I am using the GM temp sensor, which takes a 5 volt reference signal, and changes the ECU signal as the temp goes up. Does anybody know which way the voltage changes as the temp rises? Does voltage go up as temp goes up? I know I could just measure it, but it's more fun to get a thread going. I want to try and trick the ECU with a circuit that will allow me to tweak the AF ratio on the fly by modifying the ECT temp signal to make the ECU think the engine is colder than it is. There is a device on the market for pretty cheap that is made to fool the O2 sensor for those who want to lean out their EFI, and I was thinking of using that in the ECT sensor circuit instead. This device can be adjusted on the fly to add as much as .55 volts, and after talking to the maker, he thought it could be made to modify the temp voltage by as much as 1.5 volts. He also thought it could be wired in such a way as to reduce voltage. .Thanks.

Sam

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Sam,

The GM sensor is a variable resistor. Usually the voltage as measured at the sensor will drop as the engine warms up. However, if the Accel ECU switches bias resistors or does some other sort of trick, the voltage may make an abrupt jump at some point. The voltage will depend on the bias resistor value, the bias resistor being a part inside the ECU.

Also, since coolant temperature sensors use resistance and not voltage, hooking a voltage source to one could result in unpredictable effects. It depends on what exactly is inside this black box. If it's what I expect, an op amp circuit with an adding circuit in it, it could end up not working at all in a temperature measurement circuit.

Does the Accel system have something like a table switching input? That might be an easier way to make on the fly changes. Usually these tuning aids are used with non-tuneable ECUs.

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

I don't know the answer to the table switching inp;ut question. Is this something that would be accessible without the laptop. I am trying to make changes without having to fire the lap top up and look over at it while driving down the road.

I have not been able to get ahold of any Accel tech people since the Sema show two weeks ago. Their phone message says they will answer the phones after 11-5, but they are not doing so now.

All I can tell you is the black box is not really a black box, if you are an ee type. I have a circuit design for it, with all parts listed etc, but it looks like by the time you tracked down everything you would need to build it, you might spend more than just buying the assembled kit. I can send you a diagram if you would like to see it, although I don;t have a scanner to send it electronically. I could put it in snail mail.

Sam

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I went on line and found another divice made by someone hoping to get better mileage out of a fuel injected car that fools the MAP sensor. I don;t know how they think they are going to get better mileage this way, but, the device is made to work with a five volt circuit. Maybe I could incorportate this into the temp sensor circuit annd fool the ECU into thinking the engine was cooler than it is, and thus erichen the mixtures those times when I felt it was needed.

Here is what is going on: After driving the Dart for about an hour,the mixture starts to get leaner, even though all the temps and such are the same as they were 20 minutes ago. It only seems to be a problem when I come to a stop, and it has to idle at very high AF ratio. I suppose it would not die, but I get worried about it when it is trying to idle at 17:1. It does not feel thoroughly dependable under those situations.

Now that I think of it, this car behaved the same way when it was carbureted. There is something different about the way fuel gets atomized when it get really thoroughly warm, through, and through.

I could operate it in feed back mode, and that would stabilize things, but I want to be able to cruise at 17:1, not 14.8:1. Maybe I could engage the feedback loop mode only for idle. I think I can set the RPM min and max for this. It just occured to me as I am typing here that I could buy the device to fool the O2 sensor, and use it as designed in feed back mode with the ECU. In this way, I could set it the ECU for feedback and and tune the AF ratio on the fly with the O2 signal enhancer. Any thoughts?

Sam

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I'd probably check temperatures and see if anything in particular is getting hot after a long drive - I'd first check the temperature sensors the ECU is reading, but I'd then check the temperature of the manifold and fuel rail as well. For that matter, I'd make sure you don't have something causing the fuel pressure to drop.

Can't the Accel use wideband feedback to cruise at 17:1 or some adjustable point?

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

The ACcel ECU has its own wide band kit, but it will not use my Inovate gauge output. They want $1000 for their kit, and I don;t want to spend that money at this point. The fuel pressure is stable. I have a gauge in the pass compartment for that. Something that might be changinh is the intake manifoldsurface temp, which their is a sensor on, and which is used to calculate the fueling rate. But I don;t know how it works, and Accel's manual tells you nothing aobut how to adjust it.

Sam

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Does the tuning software let you view what information the sensor in the manifold is gathering? I'd check to see if the temperature on the sensor is going up or not. This could be a manifold heat soak issue, which can often be cured by moving the sensor from the manifold to the charge piping upstream of the throttle body. I'd try relocating the sensor first; this often will often cure issues where an engine runs lean when it heats up.

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

The temp sensor is up stream of the TB. by about 8 inches or so. I have a new, or rather old problem now, which is of greater concern, but might be somehow related. I will start a new thread about it.
Sam

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If I had to guess I would say that temp of the intake is causing mixture problems as you suspect. There is a ajustment for that in the Accell software, I cant remember but it seems like it was called "Tal" something. But I am not sure it could be ajusted to respond with themp changes. It is a ajustment that allows for the fuel that is sticking to the intake walls, the more that stocks to the walls, the richer the mix reaching the cylinder. If none sticks to the walls (it evaps) then things lean down.


How about getting some of that real good heat shielding to line the bottom of the intake with so it dont get heatsoaked. Or if it has water hook ups (the intake) change it to the opisite of what it is now.




BTW Sam, I noticed in your sig that you are using the Edlebrock Shocks. How do you like there shocks? My Cuda has gas shocks that are new (they came on it) but they are so stiff it rides like it has air shocks all the way around. I am going to change the shocks & it seems many people are liking the ride of the Eddy shocks. WHats your thoughts on the way they perform?


Jess

Thanks for the tips Jess. This manifold has coolant lines that are unused at the time. Do you think that would make a difference? That is an easy thing to try. The TB also has unused coolant lines to heat it up. . Should I plumb this all as a "T" off of the heater hoses? I can't remember if there are plugs under the manifold that I may have left open. I guess I can stick a mirror down there to see. Boy there are alot of hoses under the hood on this thing. I would be happy to put more if they will make things better.

I love the Edlebrock shocks. They have excellent control, and ride much smoother as well.

Sam

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