Hi,
I have recently purchased a 1966 250 SE 108.
It is hard to start cold but runs very well when started to operating temp.It will restart but runs rich,sooty plugs,oilthat smell of fuel, sooty exhust,bit smokey.It will idle nicely and revs well.When it cools down it is hard to start again.I have taken the air filter of the injection pump and it sucks hard when cold and slows down when warm,but will not shut off compleatley at temp.Does eny one know the method of checking the cold start system,and the adjustment of the cold amd warm running systems,The car is in excellent straight dry condition and I plan on using it as a daily driver, so any other usefull information would be helpfull and appreciated.
Next to the air filter for the MFI is a pipe looking thing with 2 water hoses running into it.Thats a wax stat.inside it is a brass tube which pushes down into the MFI to enrich the car when cold.If it doesn't shut off when hot,the MFI keeps supplying too much fuel giving the symptoms you describe.Start by fitting a set of new (or very plugs) remove the thermo stat,start the car let it run until hot and either take a reading from the exhuast with a analyser or visually ensure it's not fumy.
check the plug conditon to ensure they either brown or light brown ,but not black.
The Idle mixture is on the end of the pump,NEVER turn that knurled nut with engine running,you will destroy the MFI[}:)][}:)][}:)][}:)][}:)].
There is a little hex head nut with a slot in it,thats the dip stick for the governor.
Unscrew it and check the oil level.If it is high ,use a turkey baster to suck the excess out.In fact suck it all out and replace it with 200 mls of Mobil 1.Excess oil in there causes the governor to hang up and make the car rich also.[:)][:)]
P>S what is the Number of 6.9?
Hi Thanks for the reply,Good tips that I will check on the weekend.I will post my findings.I am also going to give the whole cooling system the works as the heated water pipe to the warm regulator was compleatly blocked.These forums are great because there are genuine people out there that are willing to help each other.This means that we all have a hand in returning great old Benzes back on the road where they belong. The 6.9 ? 116-036 No 4221 1978. Magnetite Blue,Blue velour interior, straight and honest.
I'm a member of the m-100 group and we are always trying to track down the remaining 6.3's and 6.9's .Have you posted your car in the registry @ www.M-100.cc ?
With these cars getting older we are trying to keep them all going,even in the face of rising fuel prices.
Ron B ? No im not in any registry.I have been following the M100 posts for over a year now and have made a few posts.I may become more involved sometime as I totally agree that these cars should be preserved, and the forums are a fantastic way of keeping a few more grand cars around, and properly maintained.After 20,000 klms of trouble free driving I must say they are reliable and hold their ground at whatever you dish up to them.Should put a pic up one day....
Thanks to the good advice it now starts cold.The CSV was totaly jammed full of crud and stuck fast. Someone had also soldered closed the inlet on the pipe side. I drilled this out, freed up the valve,fitted new o rings and cleaned it all up .I also fitted a relay to supply straight 12 V to the CSV. Bingo after a couple of cranks it started.The Temp unit was als compleatly blocked.After a good clean ,it now sucks hard when cold and nearly stops when warm.The idle also drops gradually as she warms up.It will still run,but idle drops a little when I put my finger over the air intake on the mfi.
The exhaust is a lot cleaner ,but some times it dies when idling but re starts easy and after a couple of revs it settles back down to a nice idle.
Looking good so far,and I think it might be close,but I cannot take it for a good drive as the brakes need work.Bad master from sitting for 4 years.looses retention.
How do I adjust the mixture and set it up correctly?
Any thing else I should check?
Many thanks again for your help ,you were right on the money.
Regards,
Darren.
Ha Ha ,as Soon as I saw the gum trees and the mozzie nets on the front i realised you are in OZ.
To adjust the idle mixture correctly is a real chore actually.
It involves getting the acelerator linkage is step between the throttle body and the injection pump.
The pump mixtue is set by that thumb screw on the back of the pump.It must be done with an analyser ,the car must be warmed up and idling,the mixture (C/o) level noted.If too rich ,STOP the engine.PUSH in the the little round knob and turn 1 Click to the LEFT,resart the engine and check C/O levels again ,if too lean turn to the right.
Never push the knob in with the engine running.the knob will engage with the govenor and destroy the pump.
I usually start here with these jobs,and then to further tune it,i remove the push rod from the pump to the cross arm and set the idle with the car in top.(and a good chock under the wheels[:D][:D]
As a rule of thumb,if the idle speed goes up and down slightly,the mixture is too rich and if the engine seems to vibrate or not run on all six ,it's too lean.
Whatr you did to the waxstat is getting more common as these cars age and people insist on using ordinary water.Fatal in someparts of OZ as it's like using acid in the radiator.
One last thing,get under the car and clean the tank bung filter,and replace the fuel lines to the pump,they will be buggered by now and use quality EFI hose.
The secret Merc mechanic trick is to also shove a peice of wire down the return pipe in the fuel tank,(the samller upper steel pipe) i 'll bet it's blocked.In fact i've had to replace some tanks because the pipe was actually Rusted up.it's a real common problem on all the W110 -109 cars.
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