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Starts/Runs Sometimes, Sometimes NOT

806 views 10 replies 5 participants last post by  Fonzi 
#1 ·
So I bought a real pile of junk 1993 300se m104 3.2 w140 with a no reverse, a salvage title and a cheap body kit with a rattle can flat black paint job. The interior is actually nice, but I bought it thinking that for the price, the m104 will be nice to have around.

I was able to drive the car across town on at least one occasion, but driving it back, it died on me and I attributed it to running out of gas since I did ultimately get the car back to the shop after pouring gas in.

But once back at the shop, a day or so later maybe, I made the mistake of taking it for another run. As I was turning around, driving slowly through a deep puddle, the car died. We had to drag it back and push it back into a parking spot.

A few days later, it starts right up. I knew better than to move the car.

Yesterday, no start. It did the same thing that it did before, giving me a little combustion right as I let off the key almost every time. I thought this was strange behavior.

I realize this car has a lot of electronics, a biodegradable wiring harness, no reverse and a salvage title. But I am incredibly curious as to what the hell is going on. Is it likely to be a wiring harness short? Everything seems normal when the car runs. And the car hasn't even moved since it was last started.

I read something that seemed strange and may have been similar to what I've seen. Adding just a few ounces of fuel to the tank and the car starts. Huh? Is there a vacuum line I'm filling with vapors or something?

I'm sure I'm not the only guy with an intermittent start w140.
 
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#2 ·
You show that you own 5 MB's and have posted almost 19,000 times in 6 years for an average of 8 posts per day. I would think that by now, a little knowledge would have rubbed off. However, take a look at the "Search" feature and try a few words. Sounds like fuel might be your first problem. Splurge and buy 10 gallons of premium as a start.
My second thought was why did he buy this car?
Anziani
 
#4 · (Edited)
Thanks guys. I honestly hadn't even thought of the fuel pumps. I jumped to the conclusion that something like a Klima relay or something like that went bad. I've had a lot of MB, but this is the newest one I ever bought. I think I'd like to put an m104 into an older MB like a w111 or w108. My friend has a warehouse that's currently full of about 20-25 parts car grade vehicles. We honestly look at the w140 as a complicated electronic beast and love the old points ignition cars with very simple fuel systems that we understand far better than the black magic of vehicles with crazy witchcraft like O2 sensors and working air conditioning systems. ;)

Edit: here's the only other thread I've created in this w140 forum of space shuttle grade complexity. ;)
http://www.benzworld.org/forums/w140-s-class/2737202-uh-oh-am-i-going-regret.html
 
#5 ·
I'm gonna chime in with fuel system as well. The fuel pump and filter are on the bottom of the car, and there's supposed to be a plastic cover over them which may not be there anymore. Driving through a puddle may have messed something up or aggravated something already messed up. Have a look at the pump and filters and see if anything looks obviously wrong.

I'd definitely put a full tank of premium in there along with some good fuel treatment/stabilizer to kill any moisture that may have accumulated also.
 
#6 ·
Have any of you guys had that strange behavior where the engine seems to combust right as you stop cranking the starter?

The last time it started right up was right after taking the battery off the charger. So I was wondering if maybe a weak battery could be a major issue in these cars, like maybe spark only happens when I'm not sending all the juice to the starter anymore.

I like that fuel pump theory with the puddle, but last time it fired right up, the car was sitting in the exact same (terminal?) parking spot it is in now.
 
#8 ·
I will charge it up again and see if history repeats itself. Maybe I will just try it with a freshly charged jump box first.

(I know. Key out when flipping the switch on that jump box, just like you should connect cables and then start the jumping vehicle before sticking the key in when jump starting one of these. I had to learn that voodoo with my k-jet 1992 500sl to assure I didn't feel like a blew up the computer every time I connected or disconnected a wire. I believe the protocol is the same despite the fact that this is motronic, not k-jet.)
 
#9 · (Edited)
It seems it was the cap and rotor were all covered in corrosion all over the contacts. Sanded them up and the car seems like it's going to run fine for a while.

Edit: I was really thinking that there was an issue with the computer because after starting the car and Les sting it run a while (only after what senses to have been a lucky start with lots of cranking to get the engine going), as soon as I touched the gas pedal, the car died.

In hindsight, I'm guessing that the spark timing simply gets a little advanced when not at idle (as spark at idle will often be retarded). That would make the spark occur at a different location on the rotor tip where it seemed to have far more corrosion on the leading edge (where spark would jump when the charge is fired from the coil advanced).

If this is my theory about why the car would run sometimes and not others, I would have to say that the motor dying at virtually any time without warning would only make sense with something like automatic climate control that would kick on the AC which would advance the spark even at idle. I don't know when the AC is going to kick on in this car.

Anyway, it seems to be running once again, and seems to be that common, sideways distributor cap full of condensation junk, just like my 1992 m119 500sl, and the m103 1989 300te wagon that's given @rwd4evr so much trouble.

I say, "if you have any running issues, and you've got one of those sideways distributor caps, check it early and often."
 
#10 ·
This may be way out in left field, but you can have it for free. When I brought my first w140 home I stopped at the store for a moment. When I came out it would crank and crank with no start. Never did it in test driving. Odd thing was every time I let off the key it would fire once and then die. Call wife, get ride home, look on benzworld, possibly immobilizer. Back to car go through lock-unlock sequence, then it starts right up and runs perfectly. Is there any way the theft prevention immobilizer could be getting activated? Maybe weak battery in combination with worn mechanisms etc?


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#11 ·
I don't know. We did think of that (due to the combustion at the end of cranking) and assumed that an anti-theft immobilizer. That's why we put the spark plug wire and spark plug on the cap in place of one of the wires (and got consistent spark). Since it started and is now running nicely after doing nothing other than cleaning the cap and rotor, I have to assume that there's no theft immobilization.
 
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