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It's important to understand if your wideband O2 sensor is set for a stoichiometry of ~14.7, or if it's set to E85 (9.00).
If your wideband is set to read 14.7:1 (regular gas), then these numbers are as you think they are. If your wideband is set to read 9:1 (E85), then buddy you are tremendously lean.
A factory car at factory boost levels with no tune in it should not be experiencing knock, if using the recommended octane. If you've turned up the boost with a pulley or something, and running a stock tune, then that would be a huge problem.
Some widebands may not have an adjustable stoich. Please let us know what wideband you are using, and what you have the wideband set to display.
It's important to understand if your wideband O2 sensor is set for a stoichiometry of ~14.7, or if it's set to E85 (9.00).
If your wideband is set to read 14.7:1 (regular gas), then these numbers are as you think they are. If your wideband is set to read 9:1 (E85), then buddy you are tremendously lean.
A factory car at factory boost levels with no tune in it should not be experiencing knock, if using the recommended octane. If you've turned up the boost with a pulley or something, and running a stock tune, then that would be a huge problem.
Some widebands may not have an adjustable stoich. Please let us know what wideband you are using, and what you have the wideband set to display.
You would think that they wouldn't knock from the factory but these cars do. I did data logs with the cars stock with 93 and it knocks. I switched to E85 and data logged and it still knocks. Not really bad but it's still there. I'm running an AEM wideband. Which I setup on 93 before I switched to E85. And yes the car is a factory flex fuel car. The wideband reads 14.8 at idle and cruising speeds. I had the car on a dyno after I bought it and he thought it was running a little rich being in the 11's so he pulled a little fuel and it started knocking so he put fuel back in and it got better. It's a strange little car. I went as far as logging with everything stock to see the factory AFR to be sure I wasn't way off. So I'm not concerned about it running lean. After all the modifications I have the AFR set very close to the factory tune. I'm guess it's the 11.5:1 compression that makes it wanna knock.
I didn't realize the car was flex fuel. I thought you converted it. The wideband must be reading in a stoich of 14.7 then. The actual air/fuel ratio at WOT if probably more like 7.2:1 on E85, but your wideband was not programmed for this new stoichiometry, so it still reads in the same old 14.7:1 setting it always has. And that's just fine.
FYI, you can avoid all confusion by working in units of Lambda. Air/fuel ratio varies depending on stoichiometry. Lambda does not. It takes a little getting used to, but once you've got it down pat, it's much easier and more accurate.
I didn't realize the car was flex fuel. I thought you converted it. The wideband must be reading in a stoich of 14.7 then. The actual air/fuel ratio at WOT if probably more like 7.2:1 on E85, but your wideband was not programmed for this new stoichiometry, so it still reads in the same old 14.7:1 setting it always has. And that's just fine.
FYI, you can avoid all confusion by working in units of Lambda. Air/fuel ratio varies depending on stoichiometry. Lambda does not. It takes a little getting used to, but once you've got it down pat, it's much easier and more accurate.
I'm really good with car but I'm still fairly new to the electronic side of it with all the different settings for everything. I managed to get the wideband setup and working properly mainly to tune the nitrous. All I'm messing with is WOT fuel and timing. That's really all I've figured out so far.
I'm really good with car but I'm still fairly new to the electronic side of it with all the different settings for everything. I managed to get the wideband setup and working properly mainly to tune the nitrous. All I'm messing with is WOT fuel and timing. That's really all I've figured out so far.
If you don't have some education in tuning, be careful. There's a lot to it. If you don't have a full understanding of the table you are modifying, and how it will affect your car, you can get in real trouble.
Make sure your wideband (if programable) is set up to have a stoichiometry setting of around 14.7 (standard gasoline). Some widebands don't have an adjustment to this display, so you would just have to read the directions to see what it's set to.
The relationship between timing and fuel is inter-related. Adjusting one has the net effect of adjusting the other.
So using this timing retard box I'm getting a code P2199- Intake Air Temp Sensor 1 / 2 Correlation (Pending) (Old) (Current) (Immature). The whole time the box is activated the code is there. If I clear it with the box on it comes right back. If I leave the box off and clear it it doesn't come back until the box is on. Does anyone know why? Is there a way to change something so it doesn't get the code?
So using this timing retard box I'm getting a code P2199- Intake Air Temp Sensor 1 / 2 Correlation (Pending) (Old) (Current) (Immature). The whole time the box is activated the code is there. If I clear it with the box on it comes right back. If I leave the box off and clear it it doesn't come back until the box is on. Does anyone know why? Is there a way to change something so it doesn't get the code?
Apparently, your car has two different IAT sensors. That may be a Cylinder Head Temp Sensor, an upstream and a downstream air temp sensor, or a Manifold Air Temp sensor and intake air temp sensor.
Somehow or another, you have two temp sensors. On a supercharged car, it's likely that you have an air intake temp sensor (pre-throttle body), and a manifold air temp sensor (after blower in lower intake). The PCM uses both of these sensors to model what it thinks the actual temperature of the air entering the cylinder is.
The computer would then also know if one temp sensor reads one thing, another temp sensor should read a certain amount as well. When the PCM sees one super low temp, and it does not see the other sensor agreeing with that, it's going to throw a code for temp sensor 1/2 correlation.
Unless you have two air intake temp sensors somewhere before the blower, I'm afraid this trick is not going to work for you. You can't lie to the computer about the post-blower air temps, or the computer will add a considerable amount of timing thinking its got cooler intake temps.
In this case, the IAT mod trick is out, and you would have to just pull timing in the tune. Or possibly trick the MAT sensor (after blower) into thinking it's HOTTER than it really is. That could get dangerous.
I just realized it may be possible. You could shut off that correlation code. But then I'm not 100% sure what would happen. You would have to carefully test! With the nitrous off, of course.
Best you don't screw with the post-blower MAT sensor.
The weird part is its pulling timing like it should when the box is on with the code. No CEL though. Idk where a second sensor would be. It's a n/a car with IAT sensor built into the maf.
I'm confused, I thought you said this was some supercharged 6 cylinder Cadillac that ran 11's. It's just a naturally aspirated Cadillac? In that case, there probably is only the one IAT sensor, and it likely is built into the MAF.
In that situation, the IAT mod should work fine. You just gotta make sure not to pick a resistor that makes it read so cold that it catches the diagnostic portion of the sensors range. Usually, a 0-5 volt sensor will read bad when you get near the outer edges of that voltage, like below .2 and above .8. I don't know exactly where GM draws that line, but you should be able to use temps somewhere around -20 to 0 degrees for doing this.
From what I've seen, when GM fails a sensor, they keep using the last known reading from that sensor before it's voltage went into the diagnostic range.
I'm confused, I thought you said this was some supercharged 6 cylinder Cadillac that ran 11's. It's just a naturally aspirated Cadillac? In that case, there probably is only the one IAT sensor, and it likely is built into the MAF.
In that situation, the IAT mod should work fine. You just gotta make sure not to pick a resistor that makes it read so cold that it catches the diagnostic portion of the sensors range. Usually, a 0-5 volt sensor will read bad when you get near the outer edges of that voltage, like below .2 and above .8. I don't know exactly where GM draws that line, but you should be able to use temps somewhere around -20 to 0 degrees for doing this.
From what I've seen, when GM fails a sensor, they keep using the last known reading from that sensor before it's voltage went into the diagnostic range.
I have it set to -26 degrees so maybe Ill try bringing it up to 0 degrees. Idk what else to do. I'm pretty sure it only has 1 IAT sensor. I put the tune back in that has timing pulled until I can get this figured out. Hopefully it's as simple as bringing the temp up a little bit more
Seems as though I got it working right finally with no code. I brought the IAT up to 6*F which took the code away. At -6*F the code would come back after a few minutes so I raised it to 6 and haven't seen it again. I also installed an LED display attached to the IAT sensor voltage so I can verify that it is working properly before I spray it. Here's a link with a video of the LED display.
this is what I use for f-bodys, only requires 1 relay and 1 resistor. This will work for many vehicles as long as the 5 volt reference wire is identified. I also use a 130 ohm resistor to trick the computer to believing ECT is 230* (a temp you should never see if fans are set appropriately and if you do so be it).
I chose to use ECT because once at operating temp ECT doesn't float as much as IAT. There are several other reasons why I use ECT that I won't get into but I just believe it to be a more superior method. However, there are more than 1 ways to skin a cat.
Hey guys, i need to bring back this old thread. I am building the box as Rocket5979 did and I have a couple questions on wiring. Both Pin 87a wires go to the IAT sensor signal wire? My other question is can pins 30 be tapped into the wires on the back side of the OBD connector?
On Rocket's box, he has pin 87a going to each wire of the IAT sensor. There's two relays, so there's two wires. The sensor has two wires, so one wire goes to each relay on the 87a terminal.
Pin 30 is not a power source in this case. It's a signal wire interruption. Where he says "from 5v ECU", he is talking about the 5v signal wire that comes from the ECU and goes to one side of the IAT sensor.
The other pin 30 on the other relay goes to the other wire coming from the computer to the IAT sensor.
Honestly, his setup is overly complicated. This IAT mod only requires one relay and one resistor. By doubling the number of relays, he has doubled the chances of failure. But let's be clear about how a relay works, and I think you will understand better.
A relay has two sides to it: The control side, and the load side.
The control side is rather simple... if you hook power and ground to the control side (pins 85 and 86), that turns the relay on. It does so by creating a magnetic field around the coil windings, which pulls a switch up.
The load side is also simple, but in this case it is a fork. Pin 30 is the incoming power (or in this case an incoming signal). Pins 87 and 87a are the outgoing power (or in this case outgoing signal). The relay will always be connecting pin 30 to either pin 87 or pin 87a, one of the two, but not both. When the relay is NOT on, pin 30 connects to pin 87a. When the relay IS on, pin 30 connects to pin 87.
So when you look at his box, basically he uses two relays to connect to the IAT sensor normally when the relay is off, and to run the 5v signal wire thru a resistor when the relay is turned on.
He is using two relays, because he feels that the signal wire must always be connected to the ground wire, either thru the resistor or thru the IAT sensor, whichever he is wanting to do at that moment. And that's fine... it's just a more complicated design that requires two relays. If either relay fails when the other does not, the signal wire will be cut and connected to nothing. It would be like unplugging the IAT sensor.
Here's a more simple design using just one relay. With this setup, you are basically placing a relay in the middle of the IAT sensor signal wire. When the relay is off, it's like the relay is not there. When the relay is on, the signal wire goes thru a resistor to ground. This pulls the 5v signal wire down in voltage, and causes the PCM to read a lower temperature. I recommend using a resistor that achieves somewhere around 0 to -20 degrees IAT temp. Then go into the tune and make sure that every table related to IAT temps is set up to pull x amount of timing when the PCM sees a temperature anywhere near what you've set the fake temp to. To install this relay, just cut the IAT signal wire, and connect the PCM end of the cut wire to pin 30 and the sensor end of the cut wire to pin 87a.
One final note. If you've switched over to Speed Density only, remember that the IAT signal is going to affect the speed density mass air flow calculation. The colder air temp reading will make the PCM think that the air is denser and has more mass, so it will increase the airflow number and also increase the fuel delivery.
Last edited by Pontisteve; 11-12-2015 at 04:33 AM.
Thanks for the reply PontiSteve....I will use your schematic as it seems to simplify it. I do have a question. MY IAT sensor has a 5volt reference wire as well as a separate IAT Sensor Signal wire. Am i using only using the signal wire coming from my IAT sensor? Guess whats confusing me is you wrote 5v Signal wire.
Also, any issue if i use 14 degrees as my reference temp? Here in Tampa area i dont see it dropping that low.
Thanks for the reply PontiSteve....I will use your schematic as it seems to simplify it. I do have a question. MY IAT sensor has a 5volt reference wire as well as a separate IAT Sensor Signal wire. Am i using only using the signal wire coming from my IAT sensor? Guess whats confusing me is you wrote 5v Signal wire.
Also, any issue if i use 14 degrees as my reference temp? Here in Tampa area i dont see it dropping that low.
14 degrees probably works, but it is possible to hit those temperatures, even in Florida. I would put it closer to the zero degree mark if it were me. What you can't do is use the full resistance (-40F). That fails the sensor and the whole thing doesn't work in that case. The area between 0 and -20F is a good area to use, in my opinion.
I'm confused about your statement on the sensor signal wire. So let me explain how the system should work, and if you have more than two wires in total going to your IAT sensor, let me know. I can't say I've really ever seen more than 2 IAT sensor wires. Most thermistors are 2 wires sensors, while most other sensors in a car are 3 wire.
So the way a 2-wire temp sensor works is like this. The computer has an internal 5v regulator, that regulates it's 12v input voltage down to 5v. This is often called Reference Voltage, or VREF. Most 5v sensors in the car share this same internal 5v regulator and VREF circuit. The 5v is sent to in internal resistor inside the PCM, thru that resistor, an down to your temp sensor. That's wire #1.
Wire #2 is signal return wire. That's basically a ground wire that all sensors use and share. They all ground back to the same pin on the PCM, which is internally connected to the PCM ground. With all sensors referencing the same ground, they all have the same ground offset (if there is one), so right or wrong, all sensor grounds are at least on the same page. This ground (signal return) wire is simply ground voltage (near zero volts) all the time.
The Thermistor will take some of the 5v coming in, and send it off to the ground wire, basically killing some of that voltage. How much of the 5v signal that's being grounded off depends on how hot the sensor is reading. The sensor itself is providing resistance between the ground wire and the 5v signal wire.
The PCM is internally monitoring the voltage on this 5v signal wire, and comparing it to an internal ground. When the sensor pulls some of this 5v down to ground, the voltage on that wire drops. The computer monitors this voltage.
So this is a strange case where the 5v power wire and the sensor signal wire are actually one and the same. The resistor inside the PCM prevents the entire 5v VREF circuit from being grounded out, and only drops the voltage after the resistor. So the PCM monitors voltage on this wire somewhere between the resistor and the PCM terminal.
In many other sensors, there's a 5V power, a Ground, and a signal wire. In those 3 wire sensors, the 5v stays 5v, the ground stays ground, and the signal varies in voltage depending on what the sensor tells it to. But that's not how it works with thermistors. As stated, because of the internal resistor in the PCM on temp sensor circuits, the 5v stays 5v before the internal resistor, but drops voltage after the resistor based on how much the sensor tells it to. The sensor is taking some of that 5v and pushing it off into the ground wire. The ground wire (signal return) remains 0v all the time... or at least it should.
What we're doing here is putting a relay in between the PCM and the sensor in the 5v wire. When the relay is off, both sides of the wire remain connected (30 and 87a). When the relay is on, 30 (the PCM end of the wire) now connects to 87 instead of 87a. And we hook 87 to a resistor and then to ground.
So now the 5v circuit is not being grounded or used by the sensor. Instead, we're redirecting it (via the relay) to go to a resistor and eventually to ground instead. The resistor value determines how much the 5v signal is being pulled to ground, and what that 5v signal drops to. The PCM monitors this voltage, and the tune reacts accordingly. We're using a fixed resistor value that simulates -20F temp all the time, and then tuning the car to pull timing when it sees -20F. Or some temperature near that.
Homeboy used 2 relays because he felt the signal wire either needed to run thru the resistor or thru the sensor. My method (when relay is on) goes thru the resistor to an external ground. He wanted it to go thru a resistor to the factory signal return (ground) wire. That's fine, but it doubles the number of relays and potential failure points.
If you do it my way, and get the right amount of resistance, you should be able to turn the key on, and as soon as you hit the nitrous master arm switch, the IAT should immediately jump to a fixed value. That value depends on the resistor value. I forget offhand what resistor I use, but if you go back and search thru this thread, I probably mentioned it somewhere.
To find the exact resistor I needed, I rigged up an audio potentiometer inline to the 5v signal wire. I then turned the ****, changing resistance, and changing the IAT temp reading until I got the reading where I wanted it. I then unplugged my stereo **** and measured the resistance of it, and bought a resistor of very similar value. It worked perfectly.
12-09-2014, 10:09 AM
