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Old 07-27-2010, 05:49 PM
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lowering fan temps on OBDII

hi guys,

i was wondering if there is a way to lower the fan temps via the aldl port in the car on my 96 OBDII conversion... i know there is a program called Hypertech, but its 300 bucks, and you need to use a special plug/cord to do any tuning. I know you can tune the OBDI systems through the aldl... can it be done on an obdII the same way? if so, what software is needed?

thanks!

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Old 07-27-2010, 07:49 PM
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you have to change the prom on obd 1 (gm) and on obd 2 you need a passthru device that runs about 1500 bucks and you have to hook it to a laptop with high speed internet and pay for a flash subscription or in your case buy the software for a custom tune.why you wanna change the temp setting?

Last edited by latech; 07-27-2010 at 07:55 PM.
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Old 07-27-2010, 08:00 PM
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i wanted to change the fans turn on temp without adding a switch, maybe mess with the shift tables a bit... i dont know just explore a bit i guess... ideally i'd like to remove the rear O2 sensors, currently i dont even have em hooked up!
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Old 07-27-2010, 08:08 PM
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the rear o2 sensors are for monitoring catalytic converter health is about it. They have very little effect on performance if any. If you are going to change things around you should work with 92 or 93 octane and see what you can do with timing and mixture so to develop horsepower
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Old 07-27-2010, 08:13 PM
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so i can leave them disconnected and i won't run the car rich, etc?
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Old 07-29-2010, 05:19 AM
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no wont run rich just they read temp an flow from cats exiting them! also you can change the temp sensor for ECU to a lower one if you wanting to change the fan turn on an off temp! JEGS an SUMMIT both have a temp sensor to lower the fan temp on an off temp. in the LT1 N LS1 section of there catalogs
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Old 07-29-2010, 11:23 AM
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is this the temp sensor your're talking about? if so, it seems like a great idea... i'm surprised GM didn't offer a temp sensor that activates at a lower temp...

http://www.jegs.com/i/Painless+Perfo...30110/10002/-1

does it just trick the PCM into thinking its hotter than it is?
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Old 07-29-2010, 06:11 PM
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Lowering the temp would make it tougher for GM to meet EPA standards and it would be a real problem for them. I would say their money for R+D is spent making them get better fuel mileage.the temps and other parameters of the system are setup for the best possible amount of efficency i e ; timing , fans on and off temp, injector pulse width etc. Downstream oxygen sensors just monitor cat converter health. the system measure differences in voltage switching verses times per second and if the cats get degraded or become inefficient the the downstream reading too closely matches the upstream readings and will set a p0420 or a p0430
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Old 07-29-2010, 06:17 PM
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I saw you had an earlier post about the fans not coming on even at 260 . are you still having that problem? Pepi gave very good diagnostic advice I read it.
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Old 07-29-2010, 06:44 PM
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still haven't figured it out... nolan is helping me on a different thread... maybe you have some input? its either a temp sensor or PCM problem, or so its been reduced to...
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Old 07-29-2010, 08:23 PM
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I hook up the scanner and look at the coolant temp first and I watch the temp and verify it at the t stat outlet with infrared thermometer , if that checks out then i monitor the coolant fan request and you want to have a test light hooked to the cooling fan relay control side(coil side) to verify it is being activated by the pcm when it says yes in the cooling fan request PID.
Most relays are powered up when the car is running and the pcm controls the ground side of the relay.Some pcm s allow you to perform an output state check ,Lots of the obd 2 cars do. one of the selections is cooling fan operation on or off. This will speed up the process.If you command the fans to run and they do but they wont run by themselves when they are suppost to then it is a pcm problem. If the fan doesnt run at least you can check to see if the fan relay clicks or not and wether it is turning the power to the fans on and off.A relay can "click"on and because it does does not mean that it powers up the circuit. you must verify that it does as a relay is a set of points and points as you know can burn out so verify it.
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Old 07-29-2010, 08:25 PM
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dont forget to verify the power circuit to the relay that supplies the fan circuit its power as well as the pcm part of the circuit.
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Old 07-29-2010, 08:32 PM
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changing the temp sensor to turn the fans on at an actual lower coolant temp will also have an effect on the rest of the system parameters like injector pulse width and timing . It can actually lean your engine out as it sounds to me like it would register a higher than actual temperature to force the fans on earlier or at the lower desired temperature
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Old 07-29-2010, 08:37 PM
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I think you can change the fan on off settings in the 95 Lt1 pcm as it has an eeprom instead of the older prom which is not programable. It requires a gm tech 1 scan tool.
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Old 07-29-2010, 08:42 PM
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whoops just reread your post. your doing a 96. That is obd 2 and it requires a tech 2 to reprogram. but it is do- able.
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