1977 Mercedes Benz 450sl won't start

MONTY747

MEMBER
1977 MERCEDES BENZ 450SL
V8
2WD
AUTOMATIC
132,000 MILES

Vehicle was stored, and started once a month. I missed a couple of months, now it tries, but won't start. I've changed the gas, new injectors, new spark plugs, new cold start valve, checked the fuel pump. Can't figure it out. It has spark, and seems to be getting gas.

I had changed the fuel filter, checked out the fuel pump (it is pumping properly), and the injectors do pulse, at least the two that I checked do.

Any ideas? Monty747

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
42,904 POSTS

Hey Monty747,

The Bosch K Jetronic system is a CIS setup - the injectors spray a constant stream of fuel when the fuel pressure goes high enough to open the spring-loaded valve in the injector.

If you've verified the fuel pump works, and you've replaced the fuel filter, I would next want to check the Warm Up Regulator (badly named, because it controls much more than just the warm up cycle) and the fuel distributor.

The WUR sits at the front of the engine and establishes the control pressure during operation. Basically it's the gatekeeper for the gas. It has to work for the car to run. The fuel distributor is under the air filter housing and it looks like a post-modern spider.

It does just what the name implies - it distributes the fuel. If bad gas got into it, that's enough to kill it. If the diaphragms on the WUR went bad, that's enough to kill it. Unfortunately testing either of these gets into advanced skills that I wouldn't recommend for the average shadetree mechanic.

There is a 3mm allen head tool that is used to readjust the injector hat to see if you can get it running but it has been may experience the injector hat is bad and you will need a new one.

Please let us know happens so it will help others.

Best, Ken