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Fooling the Computer


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7 replies to this topic

#1 bigjim5551212

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Posted 16 July 2004 - 02:30 PM

I have a 88 GL Turbo. When it is cold, it has way more power than when hot. Is there any way to fool the computer so the car has more power all the time. Can you do something with the water temperature sensor? Is there anything else I can do? The car has a stock intake and a catalytic with no muffler.

#2 newsance

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Posted 16 July 2004 - 05:19 PM

Sorry, you can't fool physics.

The issue is temperature. As incoming air to the engine is heated, it becomes less dense, occupying more volume. So, your engine ingests less oxygen when it is fed air at 150* vs 50*. Thus, it makes less power.

The general rule of thumb is that for every 10* intake air temp increases, you lose 3% in power, ceteris paribus.

As the motor heats up, the motor proceeds to transfer the heat into the incoming air. Thus making the motor run cooler, and limiting the engines ability to transfer heat improves performance.

I would look to improving your cooling system and looking at using a lower thermostat. Adding an intercooler will make tons of difference as well.

#3 subarubrat

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Posted 16 July 2004 - 06:45 PM

There has been a trick for a long time that works on fuel injection systems that have a seperate map for cold Vs hot running. It is commonly reffered to as a Tourqe Chip. They are available for Imprezas and they modify the coolant sensor reading to stay in the cold map and it does produce more power that way. Now, if your car has a "cold map" this trick should work for you.

Now, as far as the above post, this is true of the intake air temp. Your solution to that is to make a free flowing intake that draws air from outside the engine compartment.

#4 RenaissanceMan

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Posted 16 July 2004 - 09:05 PM

ok guys, this one isnt that difficult to mess with. What you do is disconnect the ect "engine coolant temp sensor" and replace it with a 5K variable resistor. This way you will at least be able to change the reading if you need to. When the resistor has a resistance of around 3K ohms the computer will think the engine is cold and dump more fuel in it. when its around 200 Ohms of resistance your computer will think the engine is warmed up. and so on for resistances inbetween. You can start making a scale to figure out your preferred setting. HOWEVER.. beforewarned that long term running at a rich mixture will cause your spark plugs to foul, deposits to build up in the combustion chamber, and eventually burn up and kill your cat if you still have it on there.

btw, if there is only 1 wire on the sensor, connect the other end to ground.

what you really might wanna think about is adding a switch to the wiring to be able to switch between the computer reading from the ECT, and your "modification"

anyone that doesnt know anything about electronics and wants to be able to do this PM me and I can help further.

#5 newsance

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Posted 16 July 2004 - 11:20 PM

So why will making the car run rich improve performance again?

#6 RenaissanceMan

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Posted 17 July 2004 - 08:51 PM

best economy mixture and best power mixture are slightly off from eachother. Your car is supposed to use stoichiometric, which would be around 14.7 parts air to 1 part fuel (by mass). You can slightly improve power, but the fuel economy drops off, by going to a mixture of around 12.5 to 1 or so. Achieving exactly around that mixture is difficult with fuel injection, so if its overly rich, the unburnt fuel causes deposits.

The reason it cant precisely obtain around that mixture is because first off your computer doesnt pay attention to your oxy sensor when it is cold. also your oxygen sensor isnt designed to give you a reading like that. The oxygen sensor is sorta an "approximation" for the computer. Its designed to give around .2-.3 volts when lean, and .8-.9 volts when it is rich (comparing to stoichiometric 14.7 to 1). so it doesnt have a very large range. basically anything richer than 13 or leaner than 16, isnt really measured. the computer just sees it as "rich" or "lean".

Modern OBD2 fords or GM's, I cant remember, use a new type of oxy sensor that is more precise, and is measured by the computer in current, not voltage output


So after all that. your problem might actually be your oxy sensor. Hook up a volt meter to it and a good ground when it is hot. at idle it should read .8 volts-ish. rev the engine up to around 2500 and hold it, and you should then see the voltage start to bump back and forth between .2 and .9 volts. if it doesnt, or the voltage is low, persay around .4 at the most, then something is wrong.

#7 rallyruss

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Posted 19 July 2004 - 12:49 AM

I also say Intercool it. the intake temps rise rather high without an intercooler. there fore reducing the density of the air charge. dont mess with the temp sensor. there are adverse effects to making a daily driver run really rich. besides under boost the car changes to a fat (rich) mixture any way.

oh yeah a good o2 should cycle at idle when hot as well as off idle.

#8 Vegablade

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Posted 20 July 2004 - 12:51 AM

I just took out my thermostat, it makes it run alot colder, just remember to put it back in in the winter.:)




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