E300 intermittent no start

[e300nocash]

My 98 E300 has recently developed a problem where it sometimes fails to start after a hot shutdown. It will crank normally, but it just won't catch. Sometimes it will start after repeated attempts. Last night I had to abandon it. I had left it idling and gone into a store. I came out of the store and got within ten feet of the car and it stumbled and then stalled. That is the first time the problem has caused it to cut off. It did not even sound like it wanted to catch after that. I went back this morning and it fired right up. The strange part is it will always start normally when cold.

The car has no fuel leaks. Over the course of the last four years, I have replaced all the clear fuel lines. The o-rings on those lines, the delivery valve seals, and the shut off valve o-ring are all Viton. There is no odor of diesel fuel under the hood, so no fuel is leaking, but some air is getting in. Bubbles are visible moving in the line from the shut off valve to the lift pump when I rev the engine. No air is visible in the lines near the prefilter (other than the usual small bubble when the engine is off). I replaced the filters and associated o-rings when the problem began a week ago, with no change. I loosened the main filter this morning to see if air had accumulated in it. It was full to the top with fuel. By the way, I had a full tank and was parked nose down when the the engine stalled last night.

I plan to replace the o-rings on the clear line between the shut off valve and the lift pump tomorrow, but I am not confident that is going to fix it. I don't understand why the problem never occurs on a cold engine. Could the shut off valve let air in while not leaking a drop of fuel? Could the problem be the lift pump or is there something else going on and the air is not the main problem? Thanks in advance.

[TMAllison]

Any delayed shutdown when key is turned off? Sounds like your leak is at the SOV. Check up under the SOV with a mirror and light.

Resolve the air first.

K40 relay can also cause shutdown. With hood up and window open you should easily hear the SOV "click" open when the key hit pos #2. No click, no start.

[e300nocash]

No delayed shutdown. The engine has been stopping normally.

I just double checked under the SOV with a mirror as you suggested. It is bone dry.

A Good Samaritan (who is also a diesel mechanic) in the parking lot where I broke down listened for the click at the SOV. He said he heard it.

I am still puzzled because the o-rings have only been in there about a year and they are tight, but I will be happy if that is the only cause of the problem. Thanks.

[TMAllison]

Originally Posted by e300nocash

A Good Samaritan (who is also a diesel mechanic) in the parking lot where I broke down listened for the click at the SOV. He said he heard it.

With hood up and window down it is not difficult to hear the click of the SOV openning. If you didnt hear it from the drivers seat it probably didn't open.

Cycling the key a few times sometimes works if the K40 is in its usual intermittent phase.

[Chris W.]

Don't overlook the lift pump itself. Relatively cheap and easy to change. You don't say how many miles on the car, but I think it's worth replacing. I did mine when I was having a stalling issue and it took care of it.

Rgds,
Chris W.
'95 E300D, 293K

[nhdoc]

after re-reading your post I decided that I would replace the K40 relay and see if that fixes it...it is cheap, easy to replace and can easily cause the problem you have described. Could also be the lift pump though I would think you would see the lines full of air when it stalled and also don't understand why it would start normally when cold. That's what leads me to believe it is electrical and not fuel which is causing it.

[Diesel911]

You might look in here and see if you can come up with something.
http://www.ps2cho.net/downloads/MB%20CD/W124/Index/605_606index.html

[hobbitss]

I recently had all of the clear lines and IP outlet seals replaced on my 98 to mitigate acceleration lag and a light aroma of diesel in the engine compartment... The indy where I had the work done mentioned that there was a service bulletin on the rubber hoses that connect to the metal supply and return fuel lines... It seems that the rubber dries out, cracks under the hose clamps and leaks air creating a similar situation as leaking plastic fuel lines... He said you can replace the rubber lines or just cut an inch or 2 off of the ends and reclamp them in place, which is what he did for me... It turned out that only one of my plastic lines was damp with diesel and the IP seals were fine... After a full tank or 2 the air was clear from the lines and the car has run fine since...

[e300nocash]

Update:

New SOV, no change.

K40 looks good, and I have heard and felt (with my finger) the SOV activate when the engine was failing to start.

At dusk with fresh batteries in my flashlight, I have seen a fine, steady stream of bubbles in the line from the bottom of the prefilter to the SOV, and in other lines downstream. I have also seen an occasional larger bubble enter the top of the prefilter from the fuel thermostat. I removed the intake manifold and trimmed the rubber hose supplying the fuel thermostat as suggested by hobbitss. The hose did look rough on the end, but this did not stop the air leaks. I have replaced the prefilter and its o-ring twice in the past week. I used silicone grease on it as suggested by TMAllison in other posts. I have also replaced the o-rings on all the clear lines on the suction side, and checked that the hoses would hold a vacuum. I seem to have the classic air leaking past the o-ring problem, but all the o-rings are new and tight.

I got a "check engine electronics" message yesterday. The code was 0725 "engine speed sensor circuit malfunction". I cleared the code and it has not recurred. The car always starts fine when cold, and half the time will even start hot, but occasionally will die after a few minutes of idling. There is definitely air in the fuel lines. I checked the main filter after a failure to restart and it was full, but quite hot. I know the fuel thermostat heats the fuel, but I had to hold the filter with a rag. It was not hot enough to raise a blister, but it was uncomfortable. Is that normal?

I plan to keep fiddling with the lines around the prefilter in a effort to pinpoint the air leak. I don't know what else to do.

[TMAllison]

Concentrate up stream of where you saw air.

That would be the pre-filter oring, hold down washer providing pressure on the prefilter and the opposite end of that line which attaches to the fuel thermo in the head most often. The latter is most difficult to seat as you can't get your hand or fingers on it with the intake manifold installed. I've used a screwdriver and two hands to get sufficient leverage/pressure to seat it in the past. Make certain you hear or feel a good double click of both fuel line shoulders seating. You would not be the first person to receive a pre-filter with a crack in it that wouldn't seal or to have a fuel line that was cracked and allowing air to enter under certain conditions..............

Back from there is mostly metal fuel line to the tank with some short stretches of rubber. Since you already checked the rubber connection to the thermo if the above checked out I'd prob go back to the tank end of things and check those metal/rubber connections.

[nhdoc]

The thing which is strange is the way the OP describes the problem as being one which 1) only occurs when the engine is hot, 2) doesn't want to restart when hot but restarts perfectly when cold. If a fuel problem was causing the engine to stall I would suspect it would not restart easily when cold since it still has to prime itself. I'm wondering if the problem isn't electrical after all? I would say 99% sure it was not fuel/air leaks if the problem occurs with a full or near full tank of fuel...if that was confirmed I would concentrate on electrical issues.

On gas cars there is a crank position sensor which frequently fails and causes exactly the symptoms he's described. I don't know if our cars have an equivalent sensor although there must be some sensor which feeds the ECU with engine speed data and to provide a signal to the tachometer. Does anyone know where the engine speed data is taken from? The fact that he got a code about that may not just be a red herring.

[nhdoc]

Update...I saw on peachparts there is a crank position sensor listed as a replacement part on our E300...I'd be looking closely at that since they do typically fail exactly as he described (under hot-soak conditions)!

http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1998@@1998&makeid=63@@MERCEDES+BENZ@@X&modelid=6384%3AMBC|1572%3AED|814%3AFT|6@@E300&keyword=sensor@@sensor&catid=All@@All&subcatid=P%3A242838@@Crank+Position+Sensor&applicationid=W0133-1716592&mode=PA

If that isn't it then I would replace the K40 relay. Even though he said it "looks OK" they are so frequently faulty and you certainly can't see every fault it is very likely to be the problem if the CPS is not.

[TMAllison]

On gassers, the CPS provides critical reference timing for spark and fuel delivery and causes intermittent cutout/no starts when it begins to fail.

On our diesels, that sensor provides some emissions data and the input to the tach. I don't remember anyone replacing it? Mines OEM at 272k.....