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

Will check today.

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

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).

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

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

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

also, alternator tests 13.74 volts at idle and maxes out around 13.80 at higher rpm.

another thought was plugged cat. there seems to be a leaky joint below the exhaust manifold and not much exhaust coming out tail pipe. could it be excessive back pressure, or exhaust leak?

anyone?

hello,i see many great points,have any of you checked for a defective electro hydraulic actuator,its designed for helping with cold starts,it can make the engine run horrible when its defective,hard starting,engine bogging down,popping in the plenum,backfiring,a strong smell of unburnt gasoline,try unplugging the sensor its located on the rear side of the fuel distributor,its a black box with 2 large flat head screws in the top,with a 2 prong electrical connector facing the fuel injectors,please becarefull when loosening the screws,this actuator is under high fuel pressure.release the fuel pressure by loosening up the cold start valve fuel line on the fuel distributor,make sure to have rags to absorb the leaky fuel,there wont be much at all,check the continuity of this sensor,it is a very costly new sensor up to $350.00,you can buy a quality used one for $50.00.good luck.