W108 280SE M130 only running on 5 cyl

[laegaard]

Hi

My 1970 W108 280SE M130 is only running on 5 cylinder
I just changed the spark plugs, the old one's were bosch W7DC. bought new denso that should be the same as W7DC.
After i changed the spark plugs the engine actually ran fine, but today (200 km's later) it's running on 5 cylinders again
I have checked the ohm reading on both ends, and they are both around 1 ohm.
Any advice on where to begin ?

Do i need a new coil, or should i look for something like this electronic ignition from 123:

http://www.123ignition.nl/id/25.html

Or do i need to adjust the valve timing ?



Regards

Mads

[cadurning]

Just from experience, replace the plug wires if they are old. Also did you look in the distributor cap for carbon tracks or cracks?

[Pooka]

If the inside of the Distributor cap shows any arcing or scoring it should be replaced. The distributor rotor should be replaced as well.

The scoring is just from being used up. The arcing will show up as a blue color or powder. Check the top of the distr. cap, too, where the wires plug in. If there is any blue powder in any of the holes that is arcing and shows that the spark plug wire was not seated correctly. This can usually be cleaned up and no replacement is necessary.

One very old trick that sometimes works..... Park the car where the entire bay will have no light shining on it at night. Use a flashlight to walk around since you want the area to be as dark as possible.

Start the engine and raise the hood. If the wires are worn out you will see blue pulses of light leaving the distributor and going to the spark plugs. If you see this it is time to replace the wires!

[laegaard]

Thanks for the input, the wires are only a few years old, 15 ohm silicone type.

Mads

[t walgamuth]

Was the plug clean looking that stopped firing?

[peet230e]

What about the fuel injector on that cylinder, is it functioning?

[laegaard]

The sparks on cylinder 1, is 'wet' so it seems like its getting fuel. When i take the plug off, an put it on again, i fires the spark plut maybee 1 or 2 times.

Mads

[laegaard]

How do i test the injector ? the pressure from the pump seems to be fine. When i unscrew the pipe to the injector, gas comes out.

Mads

[peet230e]

Have you got the silver bosch suppressors on the sparkplug end of your plugwires? If so these go dead often, change it out with another cylinder and see if it then fires.

[mak]

Do check the valve adjustment ; 0.10mm intake 0.20mm exhaust.Cold engine
if it was marginal then the valves will not close when hot and a missing cylinder.

electronic Ignition upgrade to a Pertronix or Hot spark will make it reliable.I have had good results with pertronix in my 108
The ignition wires are correct if solid type with very low resistance .
A new rotor and cap will give a good spark and eliminate any borderline wear . The gap between the rotor and cap terminal erodes with time and the spark jumps to ground .
mak

[Pooka]

From I have read here might I suggest you install a new spark plug. Not all of them, just the one.

Spark Plugs can break down inside or just be bad from the factory. Try swaping the number 1 with another plug and see if the plug you know is firing in its' current cylinder fires when it is installed in cylinder number 1.

A plug breaking down is easy to spot if you spend about $15,000 US Dollars on an engine analyzer and know how to use it. Or you could just test this theory by swaping the suspected plug with a known good one.

[t walgamuth]

Sounds like the injector might be the problem.

[Chas H]

Originally Posted by laegaard

How do i test the injector ? the pressure from the pump seems to be fine. When i unscrew the pipe to the injector, gas comes out.

Mads

Swap the suspected injector with one from a good cylinder. But do a compression test before you do much of anything else.

[t walgamuth]

Originally Posted by Chas H

Swap the suspected injector with one from a good cylinder. But do a compression test before you do much of anything else.

good idea!

[laegaard]

Now this is strange, The spark plugs has only done about 300 km. I put a new spark plug in the not running cylinder, and now the engine is running on all 6 !
i don't any visible defect on the 'old' spark plug.

Mads