I had an identical situation a month ago. However in my case I had been replacing parts (Fuel dizzy, EHA, injectors, etc). Drove it for a few days and then one day just wouldn't start.

Its pretty much gotta be 1 of 2 things: Fuel or Ignition.
Assuming your airflow plate is moving freely?

I confirmed the fuel pumps were running and even jumped the relay to manually keep the pumps on with no change in starting.

I pulled a spark plug and it was BONE dry.
This indicated to me there was probably spark, but no fuel going to the cylinders.

I Jumped the fuel pump relay to engergize the pumps and depressed the airflow plate and nothing happened. The tell-tale "singing" of the injectors wasn't there. They make a distinct sound with the pumps on and the more you deflect the airflow plate (you will be flooding the cylinders).

I opened the fitting on the side of the fuel dizzy for testing fuel pressure with a 12mm socket, relieved all the pressure, closed it and tried again. Fired right up.. Never done it again.

Maybe the EHA was stuck? or the DPR?
Got me, never done it again, but I re-adjusted fuel pressure differntial after that.

Pull a plug first: Wet = ignition or flooding. Dry = fuel flow.
Wish I could be there to help.

__________________
*****
Thomas Johnson
Phoenix, AZ USA
1988 560SEC

He took the air filter cleaner off and he said it was like it was spring loaded... it went down, but came back up.

Update - We checked and its getting fire to the plug wires. I dont know if he removed the plugs to see if they were gassy or not... I will check.

Nope, dont have a fuel pump jumper or any wire... maybe I can find some.

edit - I have discovered that this is actually the A/C relay by another forum and the poster below - thank you.
Anyway, is this the fuel pump relay? I just removed it and took a pic of it. (It was the one closest to the brake booster). Appears its been tested/replaced before... is there any way to test these?

To recap... we have fire to the plugs, fuel pump is "hissing" when switch is on... car will "try" to start, but will not. Maybe at this point replace the fuel filter and see if thats any help?

Thanks once again!

Another update - put the relay back in to try to start (someone said it could be the alarm system malfucntioning causing it not to start, but I dont think so on one this old- disabling the fuel flow), but it did finally start and run good at idle, but it would miss and stumble on acceleration and exhaust smelled strange. I turned it off, then it would not start again.

That's the A/C compressor relay, not the fuel pump relay. Should be right next to it, though.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Thanks. Yeah, someone on another Mercedes site informed me of this as well... I had forgot to edit.

Guess we are going to get a new rotor for the dist cap tomorrow and see if thats the problem... if not, going to try to purchase a used FPR and go from there. Seems like it could be so many different things.

The rotor is cracked and looks burned... going to replace and go from there....

I've been following this thread and I hope that fixes your problem. Of course the first thing to check is the basics, but sometimes that's hard to get across and people tend to think it's something more serious.
Here's a rotor that worked fine for a long time then one day the engine wouldn't re-start.

Good luck.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Wow thats bad. Well, that apparently was not the problem. Car is still running poorly and missing. He had to "prime" it to even get it to start. I am betting its the FPR... but hate to pay $90 for a new one if thats not the problem. Mom needed the car like yesterday. Oh well.

Did you try putting a jumper on the fuel pump relay to run the fuel pumps so you could verify if the relay is bad?

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Well, the car may not even be worth repairing by the time my dad gets done with it... messing with things he dont know anything about. Went out and he was about the remove the gas lines to the FI system to check for pressure, etc. I told him that here and most other sites are telling me that its 90% likely that its the fuel pump relay. I am going to get him to call my uncles Mercedes mechanic in South Carolina... supposedly the best there is.

most likely it will turn out to be the fuel pump relay if its still the original old one.
For testing i had replaced mine ,a 9 pin with a !0 pin one .it worked perfectly except it will have a lower cut off point of 4500 RPM ;4 & 6 cylinder variations
mak
300se

Thanks. They had tested that and apparently it was OK. They "jumped" it somehow and the car still would not start. It was funny... some days it would not start at all... some days it would idle rough, some days it would idle fine for 20 minutes, but when you gave it some gas it would start missing, then stall out, etc. New coil and its ran fine... he drove it all over today, then I drove it about 45 miles this evening when I got off of work. I dont know, I hope that was the problem... no one knew, could not find any good mechanics to check it, closest MB mechanic was 30 miles away (and would probably have charged $600), etc. LOL, one mechanic told my dad that it probably had broken the timing BELT. I told my dad that car didnt have a timing belt. Only thing now is that there is a gas smell coming from the gas tank cap area... I guess the cap seal is bad... so bad that fumes come in the car... none under the hood, so it has to be blowing back in. Guess a new one is in order. Just wondering if an aftermarket one would be OK, of if I should purchase an OEM one here for $18.00.