6.9 Distributor rotors

[TJ 450]

Good evening all,

I finally got my 6.9 running again (of sorts) today. However, it still has a big missfire and runs very roughly, there is a characteristic put-put sound of a very rhythmic nature suggesting that at least one cylinder is not firing correctly. Ignition timing appears to be way off (retarded), as the "0" mark is way down at the diagnostic sensor. The reference point is up the top just under the w/pump, is that correct?
Bill, I noticed in one of your tutorial pics, your distributor rotor. Is that offset? Someone has fitted the standard M117 rotor at some point, could this be part of my problem? The distributor was, and has been, advanced as far as possible.

By the way, for those who were unaware, this is the list of work required and items that have been replaced/checked so far relating to this.

*Compression test - all withing 5% (according to my gauge!).
*Ignition leads replaced with the correct part, distributor cap replaced with known working part.
*Spark plugs changed before ignition leads - potential problem, plugs were dark grey/black in appearance (not wet).
*Full set of injector nozzles, lubricate airflow meter, clean out fuel dist. with carb cleaner etc.
*Timing chain will need to be replaced as it is obviously worn (original).
*New exhaust system installed (OEM).
*Valve train looks good, oil pressure is excellent.

Tim

[koan]

Ignition timing appears to be way off (retarded), as the "0" mark is way down at the diagnostic sensor. The reference point is up the top just under the w/pump, is that correct?

There's something seriously out of wack here.

If a timing light connected to #1 is illuminating the TDC 0 mark on crank pulley in the region of the diagnostic pickup, that's a lot of advance not retard, a minimum of 50 to 60 degrees.

I'm surprised it's even running.

Is it hard to start?

What happens when the throttle is opened a bit?

koan

[WGB]

Hi Tim the reference pointer is right up under the water pump on the opposite side to that found found on a 117 motor and can be seen on my Timing chain replacement pictorial - disregard the titty and the sensor as that is to do wiht workshop diagnostics and is not related to what you are doing.

It sounds like you are way too far advanced and will have to pull the distrubutor and move it back a gear tooth or two.

If you get the motor  at TDC on No 1 cylinder there is a mark on the distributor body (On the surface that abuts the distributor cap - can be quite faint) that when centralised on the rotor is the TDC point for no 1 cylinder if you have your leads on correctly.

Check you haven't got your leads one space out on the new cap.

No 1 is found as per above description and the firing order is embossed on the rear of the right cam-cover.

Bill

[TJ 450]

Hi Koan,
It's slightly bizarre, I'll have to check I didn't accidentally connect the timing light to #4. It starts easily and the revs pick up when I open the throttle as normal.

Hi Bill,
That could be it, I'll see if the marks line up when the crank is at TDC... maybe someone pulled the distributor at some point and didn't reinstall it correctly.
Tim

[WGB]

You are probably aware that the rotor moves clockwise - looking down on it - and that  Mercedes convention is cylinders 1 to 4 are right bank front to back and 5 to 8 are left bank front to back.

Here is the rotor at about  TDC No.1 cylinder



Here is the plastic liner lifted to show the No 1 cylinder position scribed on the surface which should be about the centre of the rotor with the lead positioned at this point when the cap is on for No 1 cylinder.



That should give you your static timing which then should only need a little adjustment for tdc when running.

Thats it from me - I'm off to Hong Kong in the morning so must away.

I'll log in from Honkers and see how you got on - best of luck.

Bill

[koan]

WGB has one of the rev limiting rotor arms, I have the normal straight version which I think is used in some Holden Bosch distributors.

Left and right refer to looking forward, in the "driving direction" to use M-B terminology. #1 cylinder is the frontmost one on the driver's side (RHD).

I can't think of what could cause your apparent timing error, being on the wrong plug lead could be about the only thing. Having the plug  leads out by one on the cap isn't the answer, provide the timing light is connected to #1 plug at the plug and not #1 at the cap.

The one other possibility is that the crank pulley TDC 0 is not #1 TDC which is a very remote possibility.

koan

[TJ 450]

I had a look at the timing light this morning and realised that the "advance setting" was around the 40deg mark, so the timing would have only been out by a few degrees (I think). I think the miss must be some of mechanical problem, or fuel related.

Tim

[Big_Richard]

TJ, I'd be more than happy to offer my unprofessional opinion next time I'm in the area. I'll just need to clap my hands and wait for my chauffeur to arrive in the 6.9. No, I wouldn't really expect Nathan to drive

[TJ 450]

Sounds good PB, I just need to get my suspension fluid reservoir back in... I have ordered some Penrite MB-15 levelling fluid, so I removed the reservoir to clean it out, change the filter etc. If all goes as planned, it will be back in on Saturday morning and the car will be running then. I will also set the ignition timing properly as well 

Tim

[nathan]

PB,
ill gladly give you a lift, but only if i can pick you up from your joint then drive you back (shit, ive already done this)...
least the car is running of sorts Tim!  maybe we couold swing by on the weekend and PB can give advice whilst i sit back and shake my head like i know something about this matter....hmmm, yeah, exactly...

[WGB]

I hope the miss is a simple problem.

Should be easy to workout which cylinder by removing the leads one at  time.

I am not sure about the 6.9 motor but the 450 motor will foul a plug very easily if not driven enthusiastically and often.

Bill ( from 7 1/2 hours flying time to the north)

[TJ 450]

Hi Bill,

That's interesting, as my 450 originally had the same issue... a major miss at cylinder no.4 due to a fouled plug. All I did was change the plug, and since the car is mostly subjected to long enthusiastic runs ie. not down to the shops and back like before, it has not been a problem since.

On the 6.9, the plugs could still be the issue, as I have not changed them since I had the original leads on the car. At an earlier stage, I did pull them for inspection though and found the plug at no.6 slightly fouled (wet, smelt like fuel), while the rest were brownish and dry.

When I removed the fuel injector nozzle on no.6 I found it to have moist deposits all over it... not very pretty, but there is now a full set of new ones in there. I think checking the plugs again is next on the list, it might still be fouled from before.
By the way, I ordered the rev-limiting type distributor rotor anyway, as that's obviously what's meant to be in there.

That sounds good, Nathan.

Tim

[Big_Richard]

A new set of plugs is definitely a good idea.

all it takes is one slip of the hand to put a hair line crack that you cant even easily see in the insulative end of the plug for it to completely fail. Done this too many times to mention! However, that usually results in a satisfactory idle, but missing under load, as the plug fails to fire when the air density increases in the cylinder...

It might also be worth a check pulling out the misfiring cylinders injector, plugging its hole in the intake and sticking it in a jar and measuring its fuel delivery over a precise period of time. and comparing it with a known good cylinder. If there is major variation, you need a new fuel distributor.

[TJ 450]

Sounds good, PB. I'll pull the plugs and inspect them. Hopefully it isn't the fuel distributor, but considering the fact that the car was left sitting for such a long time, it's highly likely. With a bit of luck it will be the plugs. I did inspect the fuel distributor when I removed it, including the strainers and found them to be quite clean. The metering plunger doesn't show any real signs of wear, but I suppose it could be gummed up with varnish inside. 

Tim

[TJ 450]

Well, I pulled the spark plugs tonight. #1 was dry carbon fouled, #2 was covered in what looks and smells like WD-40, obviously not firing. All the others are good. Perhaps that light oil is WD-40 from when I injected it into the cylinders and it was not firing due to the previous dodgy ignition leads. Obviously the plug is still fouled so even though the leads are new, it's still not firing.
I'll find out on the weekend when I get a new set of plugs and my hydro fluid/filter/o-rings.

Tim