W107 350SL Fuel system question

[BBAY]

I recently picked up a 1973 Euro 350SL from an estate sale with 105k indicated miles. It had been in enclosed storage since 1992. After doing the typical (flush fuel tank, change fuel pump and fuel filter, replace plugs, clean injection trigger points, set timing, it started and seems to run well. On the first test run, it ran well at speed for about 5-6 miles, then began to have an engine cut out every two seconds or so. The longer the run the worse it became until finally only managing 20 MPH. The cut out frequency corresponded with the change in tone of the fuel pump. (spin-rattle-spin-rattle-spin-rattle=run-cutout-run-cutout-run-cutout). I checked the fuel tank and saw some contamination so reflushed and replaced the new pump with another and installed a new fuel filter. Same story. Runs fine for 2-3 miles then starts cutting out. A feathered throttle seems to allow some normal running up to 2000 rpm. Great the throttle open the more pronounced the cutting out. Let in rest for 5-10 minutes and the 'run well for several miles then cut out' cycle repeats. I'm think possibly a fuel pressure regulator problem but thought I would put it before the board before digging deeper. Ideas?
Thanks
BB

[psfred]

Jumper the fuel pump relay and see if it persists. If not, replace the relay (behind the passenger side kick panel, top one in column of three, front side, I think). Variable fuel pump sounds is probably intermittant operation from bad electrical supply OR a bad ground -- chase down the ground wire and make sure it's not corroded.

Have you run a bottle of Techron through it yet? These systems are notorious for getting sticky from old fuel, the injectors could be cutting out.

I'd also pull the cap and check the points for crud, they tend to get dirty fairly easily. Clean with some linen paper of a new dollar bill by opening by hand, inserting paper, pulling about a quarter inch or so, then opening again to remove paper. If you just pull it out, you tend to pull shreds off the sides and hold the points open. Carb or brake parts cleaner works, too.

If that doesn't fix it, it's an intermittant electrical connection or the trigger points in the bottom of the distributor, pull dizzy and points and clean with brake parts cleaner (make sure it doesn't contaim methylene chloride, that will melt the plastcs!).

I would also check the tank for crud -- its' possible that the screen is plugging.

Fuel pressure in the main (before the regulator) should be 29.5 psi.

[BBAY]

Thanks for the pointers. Funny you mention the pump relay ground, as that was an initial problem. I had no power to fuel pump and found that the ground ckts for both the pump relay and cold start relay pass through the #8 multi pin connector and into the engine bay. I could not get good grounds through the connector so had to ground them near the relays themselves.
It seems that this is a gravity fed pump, correct? With fuel line from tank disconnected, fuel flow from the outlet slows until compressed air is introduced into the outlet tube. I will try and remove the tank filter screen as that might be the problem. Can the filter usually be removed from underneath the car without removing the tank?
Thanks BB

[psfred]

Yes, fuel strainer is the very large nut where the hoses come out, I think, assuming the tank is behind the rear seat and not under the trunk floor (I don't remember!). If under the floor, it's the very large nut in the middel of the tank.

Drain tank completely first, else the remaining contents will pour out on you, causing a SEVERE fire hazzard!

I'll bet there is an inch of crud in there!

Peter

[BBAY]

Thanks for the tip. I pulled the tank and was stunned to find about a quart of debris (rust as a fine sand-like material). I had it flushed and treated and now it runs well without the previous problems. Thanks again. BB

[CONRAD]

ALLO.

I have a 1975 450SL. The joy of driving has been replaced with the fear
of not being able to make a round-trip....

The local ind. (german motors) garage said I need a new 'Fuel Pressure
Regulator'. pls locate this device on the car for me. I cannot see it
as I scan the engine area.

The car is fuel injected model. does this car have a FPR ?

Pls advise....

many tks conrad

[psfred]

The fuel pressure regulator is under the air filter housing at the rear of the engine. It is connected to the pulse dampner and the return line to the tank. The pulse dampner is connected to the ring main for the fuel injectors.

It will not run properly with a failed regulator, as the pressure and open time of the injectors determines the amount of fuel added. The D-Jet system does not have a feedback setup, it just measure engine and air temp and intake manifold vacuum, so if the pressure is too low it will run way lean, it the pressure is too high, it will run way rich.

Peter

[CONRAD]

MANY TKS, PETER

'Tis a terrible ride down the yellow brick road, knowing it's a one way....

We'll try this 'cure' and see if the car can make it a round-trip.....

Again, thank you. I'll up-date as soon as possible.