Hi everyone!
My friend’s '86 300E starts ok when the engine is cold and runs fine without any problems until it is switched off. He can't however start the car once the engine is warm. Apparently the starter motor turns the engine over but engine fails to start.

I know a thing or two about cars but I have limited knowledge on Mercedes cars. I have searched for some pointers related to this problem on quite a number of Mercedes forums on the net but I could not find anyone having this kind of hot start problem.

I know above info is limited for a proper diagnosis over the net but I have yet to see or test the car. I'll only be able test it tomorrow to get a better idea on what the exact symptoms are and I’ll post my findings here. In the mean time, I was hoping that someone on this forum may be able to shed some light on where to check, what to test or how to diagnose this kind of problems.

I do appreciate your help on this and thank you very much in advance...

 

try the air duct be low the throttle houseing make sure no crack
2----mixture adjustment
just a idea

 

Check the fuel pressure. See if it's bleeding down after you shut the engine off. If it does you need to find out where. The system should maintain at least 60% of running fuel pressure for one hour. Possible leaking pints, fuel pump check valve, injectors, fuel pressure regulator or fuel dist.

 

bbs138, thanks for the reply...apparently the car starts and idles well, and runs smooth until it is switched off. Based on this I assume that there is no vacuum leak in air intake system and also the mixture adjustment is right. Am I on the right track with this assumption? Does this crack at the air duct you mentioned relevant only to warm starts? I'd appreciate your reply...Thanks...

 

benztech, thanks for the reply...I read a number of posts concerning warm start problems on various forums on the net and most of them point to the same areas you mentioned. However, I could not find any indication in these posts that fuel pressure leaks cause car to fail completely during warm starts. In almost all these cases, the cars have problems with warm starts but they start nevertheless. In my case the car doesn't start at all when the engine is warm and yet no problems with cold starts, idling or when it is up and running.
Based on this info, do you still suspect fuel pressure leak is the culprit here?
Thanks a lot for all the help....

 

Ok...I had a chance to see the car today and have got fairly detailed history of what was wrong with it what have been done until to this point.

Problem #1: Difficult to start when the engine is warm. No problems during cold starts and idling or under normal running conditions.
Problem #2: Intermittent misfiring at cylinder #5.

Here is a list of what has been done for these problems. (done couple of months ago and the car was lying in workshop since then)
-changed fuel pump (new)
-changed fuel distributor (swapped with a good one)
-changed spark plugs (new)
- changed fuel filter
-changed ovp relay (swapped with a good one)
-changed ecu (swapped with a good one)
-changed ignition coil (swapped with a good one)
-changed ignition system control unit (swapped with a good one)
-changed cylinder head gasket
-changed camshaft
(Notice; number one suspect “Fuel Accumulator” is not in the list.)

Unfortunately, none of these steps were successful in solving the problems. What is worse now is that the car has a new problem. The problem is the engine starts right away but dies after a few seconds. There is no amount of throttle helps it simply dies in a second or two.

The mechanic who did the above repair work swears that it was ok last time he started the car couple of months ago but he has no idea what’s wrong with it now.

Anyway, I checked the fuel pump by removing the fuel line from the fuel pressure regulator and found out that there is sufficient fuel pressure is present (not a scientific observation though). I checked all the possible vacuum leak points but could not find any indication of a large leak that can cause such problem.

Also, there is no indication of fuel overflow but instead there is a strong indication of engine starving for fuel. After the engine starts and runs a few seconds it dies as if it ran out of fuel. At this point I have to wait approximately 10 seconds to get it successfully fired up again for a few seconds. It does not start at all if I try to crank the engine within a few seconds after the previous attempt.

What would you suggest I should do to get this car started so that I can check the problems #1 and #2? Thanks in advance...

 

[8D]may see some point that look like your fuel pump relay have the problem when hot,\.

you can take out the fuel pump relay and open up .look at the circuit board that have some component welding have over heat cos by the bad fuel pump.the weld point is mis-connect with the board when hot .when cool down they got back the contact
if you change the fuel pump relay before ,see you have the one that made in korea is after market. if do,better buy it from the dealer,,,,

 

I second the fuel relay solution. My 89 300E had a starting problem much like you have described. The problem got worse fairly quickly until the car wouldn't start under any conditions. New fuel relay and no more problems! Cheers

 

Had the same problem with start while hot on my 87 300e, new fuel pressure accumulator solved the problem.

good luck

 

I have a 92 300e with the same problem and I found the answer to be a bad crank sensor