe it sounds more like a miss or "no-ignition". I doubt if the cetane boost or the EGR will have any affect on the problem you describe.

You said it runs fine at 4000 RPM? Is this driving down the highway or with the engine racing while the car is parked? It will make difference in understanding how much fuel is being used by the engine. If you are screaming down the highway at 4000 RPM and I am guessing 85 MPH then you are using quite a bit of fuel. However, if you are racing the engine while it is parked, it using very little fuel to get the engine at this RPM.

Number one rule with diesel engines when they start giving you grief is to replace the fuel filters. If you take it to a diesel mechanic that is what they will do. Since the next step is to run some diesel purge through it to clean out any gunk out of the system, you might as well run the diesel purge through before you change the filters. After that I would start looking to see if you have a bad injector or a worn injection pump.

TimK

WINGAS 06-20-2007 09:49 PM

TimK, please note the last sentence of my post. that was done 3K ago Whn I brought the car home. The purge was nothing more than priming the fuel system with it after the injectors and lines were out.

I'm calling it pre-ignition so as to NOT call it nailing. As I fear the "Italian tuneups" i did, did nothing more than beat up a beat up cylinder head even more.

To be specific its at part throttle, and if you go WOT it will "rattle" for a bit until you hit 4000 at which point the engine sounds normal and healthy at the end of its useable rpm range. Not bad accel for a n/a engine running poorly.

Hey, I got a spare filter and was just about to order a few more as the engine will see its first ( I assume) bio in the next few weeks. I could repurge it, but I dont think it'll cure what ails it. Nonetheless, I'll purge it and refilter it. Due for an oil change soon as well.

Worn injection pump eh? How would one diagnose that? Process of elimination I assume.

winmutt 06-21-2007 12:45 AM

Quote:

Originally Posted by WINGAS (Post 1541794)
TimK, please note the last sentence of my post. that was done 3K ago Whn I brought the car home. The purge was nothing more than priming the fuel system with it after the injectors and lines were out.

I'm calling it pre-ignition so as to NOT call it nailing. As I fear the "Italian tuneups" i did, did nothing more than beat up a beat up cylinder head even more.

To be specific its at part throttle, and if you go WOT it will "rattle" for a bit until you hit 4000 at which point the engine sounds normal and healthy at the end of its useable rpm range. Not bad accel for a n/a engine running poorly.

Hey, I got a spare filter and was just about to order a few more as the engine will see its first ( I assume) bio in the next few weeks. I could repurge it, but I dont think it'll cure what ails it. Nonetheless, I'll purge it and refilter it. Due for an oil change soon as well.

Worn injection pump eh? How would one diagnose that? Process of elimination I assume.

Check timing for each element of the IP, the instructions are in the FSM. You should be able to get a replacement pump at pull a part for $40 or so. Are you sure the noise is coming from the engine? Injectors have been redone, what does that mean? Rebuilt and pop tested? Does your turbo spin freely? Are you seeing lots of smoke?

Kuhlrover 06-21-2007 12:58 AM

Wingas,

I missed the part about you already doing a diesel purge. Definitely change the fuel filters if this had not been done after the purge. The diesel purge can break stuff loose and then it gets trapped in the filters.

When you get to the top of the RPM range the governor in the pump starts to restrict the fuel to prevent you from over revving the engine. There is also a screen in the tank that can get clogged. This can easily be removed and cleaned. I think it is one of three things; 1) Fuel Flow to the IP. 2) bad injectors. 3) failing injection pump. Solving number 1 is the cheapest and easiest to start with.

TimK

FlossHogg 06-21-2007 01:52 AM

Your timing is far to advanced. This is the case when the car is slow and idling very choppy but at high rpm it behaves like a sports car. Maybe you valves are adjusted improperly or your timing chain has stretched and needs to be compensated for.

WINGAS 06-21-2007 06:01 AM

Actually paid the MBZ dealer pro to check the timing with their fancy $500 lights. 14 spot on. Chains, therefore, should be tight and spot on. It was one of those basic thigns i needed to know before I set out tuning the thing.

Did I get screwed there, did he even check it? Did the guy who rebuilt the inj's eff them up??

I must say that I dont prefer relying on other people, as I have no precedent to know whether they're any good. None of my mechanic buds ( who are utterly reliable) will touch the oil burner!

Anyway, I must assume that IP timing is spot on, and the injectors have new nozzles and have been tested. All new fuel lines from the filters to the IP.

Shorebilly 06-21-2007 07:16 AM

I haven't had any time to think this out.....But....
 
It seems to me that your timing may be off, just as has been mentioned....

You said that your timing is "spot on" in relation to what??

If your timing chain has stretched, then it changes the relative relationship between the camshaft and the crankshaft......if your MB folks simply timed your FIP with either of the electronic testers mentioned in the W123 service manual, then the FIP is timed to the crankshaft.....and if your timing chain is, in fact, stretched......then the FIP is in time with the crankshaft (fuel is injected at the proper point relative to piston location within the cylinder.....BUT.....the camshaft may be a bit off time with the crankshaft, thus having your valves being opening or closing (whatever) at a slightly different time relative to piston location within the cylinder.......I hope that this makes sense to someone, other than me......:D

This is the reason that MB makes and sells "offset keys" for the camshaft....to restore the cam to it's proper timing to the crankshaft.....

SB

winmutt 06-21-2007 08:47 AM

Quote:

Originally Posted by FlossHogg (Post 1542037)
Your timing is far to advanced. This is the case when the car is slow and idling very choppy but at high rpm it behaves like a sports car. Maybe you valves are adjusted improperly or your timing chain has stretched and needs to be compensated for.

Not entirely true. I have a similar problem until the engine is warm. 100% certain at this point that it is missing balls in the PC.

WINGAS 06-21-2007 09:19 AM

I might be missing balls too Winmutt. The thing I should have done is to visually inspect the PC through the injector holes AND also do a compression test while the injs were out getting rebuilt. ( btw, finding a diesel at a pick a part in Buffalo is IMPOSSIBLE. Just didnt sell them up here.)

SB, read you loud and clear. I've put a few cams in before, and I've degreed a bunch of them. Can I, with a dial indicator, roll the motor over by hand and check opening/closing of the cams. Oh wait, thats relative to crank position, but still if I had a cam card I could see where the cam sits relative to crankshaft and then compensate the ip OR offset key the camshafts. And yeah, the 606 gots TWO of them.

I find the FSM dreadfully vague. Heck man, I couldnt even find a list of torque specs! this on that bogus CD/Rom version. Cam timing. Dream on. Not there.

Fellas, thnx for all your input and apologies in advance for being a diesel stooge. I'm learning though.

The car is now my daily, as I;ve given back the POS lease car I had. 42K and a bad rear wheel bearing. What crap.

This morning's ride in was better, with the EGR back on, the flappers seeing vacuum again, cetane boost in the fuel. Better. Much better. But, unfortunatley being quite fastidious about certain things and I cant leave it alone knowing its not right.

BTW, no 'puter in this 95, but what function does the "airvalve" or "opening sensor" serve just upstream of the air filter? Its not an electrical connection, but a vaccum one. What does this device control? Connects into the same fitting the EGR connects to, it seems. Mechanically connects to the throttle rod.

MPG is till stellar even with the anomoly going on. Cant imagine this car will get near 40mpg when its in proper tune.

Cervan 06-21-2007 04:52 PM

... this isnt that hard. check your chain stretch. if its over 4 degrees change it. the rattle you are talking about is that your only running on 3 or maybie even 2. at idle it sorta jumps around correct? i would take the head off and inspect the cylinders. my 240d started usuing a gallon of oil every day. so i took the heads off sure enough there was significant scoring of the cylinder walls and rings were in some serious need of help.

Shorebilly 06-21-2007 05:00 PM

Unfortunately I have never even driven a vehicle with an OM 603.xxx
 
Although I know very little about the OM 603.xxx engines (I think that's what's in a '95 E300D).....the Germans generally don't stray too awful far from tried and true technology......

So, your vehicle should have some sort of timing marks on the balancer, and thus you should be able to locate mechanically the TDC of zylinder # 1......if not it can also be done thru the glow plug (but it seems that the glow plugs on a 603 are kinda hard to access).....or you could also pull the injector on # 1 and locate TDC with a dial indicator.....

I don;t know the specs for the 603....W123 Engine Service Manual says "Note this is Not a direct quote"
Locate TDC on #1
Neutralize valve lash .....adjust out all valve lash.....on #1's intake valve
use a dial indicator on the intake valve of #1
Rotate engine to TDC of #1 and #1's intake valve should open 2.0mm
and there may be a mark on the balancer that indicates #1 valve opening that is in alignment with the pointer.....

Anyway, you should be able to check the camshaft timing against the crankshaft.......and if you are really having trouble understanding how to go about it on a 603....try phoning up Roy Hunter at Fastlane....his phone number and e-mail are listed in the "Buy Parts" tab at the top of the page....

SB

Also of note: The Germans generally do not change their file numbering system either....so try looking at 05-215 of your FSM

BioPOWER 06-22-2007 01:01 AM

The '95 E300D has the 606.910.
All 60x engines use hydraulically-adjusted valves. No need to do manual valve adjustments like on the 616 and 617.
Also, yes, the 606 is a dual-overhead-cam engine, but the timing chain only winds around the exhaust cam sprocket, necessitating only one offset key (if it is even needed). The intake cam is gear-driven off the exhaust cam.

Good luck diagnosing your problem. My E300 (606.962) has developed what I would describe as a "lumpy" idle (not the typical, even diesel purr), could be delivery valves or injectors in need of balancing.

WINGAS 06-26-2007 11:01 AM

Gentlemen, thank you. This is a protracted process indeed. Right now the highly boosted fuel is flowing into the IP and there is no more pinging. Still some "nailing" or rattle. But the preignition has been eliminated by a high level of Power Service Cetane Boost.

I am hopefull the rattle is one bad pre, and pray the GP ( which are working well btw) comes out of that cylinder! I wont mess with it for a few months.

Must say that I dont really want to change the cam timing. Car pulls strong ( as well as a turbo I should think) and gets over 700 miles on a tank w/o AC just under 700 with A/C on nearly all the time ( like now). Sure dig its hum when its runnign smooth!

Putting this lil' black girl on a diet next week. A biodiesel diet. See how it likes that cetane rating. Dont know where I'll start though 50% 20% 70% ??? Buying a few fuel filters in anticipation, and trying to identify a few good sources for my " WINGAS" !

winmutt 06-26-2007 12:00 PM

Quote:

Originally Posted by WINGAS (Post 1546748)
Gentlemen, thank you. This is a protracted process indeed. Right now the highly boosted fuel is flowing into the IP and there is no more pinging. Still some "nailing" or rattle. But the preignition has been eliminated by a high level of Power Service Cetane Boost.

I am hopefull the rattle is one bad pre, and pray the GP ( which are working well btw) comes out of that cylinder! I wont mess with it for a few months.

Must say that I dont really want to change the cam timing. Car pulls strong ( as well as a turbo I should think) and gets over 700 miles on a tank w/o AC just under 700 with A/C on nearly all the time ( like now). Sure dig its hum when its runnign smooth!

Putting this lil' black girl on a diet next week. A biodiesel diet. See how it likes that cetane rating. Dont know where I'll start though 50% 20% 70% ??? Buying a few fuel filters in anticipation, and trying to identify a few good sources for my " WINGAS" !

100% Just be prepared and alot extra time if needed. You can reuse the prefilter many times by taking it out and shaking it.


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