Ron,
The MPS is very sensitive. 1/8 of a turn makes a big difference. What makes you think it is bad? Have you checked it using the values given in the manual (section 7.4)?
When my car was running rich, it turned out to be worn trigger points. There have been several threads here about that. The rubbing blocks wear, then the ecu fires the injectors either too often or at the wrong time? I don't know exactly, but replacing the triggers cured the problem. Look for the thread where we discussed removing the distributor, attaching an ohm meter to each set of points and measuring the angle that the points stay closed. It should be in the 100-120 deg range (No specs that I know of). But I had one that was so worn it stayed closed for about 180deg.
Otherwise, your method of adjustment sounds about right. I wouldn't worry about the idle CO - just get it idle evenly.
BTW - If you rotate the distributor CCW timing advances. You need to be turned almost all the way to the end of the slot to get near to 30deg BTDC at 3000rpm no vac (best setting for these old cars!) At that point, tdc will be to the left. Put a paint or chalk mark at 30BTDC (clockwise from TDC) and try to adjust to it.
I just got back yesterday from a few months in SC, so am a bit rusty on this stuff. I am sure others will correct above if it is inaccurate
Hooked up the battery on the SL today and it started almost before the starter turned the engine! Went for a run and she ran beautifully.
BTW - The car does run on rich side under load. This is a post I made some time ago on BW (you may have seen it). To do teh full load test, you need to be going up a steep hill, or have your foot on the brake while maintaining 3000rpm.
Quote:
The emission specs for the 117 engine according to the MB Technical Data Manual are:
Full load shifter position S 3,000 rpm = 2% - 5%
Upper partial load position S, 2,500 rpm 300 mm Hg vacuum 0.1% - 0.5%
Lower partial load 3rd gear shifter position S, 1,500 rpm 300 mm Hg vacuum = 0.2% - 0.5%
Idle neutral, idle speed, oil at operating temp = 0.5% - 2.0%
All % CO and would apply, I guess, to either dyno or road testing. I just used the idle and the full load for setting MPS & ECU.
Those are the North American specs. Euro are slightly different.
What type of meter do you have? Some of the old Wheatstone Bridge ones are apparently susceptible to moisture and kind of useless. If it is not one you can take in the car with, then you could try this:
First set timing so you have 5-8deg BTDC without vac and with A/C turned OFF. Check that you have good vacuum at idle (16-17" is normal). Also make sure your Throttle Position idle switch is functioning properly. Method is in engine manual (also HERE and in pdf attached)
- Warm the car by driving it for at least five miles.
- Disconnect the throttle position switch plug (so as to disable the idle circuit) and set the ECU knob in the middle of it's range which is 11 clicks from right or left.
- Adjust the 4mm MPS screw in VERY SMALL increments so that you get about 3.5 percent CO at 2500-3000rpm. (at least as a starting point)
- Shut engine down and reconnect throttle plug.
- Start up again and set idle speed to about 750-800 rpm's.
- Use the ECU knob to set the idle co to about 1.5- 2.5 %CO. (rev enginel in between adjustments and taking new reading)
-Take car for a drive and then recheck CO at same conditions.
On my own car, I used this procedure. At first, I had a loan of an older CO meter - But it did not give consistent results. Since then, I have purchased a wideband Air/Fuel ratio gauge. (There are a number of manufacturers - mine is an AEM and is a permanent mount. Innovation makes portable units. Cost $200-$350 and well worth it.) This allows me to monitor AFR at all times. Better than watching TV
My car currently cruises at an AFR of 13-14 and idles at about 13.5. But I can set these wherever I want. Car seems to like to run on rich side. But for economy, it could be leaned out (but not too much or you could burn valves pistons etc!) But who cares about economy on and old SL
Sorry this is so long winded. I have had my 350SL for 20 years, but with AFR gauge, have finally got somewhere this year!
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