280SL with M130.981 engine tuning problems

[Berggreen]

Dear All

I am the currently (un)happy owner of an originally US specs silver 11/70 280SL with manual gear and the following configuration:

Engine: M130.981 (installed at some point from a w109, but with the same engine number stamped in as the original 983, except for the 981 - have you seen this before?)
Camshaft: 05 (with some wear on the cams)
Fuel injection pump: R24Y
Distributor - before: BOSCH 0231.116.062
Distributor - current: 123ignition
US throttle housing with constant vacuum

I have had the car since 2017, but it first came out of body renovation this summer, where I started driving it. I also have another 280SL (with aut. from 02/71) and I immediately  noticed that the car was a lot weaker compared my other 280SL. So the first thing I did was to have the valve clearance checked and adjusted, and to replace the US emission control 062 distributor, which did not do anything good for the car, especially as none of the original emission control features like vacuum drive, the black box relays etc. worked anymore. I therefore installed instead a 123ignition like in my other 280SL, where I have very good experience with running it in program 8 and 0-3 degrees ADTC advance at idle (750 rpms). So I chose the same program 8 and set the advance to zero degrees at idle (750 rpm). I did also record a better and more precise ignition with the 123. However, I still lacked power!

My attention now shifted to the linkage system following the linkage tour here on sl113.org. I followed the procedure to the point, but recorded that the linkage to the injection pump had been set deliberately too long to around 245 mm to force the pump not to go to zero position, when at idle. I thought this was the key to the lack of power, and I therefore adjusted the fuel rod back to the factory 233 mm in accordance with the linkage tour document.

I now tried to tune the engine, and I first had to increase the fuel-air mixture a lot to compensate for the leaner mixture with the shorter 233mm fuel rod, and now letting the injection pump go to zero at idle. Instead of using the procedure in the linkage tour with the vaccum-meter and monitoring the idle speed, I instead used a CO meter in the exhaust aiming for the 3.5-4.5 %CO range at 750 rpms.

However, when now trying to tune the engine, I found it impossible to force the rpms in idle down below 1000 rpm, even with the air idle screw all in. Also the idle screw had very little to no influence on the idle speed. In that process I also noticed that the tip of the old idle screw had a large V-notch, which I found very odd, and assumed this was the reason I could not get the rpms down, as it was pulling air even with the screw all in. I therefore bought a new idle screw and installed this instead. But it still had no influence on the idle speed! :-/

Also, by reving the engine in neutral as well as driving the car, there were misfires and almost complete lack of power. But increasing the fuel mixture as well as increasing the ignition advance to mitigate this only made the idle rpms higher.

So the only options to arrive at lower idle rpms seemed to be by either lowering the ignition advance at idle to negative (BDTC), but that would give very poor performance at higher rpms, OR by again increasing the length of the fuel injection linkage rod, like it was initially, to effectively drown the engine down to 750-1000 rpms, but at the same time compensate on the fuel mixture screw on the pump to reach 3.5-4.5 %CO at 750 rpms.

Yesterday, I partially did this, but only forced the rpms down to 900-1000 rpms and adjusted the ignition at idle to around zero degrees to try a compromise setting. Fuel mixture was adjusted down to around 5.0-5.5 %CO. I also moved over into program F, as this seemed to give a much smoother engine response compared to program 8, when reving the engine in neutral.

I then drove the car for a longer distance (60-80 km), and it first went acceptably well on the highway at higher rpms (3000-3500 rpms), but on the return trip on smaller roads at lower rpms (typically 1500-2500), the engine gradually responded worse and worse with loosing power and misfires/engine cut-outs. I even had to increase the fuel mixture on the pump one click up on the return trip, just to get home.

My plan is now to return to the initial configuration with a much longer fuel rod length and a higher advance at idle - aiming at around 8-10 degrees ADTC and idle at 750 rpms, and trying to get back to program 8 on the 123ignition. But I suspect my poor power delivery will return and I will be back to square one! :-/

But before I do this, I would highly appreciate your input and reflections on my story above:

1) What do you think of my story/procedure above and my final adjustment plan?
2) Do you see me doing anything wrong, or could I do something else to make it run better?
3) What do you think the problem is with the engine, injection pump, ignition, etc.?
4) Remember I have a worn 05 cam in the engine. Do you think this could be a significant factor for the poor performance?
5) Same goes for the US air intake housing with constant vacuum supply - however I also have that on my other 280SL, and there it does not cause any problems with the 123ignition in program 8.
6) I don't know, if the fuel injection pump is out of calibration. Do you think the symptoms reported above indicate that this could be the case?
7) Any other thoughts, comments, suggestions?

I look forward to hear your reflections and comments. :-)

Best wishes and thanks in advance!

Christian

11/1970 MB 280SL (man)
02/1971 MB 280SL (aut)
1969 Volvo 1800S (man)

[teahead]

Have you checked your timing?

W/the later throttle body, you're getting constant vacuum, thus constant retard.

If you're running like 20 degrees at 3000RPM, there's your power right there.

Either fix your emissions equipment and change to tune "E", or get an early TB where you have progressive vacuum.

[Berggreen]

Thanx for your input.

I also have the constant vacuum / retard TB on my other 280SL, and is able to run in program 8, and still get around 30 degrees at 3000 rpms, even with an idle timing of around 3 degrees. Thus, I would expect this would also be possible here.

It is very difficult to get the euro spec TB’s in decent condition for a reasonable price. They are all very worn or very pricey. :-S

[Tyler S]

If advancing the timing smooths out the idle then this can be an indication of a lean condition. As well as having the pump adjusted off of its stop. If your throttle valve plate and idle air screw are fully closed then the engine should barely run. You may need to remove the intake boot and visually verify the throttle plate is indeed closed. Someone may have messed with the lever to plate shaft adjustment. If this checks out then start looking for “Pirate Air” as I like to call it. Remember that an engine needs to breathe in order to run. Any vacuum leak present such as a bad brake booster, hose or a WRD slide valve that doesn’t function properly will create a lean condition. A severely worn motor can also cause lean issues. This could be checked by using a vacuum gauge. A low vacuum reading would show.

[Berggreen]

If advancing the timing smooths out the idle then this can be an indication of a lean condition. As well as having the pump adjusted off of its stop. If your throttle valve plate and idle air screw are fully closed then the engine should barely run. You may need to remove the intake boot and visually verify the throttle plate is indeed closed. Someone may have messed with the lever to plate shaft adjustment. If this checks out then start looking for “Pirate Air” as I like to call it. Remember that an engine needs to breathe in order to run. Any vacuum leak present such as a bad brake booster, hose or a WRD slide valve that doesn’t function properly will create a lean condition. A severely worn motor can also cause lean issues. This could be checked by using a vacuum gauge. A low vacuum reading would show.

Thanx Tyler!

The idle is as such not uneven now. Only the rpms are much too high, and even higher when I try to advance the timing more than where it is now at around zero degrees, and I cannot lower the rpms with the air-screw. The only way to lower the rpms is to increase the length of the pump rod linkage, and then back down the fuel-air mixture on the pump mixture screw to arrive at around 3.5-4.5 %CO.

But good point that the engine is getting "pirate air" from somewhere. I have actually already tried with some diesel-starter spray, to spray on different potential areas where a leak could maybe appear, but with no success - I don't see any sudden increase in rpms due to the diesel-starter. I also sprayed on the small air filter on the injection pump to rule out that the thermostat for the warm-up device was not closing the air-supply fully at normal operating temperature. But I did not notice any increase in rpms either, when spraying on the filter with the diesel starter.

By the way on a side remark: I have a new thermostat for the warm-up device, but I cannot remove the two screws holding the house. They are rusted stuck. Any good ideas how to get them loose, without breaking them down in the pump, so that have to be drilled out and a new thread to be made?

I also changed the air-hose from the main air-filter to the air-screw device with no difference as a result. But I have not yet tried to remove the boot on the intake to check the throttle plate. However, when adjusting the stop position, I can feel that the throttle plate is sticking, when moved to zero. Thus, I assumed it is closing shut and is air-tight. But I will double check by removing the boot.

I have not checked the brake booster. How can I check if it is leaking? The car is braking normally.....

If I check with a vacuum gauge, where will you connect the gauge, and what vacuum values should I read and accept / not accept?

Thanks for all your help! :-D

Christian

[Tyler S]

Since you are checking the vacuum at idle you can just “T” into the line at the throttle body for the distributer. I’ll post a vacuum chart below. To disconnect the brake booster, remove the brake booster hose from the intake manifold and plug the manifold port.

[Berggreen]

Since you are checking the vacuum at idle you can just “T” into the line at the throttle body for the distributer. I’ll post a vacuum chart below. To disconnect the brake booster, remove the brake booster hose from the intake manifold and plug the manifold port.

Fantastic - I did not know you could know so much about the engine condition by reading the vacuum! :-D

Will it also work to T into the vacuum line for the distributor, when I have the constant vacuum throttle house, originally meant for the 062 distributor?

Thanx,

Christian

[Tyler S]

Yes. Vacuum line for distributor. That's the easiest place without getting creative. The gauge test is more guidance than anything else. Always verify your findings.

[teahead]

Shouldn't 15PSI at idle be what's normal on a late M130?

[Tyler S]

Teahead, Yes 15 is about right. Like I said the chart is more of a guide. Not specs for our cars. But it is a good tool to point you in the right direction.

[ctaylor738]

Pardon me for being late to the party.  I don't think you'll have much success with the 123 and the US emissions throttle body.  For the cars to run right, like accelerating in normal driving, they need the "snap' of advance as soon as the throttle plate moves off idle.  You only get that with the earlier throttle body with the vacuum opening behind the plate.  Gernold at SL-Tech can modify your throttle body, and then you can use curve "D" on the 123.

I hope that you find your false air (as I call it).  My guess is that it's leaking past the throttle plate.

Good luck,

CT