Author Topic: Please help with my CO numbers! (Read 22592 times)

mrfatboy · « **on:** February 02, 2012, 00:41:00 »

Hey Guys,

I was hoping somebody could help me out with my CO numbers for my 69 280sl stick. I have borrowed a Gunson CO meter and come up with the following information.

650rpm Idle w/vac (I can't seem to get it higher) is 3.5% - 4.5%. Within spec from the manual.
1500 rpm is 11%-12% (should be 1.5 -3.0) From the manual
3000 rpm is 11%-12% (should be 0.2 -1.5) From the manual

The manual states that the 1500 & 3000 rpm should be under partial load. I don't have a dyno so this is all done parked in the driveway

What should I be able to gleen from the 1500 & 3000rpm CO readings if anything while just sitting in the driveway doing these tests? Can I use the numbers to make my CO adjustments. If so, I assume I could lean out the 1500 & 3000rpm ranges by removing shims in the WRD or BC and then increase richness at idle using the knob on the back of the pump. I have an adjustable bolt in the FIP where the BC goes to adjust the fuel mixture across all ranges.

Is the doable? Can I even look at 1500 & 3000rpm CO numbers without being on a dyno?

Here are my other specs:

Dwell 37.2
WRD Tested and working. Sucks in air when cold. No air getting sucked in when warm.
CSV & TTS Testing and working
Linkage to spec as per the linkage tour
Timing (w/vacuum) is 2 ATDC
Timing (w/o Vacuum) is 8 BTDC

Spark Plug Wires: New type. All measured at 1k Ohm.
Coil: Silver with Red Label
Ballast Resistor: Red (1.8ohm)
Distributor: 051 Cast iron (Retard with matching Retard Intake Manifold (vacuum connector on bottom)
Plugs: NGK BP5ES (Based on you recommendation several years ago

)

I have not tested timing at 1500 or 3000+rpm yet. Will get numbers tomorrow when fellow member 66andBlue comes over to help.

thanks

twistedtree · « **Reply #1 on:** February 02, 2012, 02:06:50 »

Let's see what the more experience folks have to say, but I wouldn't think the CO w/ and w/o load would be close to the same, i.e. you are running rich. Your bolt should make it easy to experiment - just keep careful track of the changes you make so you can reverse them if needed. And yes, if you lean out across the full range you will need to richen the idle back up

Benz Dr. · « **Reply #2 on:** February 02, 2012, 02:57:39 »

OK. Lets start with the basic stuff. You have done some pretty good diagnostics but now we have to try and figure out what those numbers are telling us.

What coil are you running? The standard black one or the later blue one? Which distributor is on the engine 051 or 062 ? Which spark plugs are you using - NGK or Bosch? Any carbon core wires in the system - IK ohm spark plug ends?

I am now using NGK BP5ES which about similar to the old Bosch W9DC. No carbon core wires which I often find on the coil wire and no other resistors other than at the spark plug ends. If you have the black coil you can upgrade to the red one and a 1.8 ohm ballast resistor.

If you have the cast iron 051 distributor, it should advance about 10 degrees when you pull the vacuum line off. Do all testing with the lines attached. If you are running the 051 or similar, set your idle timming to about 5 - 6 degrees BTDC. Total advance should be about 35 -36 degrees at 3,000 RPM. The 30 degrees at 3,000 RPM often stated is how much the distributor should advance but you also have to add the idle setting to obtain the full amount.

If you have the later 062, this is a bit more complicated. You should have full vacuum going to the distributor until about 2,200 RPM. The speed relay should shut off the vacuum via the switch over valve and the distributor will advance about 20 more degrees. On this system timing is advanced by mechanical up to 2,200 RPM and then the vacuum advance kicks in. If you have the vacuum line from the throttle body connected directly to the distrbutor, ( like I see on so many cars ) all you will have is about 20 degrees of mechanical advance. The engine will lack mid range power and will be very thirsty. The vacuum line should go from the throttle body to the center port on the vacuum switch over valve and then the outer port should connect to a line that goes to the distributor.
Idle timming should be about 3 or 4 degrees ATDC at idle on this system and you should have about the same 35 degrees at 3,000 RPM. You can set the timing at full advance and then check it at idle which should be somewhere ATDC. If it is, then everything is working. Don't disconnect this system thinking it will work better - it won't. Hooked up and working properly, it's very effective.

Dwell should be 30 degrees for the aluminium distributors and about 38 - 40 degrees for the cast iron versions. The points are designed differently on these two models and the angles are different which calls for certain dwell angles. The point gaps are the same but the dwell angles aren't.

I've seen CSV's leak but they had no outward signs that were. Under the vacuum of a running engine they can do unexpected things.
If you can't get the pump to lean down your best bet is to have it gone through. It remains one of your best investments relative to making the engine run properly. All new engine rebuilds are generally done with a IP rebuild, new oil pump, new water pump, distrbutor rebuild and rad recore if needed. The intent isn't to have people spend more money but rather to have a base line of new parts that you know are going to work for you. If any of these parts were replaced or done a few years prior to an engine rebuild then you probably wouldn't need them.

You shoud also check the usual stuff like fuel volume and if fuel is returning to the tank. This is basic stuff but still important.

mrfatboy · « **Reply #3 on:** February 02, 2012, 15:31:35 »

Benz Dr.

Here is the additional information that you requested. I have updated my original post also.

1969 4 speed manual transmission
Spark Plug Wires: New type. All measured at 1k Ohm.
Coil: Silver with Red Label
Ballast Resistor: Red (1.8ohm)
Distributor: 051 (Retard with matching Retard Intake Manifold (vacuum connector on bottom)
Plugs: NGK BP5ES (Based on you recommendation several years ago

)

I am definitely confused about the timing specs. There have been all sorts of numbers floating around this forum and suggestions that the book and haynes are incorrect. According to the 280SL book and the wiki timing specs are stated as followed:

Timing @started speed: 8 BTDC (w/o Vacuum)
IDLE: 2 ATDC +/- 1 (w/Vacuum)
1500RPM: 12-19 BTDC (w/Vacuum)
3000RPM: 30 BTDC (w/Vacuum)

Just to double check, which specs should I actually be following? I would have to check again today but I think my car runs better on your specs. I would appreciate it if you or somebody could clear up the correct timing specs. Once 66andBlue comes over today I will post my new timing information at higher rpms.

Also, can you confirm if I can use any CO information at 1500 & 3000rpm from the Gunson CO meter while parked? If not, how to you check for lean and rich at higher rpms? Is it just by checking the plugs?

Thanks for all you help

Benz Dr. · « **Reply #4 on:** February 02, 2012, 16:10:08 »

2 - 4 degrees ATDC is for the later ignition system with the 062 distributor - so that's correct, but not right for your car.

Use my specs for the 051 distributor at 5 or 6 degrees BTDC at idle. 30 degrees is how much the distributor should advance but you want a total advance number of about 35 degrees BTDC at 3,000 RPM. You may find that you get that amount before 3K or slightly after. The main thing is to have at least 35 degrees total advance. You can check it at 4,000 RPM if you want - it's the total amount that you're looking for.

Sounds like you have all of the right ignition parts in your system. I would change your dwell angle to 39 - 40 degrees. The point gap will be a little bit closer which can help if you have any dwell loss at higher RPM's. This is caused by worn bearings on the main shaft or by a small amount of wear between the main shaft and the cam lobe piece. This can be fixed
but I won't tell you how I do it.

Run you engine and pull the vacuum line off while testing with your dwell meter. If the dwell changes more than a degree or two, the advance plate is worn. Sometimes I can fix them but it's about a 50% rate. It depends on how badly they're worn. All of these wear problems are caused by a lack of lubrication and servicing.

You should drive your car first before doing any testing so the engine is fully warmed up. Most of my testing is done by spark plug colour, the sound of the engine, how it smells while running, and how it feels on the road. A 280SL engine should have a smooth idle, quick throttle response, and should pull hard when you feed it some throttle. The front of the car should lift a little bit and you should be able to feel it pushing you back into your seat. In other words, it's something you can feel as well as hear, when you have it right.

Pull your plugs and lay them out on a table in the order you remove them. If they're black and sooty looking the mixture is too rich. A light tan colour is preferred. The IP should be rich at idle and lean during mid range while quite rich at full throttle. This is mostly done through throtle linkage where the air valve opens faster through the mid range than does the IP.

mrfatboy · « **Reply #5 on:** February 03, 2012, 01:30:26 »

Benz Dr.,

Here is the new info with your specs. BTW, my 051 distributor is the cast iron type.

IDLE: 5 BTDC (w/Vacuum)
1500RPM: 23 BTDC (w/Vacuum)
3000RPM: 40 BTDC (w/Vacuum)

Idle was 750-800rpm with the CO reading 4.0 - 4.5%

The engine would miss a little as you rev'd the engine thru it's range while parked.

I then tried something different and set the timing @3000rpm to 35degrees BTDC. The numbers came out like this:
IDLE: 0.0 TDC (w/Vacuum)
1500RPM: 18 BTDC (w/Vacuum)
3000RPM: 35 BTDC (w/Vacuum)

With a little tweaking of the air screw idle was 750-800rpm with the CO reading 4.0 - 4.5%

The engine would rev much better thru it's range with a hint of missing (while parked) once in a while. However, when taking it for a road test the engine missed a lot.

What would cause the missing while driving? I'm thinking it is too lean in the mid to upper range? I didn't get to take the plugs out after the last test drive because it got late.

Thoughts?

twistedtree · « **Reply #6 on:** February 03, 2012, 01:42:43 »

What's the CO now at the higher RPMs? I wouldn't expect timing changes to impact CO, so although you've probably cleared up some ignition issues, I'd guess you still have a mixture problem just like when you started.

mrfatboy · « **Reply #7 on:** February 03, 2012, 03:26:45 »

I think the CO numbers are the same as I stated in my first post. It was getting late and I forg0t. I will have to check again. But aren't those numbers bogus anyway since I'm parked and not on a dyno?

twistedtree · « **Reply #8 on:** February 03, 2012, 03:52:06 »

I would think they are good, or at least indicative of the problem you still have. Removing a shim from the barometric compensator will lean out the mixture across the board and could be an easy and interesting experiment. Just keep in mind that it will affect your idle mixture too, but if it improves performance while driving then you will know you are on the right track.

mrfatboy · « **Reply #9 on:** February 03, 2012, 04:31:10 »

I replaced the bc with an adjustable bolt for on the fly adjustments. I will be test running the car this weekend and report back.

Benz Dr. · « **Reply #10 on:** February 03, 2012, 06:23:09 »

Your distributor isn't working right and is advancing 5 dergees more than it should. Go back to 5 degrees BTDC. You probably have fouled out spark plugs.

I think your IP is pooched.

mrfatboy · « **Reply #11 on:** February 03, 2012, 17:54:11 »

@benz_dr

Thanks for all your input (also twistedtree) . Can you help me understand your reasoning for setting the timing to 5 BTDC at idle? I have been reading (and trying to comprehend

) all of the distributor posts in this forum. Do you think the 280sl just runs better at that setting? Are you trying to compensate for worn parts? It seems that everybody is following the MB Book specs and setting the timing to

Timing @started speed: 8 BTDC (w/o Vacuum)
IDLE: 2 ATDC +/- 1 (w/Vacuum)
1500RPM: 12-19 BTDC (w/Vacuum)
3000RPM: 30 BTDC (w/Vacuum)

Sorry for all the questions. I'm just trying to get a handle on all of this.

thanks much

ja17 · « **Reply #12 on:** February 04, 2012, 06:02:10 »

Hello,

I would try the split linkage test at higher rpms and see if the engine miss goes away as you induce more air by opening up the linkage going to the venturi. Looks like your upper rpm ranges are rich. You can lean them out easily by removing a shim under the baro. compensator, or adjusting the rack. Since your idle mixture is currently ok, you will need to richen it up a bit with the thumbscrew after the shim is removed.

Shim removal under the baro. is a lot easier than the main rack adjustment on the IP. Also it is easier to put back as before if needed.

Benz Dr. · « **Reply #13 on:** February 04, 2012, 06:31:37 »

Quote from: mrfatboy on February 03, 2012, 17:54:11

@benz_dr

Thanks for all your input (also twistedtree) . Can you help me understand your reasoning for setting the timing to 5 BTDC at idle? I have been reading (and trying to comprehend ) all of the distributor posts in this forum. Do you think the 280sl just runs better at that setting? Are you trying to compensate for worn parts? It seems that everybody is following the MB Book specs and setting the timing to

Timing @started speed: 8 BTDC (w/o Vacuum)
IDLE: 2 ATDC +/- 1 (w/Vacuum)
1500RPM: 12-19 BTDC (w/Vacuum)
3000RPM: 30 BTDC (w/Vacuum)

Sorry for all the questions. I'm just trying to get a handle on all of this.

thanks much

Those are all specs for the later engine with switch gear.

Set it at 5 degrees BTDC for the 051 cast iron distributor.

mrfatboy · « **Reply #14 on:** February 11, 2012, 00:40:30 »

I spent the afternoon tweaking the FIP today. Long story short is that after adjusting the pump so the car is running correctly at mid and high range (1700 and up rpm) with nice golden brown spark plugs the idle mixture remains too rich. The lowest I could get it was 9.5% CO (spec is 3.5% - 4.5%). Of course if I removed shims from the WRD or BC the car ran and idled nice but way too lean at the mid and high range. Spark plugs were bright white. This is just another confirmation that these pumps wear rich at the idle.

The only thing I have not checked is if the FIP was installed incorrectly at 20 BTDC instead of 20 ATDC. Is there a way to check this without taking off the FIP? I seem to remember one of these threads mentioning a toothpicks in the injection pump trick to see if it was aligned properly. Maybe that was in reference to something else. I will have to search for that one

ja17 · « **Reply #15 on:** February 11, 2012, 03:50:23 »

Hello,

Idle mixture is easiest to adjust. Just turn the idle thumbscrew, on the back of the IP (with engine off only) a few clicks lean, you should see immediate results in idle mixture. Oval shim removal may only change mixture (all ranges) until the engine is warmed up.

mrfatboy · « **Reply #16 on:** February 11, 2012, 05:01:15 »

I guess I was not clear in my post. I had the pump all the way leaned out. I turned the knob CCW as much as it would go. The lowest CO I could get was 9.5%. I could get it lower and perfect at idle if I removed shims from the BC but the leaned out the mid and upper range too much.

For kicks I started increasing mixture (CW) one click at a time and recorded the CO%. As I stated, it started at 9.5% but increased proportionately to 11.3% by click 14. Clicks 14 - 20 resulted in a very rough idle with engine almost dying. The CO bounced around in the 10-11% range during these clicks. I'm not sure what to make of that.

twistedtree · « **Reply #17 on:** February 11, 2012, 06:00:40 »

Yes, it sounds like rebuild time on that pump. If nothing else it will save you an awful lot of frustrating experimentation.

ctaylor738 · « **Reply #18 on:** February 13, 2012, 23:31:07 »

First, I'll ask the obvious. Sorry. Did you actually engage the slot with the knob when you backed the idle mixture adjustment out? Did you feel it click?

Second, I wonder if you are getting enough air through the idle air screw and the hose. I am suspicious because you said originally that you could not raise the idle.

mrfatboy · « **Reply #19 on:** February 14, 2012, 00:16:15 »

Yes, the fuel mixture screw is absolutely engaging. I have actually leaned it all the way out enough to feel the internal screw hit the fitting of external screw. I then turned clockwise enough to make sure everything turned freely. The air screw is opened all the way.

I just got through doing JA17's test to see if the IP was install 180 degrees out of time. Unfortunately, it was installed correctly so it looks like it's going to be rebuilt. It's worn rich at idle.

I will be posting a 'How to" with pics using JA17 method.

ctaylor738 · « **Reply #20 on:** February 14, 2012, 02:44:45 »

Well, you may be rich at idle because you are not getting enough air through the valve and tubing. Have you checked that out?

mrfatboy · « **Reply #21 on:** February 15, 2012, 00:47:24 »

I spent the day today putting back together the IP and getting idle all set to specs.

My timing is now at 2 ATDC (as per book specs)
Dwell 38 degrees
Warm Idle is 650 -750 (digit rpm gauge bounces a bit but engine sounds good)
CO 4%
Warm start is great
I have not tested cold start yet.

Since my IP was leaned all the way out (CCW) I enrichened the IP 15 clicks (CW) so I could have room to play with later. I did some experiments yesterday that showed my IP adjusted the CO % about 2% over 15 clicks. So in theory, I should be able to back down the pump (CCW) 15 clicks (my max lean) to lean my CO% down to 2% (4% -2% =2%)

I used my BC Bolt hack to adjust the IP across all ranges to get the idle CO% down to 4%. I then took out the bolt and measured it and translated that length to my BC. I used a micrometer to measure the bolt and BC but I found that I need to add several more shims (fine tune) to get it where it was. Very easy. Using the BC Bolt Hack make life easy

Now with everything back together I went for a short 2 mile drive. The engine sounded great. NO missing. Very Strong! I have gotten the car to this point before but the mid and high range while driving was always too lean. Plugs were bright white.

So...... Before I start messing around with the mid and high range of the IP (Black and white screws) I would like to get opinions if you guys think the plugs are way too lean or OK. I am terrible at plug diagnosis unless it is extremely obvious.

I have attached two pictures. Frankly, they look the same to me. The idle.jpg was after a 5 minute idle at 4% CO. I pulled the plug again right after a 2 mile drive in the other.

What do you guys think of the plugs? Lean or OK?

twistedtree · « **Reply #22 on:** February 15, 2012, 01:01:47 »

I'm with you on reading plugs; it's fine for judging gross problems, but no way to fine tune. For fine tuning, I'd go based on how the car feels, smells, and the CO numbers.

Do I understand that you now have reasonable CO numbers across the RPM range? If so, that's a significant change from where you were before, right? Any idea what you "fixed"?

Benz Dr. · « **Reply #23 on:** February 15, 2012, 01:09:17 »

You have the 051 distributor, right? It runs great at 2 ATDC? OK.............

5 - 6 degrees BTDC is where you want it. 35 - 36 max advance at 3,000 RPM anmd above.

twistedtree · « **Reply #24 on:** February 15, 2012, 01:15:45 »

For the 051, the BBB calls for

2-4 ATDC @ idle w/ vacuum
12-19 BTDC @ 1500
30 BTDC @ 3000

Dan, it sounds like you've found other numbers work better?

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Author Topic: Please help with my CO numbers! (Read 22592 times)