1994 E320 (M104) No Start - Common Causes?
 

I bought a cheap 1994 wagon, installed a used radiator and started driving it. It had an occasional no-start condition which has now become a constant no-start condition. What are the common causes?


It has about 195k miles, and fuel consumption seems to be high - used about 3/8 of a tank over just 100 miles or so.


I can think of a fuel pump or fuel pump relay failure, are those common?


How about crank shaft position sensor? How test, or just replace?


What else are the typical causes and how do I test?

Sounds like this is a crank but no start situation, yes?

Fuel pump relay yes, check for voltage at the pump or jumper it.

Crank sensor yes. Does the tach bounce even slightly when cranking? It should. They usually fail to start on a hot vs cold start, check it with an ohmmeter and tap on it with the plastic end of a long screwdriver to see if the readings become erratic, they shouldn't.

Good luck!!!

Thanks, I'll check to see if tachometer bounces while cranking. Where is the CPS? I know very little about this engine, first Mercedes gasser ever after many years of owning diesel powered cars.

Fuel pump relay behind the battery, right?

CPS is at junction of bellhousing and back of block around starter IIRC.

Fuel pump relay, yes behind battery.

Good luck!!!

It cranks but won’t start? I’d look at the fuel pump, all my fuel pumps have died around 200k. When you turn the key to the on position do you hear the pump running?

Yes, cranks but no start. I have not heard the fuel pump before, so I'll have to get a family member to help me check for noise.

While cranking have someone tap lightly the overvoltage relay behind the battery,its the 1x1 inch relay with the fuse in the top, it supplies power to ecu =hfm control module, tapping on the relay may get the relay if its not working to supply power, next the fuel pump relay is to the side of the battery its green, the fuel pump relay can stick too.

Check for voltage and good ground at the fuel pump if it doesn't run.

Failed fuel pressure regulator leaking fuel into the intake manifold and failed purge valve leaking vapor into the intake manifold. Either or both will flood the engine causing a no/difficult start. Very common overlooked problems.

Double check the OVP relay as well

Is the no-start condition a complete no start or just longer and longer crank times before ignition? Bad CSS that car won't start at all (including the EZL 99% of the time) Longer cranks might be a leaky injector...my two cents based on what I've read. Also, not sure if there's a check valve or not on the fuel pump itself on the 124 e320s. Also could be a starting issue.

A friend suggested using starter fluid to help determine if the cause is lack of spark or fuel. The car started immediately with the starter fluid, and while it was idling I looked under the car a found gasoline dripping from around the cover over the fuel pumps. so I need to figure out and fix the source of the leak.

Ive had extenisive exp. with similar issues of no start, on an intermittent and increasing basis. I confirmed it was fuel supply by using start fluid which fired the engine right up. But I never had the excessive consumption you have.

Yes check the relays to the pump and fuses..And that OVP relay is a common cluprit on these cars. It kills everything.. But if yours cranks its likely not the OVP relay. Try starting fluid and it may fire right up.. Then check the pumps.

This car has dual tandem fuel pumps and they fail intermittently and will work when tested then not work..And both will fail at the same time. It will run on one only and I suspect failure is often the little check valve becoming obstructed with corrosion out of the tank..and this s pre-filter so you might pull the pumps and test and just clean or change the check valves before replacing. Theyre both very easy to remove and replace..

Correct, there are two pumps. I used starter fluid, after a couple tries it started up and ran fine.

The fuel leak was at the banjo fitting on the filter. I put in a new filter, new copper washers, fixed the leak. Drove the car around a bit. Shut off and restart just fine about seven or eight times. We'll see tomorrow morning when it's cold.

Could a simple fuel leak, just a drip drip every second or so, cause a no start when cold? Doesn't seem like that would be the cause.

Car started just fine this a.m. when stone cold, ambient was about 45 deg F.

Could the no-start have been caused by an old plugged up fuel filter, or the fast drip leak, or is this still an intermittent problem?

Both fuel pumps were running yesterday, I need to put my mechanic's stethoscope on them to hear them running.