Cold Start issue in 91 300E
 

Hey everyone, well I've been having this issue for awhile, when the engine is cold and has sat for a long time it has trouble starting. Sometimes it'll stumble, then catch or stumble, run and be on a few cylinders but then after 5-6 seconds they all come on and it runs fine OR will sound like its not going to start at all but once you give it some gas it eventually does start right up. When the car is warm though it has no problem starting right back up. Sometimes even when it is cold it will start right up, just fine!

I thought it was spark plug wires because mine were tore up from the floor up and at night I could see sparks coming from them so I knew they were bad. I went ahead and replaced them as well as the spark plugs with bosch made in Germany plugs. It did help but it's still having trouble with cold starts. I'm taking this car on a 2,000 mile trip on the 9th so I'm wondering what it could be, what do you all think?

Since you are not having any problem with starting the car when it is hot, then I suspect that your cold start injector may be intermittently working. There are methods to test it. This part is no longer available from the typical suppliers, but a few still have some in stock should you need to replace it. Try searching to forum for 'cold start injector/valve'.

If your 300e is one with a M103 engine (12valve) - then check the OVP and the fuse(s) on it.

Thanks for the reply! Do you know where its located on the m103 engine? I will search the forum and see if I can find anything! Thank you!

How do you check the OVP? To see if it's in correctly or should I check the output or take it apart?

hello,definatley replace the ovp,its located behind the black plastic shield,located behind your battery,the cold start injector could be an issue,but most likley you may want to check the eha,its located on the back of the throttle body its a black square sensor with a 2 prong plug facing passengers fender,these go bad and cause cold start issues,its $250.00 new $40.$60.00 on ebay,if its defective you will want to replace it and have the air fuel ratio adjusted.,most common diag for a defective eha is a strong smell of fuel when starting,and hard cold starting,with ruff almost stalling idle,after 20-30 second the idle will level out.good luck.

Thanks for the reply! I definatley want to change the OVP but it won't be until after this trip due to it being 200$+ the symptoms of the bad eha sound very similar to mine, I do get the gas smell when it starts really ruff but I always thought it had something to do with my tank vent valve which is missing lol the idle can be seriously rough and it won't run on all cylinders for around 5-6 seconds but then they come back on and it runs smooth.

Another thing is, this car had amazing idle, when we got it with 127,000 I always double checked to make sure it was still running cause you couldn't feel the engine, but then on occasion it gets these little very noticeable dips in Rpms... Don't know if that has anything to do with that.

The only reason this really bugs me is when it sounds like it's not going to start at all, it scares me cause I'm not sure if it will, but I just have to give it gas and after a try or two more she kicks on. And to make it even more weird, sometimes it starts just fine! LOL

I will definitely look into all those mentioned in the above posts, although I'm not sure if I can afford to replace them until after this trip to Texas. :(

The OVP has a fuse or two in top - depending what revision you have.
They are not $ 200.00
You can get a second hand one cheap from that great auction site to test out. If this is the problem you can get one here - forum sponsor for $80.00

see this : http://catalog.peachparts.com/ShopByVehicle.epc?q=1991-Mercedes--Benz-300e--Base-Body--Electrical&yearid=1991%40%401991&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6195%3AMBC|1507%3AED|10 000013%3ASM|20%3AEB|613%40%40300E+Base&catid=241959%40%40Body+Electrical&subcatid=242003@@Overload+R elay&mode=PA

my mistake i was thinking of the eha,$250.00 new,used $40-$60,the ovp brand new is only about $25.00. you issues sound exactly like mine,then i replaced the ovp,and eha,then had the air fuel ratio recalibrated,small things, like a jigsaw puzzle 1 piece at a time,sometimes unplugging the eha can over ride it you may want to unplug it then see how it runs,if it improves stlightly then leave it unplugged till you can get it fixed,it controls engine lean and rich conditions upon starting.

Wow. I have a '91 300E and it does exactly what this thread is talking about! I usually have to take out the plugs, dry them off, let the gas evaporate, spray some starter fluid into the plug holes and then go for long, extended cranks to get her going, but she eventually does and then smooths out and idles perfectly. I have noticed that this happens where I live (So. Cal, Orange County) when there is more moisture in the air and it gets cool. During the day, it starts on second crank of the engine. I'm wondering if it is possible to clean out or repair these EHAs because they are $265.00 from *********.com. Any thoughts?