M130 Fuelling Issue

[travisdutton]

Good day members,

My 280 SL is running extremely rich to the point where it does not even hold idle anymore. I have tried to diagnose the situation, and had someone else work on it too, but unfortunately to no avail, and if anything, it has become much worse. Here is a bit of background on the car recently:

1: The mechanic who did work on the car did not keep any records whatsoever regarding the work that he did. In addition, he did all his work with a W123 fuel pump installed, and a fuel tank that was horrendously rusted out. The car was driven about 150km in this state, as he did not bother to check the tank and its contents.

2: The fuel tank and fuel pump has been replaced with an original short pump, although the pump has been reconditioned. There is a T-piece fitted from the short pump to the return line to the tank (I am not sure if this is correct)

3: The cold start valve has been rebuilt too, but however is not connected as I believe it is not atomising fuel well enough and also running constantly, would would make the rich mixture even worse. The air line to the valve is however still connected, and the WRD still sucks air when the engine is hot.

4: The car does not start in a zero position on the throttle and injector pump, and will only start with some throttle actuation, as well as only running decently with some throttle input.

5: I have since adjusted the idle mixture fully counterclockwise to lean out the mixture, which has drastically improved the idling of the car, but have found out that it runs even better with the return line clamped?

This has totally confused me, as I would suspect that the closed return line would mean more fuel and a richer mix?

I am aware that these adjustments are merely a temporary fix, but I would like to find out the best steps going forward, and maybe if I have missed anything in diagnosing this issue.

Kind regards

[Klaus Pieper]

Hi Travis,

I live just down the road from you in Westville.  I have had my 230 SL for 20+ years and although I am not by a long shot an expert on these cars, I might be of help.  If you wish, you are welcome to contact me on 083 256 5588.

Regards
Klaus

[ja17]

Check your fuel pressure. The return fuel line fitting on the injection pump serves as a basic kind of fuel regulator which restricts fuel from easily flowing back to the tank. There are two different types of this fitting. One has a check valve and the other has a tiny orifice. Both serve the same purpose (to raise fuel pressure at the pump).  If your system uses the "t" fitting and by-pass line at the gas tank, you should have the return fitting with the check valve. In any case check your fuel pressure in the system. It should be 12-15 psi. If it falls under 11psi, you'll start having running and starting problems.

[ctaylor738]

Also, put a pan under the injection pump, and remove the dipstick from the lower rear of the pump.  Use a small tube and a pump to suction out the oil, and refill to the mark on the dipstick with clean engine oil (200 cc).  You can use the mechanism out of a spray bottle but a pump will make this faster and easier.  This has improved several rich-running situations for me.

Good luck,

CAT

[rwmastel]

I have tried to diagnose the situation, diagnosing this issue.

What have you done and what were the results of each step?

The cold start valve has been rebuilt too, but however is not connected as I believe it is not atomising fuel well enough

Why do you believe that?

I would like to find out the best steps going forward, and maybe if I have missed anything in diagnosing this issue.

Let's work with facts.

First, create some known facts.
- Set the fuel injection linkages to base level using the procedure on this site, so you know it is good.
- I believe there is a process to set the injection pump to a base setup?  You need to know it's set right.
- Others can recommend some other things to set to a known good baseline.  Maybe adjusting valves?  I don't know what else to adjust to factory spec.

Next, collect some facts.
- Read the spark plugs to see how rich the engine is running.
- Measure the fuel flow rate produced by the electric fuel pump.
- Also, measure the fuel pressure.
- Confirm if the cold start valve has a leak, contributing to rich condition.
- Confirm the spray pattern, a working csv should help starting without touching accelerator pedal.
- Ensure the csv is activated for the proper time duration and stops.
- Confirm when the airflow starts or stops in the WRD.
- Is the barometric compensator letting air in?

What else can we recommend for fact gathering to understand the current status of the car?

Travis - let us know what you learn from this and other recommendations and the group will help through troubleshooting.

[rwmastel]

Also, put a pan under the injection pump, and remove the dipstick from the lower rear of the pump.

280SL still had the dipstick?

[ja17]

If your WRD is still sucking a lot of air when the engine is warm, it might be stuck causing a rich mixture.

[Benz Dr.]

If your WRD is still sucking a lot of air when the engine is warm, it might be stuck causing a rich mixture.

It would be, and it is likely the main cause of this rich running problem. Not sure why a CSV would stay energized all of the time..........

[ctaylor738]

Also, be sure that the injection pump lever is sitting on the stop at idle. 

[travisdutton]

Hi Travis,

I live just down the road from you in Westville.  I have had my 230 SL for 20+ years and although I am not by a long shot an expert on these cars, I might be of help.  If you wish, you are welcome to contact me on 083 256 5588.

Regards
Klaus

Thanks Klaus, I will do that!

[travisdutton]

Check your fuel pressure. The return fuel line fitting on the injection pump serves as a basic kind of fuel regulator which restricts fuel from easily flowing back to the tank. There are two different types of this fitting. One has a check valve and the other has a tiny orifice. Both serve the same purpose (to raise fuel pressure at the pump).  If your system uses the "t" fitting and by-pass line at the gas tank, you should have the return fitting with the check valve. In any case check your fuel pressure in the system. It should be 12-15 psi. If it falls under 11psi, you'll start having running and starting problems.

There is just a generic fuel line acting as the return, although I did see one of those regulated fuel lines which was lying in the boot. I honestly had assumed something broke off in the line previously!

The fuel lines to and from the IP are not original, so this would explain the lack of any relevant pressure regulating device in the return line.

[travisdutton]

If your WRD is still sucking a lot of air when the engine is warm, it might be stuck causing a rich mixture.

That is true, although the thing that puzzles me is how the car is still running so overly rich even on startup. The cold start conditions don't seem to even be lean enough.

[ja17]

Make sure your WRD is operating correctly. You will also need to check the fuel pressure first. It's easy to do. Unhook the metal fuel line going to the cold start solenoid and clamp a pressure gauge on it. Some basic diagnostics like that will point you down the right path.

[travisdutton]

Hello all,

Just a quick update on the current state of the vehicle. Things have changed for the better I hope!

The attached picture of the old plugs shows that they were badly fouled. I had an original Mercedes set on order and went to collect them today, and fitted them. I also fitted a pipe which looked to have a restrictor in it (picture attached) as the return line out of the IP. The following happened:

1. Car started and idled this time - around 1500rpm.
2. No misfires, backfires or pops from the exhaust, contrary to the initial setup.
3. I turned the fully lean IP screw 10 clicks richer, which lowered the RPM TO 1200. I have left it there this evening.
4. I have fully closed the idle air screw.
5. Test drive went perfectly, unlike previous times.
6. A split linkage test showed that adding either fuel or air lowered the revs. Good mix then?

The car sits in the current state:
1. Injector pump 10 clicks from completely lean (left). It was completely lean previously.
2. Idle screw closed.
3. CSV disconnected from electrical and fuel inputs, however WRD air still supplies it.

I will still try to tackle all suggestions in the near future, but just wanted to give a small update on the situation.

One question I still have: is the replacement of spark plugs just a temporary fix or may the combination of new spark and the newly fitted restricted return line be a winner?

Thanks again.

[rwmastel]

Travis,

Great to hear you're making progress.

I also fitted a pipe which looked to have a restrictor in it (picture attached) as the return line out of the IP.

Remember, Joe A said ...

The return fuel line fitting on the injection pump serves as a basic kind of fuel regulator which restricts fuel from easily flowing back to the tank.

So, maybe your IP fitting was removed or failed?  Or, maybe you now have a restrictor fitting and a restrictor line.

[ja17]

Use the split linkage test to check the mixture with cold and warmed engine. You can also do the test at different rpms (a little more tricky).  By "fully closed idle screw" are your referring to the large air screw or the intake venture stop screw?

[travisdutton]

Use the split linkage test to check the mixture with cold and warmed engine. You can also do the test at different rpms (a little more tricky).  By "fully closed idle screw" are your referring to the large air screw or the intake venture stop screw?

I will try with both cold and warm, thanks. I refer to the big idle screw as I have set the intake stop screw as per the linkage tour.

[ja17]

The big air idle screw should have a little adjustment range in both directions. If yours is screwed all the way in, it might indicate your engine is getting too much air (lean). Possible causes may be a vacuum leak, venture air flap not closed all the way, or the WRD air slide not closing.

[jim 56]

Hi: Let me say the first disclaimer I am by far not an expert. I think you are jumping around too much I did the same thing.
     I think there is a procedure on this site you should start by following a set order of checking things.
     I know you have a rich condition but still start by checking the electrical side are plugs gapped right are they the right wires with right
     ohms check the point gap and dwell and make sure the timing is right.

Next start on the fuel section make sure all filters are clean tank screen, fuel pump filter.  The pump should put out 15 PSI or at min. 12 PSI. I didn't see anybody say anything about the return fuel flow which considering the problem you mentioned about the check valve on the outlet of the injection pump. At the tank you have to check that you are getting at least 1 liter of fuel in 15 seconds. Then you should check the WRD. I took mine out and put it in hot water to make sure that it is working. Watch out for the shims under it and read the tech manual about how it works. I think some air getting thru when the car is running is OK if when you block it it doesn't change the idle{when warm). Now do the split linkage test. I'm sure I missed something in here but I hope this helped. There are some videos on you tube I know one really helped me.
Good Luck
Jim

[rwmastel]

Jim,

You and I were thinking along the same wavelength.  Check and set as many things as possible to a good known state, then troubleshoot one system at a time.