1993 300E 2.8 ......hot afternoons
 

i live in the desert, and my 1993 300E 2.8 gasser is hard starting after setting in the heat all afternoon.

it starts well and runs fine until the hot afternoons hit. hard starting and surges after it does start and you're trying to keep it going.

thanks........

Is vapor lock still a possibility on the W124s?

Vapor lock is a possibility if it has a fuel accumulator that is bad or a bad check valves on the fuel pump(s).

check the vacuum line to fuel pressure regulator on fuel rail at the back of engine to see if broken or has fuel in it.your regulator may be byby.

father bob (Padre?),
had a 1993 300E 2.8 with a very very similar issue. Turned out to be a common problem component according to the dealer. A bad overvoltage protection relay starting to go bad, showing up as intermittent starting problems when engine hot. On a cool morning, no problem starting. Hot engine in the afternoon, rough start or no start at all, just cranking. Again, intermittent. After a new OVP relay, all was well.

300E similar problems
 

I have a W124/M106 engine. Similar problems. Done so far:
New OverVoltage relay, new fuel line check valves, new fuel filter, EHA replaced. (Mechanic said the fuel pumps were OK.)
Tune up. Injector cleaner (helped somewhat.) Good gas (though cannot get the grade the book recommends..... As only 89 or 93 octane available, and book calls for 91 octane.)

Cold start: Cranks at the touch of key, no pedal. Then RPM dips for a few seconds, then OK for long time.
Park in hot sun: Cranks at normal speed. Fire on plugs. Not starting. Wait & wait. Still same. (If I wait 20 minutes, then it will start.)
But.... open the valve cover-to-air cleaner tube, spray a few seconds some ether/quick-start, and presto! Starts right up !!!!

Have suspected the "7th injector" but not sure. This injector has voltage at start-up.

What purpose does that vac line serve? I thought it was just there in case the fpr was faulty and leaking fuel? I'm asking because mine is unhooked with the hole plugged on the large tube going to the air cleaner for "technical" reasons.

Engine/ coolant temp sensor?

The FPR is connected to the manifold vacuum, it pulls back the FPR at idle for lower pressure in the rail and goes to full regulated pressure at the rail with no vacuum aka wide open throttle.

Talked with mechanic
 

OK, the beast died in a 113F Kroger parking lot. Just would never crank. Even with ether assist. Towed home, tried in the morning, and presto! Started in first click of key.

I drove it to the mechanic. (He loves puzzles!) I asked him about the vacuum regulator and the small hard tube to the rubber valve cover/air cleaner tube. He said that this does not pull vacuum, but is there to vent raw gasoline in case the vacuum regulator fails.

We have heat-index in the 100s this week. The mechanic has the car.
Time will tell, and I hope to post a success story.

Is it a possible EHA maybe? Stalling out in the desert in the middle of summer is no fun....and we haven't even reached summer yet!

This car being discussed does not use the K jetronic, its the HFM - EFI engine - same as a 97 C280 engine.

Had the exact same problem here in vegas (HOT) Turned out to be the coolant temp sensor was bad.With this bad info going to the computer it did not have the right info to give the cold start valve,so when warm it would just crank away with no start! Mine is bosch KE but I think that part of the circuit works the same:)