Well gang... I've been playing with theories and ideas for long enough now its time to put them into a design and see if it actually works. We all know the 24V's seem to take a good tumble in MPG's as the winter sets in well ISX proved that with the 12V engines with static timing that MPG's don't change. Well if you look at it the only thing that could be tossing this out the window is the IAT sensor on the 24V is changing the VP44 performance. Most know that colder air produces better HP/TQ because colder air is denser and requires more fuel to keep balanced. Well if you reverse this and warm the air (in theory) the VP44 should retune and burn according to the manifold temp. So what I've done tonight is fished through my resistor pile and found 3 I'm going to use for test candidates. Orange - White - Red - Gold = 3.9K Ohm = 116*F IATRed - Violet - Red - Gold = 2.7K ohm = 132*F IATRed - Black - Red - Gold = 2.0K ohm = 148*F IAT So now tomorrow I'm going to pull 3 test runs on the same piece of highway... Seeing if the highier the IAT temp increases the MPG or not... I'll can give you something to think about... Grid heaters are NOT controlled directly by the IAT... With the 2.7K Ohm resistor in place before even starting the grid heater still where hitting as normal. So there is more to the grid heater that the IAT temps... ... On the cutting edge again...

Well they will not tell you exact number I'm sure but they will most likely confirm that we are heading the right direction.

Sorry Mike, read my last post. Quadzilla says the XZT+ doesn't fool IAT. Russ

Volkswagen, I would be interested in seeing your wiring diagram. Also would be interested in updates on the results of your install.

I don't have a scan gauge... so a pot (variable resistor) would not do. I thought that a multi-contact rotory switch would be an answer allowing me to test the resistance values. I made a trip to Radio Shack with my resistor list... but they only had a few of the needed values. I still think it's a good idea... if I could just lay hands on the parts.

I did pick up a rotary switch & 5.6, 4.7, 3.3, 2.2K resistors... I wanted 3.0, 3.6, 4.3K as well.

I also picked up another Radio Shack toggle switch #275-666. You'll recall I was questioning my sanity. But I just tested this one with my meter and YES, when the toggle is down the bottom contacts are connected... the opposite of what I had expected. So I had correctly tested the original switch & was wrong to doubt myself (in this case).

Russ

Rorary switch with different resistance on each setting - sounds like a great way to find out what your truck likes. Could it be used with the digital over head MPG display to show instant feedback? Lets say cruse controll on,flat and straight road (makes all conditions a constant and the only variable in the test is the resistor), and you switch between resistors and watch the computer change the MPG value before your eyes. I like the way you guys think.

It could be used with the overhead... realizing that the overhead is not accurate with a chip, box or programer... Still the comparison is still good. My overhead was right on compared to calculated mpg until I recently installed the Quadzilla XZT+.

Russ

--- Update to the previous post...

I was only able to get a 6 position rotary switch... I was thinking of Dad's TV tuners when I came up with this! I've ordered the additional resistors. Now I need to select which 6 of these 8 to mount:

100*F - 5.6K Ohms - Green/Blue/Red

7* jump

107*F - 4.7K Ohms - Yellow/Violet/Red

5* jump

112*F - 4.3K Ohms - Yellow/Orange/Red

7* jump

119*F - 3.6K Ohms - Orange/Blue/Red

4* jump

123*F - 3.3K Ohms - Orange/Orange/Red

4* jump

127*F - 3.0K Ohms - Orange/Black/Red

5* jump

132*F - 2.7K Ohms - Red/Violet/Red

11* jump

143*F - 2.2K Ohms - Red/Red/Red

2.2K currently mounted directly to the IAT Fooler toggle switch. I will remove this resistor & wire the toggle to activate the rotory switch.

Note: It would be possible to replace the toggle switch with the rotory switch using the OEM sensor for one setting but would reduce the available slots for fixed resistors to test. I'm not going to install the Rotory switch through the panel just yet... maybe just tuck it underneath for now.

Suggestions for Test Values, Guys?

If i were running the test, I think I'd do 5 plus the factory sensor in the 6th position, so you can have a quick honest comparison between any of them and the factory sensor. My pick of five would be 100*, 112*, 123*, 132*, and 143*. These seem to be pretty evenly spaced apart temperature wise. Then if you find the engine likes one more than the others, you can reconfigure your dial to have more resistors that are very close to the one the truck liked the most, and test them out.

Since I'm going to retain the toggle switch (sensor/rotory switch resistor array) I can have all 6 resistors on the rotory plus the OEM sensor. Those 5 are good choices...

Volkswagen, I would be interested in seeing your wiring diagram. Also would be interested in updates on the results of your install.

Got the wiring diagram attached to my previous post now.

I'm a little busy right now but the rest of my resistors have showed up for the rotary switch. If I can find some time, I'll test my soldering skills. I don't want to drill another hole in the knee panel... and I like the simple toggle (or I could have replaced the toggle with the rotary switch)... I'm thinking another piece of duplex wire between the toggle (OEM Sensor / IAT Fooler) & rotary (IAT Fooler resistance selector) switches. It's right next to the unused ashtray... might drop it in there.

Tidbit of playing... I've now tuned down to 110*F as the weather warmed up and gaining even more MPGs... Like I said this only the design phase I'm playing with the temp setting and see the result differences... I'm closer to 23.5 to 24 MPG making a trip to New Meadows, ID to get propane. No topper! Winter fronts are now off for the season.

Mike - curious with a 145*F I saw no difference in MPG in phx (ambient around 80). IS it worth trying a lower value - or for hotter climates just leaving it alone - what you think. Curious when you are in 5th on highway - assume you are getting ~22MPG - what RPM are you at at what speed ?? Like I know I will never get as a good as a manual around town due to slippage in TC ...... but I only get 20mpg on highway but i ALWAYS drive around 60-65mph in OD ...... sitting around 1800rpm. [3.54 gears]. Was wondering if I dropped to 55 what I would expect ........ problem is I reckon my RPM will be closer to 1500 and I will LUG it a little up smaller hills. Thoughts ?

Mike - curious with a 145*F I saw no difference in MPG in phx (ambient around 80). IS it worth trying a lower value - or for hotter climates just leaving it alone - what you think. Curious when you are in 5th on highway - assume you are getting ~22MPG - what RPM are you at at what speed ?? Like I know I will never get as a good as a manual around town due to slippage in TC ...... but I only get 20mpg on highway but i ALWAYS drive around 60-65mph in OD ...... sitting around 1800rpm. [3.54 gears]. Was wondering if I dropped to 55 what I would expect ........ problem is I reckon my RPM will be closer to 1500 and I will LUG it a little up smaller hills. Thoughts ?

I'm playing with the values of resistors now. So I'll let you know how it turns out. I'm at 55 MPH @ 1589 RPM's with 3.55 Gears. I don't start lugging till down to 1,300 or so at least with my truck. I normally run in the 1,500 to 2,000 RPM span. So once I fall to 50 I grab 4th gear and now I'm back up to 2,000 RPM's again. But tell you the truth if you could find back roads that allow slower speeds my sweet spot is 4th Gear @ 1800 RPM and getting better than 25 MPG. You got to remember wind drag will double from 55 MPH to 65 MPH and quadruple from 55 MPH to 75 MPH... Now looking at the 47RE ratios... 4th Gear 0.69:1 Ratio 3rd Gear 1:1 Ratio Then NV4500 Ratios... 5th Gear 0.75:1 Ratio 4th Gear 1:1 Ratio

I put a 2.2k ohm resistor in parallel with the iat and installes a winter front in back of my grill. Even with temps in the low 60s the enging temp didn't go over 190. I drove the truck 248 miles empty about 200 miles at 57 mph and about 48 at 67 mph. used 12 gallons of fuel. 20.49 mpg.Went to indy pulling a 2000 pound trailer, came back with a 2000 pound lift on the trailer. 348 miles. About 50% at 70 mph 40 % at 65 mph and 10% at 55 mph. used 23.75 gallons - 14.65 mpg

I put a 2.2k ohm resistor in parallel with the iat and installes a winter front in back of my grill.

It should not be parallel it should be across the pins of the IAT plug. IAT sensor should not be hooked up...

Or build this part of the high idle mod...

Build the ECT fooler the upper one... Then change the ECT plug for IAT plugs... Then use your resistor... This will give you control of the IAT sensor or the fooling resistor.

I'm going to say it would work the same as having it fooled the entire time. When you parallel resistors, you end up with less resistance than the lowest resistor. If one resistor is 50000 ohms and the other is 2200, then the computer will see 2107 ohms.. Not much difference. If you happen to have 2200 on the real IAT sensor as well, then it will actually be 1100 ohms. No matter what you do, the computer will never think it is any colder than what 2200 ohms is (143F). Now should the actual IAT sensor get a reading of lower than 2200 ohms (say you keep using this setup in summer), then resistance will be lower than that IAT sensor and eventually you could trip the computer's limits, but I doubt it, the actual IAT has to read over 150F to end up at a computer reading of possibly 200F or more. If it is 13F (56000 ohms), your setup will make the computer see 2116 ohms which is around 140F. In other words, your setup is fine and will work until it throws a code in the summer (if it even gets that hot).

So I need to hook it up so I am using either the iat sensor or the 2200 ohn resistor. I have a switch in line with the resistor so I turn it off to start the engine with the iat sensor only and then add the resistor. I got an iat sensor extension with the correct plugs on either end and plumbed the resistor in to it. I guess I need to get a switch to hook it up so I am only using one or the other. Thanks for the info guys!!!!!

So I need to hook it up so I am using either the iat sensor or the 2200 ohn resistor. I have a switch in line with the resistor so I turn it off to start the engine with the iat sensor only and then add the resistor. I got an iat sensor extension with the correct plugs on either end and plumbed the resistor in to it. I guess I need to get a switch to hook it up so I am only using one or the other. Thanks for the info guys!!!!!

You are fine for the time being. If you had a switch between the resistor and the stock IAT wire (taking it out of parallel operation), then it would work like normal. The resistances are not going to change much with it in parallel, it will be close enough to what you are aiming for to make it work. The only problem is in the summer when you hold it to the floor on a 100F day.. In other words, they *should* be separate, but don't take off work just to do it. I wouldn't even touch it until it's 70F out again next year. Just be sure it is indeed parallel operation, if it is in series then you will not gain anything and actually the engine will think it is even colder.

I was looking for this thread.

It is definitely in parallel. I have an off-on switch to "disconnect" it while I start the engine, then turn it on - so the grid heater works. Also this way I can keep it off during the summer. Yea, I have other things I need to do now, so I will change the wiring and switch next spring to make it so either - or is being used. I don't drive the truck every day so any increase in mileage I would get by hooking it up the correct way won't hurt too much.Thanks for your help.

It is definitely in parallel. I have an off-on switch to "disconnect" it while I start the engine, then turn it on - so the grid heater works. Also this way I can keep it off during the summer. Yea, I have other things I need to do now, so I will change the wiring and switch next spring to make it so either - or is being used. I don't drive the truck every day so any increase in mileage I would get by hooking it up the correct way won't hurt too much. Thanks for your help.

I forgot you had the switch, leave it off if it's over 70-80F out as the IAT will just be seeing the same temps as the "fooled temp". I think I would just leave it. Mike told me the highest he has ever seen out of his truck for as long as he has noticed IAT temps was 174F up a long hill or something. According to his chart, 173F is 1200 ohms, so I'll just say 1150 ohms for the extra degree. Calculating it out, your computer would be seeing 755 ohms which I am betting is 200F based on his chart (only goes to 184 @ 1000 ohms so I based it off exponential guesstimates since the curve is very flat at that temp). I really don't think you will ever see a problem. I'd like to hear what everyone else has seen for max IAT temps though. If that is the highest most people see then I would leave it all how it is, you shouldn't be using it in summer anyways. The worst that could happen is it throws a code.. I don't think the VP44 trucks have a limp mode and if they do I have yet to read about a person have it go into limp mode.