When the weather is hot and muggy, the AF ratio gets richer. It is obvious that there is not as much oxygen in the humid and hot air.

Is it supposed to compensate with the feed back from the O2 sesnsor? One of the problems here is that if I want to run an AF ratio greater than 14:8, I have to buy their wide band O2 setup which is really expensive. Is there any other trick I can employ here. I have not found a way to raise the cross over voltage as is in the Mega Squirt setup.

It pretty clear now why runners drop sooner running in hot humid air. There simply is not as much oxygen in it.

Sam

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Human runners usually drop in hot humid air due to overheating, but they also slow down just like a car does.

The inlet air temperature sensor compensates to a degree, but there is no vapor pressure sensor to account for the rise in barometric pressure due to humidity so that leaves the O2 sensor.

If you want to run richer than 14.8:1 A/F with the hardware you have you'll need to run it open loop.

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Joshua

Years and years ago, when the first EFI setup was first prowling the roads (Bosch D-Jetronic in Volvos and such), various companies offered a dashboard-mounted "power dial" that could be adjusted to "give more power" while still retaining proper adjustments needed to pass e.g. California's strict periodic and random roadside emission tests. This "power dial" was installed in series with the engine coolant temperature sensor, and was itself a variable resistor. The idea was to fool the ECM into thinking the engine was colder than it was, thereby adding more fuel. I'm a little hazy on the details, since most temp sensors' resistance increases with increased temperature and vice versa. It seems likely that a coolant temp sensor with lower-than-stock resistance was installed, and the dial's "home/normal" position added enough supplemental resistance to mimic the profile of the stock sender. Rotate the dial, take out some of the supplemental resistance, computer sees lower resistance than it ordinarily would at whatever engine temperature, thinks engine is colder, adds more fuel.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

A trick used by owners of Dodge trucks with late model engines is to insert a resistor in series with the Intake Air Temp sensor. I don't remember the value to use but I'll try to look it up. Of course, a pot in series would do the same thing and be adjustable. Also, the location of the IAT can make a difference. On a Magnum V8 with the "beer barrel" manifold the IAT was screwed into the #2 intake runner. I moved mine to the intake air hat. Others move them to the intake duct just aft of the air filter. The result is better throttle response, the cost is slightly decreased fuel economy.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Those sound like interesting ideas. Since, as I have said in the past, I am an electronic dunce, I would need to be feed spedific part numbers for such a adjustment device. . This is precisely the kind of thing that I would love to do.

Another thought I had earlier: I have an Innovate AF ratio gauge, which is designed to be daisy chained to a data logging software. There is an output coming FROM the gauge for this purpose. Innovate uses minature RCA plugs to hook the gauges up. It is pretty slick.

I think I will contact Innovate, or at least the guys who sold it to me, and see if the output from the gauge can be used as the broad band input for the accel ECU. If so, then the tuning software has a matrix of cells just like the tuning map, and spark map that lets you specify target AF ratios in a map. That would be cool! I just didn;t want to spend another $1000 for an additional broadband interface..

Sam

Sam

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Dan, double check that. As I recall most (GM) temp sensors are negative temp coefficent (temp up, resistance down). Got a chevy truck in the shop
right now that I need to check the t-stat operation. Will have the scanner pluged in so it will be an easy matter to check.

Edit:
Just got out one of my GM training manuals. It has a chart of temp sensor values.
210*=185 ohms
160*=450
100*= 1800
70*= 3400
40*= 7500
20*=13,500
0*=35,000
-40*= 100,700
Manifold ait temp sensors have the same calibration, but due to internal ecm programing, have less effect on fuel adjustment, in closed loop.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

If you already have a WB O2 hooked up, there must be a way to use that output and run it into the ACCEL system w/o a new board.

I like the potentiometer method to fool the air temp sensor ECU input. I've seen the same thing where the ECU does not compensate quite right for AT and/or humidity.

Lou

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Home of Slant6-powered fun machines since 1988

Good info, CS. That makes things a lot easier, assuming (!!) the existing temp sensor has negative coefficient. Sam, what coolant temp sensor is presently in use?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The ECT sensor is GM, as are all the Accel sensors. Since I installed the new Autometer coolant temp gauge, there is more agreement between the gauge and the ECU which is down in the block. It seems the head warms up quicker than the block but not as much as it used to indicate.

Dan, If you can figure from Charlies readings what potentiometer to put in the line, I will give it a try. It seems that since the resistance goes up as temp goes down, then we can fool it into going richer, but not leaner. Am I right in this thinking?

Lou, I will look into using this WB O2 output to the ECU. That would open up a new frontier of control in tuning. Thanks for thinking about this guys.

Sam

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I'm not as familiar with the Accel as with some systems, but it should have temperature compensation built in. There may be a temperature compensation table you can adjust somewhere.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

I believe the Innovate WB sensor can mimic a narrow-band sensor....

And I also think you can shift the output so that it acts like the narrow-band sensor at any A/F ratio you want....

So you can have the Accel unit 'think' it's running at 14.7:1 when its at 16:1.........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Since the ACcel ECU will process wide band datas, and go for what ever AF ratio I want, wouldn't it be better to see if I can't get the ECU in wide band mode with the Inovate output? Why would I want to get it to translate back to a simulted narrow band? I have a narrow band sensor already. For what it is worth, the narrow band sensor is in front of the turbo, and the wide band is after. This is what I was told to do.

Sam

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I've been doing a little reading on the trick as applied to a Dodge Magnum engine. It seems that 500 ohms is what was commonly used. The sticky wicket is that when the ECM richens the circuit to counter the perceived lower temp the O2 sensor sends a signal to lean it back at some point during the ECM learning cycle. Your best bet is probably to look for that air temp table in your ECM and tweek it there. Of course the Accel ecm may not work the same way at all. You should be able to adjust all the pertinaent tables as you see fit since you don't have to answer to the EPA for how it works.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Tuning with the laptop to accomodate seasonal changes is an option, but not too practical for the kinds of changes that are daily ones on the East Coast. I really love the idea of being able to just reach up, and trick the thing into thinking the engine is a little colder and thus enriching it. This would only work if you disabled the O2 feedback. If someone can give me a radio shack part number or at least a specific value for a pot to go buy, I would like to try this. But as I have said already, I am an electronic dunce. For real. So if I have a part number, I will try this, but otherwise I would not be likely to give it a try for fear of fouling up something beyond recognition,(FUBAR).

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