Air/Fuel ratio, is there a quick answer? |
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Air/Fuel ratio, is there a quick answer? |
Mark Henry |
Feb 7 2017, 12:05 PM
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#21
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Peak power is made around 13.5:1, .... That's theoretically ideal. But if you want to drive your car in the real world, you need to forget about theoretical. Or at least pay more attention to what the engine is telling you. No dyno-graph in the history of cars had peak power at 13.5:1. Ever.When in doubt, do the spark plug color test. I've heard reading spark plugs was more accurate on older fuels. Supposedly new fuels don't indicate as well on the spark plug. I don't have any real world experience to share in this department though. I look at them, I 'read' them, but I don't trust it much.Help me out with WOT. I played with that a little at lunch today. You want to hold WOT and see how things respond. So it's one of those annoying answers -- hold it long enough to learn what you need to know. 15s should tell you all you need to know though. You want to see AFR go rich as soon as you hit the gas and stay rich while at WOT. You want something in the neighborhood of 12:1. 15-16 at cruise will give you great fuel economy, but may be a little lean in my experience.How do you test that? I was running in third gear about 45 mph. I floored the pedal. The car picked up speed and the gauge dropped to 10-ish and the car accelerated. I only held the pedal down for about 15 seconds. Was not sure I was doing it right. How and how long? Reading spark plugs became outdated with unleaded fuels. Mark, you never really lived with leaded fuel so... (IMG:style_emoticons/default/biggrin.gif) Not totally and it also helps when looking for mechanical issues. You are still looking for a greyish or brown tan colour and oil fouling and too lean still looks the same. I use the plug check when I suspect the sensor may be failing. Way too lean or rich I don't need a meter to tell me that the engine is running like shit, but it sure makes life easier. But on top of the WB meter you should have a head temp gauge, if you do try to lean the engine for cruise you will see your head temps climb like crazy when you go too far. |
malcolm2 |
Feb 7 2017, 02:18 PM
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#22
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
But on top of the WB meter you should have a head temp gauge, if you do try to lean the engine for cruise you will see your head temps climb like crazy when you go too far. Yesterday, travelling the same route I always travel, I noticed that my CHT was slightly higher than it had been. Higher that is, when I was on the interstate, about 70 mph, going up a long hill. The normal reading was slightly below 350. I was slightly above 350. so maybe 15 - 20 *F higher. The AFR was reading 12.5-ish. So I would be concerned if I needed to set the AFR at 15-16 while cruising at 70mph. |
timothy_nd28 |
Feb 7 2017, 08:47 PM
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#23
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Advanced Member Group: Members Posts: 2,298 Joined: 25-September 07 From: IN Member No.: 8,154 Region Association: Upper MidWest |
350 degrees is not normal, atleast I hope not. Remove the thermostat cable and repeat the test.
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ConeDodger |
Feb 7 2017, 08:51 PM
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#24
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Apex killer! Group: Members Posts: 23,543 Joined: 31-December 04 From: Tahoe Area Member No.: 3,380 Region Association: Northern California |
The good thing about a CHT gauge is you know your CHT. The bad thing? You know your CHT. (IMG:style_emoticons/default/blink.gif)
These engines are highly dependent on fan speed. I found 5th gear with good stock EFI to be almost unusable! |
Mark Henry |
Feb 8 2017, 07:33 AM
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#25
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
The good thing about a CHT gauge is you know your CHT. The bad thing? You know your CHT. (IMG:style_emoticons/default/blink.gif) These engines are highly dependent on fan speed. I found 5th gear with good stock EFI to be almost unusable! 3000 rpm rule, for proper cooling never drive below 3000rpm. Don't lug those engines boys! |
malcolm2 |
Feb 8 2017, 11:32 AM
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#26
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
350 degrees is not normal, atleast I hope not. Remove the thermostat cable and repeat the test. Well this car has run between 325 and 375 since 2013. The VDO CHT gauge has 350 at 12 o'clock. Each tick is 50 degrees. So around town I am just above 300 and pulling long hills on the interstate I get just over 350, not quite to 400. Somewhere on 914world is a nice write up by Jake. He explains a lot about CHT. From what I remember this car pretty much follows the temps in his explanation. I will see if I can find it. By the time I get to the 2nd stop sign in my neighborhood the T-stat flaps are (or should be) wide open. If I disconnect them, they will be wide open for that first cold 1/4 mile. Disconnecting would have no effect on interstate driving 10 miles from home, everything is nice and hot by then. A quick video of the car in the garage. I posted this one on my AFM thread for you Tim. Notice at 11 seconds.... CHT is 325-ish. https://www.youtube.com/watch?v=BMspGlzl6Lo |
malcolm2 |
Feb 8 2017, 11:37 AM
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#27
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
The good thing about a CHT gauge is you know your CHT. The bad thing? You know your CHT. (IMG:style_emoticons/default/blink.gif) These engines are highly dependent on fan speed. I found 5th gear with good stock EFI to be almost unusable! 3000 rpm rule, for proper cooling never drive below 3000rpm. Don't lug those engines boys! I remember hearing that (IMG:style_emoticons/default/agree.gif) several years ago when I asked a question about shift points on a daily driver. I believe it was Cap'n Krusty that said to shift closer to 4000 and cruise or drive at 3000 +. 70 mph cruising on the interstate in 5th gear, my RPMs are 3200 or 3400, something like that. and CHT is 350 to 360. If I go faster CHT moves up a bit. And as I mentioned above AFR was 12.5 (that was Monday). Still in the adjustment phase with AFR. |
malcolm2 |
Feb 8 2017, 12:02 PM
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#28
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
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djway |
Feb 8 2017, 10:11 PM
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#29
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Senior Member Group: Members Posts: 787 Joined: 16-October 15 From: Riverside Member No.: 19,266 Region Association: Southern California |
When I set up my L jet that had been horribly messed up, after warming up the car I jumped on the freeway and ran at 3000rpm. WOT was running way to rich as was AF ratio at 3k. I would shoot down an offramp, tighten the spring and jump back on the freeway. When I finally got it to run at 15.8 at 3k the WOT was right where it should be. Popped the lid back on the AFM and the only problem I have had since is that when really cold I need to crack the throttle just a bit to start. The motor is old and a bit low on compression but cruises like a dream.
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malcolm2 |
Feb 9 2017, 10:15 AM
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#30
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
When I set up my L jet that had been horribly messed up, after warming up the car I jumped on the freeway and ran at 3000rpm. WOT was running way to rich as was AF ratio at 3k. I would shoot down an offramp, tighten the spring and jump back on the freeway. When I finally got it to run at 15.8 at 3k the WOT was right where it should be. Popped the lid back on the AFM and the only problem I have had since is that when really cold I need to crack the throttle just a bit to start. The motor is old and a bit low on compression but cruises like a dream. When you say WOT was "where it should be", do you mean per Chris's statement (12.8 -12.5?)? And when you say "run at 15.8 at 3k" are you cruising, downhill or decal-ing, also as Chris suggests? one of Chris Foley's posts in A:F ratio, you want to see: 13.5-12.9 on the gauge while accelerating or climbing, 12.8-12.5 at WOT, and 16-17 while cruising, going downhill or decelerating. I need to read up on all the adjustments, cause when I move the spring every level moves. I have not moved the spring this week, but I did back out the CO screw. It is about centered (4.5 turns from the btm) now, with the @20 teeth CCW of the spring(last Saturday) I get: 12.5 at @1K idle, 12.5 at 3200 cruise at 70mph 10.5 at WOT.... after about 15 seconds the needle heads back up a bit. Question for all.... How can Cruising and Decelling be the same? I have a steep hill in my hood. I coast down (leave the car in 3rd, foot off the gas) and the AF goes to 18. |
djway |
Feb 9 2017, 08:45 PM
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#31
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Senior Member Group: Members Posts: 787 Joined: 16-October 15 From: Riverside Member No.: 19,266 Region Association: Southern California |
You are running WAY to rich. At full throttle only guys with turbos or huge motors need below a 12 or 13, I don't remember which. There are a ton of post out there, and specs from Porsche. Cruising flat land the mixture should be at what is called Stoic which is short for stoichiometry which is used to figure out what is the best combination of compounds to get the max use out of everything involved. Cruising downhill you should go above 15.8, completely letting off throttle there should be almost no fuel and you will see very high numbers.
Look up factory specs and set to that at 3000rpm cruising flat land. Stoic for gasoline is 15.8 NO vacuum leaks anywhere leak test all 5 injectors check cold start valve for proper function. check the ohms on the cht sensor. I have different units with different ohm readings and they greatly affect the stoic. check the sensor and switch for WOT crank case vent system can be checked if above measure don't help checking flow rates of each injector if nothing above is helping. compression more than 20lbs from the highest to lowest cylinder can cause problems I knew nothing and read every article I could find an all the factory specs etc. good luck |
jcd914 |
Feb 10 2017, 12:55 AM
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#32
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Advanced Member Group: Members Posts: 2,081 Joined: 7-February 08 From: Sacramento, CA Member No.: 8,684 Region Association: Northern California |
If your air flow meter has been mucked with already it can be very hard to get set correctly.
I had a 78 VW Bus 2.0L L-jet that the AFM had been messed with. There is an adjustment for the wiper arm relative to air flow flapper that affects the fuel mixture as well as the spring tension adjustment. I had to play around quite awhile to get the 2 adjustments working together and get proper fuel mixture at different loads. It has been too many years to remember my methodology. I believe I ended up loosening the spring so I would get more flap movement for the same air flow but then moved the wiper to lean it out some to avoid excessively rich mixtures. Of course what I had to do to mine would have been relative to what the PO had done to it before I got it. I eventually ended up with a good running bus that ran lean enough to pass smog and get good mileage without cooking the motor. I was using a 12 volt portable 4 gas exhaust analyzer hooked up everywhere I went for some time. Good Luck Jim |
falcor75 |
Feb 10 2017, 01:34 AM
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#33
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Senior Member Group: Members Posts: 1,578 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
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djway |
Feb 10 2017, 04:07 AM
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#34
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Senior Member Group: Members Posts: 787 Joined: 16-October 15 From: Riverside Member No.: 19,266 Region Association: Southern California |
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Mark Henry |
Feb 10 2017, 10:03 AM
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#35
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
If you are running at stoich AFR on an aircooled you're cooking your heads. (IMG:style_emoticons/default/rolleyes.gif)
Buy a decent head temp gauge and see for yourself. Decel AFR is useless info, stop obsessing on it, it doesn't matter because there is no load on the engine. AFR has no bearing on mechanical braking load. As I said my FI system cuts all fuel at TPS zero on decel (except for idle between 800-1200rpm*) that's no fuel you can't get much leaner than that. AFR is important under load, WOT, hills, cruise, etc. WOT 12.5, nickies you can be just over 13:1 Cruise 13 to 13.5 max I aim for just over 13:1, nickies you can run up to 14:1 Hills basicly the same as WOT, maybe a hair more. * IIRC I'd have to check my program to see the range and my car is in storage, but 800-1200 is close enough. |
malcolm2 |
Feb 10 2017, 11:41 AM
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#36
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
On WOT are you documenting at bottom value? I tend to dip to 11, then rise back to 13. I can say that this is the 1st time I ever ran the car at WOT. Kinda fun but it is acellerating so fast i get skeerd.
I ran the CO screw out 1 more rotation last night. That got me from cruising at 12.5 to 12.8. That screw is about 4.5 turns out now. |
Porschef |
Feb 10 2017, 11:56 AM
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#37
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How you doin' Group: Members Posts: 2,162 Joined: 7-September 10 From: LawnGuyland Member No.: 12,152 Region Association: North East States |
Clark, are you referring to the screw on the AFM itself? Thats the only one I know of and is only an air bypass for idle. I found my car idled like crap if it was too rich, opening the screw helped.
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Porschef |
Feb 10 2017, 11:58 AM
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#38
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How you doin' Group: Members Posts: 2,162 Joined: 7-September 10 From: LawnGuyland Member No.: 12,152 Region Association: North East States |
Mark, i get the nickies can deal with a leaner mixture, but what about your head temps, where are they running?
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Porschef |
Feb 10 2017, 12:06 PM
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#39
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How you doin' Group: Members Posts: 2,162 Joined: 7-September 10 From: LawnGuyland Member No.: 12,152 Region Association: North East States |
IIRC, I'm at 13.2 or so at cruise. The engine seems to like that. Idle im just over 14.
Have you seen the Itinerant Air page? Kinda gives the overall impression that the engine will dictate what it wants, then you have to fine tune from there. Of course, there shall be no vacuum leaks... |
malcolm2 |
Feb 10 2017, 03:21 PM
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#40
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Advanced Member Group: Members Posts: 2,729 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
Clark, are you referring to the screw on the AFM itself? Thats the only one I know of and is only an air bypass for idle. I found my car idled like crap if it was too rich, opening the screw helped. Yeah, IIRC it is to adjust the CO. But I don't have a CO meter. SOme youtube vids on it too. Yes it is a bypass within the AFM like on the TB for idle. But this is unmeasured air that is going to increase the AF # as you open it. I believe it is the fine tune portion of the mix. I really need to open the itinerant how-to document again and read it. I am finally to a point where adjustments and tinkering with the AFM can be measured with my borrowed AFR. And they are moving the needle. |
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