Summers here and I'm having a hard time getting My 1988 300TE to start when hot.

OK, in Feb I had a valve job done and head gasket replaced and a few other parts. The shop told me that my fuel pressure regulator was not so good so I replaced it. The problem is the car starts ok in the mornings and it will start right up after you shut it off. But if is sets for 5 min or more it has a hard time starting backup. and when it starts it acts like it is out of gas and has a ruff idle but then smooths out after 30 sec or so. The problem get worst as it gets hotter out.

Try this

Turn key On and wait for 15 secs,
Turn off and back on and wait for a couple more secs and then try start.
Post results

I had the identical problem in my 89 300TE. I went through the intake system and fixed all the vacuum leaks. This helped a bunch and I did a write-up in the DIY section as it's not exactly obvious for amateurs like myself. I also recommend checking the condition of the cap and rotor (unlikely though).

I had heard that fuel leak-down is likely to cause this, but since injectors and associated parts are expensive I opted to get a fuel pressure tester and run a series of leak-down tests. Turned out there was zero leakdown, and I saved a bundle on the injectors, fuel pressure regulator, etc. It also reassured me that the fuel pressures were to spec.

And while the problem isn't 100% resolved, I'd say fixing the vacuum leaks improved it by about 75%

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89 300te 222,222
92 300e 190,000

Since the problem is at its worst when hot and after being stopped for a while, I would suggest it could possibly be the fuel accumulator (assuming no fuel pressure leak-down elsewhere). If the accumulator is faulty, fuel system pressure is not maintained after stopping and the higher temperatures allow fuel vapour bubbles to form in the fuel lines making for difficult starts.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.

I have followed this subject closely as my M103 is exactly the same and it is a common complaint.

A little bit of throttle when starting works every time. This is even what the Owner's Manual suggests for a warm engine.

I have checked all the associated fuel system parts and recently replaced the accumulator. Nothing has changed the warm start condition however I have greatly improved the response and feel by adjustment of the EHA and by having the engine in excellent tune.

IMHO it is unquestionably to do with old injectors. They don't last forever and 100k miles is the suggested life. They have done a good job already for 15+ years!! One or two leaking-down a drop or two creates the richness that causes the start-and-die. This explains the instant resart or the success of the use of throttle (more air).

It is further explained by the fact that the engine actually continues to heat up after shut-down when the cooling system is not working. This additional heat puts additional strain on the tired injector.

The benefit is that they are not teribly expensive for an M103 and can be changed DIY.

It is the only thing that makes sense although I have not changed mine as yet.

89 300CE
153k kms

At 160,000kms changed the injectors.

Fuel accumulator has been changed prior and EHA adjusted.

Whilst idling and general pick up seems smoother (still checking fuel consumption) there does not appear to be any change to the start / die / start when warm issue.

Not sure what more can be done as otherwise it runs perfectly.

89 300CE
160k kms.

This one still stumps me after several years. I also have a '92 300e with about the same number of miles (200K+)but it always starts up immediately. I can swap out the parts and haven't figured it out. The computer is different but everything else is pretty much the same.

I think the problem is in the fuel system since it starts up immediately when cold (the cold start injector helps).

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89 300te 222,222
92 300e 190,000

Hi, I also have the same problem with my car.
It starts just fine after some cranking when cold, but if I stop the engine and leave it for a while after it has warmed up, I'll have a very hard time trying to start it again, if starting at all.

I also had problems with low and rough idle, but changing the OVP Relay fixed that. After I changed it, the car runs very smooth and quiet and everything seems fine, except for the warm start problem.

I will continue my search, and post if I can sort it out.
Hope you with similar problems will do the same.

Regards
Marius

I would take a close look at the cold start valve and injectors. (if they are electrical) When the cylinder head saturates with heat that travels upwards after a shut down, the pindle in the valve could be rising up due to varnish deposits. This might leads to an over-rich hotstart, which would explain the your "gas starved sensation", (which is actually over-enrichment), then the stumbling thats present, is plug fouling until the plugs kick off the extra fuel. Pull the valve out just after a hard long run, and see if shes injecting or dribbling. When the engine is up to operating temp, the cold start circuit should be inhibited by the already heated cooling temp sensor.
dave...
The slight opening of the throttle seems to help others with this problem, as you are adding more AIR...More AIR + an Overly enriched fuel mix= proper mixture for rapid and efficient combustion. DO A LEAK DOWN TEST PROCEDURE....

If the warm engine doesn't start at all or after a long time, it is likely to be a valve next to the fuel filter.

If the warm engine starts immediately, then stalls again after 0.5 s but runs fine after trying again, then me and some others had success with cleaning the intake manifold and everything around the throttle valve.

Cheers
Tom

There is NO logic to the notion that poor warm start (only) is caused by fuel pressure leakdown.

That's because there is NO reason for pressure to leak down in the short period after running but to somehow magically not leak down over night.

The warm start problem exists because the engine is flooded.

Since a cold engine requires a richer than normal mixture, this flooding is not so much a problem and in addition excess fuel may disspate given enough time.

No, the problem is leaking injectors, which yes, is a pressure leakdown source too, but which in addition causes flooding. Or, something else causing flooding, which of course is NOT lack of fuel pressure.

Try a little open throttle with a warm start.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles