Hello, new member here but it looks like an excellent forum. I've just acquired a 1988 300E that starts fine when cold but sputters-out as soon as it warms up even a little. In 70 deg. weather, about 5 minutes or less. I have not dug into it yet but just wondered if this sounds familiar to anyone who might have a strong hunch.

I tried to do a search but the terms of my question are so common that I get a zillion random threads w/ either 300E/warm/dies/etc. in them. I know what an OVP relay is, what is an EZL? Where is it? TIA.

EZL is the German acronym for the ignition control unit, located on the left inner fender wall. Black plastic assembly with a vacuum hose and three electrical connectors attached.

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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

Have you found a fix to your problem? I dont mean to hijack your thread but I have the same vehicle with the EXACT problem and am striking out on the cause.

Engine temp sensor (at the back of the head)? ICU?

Does it restart after it stalls, or do you have to let it cool off to get it running again?

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1989 300E 144K

OVP (over voltage protection) relay is located behind the battery ... remove the battery and black plastic cover to access it. Also, it's possible the CPS (crank position sensor) is bad.

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Fred Hoelzle

If it were the temp sensor, would the temp. gauge in the dash be inaccurate? because it seems normal. I have not tested the ICU yet, Im hoping it doesnt come to that.

It will sometimes restart after it stalls depending on how warm it is, but generally you have to let it cool down again to get any kind of load on it (put it in Drive).

Will check today.

I'm also going to dig into the 02 and MAF sensors because the whole open/closed loop thing.

I would remove the fuel pump relay ,jump the pins for a pump direct operation,this will isolate any FP Relay faults if any, next to check would be the CPS . The OV relay faults cause cold starting symtoms.
I have oft repeated this ;Do replace the Fuel and voltage relay along with all the old fuses and the car will be very dependable . These three items are the major cause of unreliability ,mostly due to age related wear and tear.I had resoldered mine .
I hope this helps
regards
mak

No, there's a different sensor for the gauge in the instrument cluster.

Good advice from mak on the fuel and OVP relays. Both can develop bad solder joints, just enough so that they break contact as they flex from heating up. So, they seem fine when cold, but unpredictable when warm. They should both be considered routine maintenance items for replacement, along with plugs, wires, cap and rotor, air and fuel filters.

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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

As an update: the fuel filter was replaced and it seems to run better now, however still with issues. Once warm, it can be driven but stutters off the line, if you were to apply pressure on the pedal conservatively it will die, but if you really get on it it will take off, sputtering until it reaches 1000 rpm and then will run perfectly. it certainly seems to be a fuel issue.

Under 1000 rpm once warm is where the issue stands and is very consistent.

does this sound like an ovp or fuel relay issue? if so, can you help me a little more with details on their location and testing. I realize the ovp is behind the battery, but which is it? also, which pins do i jump? it is very hard to see inside their sockets.

also, does anyone know how to test the MAF?

thank you all very much for your help!

also, when removing the air filter housing i noticed the vacuum line to the EZL was detached (possibly as a result of removing said housing), closer inspection revealed the line to have obvious leaks. Once replaced it seemed to clear out entirely, but then on another test the problem recurred. Coincidence or part of the issue?

after confirming it is not the fpr, and hours of researching on here, im skipping to the fuel pump.

fuel pump replaced....same problem.


now I am in the intake system looking down the first valve beneath the air cleaner and there is fuel in between there and the next valve, i suppose that is the throttle body? should there be fuel residue in there? if not, where would it be leaking from? and is the only way to get in there to remove that entire unit, including the fuel distribution unit attached?

Thanks again for any help.

I had an odd problem like this last year. Turned out to be the rotor (which tested good!).

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2012 E350
2006 Callaway SC560

Any luck yet? I've got a 2.6 that has been sitting in the yard 3 years (!) with basically the same problem. New or tested good fuel pumps, fuel distributor, crank sensor, OVP, coil, distributor and rotor, etc............

Now it is at the point that I can pour fuel in the intake and it runs fine, but just turns over otherwise. I have plenty of pressure at the fuel distributor. WTF is going on? I'm ready to push this gas powered POS in front of a train. What (electronic) components directly affect the fuel distributor's operation?

Thanks,
Klaus

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‘84 300TD “Mountain Goat”
'62 300d Adenauer-350 Chevy - "Max"
'15 VW Passat TDI
'16 Dodge Ram 3500 - Cummins w/6-speed
'68 Mustang fastback
'55 T-bird
‘63 Studebaker Hawk