News:

www.W116.org - All about the Car!

Main Menu

Crank Position Sensor

Started by Jenno1981, 09 March 2021, 08:04 PM

Jenno1981

Gents,
Been a long time for me and my 450SEL. Other priorities took over 🙄

I was having a start issue - turning over, running rough for a few seconds then dieing.

Historically had intermittent turning off when driving nicely and a low idle/stall when hot at the lights.

Yesterday I diagnosed no spark at the plugs (plugs, leads, dis cap all I pretty new/low use). I was working my way backwards from the spark plugs.

A friend of mine (non-merc) said it sounded like a Crank Angle Sensor. I'll be completely honest - never heard of it.

1. Does my 78 450SEL have one?
2. If so, where is it (is it connected to infamous green wire I read so much about?)
3. Thoughts in testing/purchasing a new one.

Always appreciate the help I this forum for a complete armature like myself!

Cheers,
Jenno
1978 450SEL - Green
1999 ML430 - Also green 🤷�♂️

UTn_boy

No.  There are no crankshaft angle sensors/position sensors on a W116.....at least for the purpose of the ignition system.  There is a pick up on the front of the engine, but it's only for the diagnostic pick up plug that a factory tool would plug into to sense engine RPM on a remotely operated electronic device dealers used. 

A no spark condition can mean many things, but usually means the ignition coil, one of the ballast resistors, or the switchgear unit has quit.  The switchgear is the finned or smooth faced aluminum square box device mounted above the coil at the top edge of the inner fender well.  It'll have a green wire going to it from the ignition distributor.  The coil and ballast resistors are readily available new with affordable pricing, and should be renewed upon principle alone.  Age is not kind to ignition components.  The switchgear is still available from Mercedes, but for around $1,500.  Rebuilt ones are available from places like Programa, but I can't speak for the quality of the work. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

Jenno1981

Thanks UTn, much appreciated. I'm going to get back under the hood at the next available opportunity and start with the resistors. Simple multimeter test of resistance should tell the story?
After that, ignition coil test, how would I go about it?
Cheers,
Eamon
1978 450SEL - Green
1999 ML430 - Also green 🤷�♂️

revilla

Quote from: Jenno1981 on 10 March 2021, 04:38 AM
Simple multimeter test of resistance should tell the story?
After that, ignition coil test, how would I go about it?



Check that the ballasts are the correct value and in the correct place.  With the ignition on both should get hot and there should be about 4V across coil terminals 1 & 15.

Check also the resistance of the leads and also the rotor arm.

Measure each lead between the tip in the dizzy cap to the spark plug connector, the resistance should be between 1k and 6k.  Measure the rotor arm between centre brush contact and the finger, again around 1k.  Finally measure from the dizzy cap centre bush to the end of the coil king lead, this should be lower than 1k.

If any of the leads read open-circuit then the voltage seen by the coil will increase drastically and could be causing it to break down internally.

Hope it helps

Cheers

revilla

With ignition ON, but engine not running.
Before blue resistir 0,4R (11,8V)
After blue 0,4R (9,3V)
Before grey 0,6R (9,2V)
After grey 0,6R (5,8V)
Between T1-T15 (4,6V)

These actual readings from 1 of my cars (W116)

Jenno1981

Thank you Revilla, those values are going to be huge help and probably save me a lot of time searching for them!

Thanks again.

Eamon
1978 450SEL - Green
1999 ML430 - Also green 🤷�♂️