IAT resistor value

[scottmillera]

Mike,

I have read over the Tuning for Milage document, and I plan on using the info. to lower the lean-out limits along with installing the duel EFIE on my 2004 Ford Expedition. I believe my MAF is the variable DC voltage style, as it is the hot-wire type with the IAT sensor built into the unit. My question after reading the document is what amount of resistance should be added (in parallel I presume) to the IAT signal wire? I read that the CTS sensor usually requires about 3.9k ohm (my Ford my be more like 5k ohms), and that the IAT can be dealt with in a similar manner as the CTS. Does that mean to start with a 3.9k (5k) ohm for the IAT as well? Would you suggest using a pot. to apply the resistance so that the resistance can be varied, or would it be better to solder in a fixed resistor in parallel with the sensor? I was thinking that a pot. may be better so that varying levels of resistance could be experimented with. Also the article says that installing a resistor in parallel with the IAT sensor will retard ignition, is that a good thing or a bad thing when using a Hydrogen cell? Does retard mean that ignition will occur closer to top-dead-center, but prior to camming over, or does retard mean that the ignition will occure sooner than normal? Sorry for my ignorance, but I want to make sure I understand the terminology. It seems that with an HHO gas being added to the mix you would want the ignition of the gases to happen closer to top-dead-center than normal to keep the combustion from actually working against the rotation of the cam shaft.

Thanks,
Scott Miller

[colchiro]

Ideally, you'd use a Scangauge and use a resistor value that gets you a 10 degree increase, like the author indicates.

I'd try a 10k resistor for IAT.

E85 has a higher octane rating than gas so many vehicles tend to increase the timing automatically if they use an anti-knock sensor. I suspect HHO would work in a similar fashion since I believe it also increases the octane.

I think we should start a Tuning Results post and people can post the values they used along with the location of the sensors (pics?).

[scottmillera]

colchiro Wrote:Ideally, you'd use a Scangauge and use a resistor value that gets you a 10 degree increase, like the author indicates.

I'd try a 10k resistor for IAT.

E85 has a higher octane rating than gas so many vehicles tend to increase the timing automatically if they use an anti-knock sensor. I suspect HHO would work in a similar fashion since I believe it also increases the octane.

I think we should start a Tuning Results post and people can post the values they used along with the location of the sensors (pics?).

Thanks for the suggestion for the 10k resistor. I do have a scanguage and planned to use it for the CTS, but I didn't know where to start with the IAT. Do you think a pot. would be a good idea to allow quick adjustments to the resistance value would be a good idea, or should a fixed resistor be used?

[colchiro]

I think you could use a pot and eventually replace it with a fixed resistor. I don't like the idea of running all the controls into the cab and an unprotected pot in the engine compartment is asking for trouble. Anything under the hood should be soldered and semi-protected, IMO.

Any idea what your IAT read on the SG before adding the resistor?

[scottmillera]

colchiro Wrote:I think you could use a pot and eventually replace it with a fixed resistor. I don't like the idea of running all the controls into the cab and an unprotected pot in the engine compartment is asking for trouble. Anything under the hood should be soldered and semi-protected, IMO.

Any idea what your IAT read on the SG before adding the resistor?

I ended up with about 66k on the IAT which raised the temp. value about 35-40 degrees from the original temp the scanguage was showing. How much above actual temp. is a good starting point?

I also raised the CTS approx. 10 degrees above the original scanguage temp reading. I put a pot. on the CTS for now so that I could adjust it to see how much resistance was required to get the 10 degree off-set. After getting the 10 degree off-set, I measured the pot. with my meter and it looks like my truck needs approx. 20k ohms for the CTS.

I also hooked up my duel EFIE today, and set it to about 200mV.

Tomorrow, I'll do a test run and see if I'm getting any milage improvement.

[colchiro]

I have about a 15 degree increase on my IAT with a 10k resistor. I think you may have gone too far. If your don't get good results, I'd back off to a smaller value between 10k and 15k.

FWIW, the CTS is the critical one of the two. I'd leave that one where it's at or you might have trouble starting in the winter.

[scottmillera]

colchiro Wrote:I have about a 15 degree increase on my IAT with a 10k resistor. I think you may have gone too far. If your don't get good results, I'd back off to a smaller value between 10k and 15k.

FWIW, the CTS is the critical one of the two. I'd leave that one where it's at or you might have trouble starting in the winter.

Well I was wrong about the degree offset with the IAT, it's about 20 degrees, so that may be okay.

I have a MAF only system. It is the hot-wire style, and I thought that they were strictly the varying DC voltage type of sensor. However, I have a pot. on the signal wire (in series), but it seems to make no difference at all. Are some of the hot-wire style MAF sensors frequency based sensors? I have this same type of pot. on the MAP sensor in my older jeep, and you can really tell when you turn the knob.

[colchiro]

Sorry, Scott. All I know is what's in that Tuning for Mileage page and what I posted here with my Toyota.