I have an IAT sensor chip, but I'm not sure which sensor is exactly the air intake, I have 2 choices that I can see. I've got a 91 4.0 V6. Does anybody have a labled engine map/picture or something that would help?
Thanks :)

 

First, it's not a chip, it's just a resistor.

The IAT is in the intake tube itself, before the throttle body.

That mod will do something for an older truck like yours -- but again it's not a chip: it just fools the engine controls into thinking your intake air is colder than it actually is and advances the timing and enriches the mixture slightly.

 

I only have a 1992 manual, but I was wrong if the 1991 is in the same location. It actually appears to be on the intake. Diagram below. Look across the top, towards the right hand side and fing the "ACT" -- air charge temperature sensor.

 

Thanks for the diagram n3elz

Yeah, that ACT sensor was one of the choices, and the other was up on the actual intake tubing in a little box poking into the tube, I'm guessing that's the mass air flow sensor. I do have one of those resistor things that just trick the computer, so would it actually matter whether I put it on the MAT, or ACT?

 

Chris, I don't know for sure and I'm at work now and have no access to my CD's for that year. PM me tonight and remind me and I'll look up some info for you.

 

Alright, thanks alot :)

 

Okay, I remembered without being prompted (a rare occasion, you may all now applaud)...

You pretty much have to use the ACT (and/or ECT) sensor. The MAF is ONLY an air flow sensor and though you can mess with it it's not the most benefit.

However, it appears that to get timing advance, it may be the ECT (engine coolant temperature) sensor you need to modify. So what you could do is try it in the ACT or the ECT and see which gets you more, or modify both.

The ACT will cause some enrichment, but the EEC-IV manual I have suggests it doesn't modify timing. The ECT is the main temperature related timing input, or so the book says.

 

Awesome, thanks n3elz.
I'm gonna work on putting it in tomorrow, and we'll see how she goes

 

what year is your truck and engine size?

 

1991 4.0l V6 Efi

 

sorry i have a hard time reading sigs... is it not in the maf?

 

I thought it was, but I guess it's the ACT and ECT up by the throttle area that I'm looking for

 

u dont wanna mess with the ect... that will really mess stuff up. it should be in the head or by the thermostat. the iat is on the intake tube or in the intake itsself

 

even if I just cut my box into the ECT line, then take it out later if needed to and twist the line back together?

 

no i wouldnt risk frying the computer

 

let me find out for sure where u need to be on this thing

 

yeah, I wouldn't want that now... I'll just try the ACT and see how much of a difference it makes

 

all it will do is lie to the computer and advance the timing and may make it run too rich... but yea the act sensor is in the intake boot

 

cool, thanks for the help guys

 

The IAT sensor (and called that by then) was not integrated into the MAF until much later. I'm thinking around 2001 but it might have been sooner. I'd have to look at the manuals.

This sensor mod has been done and proven to work on a lot of older trucks. The ECT version is the most effective if you up your octane with it. In practice it works exactly like the "180 degree t-stat" mod where the engine temperature is reduced.

On newer trucks the ECT mod will do a little, but the IAT/ACT mod will do nothing. This is because in later trucks the IAT/ACT (depending on what you want to call it) was taken out of the equation for adjusting timing.

The factory service manual even indicates that the ECT will have an effect on timing.

Lieing to the computer, as it was stated lol, is a time honored and proven method of getting a little extra power on some vehicles, particularly with older computers and sensors. Modern trucks are full closed loop with much tighter controls and checks and are harder to fool into doing anything beneficial.

I tried to do this on my truck and fooled myself into thinking it actually did something. But after talking with some people (and I think Doug from Bamachips was one of the contributors) it came to light that in the new tables in the PCM, the contribution of the IAT to timing was "zero'd out".

However, you can get some benefit from the older ones. You can try it and if you have problems, just take it out. You don't want anything too rich -- but timing advance you can use to get more power across the board.

What I'm not sure of is how much advance you can get. But don't worry too much about the ECT -- only on the later trucks will it make a huge problem because on the OBD-II/EEC-V vehicles the PCM won't get into a full "closed loop" state without the engine temperature coming up to spec.

Unless you introduce an outside voltage INTO the line to the ECT, you can't fry the computer by cutting the wire, so relax on that one. However, don't just twist it together if you take the resistor out -- make sure you put a good splice, soldered or crimped, in the line and seal it.

 

Ah, I see...
If I were to buy a second resistor, and put one on the IAT, and one on the ECT, would it be even more beneficial?

 

Well, you know I can't really say. The way these mods work is not always "if some is good, more is better", lol. I would experiement with one at a time and see if you get any benefit before putting them together. You should search other places for more information on these mods. Although it is for 3.0's, this site may help you understand the impact of some of these mods since the old 3.0's used the same control strategies: http://www.rogueperformace.com

There are probably other sites as well.

 

Yeah, I'll just stick with the one I already have, they don't make that significant of a difference to worry about finding another one.
Thanks

 

I am just gonna tell u this once... From an experienced technician... U dont want to ruin your computer or risk burning up other sensors and electrical components. BE CAREFUL and know what you are doing!!!!

 

Very true and well said! I have seen people get too casual with this stuff -- but I've also seen people not do reasonable experiments that could have done so.

To piggyback on Nick's comments: if you aren't really good with wiring -- for instance, if you're a "twist and tape" sort of splicer, I don't recommend cutting any harness wires. You need to maybe see someone who practices some good wiring techniques (which really aren't that hard by the way) and learn how to do it.