300E will not run when warm:
 

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. :cool:

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.

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?

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.

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.

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!).

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

negative. same issue...though now worsening.

now at idle, once warm, it will stutter, recover, stutter, recover. according to the economy gauge its just dumping fuel to recover, why it is losing fuel i have no idea.

now the battery is junk, so today i have it hooked up to a charger, started it, then went to disconnect the charger and it began to stall, hooked it back up and it idled fine. is this an alternator problem? or some massive electrical drain somewhere? once idling, if you turn the headlights on, it stutters. could that be the extra load on the engine via alternator, and therefore the same original issue?

this only takes place while warm.

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.

What is it with these mercedes and problems when warm . Did they design them to run in the cold even out of gas.:)

Mine runs when warm , but wants to be coddled. When cold it thinks its a race horse .

Darn Benz designs them for the freezing German winters . Sorry for venting but I see a lot of unsolved problems with warm Benz's.

Did Treetrimmer give up . I have been trying for 2 months now . Hang in there everyone . Pray for an Ice Age

Until the engine is warm and the o2 sensor comes on line, I don't believe any electrical components affect the fuel distributor. After that, it's all eventually thru the EHA. The cold-start injector might be the exception.

tried this one today because it seemed to match. unplugging the sensor is the test, correct? after that it should clear up? i did and there was no change...

The EHA is effectively "unplugged" when the engine is cold. It does not come to life until the engine is in closed-loop mode.

I'm not convinced of this. In fact, when my W124 (with 103 motor) was still quite new, the dealer replaced the EHA under warranty in response to hard cold start symptoms. Cleared up the problem. Moreover, according to the FSM, the purpose for the EHA is fuel adaptation in all of the following conditions:
(1) start enrichment; (2) post-start enrichment; (3) warming-up; (4) acceleration enrichment; (5) full load enrichment; (6) decel fuel shutoff; and (7) Lambda control. Pretty much everything involving proper fuel management.

The EHA receives no signal from the computer when the engine is first started cold. Have a look at the lambda (or the voltage to the EHA). You will see it come to life after the O2 sensor is warm enough to provide some information for the computer to work with.

Or unplug the EHA. The car will start the same when cold, EHA unplugged or not.

The system is basically mechanical. The EHA only fine tunes the mixture. The engine will still run without the EHA's influence. It's a pressure fuel-injection system, just like on airplane engines - which have no electrical input at all, BTW.

190E 2.6 runs great until warm, then stalls and won't restart until cool...
 

It pays to check the normal wear items first- even if they look ok....I took a gamble and paid $800.00 a week ago on a '92 190E 2.6 Sportline 5 speed that had the dreaded "when cold runs great, after 10 minutes running and warm, dies and won't restart until cool" syndrome. I had noticed the PO had spent a bunch of cash replacing virtually all the items that are typically suggested in the various MBZ and 190 forums...ignition control unit, crank pos sensor, OVP, coil and even the computer- all to no avail and had ultimately given up and just put the car up for sale as-is. The one thing I noted that hadn't been replaced (and occasionally mentioned in the forums as a culprit) was the simple cap and rotor...

Today, with another $80.00 invested in a cap and rotor plus 20 minutes of my time, it's now running perfectly...the best $800.00 car I've ever lucked into! The other clue to me was that when it was warm and wouldn't restart, it would crank in kind of a "notchy", irregular way (that it did not when it was cranking cold) and that made me think it was ignition and perhaps cap/rotor related. Hope this is helpful info...

J.G.

I had about the same problem on my 89 300e. Found it was a bad connection to to O2 sensor under the carpet in front of the passenger seat. twisted the connector and now runs like a champ.