ron6962

I understand this is a common issue with this model and this fuel delivery type, so if anyone has found solutions, I will be very appreciative.

1972 450SL with the D-Jet fuel injector system. Engine recently overhauled, new fuel injectors, distributor with electronic points, new fuel pump, and rebuilt ECU wiring harness.

Engine starts and runs A-OK when cold. When temp gauge reaches 200+ and the engine is shut down, it still starts and runs A-OK immediately after shut down. However, after 15-20 minutes, it is very difficult to start, and takes repeated rapid accelerator pumping to get it going, then it runs very rough. After 2-3 minutes, it settles down and runs A-OK again. This also happens when the engine is slightly warm, but the outside temperature is 90+, and the car has sat in the heat for a while. In the garage it is A-OK.

I am assuming this is a vapor lock issue with the gasoline, but everything I have tried (timing adjustments, fuel pressure adjustments, etc.) has yielded no positive results.

Any advice appreciated, especially if you have experienced similar problems and found resolutions. Thanks.

tscales

I have absolutely no idea what it is, but on my E55 and SL65, I had exactly the same problem and it was the crankshaft position sensor. I have no idea what that is or if a 72 450SL has one, but what they heck

ron6962

Thanks for the reply. I have not previously heard this related to the hot start issue, but since reading some other blogs, there does appear to be a relationship. Now, I need to determine if the 72 450SL has a crankshaft position sensor, and where it is located. So far, my searches only yield results for later year model 450SLs.

Anyone know more about this? Thanks.

myway

No 107 prior to 1986 has a crank position sensor. Some '85 and older models have a TDC sensor but it has nothing to do with starting.

Yes this a common hard start issue on DJet engines. Some have increased the fuel pressure to 30-32 PSI. Another suggestion is to turn the ignition on and off a few times to fill injector lines.

Hope this helps.

ron6962

Thanks for the reply. I have tried all the things you suggest, and many more...none yield positive results. I'm pretty sure the fuel in the injector lines running around the top of the engine, below the air cleaner, is vaporizing after it sits a few minutes at high temperature. I just can't find a way to keep or get it cooler...beyond waiting an hour! Ugh!! So frustrating and embarrassing in the parking lots.

tsmith7549

Ron,
Have you found any solution for your problem? My 2005 E320 has the identical problem. Trust me I understand your embarrassment in parking lots. I have been looking for a solution for over a year. I have replaced: CPS, MAF, Fuel pump, fuel filter, vacuum lines, EGR valve and the valve cover gaskets. All these recommended by this forum or MB mechanics. None of them have worked. Let me know if you find anything. Thank you.

ron6962

Unfortunately, I have not found a solution. The only thing that seems to help (but not a total solution) is removing the air cleaner. That allows extra air to circulate around the metal fuel injector lines and delays the vaporization. My mechanic was going to try insulating those fuel lines, but has not come up with anything that works yet. I also considered setting up a small fan under the air cleaner that runs when the ignition switch is on, and with a delayed shutoff to see if that does the trick. If I ever do resolve, I will post.

Tariqhanna

I’m facing the same issue, I’ve changed the injectors and the fuel pump with no positive results.
I’ve read some comments says that it’s about the idle or the gasoline filter near the engine (black one)
let us know if you have a positive result