General Index
[1 - Overview] [2 - My wreck!] [7 - Crazy Robin!] [9 - Candy's Ranger] [10 - Keypad entry system]

Meets and Outings
[11 - Centralia adventure Part I] [21 - Centralia adventure Part II]

How-To Articles
[3 - Overhead Console Install] [4 - Overhead Console Wiring] [5 - MAF mod] [6 - LED switch mod] [8 - Homebrew Remote Bass Control] [12 - Headlight/4x4 Switch LED Mod] [13 - General LED tutorial] [14 - EATC install how-to (pages 14-19)] [20 - IAT Resistor Mod (older engines only)] [22 - Automatic Power Windows] [23 - Cruise Control Pod LED's]

The IAT Resistor Mod

IMPORTANT NOTE: This mod appears to be USELESS on later model engines, at least from 2001 up. Ford has removed timing compensation based on IAT temperature entirely until pretty high temperatures are obtained. I'm not at all sure where the "cutoff" point is for which years work and don't work for this mod. If you did this to your late model truck and it didn't work, you have my sincere apologies. FFV ("V" VIN code) engines may compensate for octane changes automatically, allowing some benefit from higher octane fuel. However, I'm still working on getting that confirmed or refuted. Certainly I saw some change going to higher octane fuel without any timing changes.

There is actually evidence that this mod HURTS performance in late model trucks. It's minimally invasive if you want to see if it works with your engine, but I can not recommend it and I'll retain it here for reference only for those of you with older vehicles. Older trucks have the IAT in a different spot, so refer to the Rogue Performance article for exact instructions.

What the heck is it?

This is a VERY simple mod in terms of what it is, but you have to pay attention to detail installing it, and you may want to tweak it ("optimizing" -- more on that later).

So what is the mod? It's a simple way to advance your timing and enrich your mixture just a tiny bit. It's based on the idea that when you PCM detects lower intake air temps it advances your timing and enriches the mixture.

Since the intake air temperature (IAT) sensor uses an RTD (resistance temperature detector) we can adjust the resistance to skew the temperature readings. Since the IAT is an NTC (negative temperature coefficient) device it's resistance got UP as the temperature goes DOWN. Adding some resistance will skew the intake air temperature and force the timing to advance.

PING! That's what you'll get if you do this and run regular gas. You can advance on SOME trucks a LITTLE bit -- but to really make this work you need to use 89 to 94 octane gas. In fact, the value resistor you use can be "tuned" to get the maximum benefit from a given octane without pinging.

Background

Props go to: Rogue Performance -- this is where I first saw it. Here's a direct link to the IAT article.

This mod has been around for awhile and it's tried and true. The only thing is not to overdo it and make your engine knock. If you go down a grade of gas, don't forget to remove it! But basically, it should be harmless as it doesn't make SO much power -- it just gives you a nice bit of extra torque by taking advantage of higher octane gas.

However, I'm only running 89 right now becaus I don't want to pay for 91 to 94 octane! 91, 93, and 94 are all available where I am -- but they are so pricey I probably won't be trying to optimize for it unless I earn more money or gas comes back down!

What is optimizing? Optimizing is getting the highest value resistor you can in there without getting ping/knock. That will maximize your power and minimize the possibility of carbon buildup. Carbon buildup is a real hazard of running higher octane gas without timing advance. In such a case the exhaust valve opens before combustion is quite complete and the interrupted combustion cycle causes carbon to form.

Actual implementation

Below to the left and right you will see my MAF as it appears standing in front of the truck looking into the engine bay. Note that the GRAY wire on the right hand side has been cut and insulated spade terminals have been placed on it. To the left is this setup without a resistor in the circuit. Basically, the wire has been cut and a female insulated spade has been put on one cut end, and a male spade on the other cut end. When they are then joined together like this, you have basically done nothing. The mod is "bypassed". Run regular gas. On the right you can see I've inserted an assembly made of a resistor (or in my case two parallel resistors) and a pair of male/female spade lugs. You simply pull apart the "bypass" and insert the resistor -- simple!

If you look you'll see my resistors are color coded. The red is a 10K assembly (two 20K resistors in parallel), the yellow is 15K (two 30K resistors in parallel), and the blue is about 24k (two 47K resistors in parallel). Why two resistors? Because I had 1/4 watt resistors laying around and the leads are so thin I used two in parallel to get the value I wanted and figured it would be a little stronger physically.

Generally, the red I don't use, the yellow is for 89 octane and the blue is for 93 octane.

To the right is a picture of a couple of the assemblies showing how they have been heat-shrunk. Colored heatshrink tubing on the resistors, and clear over the overall assembly. You can also see the inside of the insulated spade lugs. Note the dark substance inside the lugs of one of the resistor assemblies. This is an electrical anti-corrosion compound made by Ideal Industries that we use at the mill where I work. You can use ordinary "dielectric compound" available in auto parts stores. It's usually in the lighting section and is used on headlight connectors and the like.

How to use it

What you do is fill up your truck with your target octane, and try different resistor values until you find what works. The result will be better "grunt" and more horsepower -- but you will definitely notice it when you first hit the gas -- especially if you have a 3.0 like me. They are totally torque-less at low RPM! This mod helps that quite a bit.

You must put the higher octane gas in FIRST though, or you may ping like crazy. Gas first -- then resistor. Bypass the mod as shown in the top left picture on this page when "falling back" to regular 87 octane gas for any reason.

3.0 FFV (flex fuel) Engines

Here's and extract from a post I did on http://www.ranger-forums.com about my experience. I DID get more initial acceleration -- but not from the resistor and the resistor HURT my 0-60 time! I have a FFV 3.0 engine. My post follows:

This is a long post, so bear with me.

I A/B'd the performance of my truck (3.0 VIN engine code "V" -- FFV) with 89 octane and putting a resistor in and out of circuit. In fact, I made a potentiometer insert to dial up anything from 0 ohms to 100K ohms in the circuit.

The surprising results: no change in timing. With any resistance over about 10K to 15K my 0-60 time went DOWN. My 0-60 time WITHOUT the resistor was 10.28 seconds. WITH the resistor it was 13.05 seconds! Why?

After reading a bunch of stuff I think I have it figured out but I could use some help from "Dave and Julie" (am I speaking to Dave -- I sometimes don't know who I am addressing, lol) to find out some stuff about the FFV timing algorithm.

All sorts of Ford engines, including Focus, F-150 and others have had measureable gains from this mod. So did I, or so I thought. Here's what fooled me, I think: the FFV is automatically setting the timing up to use higher octane fuel. The FFV used to have a fuel sensor in the tank, but they don't anymore. Instead they watch things in the sensors to determine how to adjust to whatever fuel is in the vehicle and provide "optimum" performance.

This means adjusting fuel curves AND TIMING according to engine performance. From what I have read, a common algorithm for this is to use the knock sensor counts to optimize the timing. Basically, the timing starts at a "safe" value and the engine "hunts" up to the optimum timing for the fuel in use. At idle, my timing starts at about 9 degrees BTDC and slowly advances to 18 degrees after starting EVEN IF THE ENGINE IS WARMED UP ALREADY.

My guess, which I will confirm, is that if I put 87 octane in, the timing will change. I'm going to try this next time I fuel up. Then I'll try a tank of 93.

The maximum timing I'm getting is about 38 degrees during hard acceleration. However, at high RPM the timing is retarding back into the 20 to 25 degree range. I'll post a graph of a trial run later.

I want to check a graph of the same sort of run using 87 and see if the values change. It would explain why my truck is showing more off-the-line grunt with the higher octane fuel. It was not the resistor -- the truck was already adjusting the timing ANYWAY. I put in the resistor when I fueled up with the 89 -- and I believe the truck quickly adapted to the different fuel.

Now VIN "U" 3.0's and the 4.0 may not have this "timing override".

I really need someone to do this mod with a 4.0 and a 3.0 "U" code engine that can record the data somehow. Anyone out there?

For those who bought a kit of resistors from me -- if it doesn't help your truck, I'll give you your money back -- keep the resistor kit, lol! But don't panic yet -- it works on most Ford products (and many others) and it may still work for you. However the FFV is a wierd animal because it can adapt to and fuel mix from pure ethanol to pure gasoling and EVERYTHING in between WITHOUT a fuel sensor. That's quite an accomplishment and it may be an advantage. We'll see and I'll let you know.

In the meantime, Dave, if you can hit up your "sources" to confirm what I'm thinking about the FFV, that would be great.

I hate eating crow -- and I'm not chewing unlees it doesn't work on "U" code 3.0's and the 4.0, lol-- but there it is. I value honesty in these matters too much not to post this stuff.

If the fat lady sings, I'll have even more to say.

So, I'll be doing more investigation on this and updating this page as needed.