Any Gunson CO Tester Volunteers out there?

[mrfatboy]

I hoping somebody could help me out. I'm looking for someone that has a Gunson CO meter tester or similar device AND a car (preferably a 280sl but I will take what I can get) that is considered having a correctly running car and WRD at cold start.

I would consider a car that starts relatively quickly on cold start and has an idle of 1100rpm or so and then slowly coming to rest at 750-850 to rpms a correctly running car.

If you are lucky to have both of these things I would appreciate it if you use you Gunson to log the CO and rpms of a cold start until the car is completely warned up.

Specifically, I'm looking for the starting CO at cold start and then how the CO changes over time until the car is warm.

By having this data I am hoping to come up with diagnostic and tuning procedures of the WRD.

Any volunteers?

[ctaylor738]

I have a Gunson, but my 280SL is a long way from running.  We do have a number of good-running cars in the DC area, and I will see it they want to get tested.

[Cees Klumper]

I have a Gunson and always use it when I tune the engine. I can do this test, but probably won't get to it until a month or two from now unfortunately. And my car starts up fine cold, warms up fne, just until a certain point when the WRD starts to cut out a bit too early. I need to add an oval shim or to I think. Anyway, let me know if you want to wait this long.

[J. Huber]

And my car starts up fine cold, warms up fne, just until a certain point when the WRD starts to cut out a bit too early. I need to add an oval shim or to I think.

Cees, what happens at the point? With my car, if I reach in, turn the key, it starts right up (don't even need throttle), then it idles fine (1000 or so) as it warms up. At some point about 7-8 mins in I'd say, if I don't touch that pedal, the idle will drop below 700 and car will usually die. All of this is avoided by actually driving the car, or revving it at the 7-8 minute mark. Then it idles steady at about 8-850 and won't die... wonder if I am a shim candidate as well?

[Cees Klumper]

Hi James - my car does exactly the same as yours. Only thing is maybe it starts to falter a minute or two earlier. But other than that identical. Thing is, it's only started doing this a few years ago, never had this issue the first eight or nine years and I don't recall changing anything. Anyways, I will start by adding a shim and take it from there.

[wwheeler]

I think Cees has mentioned it before but, is it rich or lean when the RPM drops and the engine dies?

[Cees Klumper]

Hi Wallace - actually I don't know, have not done the split linkage test at that point where it starts to falter.

[twistedtree]

The other possibility here is that your WRD is shutting off at too low a temp, and needs to stay on for a few more degrees of temp rise.

[mrfatboy]

I finally took my FIP out and sent it in for work.  You can see by the rough graph below how my CO curve is.  I have no idea if it's correct or not.  I doubt it.  But it seems to represent what a lot of our pumps are doing (WRD & FIP).  The shape of the curve is the most important thing as we don't really know what the starting CO is supposed to be.  We just know that the CO is supposed to end at 3 - 4.5% at complete warm up.

Point 1 -  My initial CO
Point 2 -  Holds at 11% for a couple of minutes
Point 3 -  Drops to 1.5 - 2% CO then dies because it's too lean
Point 4 -  Completely warmed up at proper CO

This is a completely cold start and just letting it idle for 5-8 minutes.  If I actually drive it (like most of us would) I bypass POINT 3.  This is because the car gets warmer faster thus shutting down the aux air for the WRD faster.

I am guessing a proper FIP has a curve very similar but POINTS 1,2,3 are less extreme.  That's why I would like the Gunson data so we can properly diagnose what is going on with our pumps.

I did talk to my fip tech and he confirmed what has been mentioned in these forums.  The WRD closes the aux air and pushes the internal FIP pin to its stop at same time. The internal pin hits its stop FIRST(leaning out the FIP rack)and then the aux air intake closes lastly at completes warm up.  That little extra air from the aux air intake is causing the dip to 2% (POINT 3 for me) going too lean and the car dying.

I look forward to seeing what other people's numbers look like 

[wwheeler]

That curve describes exactly how my engine warms up. While not on a Gunson, I have done the split linkage test many times and that is what I come with everytime. The question is, how do make the mixture richer just for that small segment of time without effecting the mixtures at the other times? I have added oval shims to strike a balance between too rich when very cold and then only somewhat lean when it is almost warm. So far, that is the best I can get. When I change the number of round shims, it doesn't eliminate the lean time period, just changes when it occurs. I wonder if there is some part that is worn in the IP that is causing this?

[mrfatboy]

That curve describes exactly how my engine warms up. While not on a Gunson, I have done the split linkage test many times and that is what I come with everytime. The question is, how do make the mixture richer just for that small segment of time without effecting the mixtures at the other times? I have added oval shims to strike a balance between too rich when very cold and then only somewhat lean when it is almost warm. So far, that is the best I can get. When I change the number of round shims, it doesn't eliminate the lean time period, just changes when it occurs. I wonder if there is some part that is worn in the IP that is causing this?

That's why I sent my fip to the shop. .  No matter what I adjusted, the curve was always the same. I hope they find something wrong .   The fip tech mentioned that when you start  compensating with washers  or  other adjustments on a worn pump things start getting out of whack. It really is a fine balance.

Knowing the the correct CO curve for our cars would be a huge help. For all I know they really are supposed to start at 11% and come to rest at 4%. Hope not.

[mrfatboy]

Hi all

I received my  FIP back last week.  It was just calibrated and not a major rebuild.  The tech opened it up and immediately saw the problem.  The stylus was resting on the cam too far in the rich position.   This explains the problem I was having. Some one must have been in there and calibrated it incorrectly years ago.  From there, he just re calibrated everything to spec and checked the injectors and I sent up.  I am now able to make adjustments to the pump and see desired results.  Before it was so rich there was nothing I could do.

For the last several days I have been conducting cold start tests to further tune the pump and get everything running properly.  I have documented the CO cold start curve using a Gunson and Iphone.  See the attached chart for my first 4 tests.  I still have some more tweaking to do but I feel confident that I will be happy with the results when done.

I logged the Gunson data by placing a iphone in front of the Gunson display and had it take a picture of the LED every 3 seconds.  I ran the each test for 6 minutes except for TEST #4 which was for 15 minutes.  From there I just entered data from the iphone pics (360 each test) into the excel file with the chart.

I have attached the excel file with chart so anybody can use it and track their own cold start.

Feel free to PM me if you don't know how to use the excel file.  It's easy!

I'm still looking for other people with Gunson's to run this test so we can compare notes!



Overall notes:

It seems the idle mixture screw on the FIP can but NOT necessarily affect the cold start up mixture.  I assume this is because the FIP enriches the mixture so much at cold start that it might not have any affect.  This real depends on how well your pump is calibrated.

Through my observations, a CO% somewhere in the area of 7.5% and 9.5% is the desired max CO to achieve a 1100 -1200rpm for a cold start.

The WRD air slide closes AFTER the the WRD heat feeler pin hits it's stop in the FIP.  For my FIP this is making the CO dip to 1.5 - 2.0%.  I would like more data from other FIP's to confirm that this CO range is normal.  I believe it is normal but not sure by how much.  My theory is that engine designers wanted the FIP to go a lean for a bit to clean off any carbon on the spark plugs during the enriched cold start.  Like I said. Just a theory


Cold Start TEST Notes

Test #1 (10am)
Tested as it came back from FIP tech.  Needed to find baseline to start adjustments of Air mixture & Idle mixture screw.

Test #2 (11am)
Adjusted air mixture screw CCW by 5 clicks. Set Warm CO to 3.8% at end of TEST #2 by 5 CW (enrich) clicks from calibrated default.

Test #3 (5pm)
CO still ended back in the 1.5% range even after setting it to 3.8% in TEST#2. I now believe it takes over 15 minutes to fully warm up by just idling.  The CO curve is a little flat at beginning possibly do to the fact that the car was not 100% cold after 5 hours.  WRD was slightly warm to touch.    After taking car out the CO was back at 2.2%. Added 2 more clicks CW to enrich to 4.0% for Test #4

Test #4 (10am)
1100rpm was not achieved until after 2mins due to the fact that it was too rich.  After 15 minutes, 3.0% CO and after long drive 4.0+%.  I will probably dial down on click (CCW/lean) for next test.


For the sake of easy explanation I define a Air Mixture Screw "click" as one clock position (ex. 1 o'clock, 2 o'clock). Obviously, since it's a screw you have much more fine tuning.

Excel File
http://dl.dropbox.com/u/10334978/Mercedes%20280SL/Gunson%20CO%20Chart%20280SL%20%201.xlsx






Bigger chart
http://dl.dropbox.com/u/10334978/Mercedes%20280SL/1969%20280sl%20Cold%20Start%20CO%20%231.JPG

[Cees Klumper]

Impressive! I'll do the same test but it'll be months before I can get to it unfortunately. Still, this seems like a very worthwhile test to run for multiple people so we get some good data.

[mrfatboy]

I completed my final test (cross fingers ) this morning.  Now that I know even though the engine temp reads 180 degrees the WRD air slide valve still can be slightly open.  It just takes a bit to throw everything off.  Plus I would think that you might have to account for metal expansion that might close off additional leaks somewhere.

I settled on TEST #5.  It was the same at TEST #2 but on a warmer day.  It was nice to see the curve very similar.  I reset the FIP back to the default setting when it came back from the tech.  The low CO% in the chart threw me off at first as I thought it was too lean overall.

Here is the new update CO TEST Chart.


Here is a Point of Reference chart for the final CO curve.




Here are the original size pics. Maybe we should increase the picture size when we upload! My eyes are getting old

http://dl.dropbox.com/u/10334978/Mercedes%20280SL/1969%20280sl%20Cold%20Start%20CO%20%232.JPG
http://dl.dropbox.com/u/10334978/Mercedes%20280SL/69%20280sl%20CO%20Points%20of%20Reference.JPG

[wwheeler]

That is cool to see it on a graph. The curve looks like what I see with the split linkage test. The plateau at 200 secs is the same as mine and then the lean period comes on quickly just as the graph shows.

I think we all know that the air valve continues to move downward with increasing engine temperature even after the fuel rod hits it's stop in the FIP. The question is does the fuel rod hit the stop at the same time the air valve closes the opening? If not, that might explain the lean period. The air valve continues to move down even more slowly and under spring compression since the fuel rod has already hit its stop. At some point, the air valve makes a good enough seal and the lean period is over. Sound about right? 

Seems like the only way to cancel the lean period is to lower the piston on the fuel rod. In other words you would increase the depth in which the fuel rod goes into the piston. That might synchronize the two shuting off. Sound crazy?     

A thought about the air valve seal:
Since there isn't a sealing ring on it, there are only two ways it can create a seal. 1) Obviously is to close off the cylinder opening and 2) The small amount of clearance between the WRD cylinder and the piston limits the air flow. #2 is effected by a few variables such as: amount oil on surfaces (the more the better seal), the amount of wear and scoring, the amount of piston skirt below the cylinder opening and temperature of the assembly. I would imagine the piston would expand at a greater rate than the cylinder because it has a thinner wall. All that to say that the ability of the WRD to shut off the air completely is governed by these variables. 

[mrfatboy]

The WRD air valve DOES in fact close after the fuel mixture rod hits its stop.  This is by design.  My theory is that the designers have the engine go lean at the end of warm up to clean off the spark plugs during the overly rich period at beginning of warm up. Just my theory.

Until proven otherwise, I believe the chart provided is an accurate representation of the warm up CO curve.  It will be interesting to see when other people provide data!

The chart does make it easy to see what is really going on. 

[wwheeler]

How did you you determine that the fuel rod stops before the air valve shuts off?

The part on the graph that shows the lean period is interesting. It is so flat which means it changes slowly over time. All of the other changes seem to happen much faster and therefore have a greater slope. I am guessing that the reason it takes so long to finally close the air valve and relieve the lean condition has to do with the two different springs in the WRD system. One spring is in the FIP and acts on the fuel rod and the other is on the fuel rod itself. The FIP spring is much weaker and therefore will compress first before the fuel rod spring.

So as the engine warms and the wax expands in the WRD thermostat bulb, it pushes down on the air valve, fuel rod with spring and the FIP spring. Since it is the weaker spring, the FIP spring begins compressing until the fuel rod hits the stop. At this point the fuel will not change and only the air valve will move down. If the air valve has not completely shut off here, it will eventually shut off the air flow as it moves down. Since the fuel rod can no longer move (as well as the FIP spring), the expanding thermostat rod and air valve must overcome the much stiffer fuel rod spring. This requires a greater force (or more engine temperature) to accomplish. Thus the progress is much slower at this stage.

That is why I think the graph is flat during the lean period. What do you think?   

[mrfatboy]

That's exactly how I understand it . I confirmed this with the fip tech.  The last distance the air slide valve has to travel is only .5mm to completely close. The fuel rod travels 18mm to the stop and the air slide valve travels 18.5mm.   He also told me that the correct fuel output at idle is 16 cc.  Mine was set at 24cc.

[wwheeler]

So the .5mm is the distance the air valve has to travel to completely cover the air opening in the WRD housing after the fuel rod hits its stop? Of course as the engine gets hotter (freeway driving, etc..), then the air valve slides even further down the cylinder restrained by only the fuel rod spring.

If you wanted to reduce this lean period, seems like you could shorten the fuel rod thereby making the shut off points for both closer to the same.

The one thing that doesn't make sense during this period is the engine rpm. As the engine enters in the lean period, the rpm drops. Supposedly there is no added fuel and only extra air making it lean. However as the engine gets hot, the rpm rises and the mixture corrects itself. The thought is that the air valve completely closes off, reduces the air and corrects the mixture. But why does the rpm go up? The only way it can go up is to ADD fuel and air. In this senerio we take away air to correct the mixture. So where does the extra fuel and air come from? Or is it maybe that a completely warm engine doesn't require as much air/fuel to run at a given rpm?

[mrfatboy]

I don't think there is a way to reduce the "lean period".  I'm not sure you really would want to.  I'm using a digital RPM monitor.  The readout bounces around a bit so it's hard to nail it down exactly.  It usually stays in a +/- 100rpm range or so.  I have been told that is typical but I really don't know if it is or not.

I believe the air valve has two forces (springs) acting on it. The first spring that compresses in the one in the FIP that is compressed by the fuel rod.  The second spring is the one under the air slide valve which is stiffer.  The fuel rod spring compresses completely first. 

At this point, I am forgetting my high school AP physics and can't remember how two springs with different tensions react on each other.  I have to assume (uh oh!) air slide spring doesn't start compressing until the fuel rod spring is fully compressed as stated above.

If I'm visualizing it correctly in order for them to close at the same time I believe you would have to extend the pin from the thermostat bulb. There is no way to do that.  I actually tried to do it a couple of weeks ago 

[wwheeler]

Extending the bulb pin is the same as adding round shims and that changes the position of both the air valve and the fuel rod.

Here is something to ponder while looking at a cross section of the WRD in the tech manual. Wouldn't adding oval shims also change the time when the air valve closes relative to the fuel rod hitting the stop? Adding the oval shims richen the mixture by positioning the fuel rod further out and away from the stop WITHOUT the air valve moving in the cylinder. So the fuel rod must now travel further to hit the stop while the air valve's travel doesn't change. To me that seems like you are changing the timing; very little but some none the less.

[mrfatboy]

Extending the bulb pin is the same as adding round shims and that changes the position of both the air valve and the fuel rod.

I might have misunderstood you before.  You are correct here.  Added/subtracting round shims affects both the air slide AND the fuel rod at same time and proportion.  Essentially, adding/subtracting round shims affects the time (via temp) of the warm up curve.  Adding round shims would start the warm up process further along in it's cycle because the heat feeler pin and fuel rod are now pushed further down to start with.  Subtracting round shims would extend the time in the warm up cycle because now the heat feeler pin has a little bit longer to travel to start the process.  Round shims ONLY affect the warm up cycle.

Here is something to ponder while looking at a cross section of the WRD in the tech manual. Wouldn't adding oval shims also change the time when the air valve closes relative to the fuel rod hitting the stop? Adding the oval shims richen the mixture by positioning the fuel rod further out and away from the stop WITHOUT the air valve moving in the cylinder. So the fuel rod must now travel further to hit the stop while the air valve's travel doesn't change. To me that seems like you are changing the timing; very little but some none the less.

Again your are basically correct here.  Adding/subtracting oval shims under the WRD affects the fuel delivery ONLY during a cold start. They affect ONLY the fuel rod distance and have nothing to do with the heat feeler pin(air slide valve).  Once the fuel rod hits it's stop the oval shims essentially have no effect anymore.  Adding oval shims makes the cold start RICHER because the fuel rod starts leaning out the fip later (i.e. it had to travel further).  Subtracting oval shims makes the cold start LEANER because the fuel rod is closer to the stop starting the FIP leaning process sooner.

It amazes me how the engineers came up with a system so precise.  Fuel, Air, Pin Travel has to be perfectly calibrated in order for everything to work properly.  Of course you can try to compensate for it which can get you close but it's like building a house on a crooked foundation.  If you ever have been to see the leaning tower of Pisa you will know exactly what I mean. It's hilarious what they did over the years to compensate for it.

The FIP techs calibrate these pumps at the completely warmed up state.  The fuel rod is at it's stop and the air slide valve is closed.  At this point there should only be 16cc's of fuel being delivered at idle.  They have gauges with the correct distances marked on them so they know where everything lines up in the internals of the fip.  They also have a bolt that has the correct markings on it that screws into the rack at the front of the pump that tells you if the rack is adjusted properly.  It would be awesome for us to know those measurements!

We know that the fuel rod travels at 18mm and the heat feeler pin (thermostat bulb) travels 18.5mm.  Even if the thermostat heat feeler pin moves slower or faster due to colder or hotter climate or even just differences in thermostat bulbs everything should still move in proportion when it does.  It's so easy to change one thing to get a desired result one way while messing up 3 other ways.  I started to go down that path with my newly calibrated FIP.  That lean period through me off and I thought the FIP came back lean and I tried compensating for it. Big mistake.  I have heard there is usually some fine tuning on the pump when it comes back but If you trust your pump came back 100% you need to look else where

I just thought of something while typing this.  I have the original 3 oval shim & 3 round shims in my WRD. I believe some WRD's came with less respective shims but the overall thickness was the same.  So when the FIP got calibrated, it was with the original shims so the 18mm & 18.5mm spec held true.  I'm not sure what happens when you send a FIP to get rebuilt/calibrated and it doesn't have the stock thickness of round and oval shims. What does the tech do?.  Does he give you more shims and then calibrate or does he use what you have and then compensate for it and those now become the new baseline?  At that point the 18mm & 18.5mm specs would be different.  I hope they give you the shims!

I hope I explained that clearly. I retyped it several times I wonder if I will remember all of this next year   I'm glad we are documenting it.

I was going to put up a chart that shows how the start up CO curve is affected when you change the air mixture screw, idle screw, BC shim, rack, round shims, oval shims, etc.  It got a little involved so I stopped.  I might try again.  Would be nice to see it in chart form.

Once last tidbit of info. We know that adding/subtracting shims affects the CO over all ranges by adjusting the rack.  However!!!!!!!!!!!!  It affects the fuel curve DIFFERENTLY than it would by adjusting the rack by the internal rack screw in the pump. That would be the 100% correct method. How?  I have no idea. The tech just said differently.  I had a feeling this was true after I saw how the internal pump mechanism worked.

[mrfatboy]

FYI. I just realized I did a typo on the CO chart.  I settled on the settings from TEST #2 and TEST #5.  Not  TEST 3 & TEST #5.  I updated the charts and post to reflect the change.  Sorry about that.

[66andBlue]

Hi all
I received my  FIP back last week.  It was just calibrated and not a major rebuild.  The tech opened it up and immediately saw the problem.  ......

Hi Fatty,
who did the calibration? How long did it take??
Thanks.

[mrfatboy]

Robert Fairchild did it. Very helpful guy. Willing to share info.  Turn around was a week including shipping to and from. Actual work was less than a day.  He offered different levels of service depending on what was needed. I didn't need a show pump but he does offer the upgraded service from what I understand.  My pump did come back nicer looking.   I got very lucky with the price since it turned out I only needed a calibration. It was very clean inside. He told me i would not believe what he has found Inside some of the pumps he worked on. He even checked the injectors for free.

I also talked to H&R. They said the work would be only a day and could start immediately.  Shipping to NY from Ca  would  be the biggest time issue.  They seemed to offer only a complete rebuild 'show pump' option.

Gus at Pacific was given a call also. He was backed up and couldn't start work on it for a month. Still only a complete rebuild and show pump option as far as I can tell.