'88 190E 2.6, 84K miles... after a one hour freeway drive and one hour stopped the engine cranked but would not start. It initially felt like no spark.

After several more attempts, it started, but ran very rough for a few seconds while I rapidly pumped the throttle, then it smoothed out, and I was able to drive off with no further issues.

The next morning on a cold start, it cranked-started-died twice. On the third try I rapidly pumped the throttle when it fired, and it kept running, but very roughly for a few seconds before smoothing out with normal fast idle, and I was able to drive off without further issues. So now I suspect it's not getting enough fuel while cranking, hot or cold.

Ambient temperatures were in the 60s-70s...no check engine or ABS warning lights, so I don't suspect the OVP, which is original.

The other suspects are fuel pressure regulator, fuel accumulator, and fuel pump relay.

For a number of years on a hot restart it will often crank-start (on all six) -die, but I figured out how to work around this by just giving the throttle a kick once it fires, which keeps it running and it quickly assumes normal idle. Cold starts up until Saturday were normal - fired quickly and assuming about a 1200 RPM stable idle in 60-70 degree temperatures.

Does anyone have any suggestions on how to go about troubleshooting this problem? I've never done anything with the KE-system other than check the duty cycle (no adjustment required) and changed the fuel filter with the last time being 9000 miles ago, and the old filter was not at all clogged.

Duke

It all boils down to fuel pressure - all the electrical things which can have trouble, etc.

So with that said, I like the idea of connecting a fuel pressure gauge, driving around, then when the problem crops up, see if there is proper pressure or not. If not, then troubleshoot from there. Harbor freight has a fuel pressure test kit with all sorts of adapters including KE.

Are you getting any codes? Next time this happens and you are at home, try removing the air cleaner housing and put a socket extension on the throttle body next to the connector and give it a few taps with a hammer.

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1990 190E 3.0L

From what you are describing, your fuel distributor is failing or has.

There is no reason to live with such a problem. As has been mentioned, there are a finite number of reasons for this. Fuel feed, injectors ect

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

I checked the fuel pressure regulator for leakage out the vent line that goes to the PCV hose at the valve cover. It was dry and held a little vacuum applied with a Mity-Vac, so I think the FPR okay.

Turning the key to ON appears to briefly energize the fuel pump, which should be the case, but it's tough to hear them.

I also cycled the connectors on the EZL since the FPR needs a pulse signal from the EZL to energize the fuel pumps during cranking.

My next job was to test the fuel pump relay, but I couldn't get it out of the socket. Is there a release tab that must be pushed? I didn't see one and didn't want to force it.

There is no check engine light and no codes. The ABS light goes out after getting it started, so I don't suspect the OVP. The problem is only occuring on hot or cold starting. Once the engine is running stably after a few seconds, everything is normal, cold or hot, including cold fast idle.

If anyone has experienced a similar hard cold or hot starting problem and found the problem can you chime in.

Duke

Update: I wasn't able to find a helper until this morning to cycle the ignition key while I listened for the fuel pump and checked for spark.

In the meantime I wiggled/cycled/inspected various connectors for fuel and ignition system components and wiggled the fuel pump and OVP relays since they were reluctant to come out.

Upon my buddy turning the ignition on with my ear under the car I could hear the fuel pump operate for about one second, which it should. Test successful.

...pulled the #3 plug wire and attached it to a loose spark plug that I grounded to the negative battery terminal.

Upon cranking I could see spark and the engine nearly started.

...reconnected the plug wire and the engine started immediately and assumed normal fast idle.

I only drive the car a few times a month, so I'll just have to keep and eye on it and see how things turn out.

In the meantime I think I'll buy a spare fuel pump and OVP relay and keep them in the car.

Has anyone ever removed a fuel pump or OVP relay. I don't see a tab to push or any other release, but they don't seem to want to come out, and I don't want to use excessive force. What's the trick?

Duke

On the 3.0, the hardest part was getting the fuel filter and pump cover off. A nice bright LED floodlight took care of the ''in at about 45 degree'' cover screws.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

Different model, but basically the same engine , just larger bore. Worth a look:

300SE 1991 will not start when hot.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

My 88 300 CE 3.0 had similar problems... twice. The first time it was the FPR. The second time it was the rotor & ignition wires. Car would not start at all. That happened three years ago. No problems since. Dealer diagnosed & repaired both times.

Advice: Start with the cheap & easy stuff. Progress from there.

My cap and rotor are Bosch OE replacements that have been on for about 24K miles. These parts normally last a long time, but my engine developed a slight misfire at idle that caused roughness and increased emissions. The cap terminals bench tested with the proper resistance (I think it's 2K ohms), but on one terminal if I put some side pressure on the tower with my finger, it went open, so there was some internal manufacturing defect that caused an intermittent open and subsequent misfire on that cylinder.

With the new cap and rotor the occasional idle misfire ceased and HC emissions went down.

I'm still looking for input from someone who has removed the fuel pump or OVP relays. Mine don't seem to want to come out without what I consider excess force, and I don't see any release taps in the sockets.

Duke

The problem went away for a few weeks and then returned.

Additional analysis and discussion with some knowledgeable CIS guys pointed to the fuel accumulator, which can easily be tested on the car by disconnecting/plugging the hose from the backside that tees back into the supply line hose from the tank and installing a clear vinyl test hose to the nipple.

Upon turning the ignition key on, which energizes the fuel pumps for about a second, fuel filled up the test hose. The accumulator was obviously leaking internally, so the system was not holding operating pressure after shutdown, and the leak made it hard for the fuel pumps to develop operating pressure during cranking, which is why it became hard to start, hot or cold.

I had a helluva time finding one even though Mercedes probably built 3 million cars world wide that use this part from '84 to '93. Several Bosch dealers I tried starting with Pelican were out of stock, so I called Bosch USA and they are out of stock until late May. I finally ordered one from a dealer in Kansas City who offers a good discount from list. They said there was one in the Fontana warehouse, but the computer was wrong, and it had to be backordered to Germany, so it took about two weeks to get the part.

I replaced it on Tuesday and got my California ASM emission test, yesterday. It goes into storage for the summer after the Pelican show in Palos Verdes on Saturday.

I plan on disassembling the old accumulator to do a failure analysis and will start a new thread with the results.

Duke