Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: Jonny B on August 01, 2009, 20:36:18
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Jim Villers was kind enough to lend me his air/fuel meter. I put in use today. Here are the results so I am asking for some help on interpretation and potential next steps.
After warm up, at speed, the meter is bouncing between 15.2 to 16.2 %. At idle it is running at 21-22%. At about 35-40 mph the ratio drops a little to 14.7 +/-. I did stop and dial in two more clicks at idle on the enrichment crew (clockwise as you look at the back of the screw). The car appears to be running reasonably, still some shake and the gas mileage coming back from Blacklick was around 15. We are planning to get the injectors checked, and I know I need to get the valves adjusted.
Are these readings in the right ball park???
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Jonny,
JA did the advanced version of the Blacklick air/fuel mixture (CO) test on my car after you left.
It works on a simple principle: absent external forces/controls, air and fuel will want to burn at the "ideal" or (remember this word from chemistry) stoichiometric ration. All the linkages and adjustments provide these external forces and controls.
Warm the car up.
Separate the linkage above the FI pump.
Open the butterfly to add more air; if the RPM goes up, you are too rich.
Open the throttle to add more fuel; if the RPM goes up, you are too lean.
Adjust the idle richness with that screw you talk about.
DO THE SAME TEST at midrange (1800-2000 RPM) and at high range (3500). Do it by holding the air and fuel linkages together as you press them down.
On my car, the idle was perfect mix. Midrange and High range: too lean.
Note: On nearly every car I've seen this test done, something isn't right. I suspect many cars have out of kilter fuel air ratios.
It's on my list to get in the pump and richen up the entire pump, and then lean it back at ldle.
Worth a check on yours.
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Jonny,
Your c0 values seem high???
I thought the values should be more in the 5% (or less) range, give or take...
See attached .pdf
Bob
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The gauge that I loaned Jon measures air/fuel ratio. Normal "power" occurs in he 13-14:1 air to fuel. Idle and cruising can be leaner; 15:1 or greater. You should not be lean under power (greater tan 15:1) as you will have a tendance to burn valves or aluminum.
Jon ... The real value is to focus on flat spots while driving and to determine if it is caused by too much or too little fuel. then make adjustments within that range.
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Because there can be a variety of circumstances that alter the "numeric" state of perfection, Joe's test is ideal. If you strive for some set of numbers you may find these numbers don't work ideally for your car, your engine, your circumstances. While this isn't scientific, I can tell you that someone "tuned" my air fuel (so they say...) mixture with a CO meter and that gave me an overall lean condition.
There is an overall rack adjustment in the FI pump for rich/lean across the entire RPM/load range; then there are several screws for ranges (high/medium); and the idle adjustment which is external.
I suspect the best thing to do is adjust your car for the ideal, best running condition for your engine and your circumstances, and whatever the numbers are, they are...
Bob Possel: those numbers Jonny quoted are not CO %, but air/fuel ratios, I believe. That's why they sound very high. In a perfect world under perfect conditions, the ideal air/fuel ratio burns all the fuel and nearly all the oxygen and leaves a CO in the % that you are expecting. See the links below for some interesting information. Many race cars and motorcycles have these gauges built in as dash gauges.
Some info:
http://www.autofamille.com/stoichiometric-af-ratio-meter
http://www.rbracing-rsr.com/downloads/RSR_O2_install.pdf
http://en.wikipedia.org/wiki/Air-fuel_ratio_meter
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Michael ..... Your references are for narrow band sensors that are non-linear co2 sensors. The gauge that I loaned Jon uses a wide band sensor that accurately measures unburned fuel in addition to unburned oxygen. It accurately measures the air/fuel ratio from about 10.0:1 (very rich) to 20:1 (very lean).
I have found that using a wide band gauge for tuning greatly improves the process ofer the seat of the pants method. Using accurate measurements you can both reproduce the setting and also allow you to set it where you want it. You always need to verify tuning by driving. The purpose of tuning is a better driving car and the wide-band gauge is an excellent new tool.
I have a friend that swears that tuning the ignition "by ear" is better; I prefer a timing light.
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Brings to mind the old country saying 'Are you going to believe me, or your lying ears.'
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Brings to mind the old country saying 'Are you going to believe me, or your lying ears.'
Hey, that's a good one. What country? ;)
Hey, if you are running rich at 10:1, or lean at 20:1, my suspicion--just a wild hunch here--is that you don't need a [expensive and sophisticated] gauge to tell you. Just a guess here, though. The narrow band is a tool of the racing trade, working with installed o2 sensors; the wide band a diagnostic tool of high performance tuning.
If your car is good enough all around, with no vacuum or exhaust leaks, all electricals 100%, known and good engine condition, known and good fuel quality and all the other parameters that affect performance known and controlled, (and in our cars that includes things like performance of the FI system and injectors) and you want to tune your car for peak performance, well this is one tool to do it. (This is the reason why you see these devices used as precision tuning devices for high performance engines and racing--not a general tool of diagnostics. When you have a well running engine and car, they will help you tune it for peak performance.)
I'll let you know when I'm at that point. :(
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Just received my Innovate LM-2 air fuel ratio tuner. Need to buy another cable for rpm input and an sd card to record data. So my readings so far are at approx rpms.
warm idle 22
1300 to 2000 rpm 12
above 2000 14.7
I have experienced sputtering when accelerating in the low rpm range. Once I'm up over 2000 or 2500 the car runs great. This data indicates that I have a lean condition at idle followed by a rich condition in the lower rpm range.
Once I get the cable issue sorted I should be able to drive the car and record air fuel ratio and rpm data and then display/graph the information on my laptop with the included software. With some more data I can start working of fine tuning the air fuel ratios.
I've wanted a tool like this to help understand the barometric cell shims. My car seems to have thicker shimming then others. I have not touched/adjusted that stuff in the 15 years I have owned the SL.
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FYI Found a conversion table for co and afr. Here is a sample
co afr
3.5 13.20
4.0 13.00
4.5 12.83
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Jeff .... Do not worry about the A/F at idle or just reving the engine. Watch the numbers as you drive the car, specifically when it stumbles or there is a flat spot. The gauge will tell you if is too much or too little fuel. My experience is that there was too much fuel and leaning made the car run better. Every car is different so use the instrumentation to help you solve your issues. My target was 13:1 to 14:1 during both light and heavy acceleration. While crusing at a steady speed, the A/F can go higher.
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Thanks Jim,
Just got back from a 20 minute drive. I had the lengthen the o2 sensor cable. I ordered the rpm input cable and sd card yesterday. Soon I will be able to plot rpm and af at the same time. This will help show the car under load as I accelerate going through the gears on my manual transmission. I was able to get a pretty consistent af ratio of 19 crusing on a level surface at 2500 rpm and 60 mph. When hard accelerating from 3000 to 5000 rpms the af is in the 15 range and the engine feels very strong. I think this will be a usefull tool. In addition to the stumbling my car idle varies from a warm to hot engine. Sometimes it will be 1100 and other times 700. I've done everything there is to be done with the linkage and I'm comfortable with that not being the problem. The WRD works. The tts and temp switches are new and working. I have the 123 ignition system, new plugs, newly adjusted valves, no vacuum leaks, new fuel filter, good fuel pump. I've started to look at the barometric compensator and now that I can take performance data I may run some tests with different shims. Previous owner had 4+ mm shims. I don't know if thats right or wrong. I haven't touched that or the wrd shims. Should be able to record some data next week. I'll post what I get.
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Jim,
Do you know where I can find factory lambda or co data for our cars fuel injection system? I know I've seen it somewhere.
Thanks
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Jeff .... I have attached a graph from my Weber technical book on setting up Weber carburetors. The injection system should be similar.
It sounds like your injection pump is too lean. Full throttle should be about 13, cruising normally is about 15 or so.
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Thanks Jim. I agree the fip is too lean. Going to record some as is data for a baseline and then do some tuning.
Jeff
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Taken delivery of an air fuel ration tester, model LM-2, from Innovate Motor Sport. I installed a manifold air pressure and throttle position sensor so that I can display/record real time data on my lap top. The map sensor is hooked up to a the rear of my manifold that previously had a plug in it. The tps is installed where the emissions on/off switch was located on the throttle body. No permanant changes were made and all can be easily removed after testing. The idea is to duplicate the load testing specified by MB in the BBB. These test can be done on a dynomometer or on the road. Tests require specific rpm ranges and map pressure or engine loads. Preliminary testing indicates that my car is very lean everywhere but at idle. Seems prior owner mechanic had some idea about this so shims were added to the baro compensator. In order to adjust at idle my idle knob was 32 clicks from full rich. This is 4 clicks from being out of the leaning range. So I'm near the limit on trying to enrich the mixture by shimming the baro.
After looking at fuel flow rates after the filter, ignition timing, wrd, csv and baro I'm ready to start making changes inside the fip. Floowing that I will record data on a test run and then decide where to make additional changes.
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purchased a zeitronix a/f meter . with this meter you do not need the RPM cable it is included and works really well . did you put a hole for the 02 or use a clamp. by the way at idle you can not get a good reading with the clamp on the tip of the exhaust .
Thanks
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I use a clamp in the exhaust pipe to hold the o2 sensor. As far as I can tell it is accurate at idle. The o2 sensor has a preheating element that requires high current (cigar lighter) to get up to temp. It will not provide data until it is up to temp.
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tuners will not use a clamp to take idle readings since it is to close the the end of the pipe and ambient air can affrect the reading . was told this many time for my Porsche 930
Thanks
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I heard that mentioned but I've not been able to find any comparison data. Any idea how far off they say it is. I took an 18 inch piece of exhaust pipe with a 1 5/8 inch od and welded a bung 6 inches from one end. It fits tightly in the tail pipe and does not require a clamp to hold it in place. It looks awful but I have 12 inches of exhaust pipe sticking out after the bung to minimize contamination.
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What happened to lambda of 14.7 used on the Bosch CIS?
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I've been tuning my fip for the past three weeks. I've made atleast 30 test runs after adjustments in an attempt to understand what effect the adjustments have on afr so that I could tune my car to meet the MB road test specification. The BBB sets the following exhaust emission specifications for my car.
Full load road test - third gear from 3K rpm up - 13.77 to 12.64 afr
Lower part load test - third gear-1500 rpm - 11.81 inHg- 14.54 to 14.11 afr
Upper part load test - third gear - 3000 rpn - 11.81 inHg- 14.72 to 14.11 afr
Tuning is challenging and tedious. That's maybe an understatement. It starts with having to remove the fuel shut off solenoid to better access the rack and white/black screw adjustments. Some SLs have two solenoids on the back of there pump. After taking it off and on a couple of times I realized fabricating a cover plate was in order. Helps a lot. The rack screw is pretty easy to get at and adjustments are straight forward. The white and black screws are a pain to adjust You need to remove the idle thumb screw cover plate and allow a considerable amount of oil to drain. It goes all over the place and you will make a mess. I used a small adjustable mirror mounted to an extendable pole to see the screws. Now the you can see them but the image is upside down and backwards. Adjusting them is tedious because of the need for good lighting and a steady hand on your screw driver. Turning the screws requuires skill and you need to count clicks and turn the screws in the correct direction. Its very easy to get mixed up. So you need to be careful and keep a record of the changes.
I got to where I could change the rack in five minutes and the white and black screws in 20 minutes. But I had lots of practise. Any way it can be done and I improved the upper range afr to where it now meets specs. It was very lean and as a result of the changes the throttle response is fantastic and the engine is much stronger.
I'll post some more information about my experience over the next week or so.
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Here is the setup I used to see manifold air pressure and rpms so that I could run the partial and full load tests. Regulating rpms at a specific load is easier if you can find the perfect hill. If you can't the parking brake can provide an additional load.
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Just looked at some of the data charts of my afr testing.
Here is a comparison of the average afr from the original fip settings and todays "tuned" settings.
rpm 1000 2000 3000 4000
Nov 6 14.4 16.4 18.6 17.1
Nov 25 13.5 13.7 14.3 14.9
The comparison data is taken at a map of 12.5 inHg which represents a lighter load than the MB spec of 11.81 inHg. I just thought it was a good way to explain the starting condition of my fip. Way too lean!
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For those interested in tuning their fip I suggest that you purchase a portable wide band air fuel ratio meter with data logging capability. In addition to the meter you will need to weld a bung into your exhaust system for the modern O2 sensor. An alternative to welding a bung in your exhaust pipe is to buy an 18 inch piece of 1 5/8 in od exhaust pipe and weld a bung about 5 inches from one end. This can be slipped inside one of the rear exhaust tips on the back of your car.
Make sure to buy an afr meter with the capability to accept analog inputs for recording rpms and manifold air pressure (map). The rpm pickup can come from the negative side of the coil. You will need to buy a modern map sensor to measure air pressure in the intake manifold. In addition to power the map sensor needs a vacuum tap in the intake manifold. I had a plug in the rear of my intake manifold which I used to mount a fitting for the vacuum hose.
After you have the afr meter inputs available you can begin to monitor the afr of your engine. As mentioned earlier under this topic MB has a very 4 specific CO specifications. Two of the specifications require you to place a load on the engine during the test. This load requirement can be read by the map sensor. These tests require you to establish a specific load and rpm readings. Once these measurments are achieved you can read the afr and compare that to the MB specification. The idle and full load test do not require map sensor inputs.
With this data recorded you can compare you actual fip performance against the MB spec and tune your pump if needed.
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I have some pretty accurate before and after acceleration statistics I'd like to share. The acceleration tests took place on the same stretch of road almost 3 weeks apart. The test involved a full load acceleration in second gear from less than 2000 rpms to over 5000 rpms. I decided to examine the time period which elapsed between 2500 to 5000 rpms. I'ved converted the rpm numbers to mph.
Here are the results:
Nov 6 25 to 50 mph 5.16 seconds
Nov 25 25 to 50 mph 4.09 seconds
The improvement in acceleration is quite noticable as is the tone of the engine and exhaust. In my case getting the afr mixture correct made for a big improvement in performance.
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With my recent experience tuning I thought I'd take a crack at summarizing the purpose of internal adjustments of the fuel injection pump. Please offer comments if something I've stated is incorrect or unclear. It is a very difficult subject to write conclusively about. It's maybe best to read Joe's fuel injection pump tour before trying to read my explanation of the internal adjustments.
I came to the realization concerning the roles of the three separate screws: they are anything but independent of one another. In other words, it is altogether too easy to over-adjust one set of screws, and overwhelm the adjustment oelsewhere. In general the white screws adjust high rpm partial load fuel delivery. Black screws adjust low to mid range partial load fuel delivery. The main rack adjusts fuel volume at all rpm's. The white, black and idle screws set the preload on the governor flyweights by adjusting three springs of different weights and lengths. The longest and lightest spring being the idle, and the shortest and heaviest the high speed. Adjusting the fuel injection pump is a balancing act with a constant need to compromise.
From their CW stop the white and black screws can turn nine CCW turns before the screw heads are flush with the aft edges of the flat springs that provide the "detent" action. Therefore the white and black screws have an effective range of 54 clicks.
The further the flyweights are allowed to open, the leaner it will run. "Left is lean" on that externally adjustable center idle screw. Left backs it out, and allows the flyweights to open further and pull the space cam further back. It would stand to reason that holds true for the mid and high speed screws as well. Space "cam" is actually a bit of a misnomer; it does not spin as one would expect a cam to spin. It looks nothing like a cam, either. More like a small metal hockey puck. It rotates about its axis for about 90 degrees or so when pulled up and down by an arm connected to the throttle lever. It moves fore and aft on its axis in response to the opening of the flyweights which is influenced by the three spring settings.
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Jeff ..... Excellent. I have payed a lot with a wide band gauge but mine is a very basic system (read cheaper) without the logging and other inputs. Your target numbers are also close to mine even though I have not been to adjust the carburetors on my 190SL as well as you have been able to tune your injection system.
We are currently working on a 230SL in my garage; the engine is out being rebuilt. We have a rebuilt injection pump ready to install and have tested the injectors (we found one bad injector that probably led to a lean cylinder engine failure). I'll follow your tuning ideas when we get it running again. My concern is that the fuel injection volume might need to be adjusted for an ethanol blended fuel.
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To accomplish the MB road test you're going to need a manifold air pressure input of some sort. One idea is to run a vacuum line from the intake manifold into the cockpit and tape a vacuum gauge up near the tach. In that way you could see both inputs and when they meet the MB spec take your afr. Another idea is to use a modern map sensor. The sensor takes a vacuum input and outputs voltage. As the vacuum changes the voltage changes from 0 to 5 volts. With a multi meter again taped near the tach you can watch voltage and rpm. When the voltage reading is about 2.4 volts you have met the MB 300mmHg load spec. If you need the exact voltage reading for 300 mmHg/ 11.78inHg let me know and I'll get it for you.
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I think I'm almost finsihed with my air fuel ratio experiments. For $22.00 I added an accelerometer input to my LM-2 afr meter. With this device I can measure acceleration and use a set of formulas included with the data loging software to estimate rear wheel horsepower and torque. It uses data from the rpm and acceleration channels along with other data that you input. Here is what the formula uses.
Veh wgt 3000 lbs
Tire dia 24.7 inch
Gear ratio of run 2.23
Final drive 3.27
Rpm channel RPM
Acc channel accel
Frontal area 25
Drag .45
Atmosp 29.92
Temp 50
I performed the test in second gear under full accelration from 2000 to 6000 rpms. At 5400 rpms my calculated rear wheel horsepower peaked at 129.3 hp. Torque measured 114 ft lbs.
Torque peaked earlier in the rpm range at 135 ftlbs.
How accurate is the calculation?
SAE Net- In 1972, American manufacturers phased in SAE net horsepower. This is the standard on which current American ratings are based. This rating is measured at the flywheel, on an engine dyno, but the engine is tested with all accessories installed, including a full exhaust system, all pumps, the alternator, the starter, and emissions controls.
SAE Gross-This is the old process that American manufacturers used as a guide for rating their cars. It was in place until 1971. SAE gross also measures horsepower at the flywheel, but with no accessories to bog it down. This is the bare engine with nothing but the absolute essentials attached to it; little more than a carb, fuel pump, oil pump, and water pump. Because the test equipment on the engine is not the same as in SAE net, it is impossible to provide a mathematical calculation between SAE net and SAE gross. As a general rule, however, SAE net tends to be approximately 80% of the value of SAE gross.
As a very general rule, rear-wheel horsepower on a manual-transmission car is about 15% less than SAE net, and rear-wheel horsepower on an automatic-transmission car is about 20% less than SAE net.
So
MB advertised Gross HP for the 280SL 195
Less for SAE net accessories .80%
Less for power train .85%
Adjusted rear wheel hp 132
The Innovate formula set rw hp at 129.3 for my car.
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Jeff, what you have done, to adapt modern technology to tune and spec our cars, is too cool. Given that no permanent modifications are needed, for a relatively modest investment one can avoid the vagueries of CO measurement/spark plug color, etc., and the hassle of a dynamometer(!?), and get accurate measurements. Hats off!
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Thanks. It was a fun and rewarding learning experience. Setting up the equipment is one part of the effort. Depending how far you're off can lead to a simple or in my case very involved tuning effort. But is is nice to be working with accurate data versus spark plug color charts. I thought my plugs were perfect but the afr was off.