Any help greatly appreciated-no start after changing spark plugs and coolant sensor-read on other posts but just feel a bit lost here. The fuel distributor is leaking somewhat as well- so i bought starter spray to eliminate the FDand sprayed into meter plate but nothing. I checked spark by pulling a spark plug and grounding on the exhaust manifold and it was present but I read(this forum) that is not a full-proof test of spark. The rotor and cap, coil, spark plug wires have probably never been changed in at least 10 years but this occurs just after i relaced the plugs?? I put the old plugs back in (platinum) still no start. Thanks guys.

update-I changed the coolant sensor one minute before spark plugs and it appears some coolant spilled on to the crankshaft position sensor that now appears quite wet in that area/connection. Could I have done something by getting the Crankshaft position sensor wet that effect ignition,coil etc?

What kind of plugs did you use?

The M103 engine requires H9DC0 Bosch NON-RESISTOR plugs....generally only obtainable at a MB dealer or from this site. If the distributor rotor/cap/wires/coil are all original, you can start there. These are picky engines, and need to have the right stuff on them to run properly....but when they have the right stuff, they run smoooooth.

Platinum plugs should NEVER be used in an older MB engine.

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I edited my post to say that i also changed the coolant sensor and some coolant seems to have leaked on the crank shaft position sensor as it is quite wet in that area. Could that effect my ignition?

the plugs I put in where Bosch super plus-HR9 DC+ It had platnums but it ran. Would it at least not fire? Thanks

The plugs you used are Resistor plugs.... HR9DC+.....you'll have to go to the dealer or this website to get the right ones.

It should have fired and possibly run, but not if the coil/wires/rotor/cap are not perfect. It is harder for the ignition system to get a decent spark with resistor plugs....so if it is weak in any way, it won't work. As you have mentioned all those parts are real old, you should probably replace all of it. I did on my 300E and it runs perfect now.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Ok will do that and replace all. Is there a way to check the coil spark quality other than disconnecting and looking for a fat blue spark? Do you see any connection to coolant going on to the crankshaft position sensor and having an ignition effect somehow? I m accepting your advice just a bit perplexed it will not pretend to fire up for a moment but I took in your advice regarding the resistor plugs especially. Thanks again!

PS would you recommend an in-line test of the spark plugs to confirm your feelings. I read i can buy a tester and check spark quality with plugs actually screwed in to the motor-would be nice to have confirmation.

Coolant on the crank sensor shouldn't affect it, unless it was cracked or something.

You can test spark with either an O-scope or an in-line tester. There are open, adjustable spark testers you can use, or sealed units. I don't work on small engines, so I have the sealed one from matco.

I tried to link, but it didn't work.

Just go to matcotools.com, search for "spark tester" and click on the first link. It'll show you both types.

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Ok on web site and perform the test of the spark. Could my timing be off-read about the rotor actually breaking but would seem very odd it ran then not just after replacing plugs. perhaps the new resistor plugs put a strain on the old coil, wires, rotor etc which have most likely have never been changed. Thanks again for your input and advice!

If your engine was running before the plug change, it should run after the plug change regardless of platinum/non-platinum or resistor/non-resistor. May not run optimum, but should run.

If the only abberation in the job was wetting down your CPS, and it will not start, that is your problem. UNLESS of course you did something else like bollix your plug wires. Did you cross them? Did you pull on the wire to remove the connector rather than pull on the connector?

Anything you aren't telling us?

excellent questions even though i am no expert. The other issue was the fuel distributor which was leaking as the plug on the pententiometer had slid off somewhat but this happened before and it ran. I figured I should take the FD out of the equation so I used starter spray to eliminate the Fuel distributor issue entirely if i have a possible ignition issue-maybe I have not eliminated the FD?

To be honest, i was a bit awkward with the plug wires turning the socket wrench catching/pulling/knocking the wires at times as instead of disconnecting all of the wires at once I replaced one plug then replaced the wire then on to the next plug. I checked the wires for possible mix up but it seems quite difficult with the wire lengths to cross over but I may have done that in one cyclinder perhaps closer to the front of the engine. If it is the wet crank shaft postion sensor-would it be a case of simply disconnecting and cleaning it off? Thank you very much!!

update-wire connectors were very difficult to unplug now a few seem sloppy-moving back and forth-dont think that was the case b4 plug change.

I must admit ,especially to rocky raccoon, that i pulled very hard to get the plug wires off-Now the wires are sloppy in comparison. Perhaps many years since plugs had been changed.

O.K. Now, one more thing and please don't take offense. I have the impression you may be inexperienced on MBs.

Admittedly, I do not have the same model as you but almost all of the gas Benz do NOT use the threaded-on cap at the top of the spark plug. The plug connector is made to grip directly onto the threads. If you have the caps on the plugs, unscrew and discard them and you will find the connectors will fit easily and securely with a little push.

It is possible you have damaged the plug connectors by pulling on the wires instead of directly on the connectors. A simple pliers-like tool made for pulling spark plug connectors is available a very low cost at any chain auto parts store.

Let us know how you make out since it adds to the data base.

No experience with MBs at all-replaced the OVP relay to get the car to start cold but thats it apart from leak on the washer fluid pump. I checked the old spark plugs and they still had the caps on but what you say makes sense. I did pull at the wire connector housing ,not on the wire, but I did have to pull very hard. Thanks again!

Will of course try plug without cap and post result.

If it has spark, gas is making it to the cylinders, and the cylinders have compression, and it's in good timing it should make at least some indication that it wants to start. I might be wrong, but I think the CPS just let's the computer know what the RPMs are (I think I'll start my car and unplug it to see if it stalls, obviously I couldn't drive it, but it might start or run?). Anyway, I would be surprised if the CPS had anything to do with it.
But a weak spark might be a problem.

The plug wires on these engines should really only be removed with plug wire pliers. Obviously it can be done without them, but they are on pretty tight and deeply seated, with time and heat they can be clamped in there real tight. If you grab them at the wrong place and pull them it's very easy to pull the wire out of its metal connector as it comes off. In many cases the wire will still work by arcing to its connector inside the boot, [perhaps] creating a very weak spark.
Likewise, even if you don't yank any wires out of place, the boots need to be pushed ALL the way in until they are tightly gripped on the plug and all the way forward. It should feel pretty firm laterally as well, that is, they should feel relatively stiff when wiggled side to side. Once again, failure to do this could mean that the wire connector may not be in contact (or tight contact) with the plug terminal and [perhaps] causing a weak spark as above.
A combination of the two is certainly worse yet.
I say "perhaps" in brackets because an arcing spark can sometimes (if it's not arcing too far) actually intensify the juice to the plug. In the 50-60s they used to sell "spark intensifiers" that went on the ends of the plugs ahead of the wires and were basically just a measured gap for the spark to arc across. Some kits had transparent tubes so you could watch your poppin' engine give a light show. I once had a mopar with a fouling plug and temporarily pulled the boot away from the plug so the arcing spark would make the plug fire hot enough to keep it from fouling until I had the time to fix it.
Actually, with that in mind, it might help to have someone crank it at night and see (and listen) if there are any wires arcing.
Make sure the coil wire is secure on the coil, look for grey/black chalky marks on the coil wire where it comes close to/touches metal engine parts. Also, if you did the job on a rainy, damp day maybe the dist. cap got damp or is arcing out along a trace or a crack. Lastly, if the dist. cap is 20 years old the carbon center contact might be fouled or just about worn out.

All weak suggestions I know but might possibly help.

Thanks long gone. Will have to check that tomorrow night. My connectors do move from side to side and have been advised to unscrew the caps of the plugs. Do you think it would be wise to pull the spark plugs with the connectors and check for spark on every cylinder? I assume this would tell if the wires are damaged but perhap not totally. So far i have only checked one spark plug and grounded it to the manifold and saw spark. Thanks for all the great info and taking the time ouf of your evening to reply-I will reread to take it in better.

Long-gone-Ok on arcing-so will perform test as you suggest-seems my test will not be that useful if a weak spark.

Actually it's kind of hard to imagine that the car wouldn't at least try to start even if you messed up half of the wire connectors. I'm inclined that there's something else up with it.
But, maybe you ruined 4 or 5 of them, I don't know, sounds like you weren't exactly gentle with them. One other thing came to mind, when you put in the plugs the seats in the heads should be as clean as possible so they seal well and don't leak compression (and hopefully you remembered to tighten them) , but again you'd have to mess up more than half of them to be where you're at.
Just make sure the boots are pushed in tightly, you can kind of feel them lock onto the plugs. As far as the plug tips, I don't recall whether mine are on or not, I'd have to pull a wire and see, though I have no reason to doubt that they might need to be removed. Look at your old plugs, it ran okay before I presume, are the tips still on them?
It might be hard to tell if you pulled a wire out of it's connector. Maybe take a good look at the wires where they enter the boot, if it's real clean for a quarter inch or so that might mean you pulled it out. Maybe the spark tester would be a good idea, I've never used one.
There are 190's and 300Es showing up in the junk yards pretty regular now, especially after the cash-for-clunkers program. I got a set of Beru wires in their plastic cover with a cap and rotor for $10. They were virtually brand new. Maybe you could find a decent set that way (grab the coil too) and swap them out at a tenth of the regular price and see if that's the trouble.