CTS modification

Alot depends on your vehicle make. But mainly you install a resistance across the sensor. Which in basic terms means, one end of the resistor to one wire of the sensor and the other end of the resistor to the second wire going to the sensor.

To do this properly you need to look up the resistance tables for the sensor in your vehicle to be able to calculate the resistance needed. Using the folling formula will help figure out the resistance needed to get the desired affect (R1 X R2) / (R1 + R2) R1 for example is the resistance at a given temp of the sensor, and R2 the resistance you are planning on adding. You then look at the sensor table with the answer to the formula to see if the resistance puts you in the range you want to be in.

To take this one step further an average ford sensor on an eec IV system at 194 deg has a resistance of 2.8k ohms and installing a 7.5k ohms resistor parrellel to the sensor reduces resistance to 2.038k ohms which makes the computer see an adjust temp of approx 214 deg. If you look into this alittle further though at a sensor temp of 32 deg the resistance of the sensor is 65.85k ohms and when adding the same 7.5k resistor makes the computer see approx 148 deg. If you tried to start the vehicle on that 32 deg day with that resistor installed it would be very difficult to start if it would start at all.

I have a ford with the eec IV system but to keep cold weather starting ability I installed a switch to open up the circuit of the resistance added which takes it back to stock for start up and a few minute warm up, which I have to do on our cold morning we have or it will not start. So it takes alittle more research to find out what is actually needed by the system to function properly. I also went one step further and installed a 10k 10 turn pot for fine tuning without having to constantly resolder resistors to tune in the vehicle.

I am working on an idea to take this to a level that I will not have to use the switch for cold weather start ups, but I am planning on always keeping my switch in place because it allows me to go back to stock easily. I currently have adjusters on the CTS, IAT, MAP, and O2. On my ford truck I went from 14 mpg hwy to 20 mpg hwy with these and no other mods.

I have used a similar approach on an OBD1 and an OBD2 vehicles. My experience may suggest a few points.

A. When putting a resistance in parallel with any sensor I suggest avoiding a 0 ohm condition in case it would damage the ecu circuit or cause it to go to a default "open loop" condition. Mainly applies when using a potentiometer or variable resister.

B. Using the R total formulas cited I put a fixed resister ahead of the pot so I'll always have some resistance in this parallel circuit.

C. You can vary the pot in the circuit under varying engine temps to see how the particular ECU handles the variation. OBD1: I have found in one case that this CTS circuit only operates for cold start purposes, so I set it up with only a fixed resistance to reduce the cold run enrichment amount, and time active.

OBD2: In this case varying the resistance across the sensor varies the idle speed: but with decreasing effect up to 160 degF.

IAT sensor: my understanding is used to RETARD ignition timing at air temps above 130 degf, so I stopped using this mod. May need to use it if a high flame speed fuel is used like H and the knock sensor gets in the way.

Glad the site is back up, hope all the old posts become available again. :D KRMusher

How do you..." look up the resistance table for the sensors in your vehicle" ? I would really like to learn more about engine mods!

Fish

thanks for the resistance tips. i thought more resistance raised the ecu perceived temp. no wonder my truck started hard. btw, i have a 93 ford/mazda b2300 test vehicle. it seems like whatever i do sets a cel. i live in texas so that usually helps but not this time.

i'll keep doing, fish

Personally I wouldn't go that low because I suspect that when it does warm up. The 1/R=1/R1+1/R2 parallel resistance will be 62.5 ohms and might be low enough that it marks it bad, or even goes into limp mode because it figures the engine is on fire. I'd go with something like 500 Ohms to 1K fixed, and figure it wouldn't take too long to get into that range, with less chance of severe cold start problems.

Hi, why not use a thermistor in parallel with the CTS. They are available with different values at 20degrees C and will not go to zero thus safeguarding the CTS and ECU. You can vary the value by location as well ie in free air, outside the hood or inside the engine compartment or even strapped to a coolant hose or pipe. It gets around the cold start problem nicely. This is not theory, I've used them.

A thermistor is a resistor where the resistance varies inversely with any rise in temperature. In other words it behaves EXACTLY as the CTS and the IAT. This is because these sensors are in effect thermistors embedded into the bolt-in sensors. A thermistor is usually a small round device less than 1/4" in diameter and less than 1/8" thick with two pigtails coming out. As I said before they come in different resistance values usually rated at 20 degrees C. At about $1.00 each it's worth buying a few and trying them out. The great thing is that whether in series (for apparent colder temps => richer mixture/more power) or in parallel (hotter temps=>leaner mix/better economy) the voltage tracks up and down against temp. This is what the ECU expects and will not generally go to default values.

When placed in series these are a far better alternative to the "$19.95 chip to improve your power by 15HP" kind of thing and for this forum's readers use them in parallel for economy. Heck if you're smart hook a switch to your throttle pedal or TPS and have it switch between series and parallel. Power when you want it and economy at light throttle settings.

http://www.123rf.com/photo_359497.html shows a picture

Enjoy your experimenting but make sure you have a reliable method of testing.

Cheers John