CHTS reostat! Should it STAY or should it GO ? Options

[Strudelwagon]

Here's the deal! my 74' 2.0 FI has this mod that the PPPO installed and I'm trying to decide if I should keep it or remove it.

Its a reostat with on/off toggle hooked up to the Cylinder Head Temp Sensor.
The rumor is that it was a mod to trick the computer into running rich when racing autocross i assume by adding resistance and making the engine think it's in warm-up mode.

Anybody got any Pro/Cons on thi Modification? I'm thinking of just removing it and setting everything back to stock. (IMG:style_emoticons/default/blink.gif)

Thanks
Steve

[Krieger]

If you have a stock motor the stock sensor should be fine. If the motor is modified or dies when idling and warm the mod could be helpful in tricking the brain into thinking the engine is colder and giving it more fuel across the entire rpm range. An add on factory part did this with a 250 ohm resistor. Take out the reostat and meseaure the resistance with an ohmmeter to see whats dialed in. Also measure the stock head sensor. It should read 0 when hot and 2000 when cold. You may just need a new oem sensor. The PO may have used it to cover up other issues with the injection.

[Strudelwagon]

If you have a stock motor the stock sensor should be fine. If the motor is modified or dies when idling and warm the mod could be helpful in tricking the brain into thinking the engine is colder and giving it more fuel across the entire rpm range. An add on factory part did this with a 250 ohm resistor. Take out the reostat and meseaure the resistance with an ohmmeter to see whats dialed in. Also measure the stock head sensor. It should read 0 when hot and 2000 when cold. You may just need a new oem sensor. The PO may have used it to cover up other issues with the injection.

Thanks Krieger,
the PPPO has the decel valve removed and most of the large vacuum pipes off the air box removed and plugged. I would like to return it to stock so I'll have to reinstall all the bits. I'll check the resistance on the CHTS and the reostat to see what he was thinking.
The reason I use the PPPO is the PPO and the PO never got the car on the road after they bought it. It just kept changing hands til I got it.
SW

[Spoke]

I haven't fully tuned the DJET FI on my 1.8L and I need about 400 ohms in series with the CHT sensor for the engine to run well. I need to tune the fuel pressure, MPS, and get rid of the 400 ohm resistor.

[Strudelwagon]

Here's the deal! my 74' 2.0 FI has this mod that the PPPO installed and I'm trying to decide if I should keep it or remove it.

Its a reostat with on/off toggle hooked up to the Cylinder Head Temp Sensor.
The rumor is that it was a mod to trick the computer into running rich when racing autocross i assume by adding resistance and making the engine think it's in warm-up mode.

Anybody got any Pro/Cons on thi Modification? I'm thinking of just removing it and setting everything back to stock. (IMG:style_emoticons/default/blink.gif)

Thanks
Steve

Anyone else using this setup???
Thanks
SW

[jasons]

I'm not sure about the logic behind your setup. But, I have a variable resistor in place of the factory resistor on my 73 2.0 DJet setup. I needed it to get rid of hunting at idle. The added resistance stabilized my engine idle RPM. My FI has been pretty thoroughly overhauled and this was the only thing that cured the idle hunt.

BTW I don't think your 74 DJet would have the factory resistor. If it runs fine with the rheo bypassed or toggled off, why not just get rid of it?

[Dave_Darling]

A rheostat is just one more failure point. If you know that a given resistance value works "right" for your motor, use a fixed resistor of that value. Rheostats don't last forever, and they can get flaky when exposed to heat, vibration, petrochemicals, and weather.

--DD

[Strudelwagon]

A rheostat is just one more failure point. If you know that a given resistance value works "right" for your motor, use a fixed resistor of that value. Rheostats don't last forever, and they can get flaky when exposed to heat, vibration, petrochemicals, and weather.

--DD

Thanks Guys,
I checked the CTHS and it's 2.44K Ohms cold and that's in the ball park. I think the reostat (potentiometer) was strictly an attempt to richen things up under normal operating temp. I assume that would increase HP slightly and probably be killing trees at the same time.

I'm going to pull it out and see what happens. I'm just putting it all back together after paint so I won't know for sure for a few weeks.
Steve