'82 380sl vaccum advance

[W Black]

My 380 is running rough and has no power or acceleration and a small detectable rough idle. I have ordered fuel filter and distributor rotor to replace. I have replaced the distributor cap, plugs and wires. Tonight I checked the vacuum advance on the distributor with the mityvac tester and found that the vacuum advance diaphram would not hold any vacuum at all. The mityvac was connected dirictly to the advance diaphram port. Should'nt the diaphragm hold vaccum? Could this be the cause of the problem?

Thanks

[ctaylor738]

Remember that the advance works off ported vacuum, meaning that it increases, and advances the timing, when the throttle is opened. You should hold some vacuum at the distributor, but I forget if it bleeds down slowly or not. So if you are not holding ANY, then you should replace the dashpot.

The best test would be to give it some vacuum with the Mityvac with the engine running and observe the effect on the timing.

It would certainly contribute to the problems you describe.

[anakngpari]

Hi Chuck, its me again. After replacing my Fuel Pump Relay, my 1985 380SL runs great. However, this morning while driving the car I observed that the car hesitate to accelerate when I press the gas pedal (from stop to go). It was also observed that if I press my gas pedal slowly from stop to go it drives fine. Could this be a vacuum advance problem? Any input or help will be highly appreciated.

[ctaylor738]

It could be a number of things:

- Vacuum leak. Check all hoses and connections.

- Vacuum advance. You need to put a timing light on it and look for a "snap" of advance when you blip the throttle. If you don't see it, then the diaphragm in the distributor has probably gone south.

- Fuel distributor. Jumper the fuel pump relay and with the pump running, press down gently on the sensor plate. It needs to move with no resistance. If you feel resistance, the piston in the fuel distributor is sticking, which means that the piston is not moving fast enough to supply fuel for quick acceleration.

- Other fuel supply problems. Warm-up regulator, fuel filter or other supply problems, fuel pressure. You need a pressure gauge to chase this any further.

Is this happening all of the time, or when the engine is warming up?

Is the car running OK otherwise?

What is the "economy" gauge doing when the engine is at idle?

Is the idle nice and steady?

[anakngpari]

Chuck, when I try to start my 1985 380SL today to check and answer the list you want me to check, my car won't start and making a clattering noise on startup. Could this be a possible timing chain problem? My car got 137,000 mile and the timing chain was never been replace. I don't want to start the car again because I'm afraid that it could cause some major damage. How will I know if this is a chain problem or a tensioner/guide issue? Regards.

[ctaylor738]

This poor thing has its share of problems!

I'm confused, though. If it won't start, then how can it make a clatter at startup. Please explain more clearly what's going on.

[anakngpari]

Chuck, the car runs fine except for stop and go. I have to press the gas pedal slowly but when it gain speed, it runs good. The next day in the morning when I try to start the car I was hearing some clattering noise so I stop, open the hood and checked for something unusual and can't find any. I tried to start the car again for the second time and still hearing that clattering noise at start up (engine did not run) so I stop, thinking it was the timing chain and don't want to damage the engine. I'm planing to open the valve cover this weekend to find out. Chuck, could it be the starter/solenoid that did not disengage that is making this weird noise? Thank you so much for your time and help, I really appreciate it.

[ctaylor738]

Sounds like your chain tensioner has given it up, and the chain is slapping as the starter turns the engine. It would be very riskly to start the engine under these circumstances.

[anakngpari]

Hi Chuck, the car did not run on this situation. I did try to start it (2X) and stop. In your honest opinion, do you think the pistons hit the valves when I try to start the car? Regards.

[anakngpari]

Chuck, do you have any pictures or illustrations an how to replace the chain tensioner? How many tensioner are there in a 1985 380SL, do I need to replace the Timing chain and guides at the same time?

[ctaylor738]

It is possible that the chain jumped and you are hearing the pistons colliding with the valves. It would also explain why the car isn't starting.

There's one tensioner on the 380, front of the right cylinder head. It has two bolts. You unbolt the old, and install the new. I use a longer bolt on one side to pull it in far enough to get the other bolt started.

But before you do anything with the tensioner, pull the right cover off, bring the engine to top dead center, and check the marks on the cam to see if it jumped.

[anakngpari]

Chuck, when you said right valve cover does this means on the Driver side of the car or passenger side? Regards.

[Robert Squires]

* This post is to address the 82 380SL hesitation on acceleration. I'm assuming that once you get underway, it runs ok. There's a vacuum delay valve, pn 000 078 08 56, in the vacuum supply to one chamber of the control pressure regulator (K-Jetronic). If, using an engine with good acceleration, you replace that vacuum delay valve with straight hose, you'll get a flat spot on every acceleration. Of course you can watch this on a fuel pressure gauge. The control pressure should drop a little (see specs) when you open the throttle. This control pressure change does the same job as an accelerator pump in a carbureted engine.
* If you've got chain noise, it will probably be the worst after an oil and filter change. You certainly need to deal with that, but it's not responsible for your hesitation.