I am needing help on what might be the problem on not starting in the mornings. It rained last night & was raining this morning when I intended to leave. Well, forget that. It wouldn't start. I did a lot of cranking & after several waits and retries(approx. 45 min.'s) I decided to check for spark. After hooking up test meter to no. 1 cylinder and cranking it did a intermittent try at firing up. I am not sure if the test meter bridged in had anything to do with it starting to break free or not? Then finally it got up and started running. It then ran and started ok the rest of today. I drove in the rain on a 100 mile trip and the rain didn't seem to be of any consequence to the running. It doesn't always have to be raining for it to fail. A few days ago it wouldn't start when it got to freezing for the first time this year. I have had this issue going on with it since purchasing it like 6 months ago. Would like any help here on where to try to find the problem.

start with the simple stuff.....check the battery voltage, check the ovp behind the battery, check the fuel injectors.

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1990 190E 3.0L

Cold start injector? Or maybe the coolant temp sensor? (last one on the head by the firewall).

in addition to above you may concider replacing the fuel pump relay ,
always a very weak point on these CIS engines.

mak

I was concerned if there is a test set that works for the cars like mine before the OBD II? There is a plug on the driver's side fender. Is there some kind of test set or equipment that will help to pin point troubles on these older models? I don't really want to throw monies away on it randomly. I guess, I kind of like Benz, but I don't have Benz money!

Had some time yesterday evening did some testing. Have good readings on the plug wires. Did the spray testing on the ignition system & found no show there. I am trying to search an o-scope to use on it. Can anyone tell me it the 91 190e series had the defect wiring harness or not? Thanks for your help!

Fuel pump relay issues are hit or miss. The car will either die or it will run fine, not much in between.

The engine temp sensor has a huge influence on cold starts. Measure the resistance -- it should read ~3500omhs cold and ~300-500omhs warm.

Next check all idle air hoses attached to the idle control valve for vacuum leaks. If they are hard and never been replaced, get them swapped out. Even a 1/2" crack will cause a no-start or very difficult to start condition.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Still struggling on the intermittent no start on M103. I called and talked to a mercedes mechanic in a bordering city. He owns a large mercedes shop & has been working on them for years. I started to explain the problem, and he says let me tell you does it do this and he explained about a mercedes 300e they have doing exactly the same thing. He said they have replaced cap, rotor everything & it still does it. He has spark and fuel like mine does. When it goes it has no issues, but when it doesn't it won't go. He claims they have been working off and on with it for a week to no avail.

I still think its a large vacuum leak. Have you FULLY checked both idle air hoses that attach to the idle air valve? What about the boot under the airflow assembly with the fuel distributor on top?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

I will be checking what you noted there tomorrow. The thing that has been a stickler to me, as well as, the mercedes technicians I have visited with is the total change from good runner to broke. From everyone I have talked to the M103 had ignition problems. As old as it is I am not certain factory help would be an option even. This happened to a ladies white 300e about 5 years ago. She tried to sell it to me. She had it at Europa, and they changed out every thing on it to fix it, and never got the gremlin out. Finally, John told her not to worry about it ... it's just an inconvenience. John trained in Germany working for Mercedes there at the factory growing up. I was told he lived and breathed Mercedes! It's raining here today, so I will leave it out all night, and see if the problem hits again. Rain seemed to be a contributing factor in the past. Thanks much for your help!

I checked some sensors today. The coolant temperature sensor was 2100kohms vs. spec. of 2200. It was pretty close so I decided not to replace it on my order. The biggest out was on the distributor test. I am replacing it and rotor & distributor seal. Also, while I have it open there I am just going to change the seal in the upper timing cover & cam shaft seal, & the valve cover gasket. It looked like the small leakage I had was mabe just the cam seal, but I had ordered both awhile back when I first bought it. It was in the debt of winter so I didn't get done then. Will see how these mod.'s come out. It failed to crank last evening out in the rain & hope this will solve the moisture problem.