Mercedes-Benz Forum banner

1 - 3 of 3 Posts

·
Registered
79 450sl
Joined
·
208 Posts
Discussion Starter #1
OK, been chasing this thing forever. Thought i had it fixed but now I find out I don't. I originally posted this on "Feels like a governor." The conclusion was a fix when i changed the wiring to the ECU. That in fact, did not fix it. As noted in that thread, the symptoms seemed heat related. IN the boiling summer of Louisiana the engine temperatures were quite high. Thus the problem seemed to go away. Now that things have cooled back down, the problem has returned. Essentially, stall condition at 3500 rpms.

I think its ignition related because of the consistency. Also, when I changed the ECU it dropped to stall at 3200. Changed it back and the stall returned to 3500.

So here is the question. Is there a piece that affects the timing on the car at certain temperatures? For example, the thermal vacuum switch. Could some breakdown in heat related sensing cause the distributor or timing to fail to fully advance at high RPMs?

I know its a shot in the dark, but its puzzling. i can live with it, but its a mystery that i want to solve. One old Mercedes Mechanic suggested a sticking piston on the fuel distributor. That's the only part of the fuel delivery system that i haven't changed.

Car runs great in every other way.
 

·
Registered
1977 450SL
Joined
·
50 Posts
this could be a long shot, I read briefly in your last post of everything you placed under the hood, but have you replaced your relays? My 77450SL had similar problems and after replacing everything under the hood like you did, I finally pulled out ALL the relays and found out that 3 of them (main ecu and fuel pump relay) had burn marks on the pins. I replaced all my relays (I think $6 a piece) and haven't had any problems since. They get old and when the electrical current flows through them they heat up and wear out.

Just my .02 if you haven't done that yet.
 

·
Registered
79 450sl
Joined
·
208 Posts
Discussion Starter #3
this could be a long shot, I read briefly in your last post of everything you placed under the hood, but have you replaced your relays? My 77450SL had similar problems and after replacing everything under the hood like you did, I finally pulled out ALL the relays and found out that 3 of them (main ecu and fuel pump relay) had burn marks on the pins. I replaced all my relays (I think $6 a piece) and haven't had any problems since. They get old and when the electrical current flows through them they heat up and wear out.

Just my .02 if you haven't done that yet.
That's a good idea Danz. To answer your question, no. I replaced the fuel pump relay but not the others. I will get on that this weekend. I did refresh every electrical connection i could find under the hood. It's a crapshoot on this stuff. I can't find anybody that's ever had a similar situation and resolved it.
 
1 - 3 of 3 Posts
Top