450SL 30K miles - Fuel & Spark - No start

[trav]

I'm having some issues with my 450SL. The car is a silver convertible (with red interior) and has 30k miles on the clock. This car is 100% original (even the OEM tires from '79!).

Without getting into who/what/how/why, I'll skip all that and get to the issues I'm having. I didn't hear any noise from the fuel pump when I initially took delivery of this car, so I replaced that with OEM Bosch and sent the fuel tank out for cleaning. I've replaced the screen/filter inside the fuel tank, fuel pump, fuel damper & filter. I've cleaned & replaced the fuel distributor and injectors. I've also replaced the ignition cap & bug with OEM parts.

I'm unable to get this classy-lady to start. She will surely turn over and builds good compression (over 150). The car is popping as if it wants to start but sure sounds like there isn't enough fuel getting down into the cylinders, however, there is also an odor of fuel in the air after a 10sec cranking on the car.

The plugs are black (not pig-rich) but hardly wet at all so I do not believe its flooding. The pump does build TONS of pressure (like a new pump should). One thing I'm noting is there seems to be a relay that clicks rapidly if i touch the throttle while cranking.

I have tried wiring the pump to an alternative power source - same results... so I'm left to believe there isn't enough fuel being sent to the injectors? for what its worth... this car is 100% stock, vacuum lines, fuses, etc. I think the air-breather filter is the same one from '79.

I'm really lost on trying to aid this old 'gal back to health. Its strange.. when turning over the car - it really sounds like it's going to start right up (the rpms will run, the ALT kicks in - lights get brighter, oil pressure shoots up,etc) but then it'll fall on its face and go back to "no fuel" sound.

Any advice would really be appreciated. thanks!

[ctaylor738]

I suggest that you check the fuel pressure on the rail. I suspect that your pressure regulator is in need of replacement or adjustment. Here is a post by yours truly on how to measure and adjust.

Checking D-Jet Fuel Pressure

You might also want to put a timing light on it and make sure you are getting spark at the right time.

[trav]

Originally Posted by ctaylor738

I suggest that you check the fuel pressure on the rail. I suspect that your pressure regulator is in need of replacement or adjustment. Here is a post by yours truly on how to measure and adjust.

Checking D-Jet Fuel Pressure

You might also want to put a timing light on it and make sure you are getting spark at the right time.

I'm 100% sure there is pressure but I'm not sure at this point "how much".

Regarding the `fuel rail`?.. I dont seems to have an actual rail but a distribution block with 8 hard lines coming off to ea mechanical injector (in addition to the cold start value,etc).

I'll give the pressure a shot and see what comes of it. Should I be looking at anything else assuming my pressure is good?

[ctaylor738]

Well, that would be the rail.

In addition to 2 bars pressure, you need the injectors to open and close. This is controlled by the computer with input from the trigger points in the lower part of the distributor. While cranking, you can listen for the injectors clicking with a mechanic's stethoscope, or put a test light on the contacts.

Also, if you have low fuel pressure, then the cold start valve won't deliver fuel.

If you have presure, operating injectors, and spark at the right time, the car should start.

[Graham]

Originally Posted by ctaylor738

Well, that would be the rail.

Chuck,

He has a '79 - That would have mechanical fuel injection (CIS), would it not?

I don't know much about them, but I think they have a fuel distributer with individual hard piping to the injectors. There is also the WarmUpRegulator which seems to be a troublesome part on these engines.

Section 7.3 of manual cover this and methods of testing.

Trav - If you look at the '79 models in this link, they would probably have a similar engine :

http://handbook.w116.org/matrix6.htm

Go to Engine, Section 7.3

You might also try spraying some starter fluid into the intake and see if it will run for a short period. Will at least show that ignition side is good.

[trav]

Originally Posted by Graham

Chuck,

He has a '79 - That would have mechanical fuel injection (CIS), would it not?

I don't know much about them, but I think they have a fuel distributer with individual hard piping to the injectors. There is also the WarmUpRegulator which seems to be a troublesome part on these engines.

Section 7.3 of manual cover this and methods of testing.

Trav - If you look at the '79 models in this link, they would probably have a similar engine :

http://handbook.w116.org/matrix6.htm

Go to Engine, Section 7.3

You might also try spraying some starter fluid into the intake and see if it will run for a short period. Will at least show that ignition side is good.

Yeah thats her, Miss CIS system
She'll fire up on starting-fluid no problems.. just not by the injectors. The car does have good compression FTIW.

Thanks for the URL, I'll check in to this and see what comes from it.

[ctaylor738]

D'oh. Somehow I read '74 which would be d-jet. Forget what I said.

I still suggest that you check the fuel pressure, but on CIS you check it between the fuel distributor and the warm-up regulator. You need a guage with a shut-off so that you can measure "system pressure" from the fuel distributor (closed - 5.6 bar) and "control pressure" (open - about 1.4 bar with a cold engine).

A lot of engines that have sat for a while have crud in the warm-up regulator that keeps the control pressure too high.

You can try pushing the air sensor plate down with a stick while you crank it to force some fuel to the injectors.

[meltedpanda]

have you pulled any of the injectors for a look see , how long has this sat "unstarted"

[trav]

I've replaced the injectors, fuel pressure is good.
I've even cleaned the fuel lines from the tank all up to the engine bay (including the injector lines,etc).

...stumped.

[meltedpanda]

in that case, too liitle air or too little gas,
did you try what ctaylor suggested?

[trav]

Originally Posted by meltedpanda

in that case, too liitle air or too little gas,
did you try what ctaylor suggested?

I did try starting fluid - car does run for a half-moment (we could have kept it running via starting fluid but thats a bad idea).

I'm thinking there isn't enough fuel being passed from the injectors. I'm not sure why I'm stuck on this idea but I have noticed the lack-of wet plugs.

[ctaylor738]

Even if your pump is delivering, to get fuel to the cylinders, two things need to happen.

First, you need to have enough fuel pressure to open the injectors. This is measured by system pressure. You may have plenty of pressure from the pump, but if the pressure regulator in the FD is not right, then there won't be enough pressure to crack the injectors.

Second, you need to get the fuel to the injectors. This is controlled by a piston in the fuel distributor. The piston moves as the air sensor plate is deflected by air being pulled into the engine past the throttle plate. If the piston is sticking, and not being moved, then no fuel will go to the injectors. Movement of the piston is balanced by control pressure, so if you have high control pressure, the piston cannot move to deliver fuel. Because so little air is moving at engine start or idle, the margin between start and no start is very small.

That's why I suggested removing the air cleaner and pushing the sensor plate with a stick - to see if moving it would move the piston enough to get some fuel to the engine.

One other thing you can try is going slightly richer on the mixture adjustment. Maybe 1/2 turn clockwise in 1/8 turn increments. This might forct the piston up far enough to allow fuel to the injectors.

But you are not going to get to the bottom of this without a fuel pressure check.