Do Resistors work for fooling Pcm

[HemiHill]

Miestor did some work on this,that was positive,
any details on what values work? part numbers?

Results?

[Jaak]

Fooling what? Which sensor? The answer is yes, but no, but yes.

For example, the IAT sensor. Yes, you can fool it to read colder or warmer, which does make it run leaner or richer, until the adaptive program catches up and removes the error by watching the O2 sensors. I have done this and seen it respond this way, by watching the IAT temperature, watching the adaptives and O2 sensors.

Which is why I don't believe that moving the IAT sensor on a dyno and doing a second run, means beans, 'cause the program hasn't adapted to it yet and it would tweak out the change once the engine's been run through the different rpms and loads.

Unless....

You only let the resistor be attached when the throttle body (not gas pedal) is at WOT, because then it runs open loop and ignores the O2 sensors. Then when not WOT, disable the mod.

All possible, and I would have done it already if I didn't have a job that seems to possess me!

[HemiHill]

What i was thinking about is plugging it into the lead that the pcm uses to read the engine temp,it looks like a 450 ohm resistor has resistence(on a gm car) that give a reading that the thermistor has at about 160 degrees.185 ohms is about the same as a 210 degree reading.

This is what some gm guys use to tinker with,cause a TPI car really leans the mixture out @ as little as 190 degrees

[Jaak]

Hmmm....

Well, if you lean it out, and the system sees the O2 sensors running lean, it will add fuel. Same problem as IAT, when not at WOT.

[HOT ROD MAGNUM]

[new rt]

keep going

[joseph]

I assume you're talking about all those resistors that are on sale on E-bay, that supposedly work, well I don't know if they work but it sounds like a big bunch of B.S. to me.

[Todd RT]

I was talking to a RAM1500 guy yesterday, that does this sucessfully on his 5.7L Hemi Ram 1500. He was asking me if this worked on the LX's.

[Jaak]

I was talking to a RAM1500 guy yesterday, that does this sucessfully on his 5.7L Hemi Ram 1500. He was asking me if this worked on the LX's.

I've heard of many things that add 10-20 HP that people do or buy. Like I've said other places, unless it was measured in a manner that allows the adaptives to settle in first, it doesn't mean much...

So what did he do, and how did he measure it to prove it actually made a real long term difference? Seat of the pants measurement doesn't count, because people want to believe.

[HemiHill]

Actually if the pcm is reading 160 degrees( a fairly rich mixture) each time you run then it should remove any incositency between runs due to engine temp getting warmer and ie leaning out.

What I m saying is the engine temp sensor is a thermister, the hotter the coolant temp the higher in ohms
that its resistence becomes,thus the leaner the mixture becomes,(as the pcm adjusts AFR based on that input reading)

This is very important if you are bracket racing and even dyno testing

[Jaak]

Except the PCM will look at the O2 sensors and say, temp sensor is off, it's running too rich, lean it out boys. They get the final say, so your mod would work for maybe 5-10 seconds.

[Shelby]

They tested the F5 IAT sensor mod by from http://hurricane-horsepower.com at one of the MOFOs. It had a high peak HP on the first pass and seemed to not do as well on subsequent passes.

Maybe the O2 sensors did their job like jaak mentioned.
Might work for a dragstrip pass or quick run on the street.

[Jaak]

The F5 only gives you one direction of adjustment. I built another that I sent to CV, but it didn't make it in time for the MOFO (damn couriers!) that never got tried.

If he doesn't bother trying it, he's going to send it back and I'll evaluate it it's effects in detail and post results.

This, with an additional circuit to sense WOT, could make a difference.

Just unplug the IAT, and put this between and you can dial in an offset temperature high or low and see the results.

You can see there's a switch to select if you want it to run leaner, or richer. The switch on the side is there to emulate a WOT sense. About a second before you go WOT, flip the switch, the PCM reads a different IAT, then go WOT before the closed loop can adjust. This way you can see the real impact of a modification that's smart enough to know what the PCM's doing and dance around it.

Hope he decides soon what he's going to do. I'd rather have it back, then sitting around.

[Cam]

Neat Jaak, I like it.

Hey, put this info away in your memory banks if you don't already have it. BTW, I was the person that worked on this at GIFO. And even though the unit did show some very minor gains, the variance could simply be the inconsistency of the run. These cars will not dyno exactly the same, back to back. Since this particular GIFO, Jason has developed a better method of attaining more consistent dyno measurements.

Regarding this modification, please keep in mind that Hal not only measures the input from the IAT but the ambient sensor as well (at least that what I have been told). So if you get to much variance between the two sensors Hals goes into default mod, haHA!. Please correct me if I'm wrong on that one. So if that where the case it was my feeling that the ultimate for this particular mod would be to intercept both sensors and apply the same technology.

But enough with that BS, here is all the measurements from the POT and off the IAT. Bare in mind that the resistance of the IAT could not be measured below 82deg because it was just that hot in the shop at the time I took them.

Supplied POT:
Settings:
1-176.1ohms
2-1.594K
3-3.127K
4-4.39K
5-5.6K
6-6.88K
7-8.41K
8-9.3K
9-9.33K

IAT sensor:
82deg - 8.46K
100deg - 6.96K
110deg - 4.24K
120deg - 3.74K

All heat measurements where completed using a non contact IR gun. So, your results may vary.

[Jaak]

Interesting, I'll have to dig up my notes on this, as I used the scan tool to do something similar, but not...

I looked at reported temperatures according to the PCM from the IAT, while faking it out. So while you measured the F5, and measured the actual sensor, I measured the PCM's reading of a voltage and what temperature that meant to it.