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| IAT bias to tweak AF ratio https://www.slantsix.org/forum/viewtopic.php?t=45923 |
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| Author: | Sam Powell [ Thu Aug 11, 2011 7:21 pm ] |
| Post subject: | IAT bias to tweak AF ratio |
I took the car out for a spin tonight, and had a blast dialing in precise air/fuel ratios on the fly. The change was nearly instantaneous, and it was fun to feel how this effected the way the car felt and ran. Most important, it is now possible to get the car to start more gracefully in hot start situations. This feature was GunPilot's idea and it works well. I am just beginning to play with it, and highly recommend other EFI guys give this a try. If you have a wide band gauge, you can use this feature to dial in an AF ratio of your choosing, on the fly, with no lap top hooked up. It involves placing a 3k to 5k rheostat in the temp sensor circuits to effect the fuel ratio. I put a 5K one in series with the IAT sensor which will make it richer as you turn up the resistance. Increasing the resistance between the ECU and the sensor causes the ECU to think the air is cooler, and thus adds fuel. GunPilot says it is possible to put a rheostat in parallel with the same sensor, and thus lean out the fuel. Turning the rheostat will thus make the ECU think the air is hotter than it is, take fuel out thus making it leaner. I am not sure I have wrapped my mind around this one yet. Does increasing the resistance or decreasing the resistance make the ECU think it is warmer. I would guess decreasing, since increasing it in the series wired one, made it think it was cooler. Am I close? Apparently it is possible to apply this same technique on the ECT sensor to make it richer yet for hard hot starting, or even cold start for that matter. It was in trying to solve the hot start challenge that got this conversation started. At this point, the rheostat is just wired tied on the lap top communications cable. Eventually I will make it look nice. Thanks Gun. This is fun indeed. Sam |
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| Author: | Dart270 [ Fri Aug 12, 2011 4:49 am ] |
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Old skool meets new skool. I like it. Congrats. I will probably do the same on my MSI turbo car. Lou |
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| Author: | Sam Powell [ Fri Aug 12, 2011 7:07 am ] |
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It is dirt simple. And, Radio shack sells the 5k rheostat for around $3.50. I decided I am going to mount the rheostats in the old ash try cavity. Sam |
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| Author: | Rust collector [ Fri Aug 12, 2011 7:15 am ] |
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Well, I am glad this works for you, but I still think things like letting an engine start, and run on its own, is something the ecu should handle. This is kinda like having an efi car, with a manual choke...  Well, I guess it would be a nice way to figure out what the engine likes, more like a tuning aid. Anyway, good luck with it 
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| Author: | Dart270 [ Fri Aug 12, 2011 7:20 am ] |
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That is a good analogy, Rust collector. You are right the ECU should handle this, but this is old-ish EFI hardware and a custom setup, so sometimes you might need a crutch... Lou |
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| Author: | Rust collector [ Fri Aug 12, 2011 7:31 am ] |
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Yep, I guess it came out sunding a bit negative. Sorry about that... I didn't mean to bash his work, but I just think it should work better, if you see what I mean. Still, I think this would be a nice aid while tuning, for other setups too I might try this, if I ever get my heap running again 
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| Author: | Greg Ondayko [ Fri Aug 12, 2011 1:53 pm ] |
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Cool There's No subustitute for tuning, But this can be a nice tuning aid.... Also The Warmup tables can only really be tuned when the car is cold say after over night so that proceess is time consuming say months or years to get tweaked.. But it can be done  Greg |
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| Author: | Sam Powell [ Fri Aug 12, 2011 5:49 pm ] |
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It's that hot start thing that is the big deal. LIke a said, the Accel Gen VII had a table to tune for that, which the MS does not. So if you are a motor head like we are, what is the big deal about dialing an AF ratio manually? For the average driver, yeah, good ECU tuning is nice. But I really like being able to tweak the AF ratio for a specific need, at a specific time. I would not mind driving it this way for the rest of the life of the car. I went to a cruise this evening. The Dart was surrounded by glossy, Chevy v-8 cars, and guess which one got the most air time from passers by? They walked right by the Chebbies. Been there, seen that. Then stopped to talk to me for sometimes, 15 minutes, with lots of good questions. All the spectators were car guys themselves. Very few pedestrians were there. And, when it was time to leave, I dialed in a richer mix, fired it up, and drove right off. What's more, several of the car guys saw my rheostat wire tied to the dash, and asked what it was. The explanation brought approving nods. Cool, they say. I don't care if it is a band aid. I like it. I know I will drive it more now.l Sam |
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| Author: | Dart270 [ Fri Aug 12, 2011 6:03 pm ] |
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Sweeeeet. Nice work all around. Lou |
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| Author: | Rust collector [ Fri Aug 12, 2011 6:08 pm ] |
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Great!
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| Author: | SlantSixDan [ Fri Aug 12, 2011 6:12 pm ] |
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Quote: This is kinda like having an efi car, with a manual choke...
Almost as good of an anti-theft device as a pushbutton transmission. 
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| Author: | Sam Powell [ Fri Aug 12, 2011 7:40 pm ] |
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Love the Avatar, Dan. Sam |
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| Author: | Greg Ondayko [ Fri Aug 12, 2011 7:55 pm ] |
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Quote: I went to a cruise this evening. The Dart was surrounded by glossy, Chevy v-8 cars, and guess which one got the most air time from passers by? They walked right by the Chebbies. Been there, seen that. Then stopped to talk to me for sometimes, 15 minutes, with lots of good questions. All the spectators were car guys themselves. Very few pedestrians were there. And, when it was time to leave, I dialed in a richer mix, fired it up, and drove right off. What's more, several of the car guys saw my rheostat wire tied to the dash, and asked what it was. The explanation brought approving nods. Cool, they say. I don't care if it is a band aid. I like it. I know I will drive it more now.l Sam Great Sam, Yep That Happens A bit With My junk at car shows..... I have the different stuff. As I say to my Friends etc.. Corvettes are like buttholes.....everyones got one, But not everyone has a 14 second Slant 6 car or what have you thats out of the ordinary. Greg |
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| Author: | Sam Powell [ Sat Aug 13, 2011 3:45 am ] |
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I have to say, I was impressed with how neat the engine bays looked on the Shiny Chebbies. I kind of have mixed emotions about the fact that my engine bay is a plumbers nightmare, and very cluttered looking. Of course that is one reason people looked, and asked questions. But part of me still wants it to look neater. I guess there are three approaches to this,: 1. Hide stuff with covers and shields, 2. Clean stuff up, and pretty it up with wire harness convolute tubing and such . 3. Rout things in a neater fashion. And then don't drive it, and/or spend most of your time cleaning the engine bay. An hour on the road, and the engine bay starts to collect road grime. This car cruise, which I will go back to, had its share of cool cars that were off the bell shaped curve. There was a '63 beetle set up to rally. A steel Ford 32 convertible restored to concourse condition complete with original 4 banger, etc. There was a very nicely restored 60"s Austine Healy Sprite, all home done. A personally, and nicely restored 57 Buick Special, with fat white walls, etc, etc. Here is one thing I recall that I thought a little odd. There was a a guy there who had a beautiful 90's Mustang with a Ken Bell Blower on a 4.6 v-8 that he claimed would turn 10.5 ET's. The car was drop dead gorgeous, with iridescent blue/green paint, etc. However when I asked him where the air cleaner was, he did not know.  He did seem to know how to open the hood. BE nice Sam. I was actually more impressed by the home done Sprite next to it, that would likely turn maybe an 18 second et, if that. He sprayed the paint in his garage, and rubbed it out to an authentic British Racing Green shine. I guess I should not judge. Different strokes for different folks. Sam |
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| Author: | GunPilot [ Sun Aug 14, 2011 9:58 am ] |
| Post subject: | Re: IAT bias to tweak AF ratio |
Quote: Increasing the resistance between the ECU and the sensor causes the ECU to think the air is cooler, and thus adds fuel. GunPilot says it is possible to put a rheostat in parallel with the same sensor, and thus lean out the fuel. Turning the rheostat will thus make the ECU think the air is hotter than it is, take fuel out thus making it leaner. I am not sure I have wrapped my mind around this one yet. Does increasing the resistance or decreasing the resistance make the ECU think it is warmer. I would guess decreasing, since increasing it in the series wired one, made it think it was cooler. Am I close?
Yes, that is the concept Sam.
Sam |
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