Mechanical pump went from slightly rich to lean

[glcg123]

My 230SL was running perfectly. It started well, warmed up well and had lots of power, Unfortunately it would not start after sitting for a few days. This was the first time in 17 years of driving it. It had been running rich as the exhaust pipes were sooty. The last year or so the pipes are a grey colour so it seemed to lean out. Mileage - 74,000 miles.
My mechanic and I diagnosed that the electric fuel pump was only putting out 250ml in 15 sec with a pressure of 8 psi. We installed a rebuilt tall pump and it now puts out 1.2 l in about 15 sec with a pressure of 14 psi. We also installed a new tank as the old one that had been relined do not look very good inside. So, fuel is good. Once started it ran lean, and bucked upon acceleration. I played with the idle screw on the manifold and set the idle to about 750 rpm. It was at about 600. The bucking has gone away but it does not have the low end power it used to. The next step I think would be to adjust the mixture but am leery to do so. What would cause it to go from running rich over time to running lean? The fiddling we did was minor and yet there was a big improvement. I plan to add injector cleaner in to the tank as I recall this is what my original mechanic did 17 years ago after it had been sitting for several years before I bought it. The car performed better. His saying at that time was "Try to stay away from playing with the mechanical pump. They are tricky". My original mechanic has moved away. Help!

George
1965 230SL

[ja17]

You might want to check the main fuel filter if you have not. 

[Pawel66]

Just "thinking loud": could the new pump, increasing the flow, stir up some dirt in the fuel system and clog the filters?

[glcg123]

A new main fuel filter was installed. It just seems strange that a little fiddling with it got it to increase the mixture.

[Shvegel]

 Since it is a displacement pump it doesn’t make much sense. You are in one of those areas where if I were fixing your car I would start over with your diagnostics. Before I did anything else I would re-verify fuel pressure during operation as well as flow.  If that all checks out I would perform a split linkage test.

[glcg123]

MY ERROR: The car ran really rich, not lean. It seemed to lean out after awhile. As per recommendations I just did a split linkage test. The car rev'd to 4,000 rpm and could go higher. Moving the fuel pump rod separately had minimal effect. The rpm is controlled by the throttle body. It seems the pump is delivering way too much fuel. The CSV does not leak. I see no fuel leaking out of the inspection hole with the electric pump running. The original CSV solenoid would not fire consistently. A new one has resolved that problem.

I tried to turn down the adjustment screw on the back of the pump. I only adjusted it with the car not running. I pushed it in and turned it to the left 3 notches.The problem is that when I start the car, the knurled lnob turns with the pump, not good. I do not think it should rotate.  Tomorrow I will remove the screw at the front of the pump, insert a 5 mm bolt and see if it is stuck open. Keep in mind the car had been running perfectly up until it would not start. Using spray I can get the car started but it is running rich, not lean. The original electric pump was producing 250 ml in 15 sec at 9 psi. There is a rebuilt tall pump producing over 1 litre in 15 sec at 15 psi. Tests were taken at the return line by the tank and just after the main fuel filter. I also installed NGK 5ES plugs. They are now black after a few minutes of running. Any other ideas?

[kampala]

Check the Barometric Compensator (tuna can) sitting on the injection pump.  It can rattle loose and if it gets slightly loose - car runs very rich. 

That’s what happened to me and someone on this site reminded me to check the BC and that what it was.   Here is my story:

https://www.sl113.org/forums/index.php?topic=31398.msg227770#msg227770

[wwheeler]

The B.Compensator is VERY sensitive and usually a .003" shim will make a significant change. You can also use the BC to adjust the full range fuel mixture. This would be instead of messing with the "hard to work" full range screw in the back of the pump. 

[glcg123]

I just removed the inspection can at the front of the injection pump and inserted a 5 mm bolt. The rack does not move at all. Ideas?

Everything was working beautifully previously. It sat for 10 days, and then went into a hard start, rich running situation. The car leaned out itself whilst at the mechanic's shop. We were both surprised. But, it was still running rich. Adjusting the air screw on the manifold would not have that much of an effect. After my fiddling with it yesterday (thumb screw at the back of the pump) it is back to a really rich running situation. Split linkage indicates a huge richness issue.

I did check the barometric compensator. It is tight.

[Cees Klumper]

It's possible the WRD (Warm Running Device) got stuck / the thermostat no longer closes which will I believe result in rich running. This happened to me a few months ago when I restarted by car after 2 years inactivity. The first start was perfect but at subsequent cold starts it became clear the mechanism had 'jammed' for lack of a better term.

[BartSt]

Take a couple of minutes watching this explanation

https://www.youtube.com/watch?v=F6sxlOFmoYw

and smile afterwards

Bart

[ja17]

The rack in the IP will stick when one or more of the pistons in the IP get stuck. The pistons in the IP usually get stuck when the engine sits with moisture contaminated fuel. The moisture will form rust and cause the pistons to stick in their cylinders. Moisture contamination is common with the new alcohol fuels since they can absorb moisture out of the air. Crack open all the injector lines at the injectors. Crank the engine and observe if fuel is being delivered to all six cylinders. If you have one or more cylinders not being supplied fuel, you may have a stuck injection pump rack/pistons. I would definitely check to make sure that the WRD is working freely first. It has a slide valve (piston) in it which can also become stuck.

[glcg123]

Thank you for all of the suggestions. We did not want to risk damaging anything within the injection pump by trying to free it up as we suspected the rack was seized in the "full open" position. The pump was removed by my mechanic and sent to Jerry Fairchild Industries in Northern California for repair. Robert Fairchild advised that the rack was stuck in the open position due to to its seizing internally. It was not a stuck plunger. He said that he had only seen a couple of these before during all his years of working with these pumps. The seizing was caused by rust due to moisture within the pump crankcase. The car is 57 years old! He freed it up, cleaned up the rust and said it would not happen again. At the same time he replaced all seals, gaskets and re-calibrated it. I had also sent the WRD device, start solenoid at the back of the pump, and CSV (which I had cleaned using Sea Foam). Everything checked out OK.

We added 250ml of 10-30 oil to the pump after installing. We had initially drained the oil prior to sending it to him. It seemed to be the right amount although we did not measure it. In hindsight I guess we should have measured how much was originally in there.

The pump has been reinstalled and while it was hard to start the first go round settled down after we readjusted the air valve. The WRD worked perfectly as before. The plugs though new had really sooted up due to the rich running condition. I will replace in the spring as the car has been put away for the winter.

Thank you to everyone who contributed to the Technical Manual. My mechanic would not have been able to work on the car without it. I have owned the 230SL for 17 years. I am the  second owner, the original owner lived three houses down from me. The new fuel system from tank, to transfer pump, to injection pump will definitely add to its value and be a treat to drive this spring.