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Fooling PCM, engine temp

matuva

matuva

Tropical 6.5er
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Location
New Caledonia. An island in south west pacific, cl
Good day all,

I ned to fool PCM on a 1995 K1500 single T-stat, to let it believe the engine has reach the good temp (170°F IIRC) so I can time the IP.

The guy has modified the T-stat, and now the engine always under that temp, usually around 70° celsius and no more.

He doesn't want to re-modify the T-stat to stock configuration, and I don't want to "fight" to convince him.

Anybody already did that? a resistor may be, or a pot, which value?

Thanks.
 
Temporarily Put the sensor in a cup of hot water and plug the hole where sensor was?? or run a pigtail from connector to another vehicle at operating temp and plug into that sensor.
 
matuva said:
Good day all,

I ned to fool PCM on a 1995 K1500 single T-stat, to let it believe the engine has reach the good temp (170°F IIRC) so I can time the IP.

The guy has modified the T-stat, and now the engine always under that temp, usually around 70° celsius and no more.

He doesn't want to re-modify the T-stat to stock configuration, and I don't want to "fight" to convince him.

Anybody already did that? a resistor may be, or a pot, which value?

Thanks.
Click to expand...

Al you could put in a 244 ohm or less resistance between the 5 volt reference signal and the yellow wire back to the pcm ect signal. The warmer the engine gets the less resistance through the coolant sensor> Hope this helps.
 
It is never going to run right that cold. Even if you do "fool" the computer that the engine is at proper temp it's going to be a messed up deal. I'd tell the guy that IF you do it at all there are no guarantees of any type. The thing is going to be in a cold cycle all the time. He needs to put the correct thermostat in the truck.
 
Cardboard in front of the radiator will warm anything up. Add a brake stand if needed. Drop the brake pedal to the floor and the accelerator nearly to the floor for 30 seconds at a time wait a min or two and try again. This is to keep the TCC temps in check while warming the engine. MT units you will have to drive to warm up with cardboard.

You can mention MPG improvements members here have claimed at the proper warmer temps. Mine with a lower temp t-stat and fan can be timed.

I would check the oil cooler for the famous mat behind it and fan clutch age. You may as well explore why it has an overheating problem - as in find out why did he mess with the cooling system like that?
 
matuva said:
Good day all,

I ned to fool PCM on a 1995 K1500 single T-stat, to let it believe the engine has reach the good temp (170°F IIRC) so I can time the IP.

The guy has modified the T-stat, and now the engine always under that temp, usually around 70° celsius and no more.

He doesn't want to re-modify the T-stat to stock configuration, and I don't want to "fight" to convince him.

Anybody already did that? a resistor may be, or a pot, which value?

Thanks.
Click to expand...
Or :hihi: you could tell him to come back after he gets a clue. I don't mind helping out a the helpless but not the clueless.
 
Good day all,

Dennis, I didn't read your post correctely and tried to fool the PCM with a resistor at the temp sensor, which didn't work.
I will try again at the PCM itself.

In fact, all my problems were solved as soon as I swapped to Kojo multi stage chip. It just took few minutes to me to time the IP, even at 155°F with GMTDScan Tech.

Looks like the stock PROM is damaged, so may be the previous IP was just about good.... no worries, I have now a new one, the former will stay as a spare

Thanks all ;)
 
IIRC Kojo can make them as well for obd1, I think he said it was possible with obd2 but didn't want to do any soldering on the boards.
 
You're absolutely right Leo. Teemu have an idea of should be done to make an OBD-2 multi level PCM, but doesn't feel comfortable with desoldering/soldering chip on the motherboard.

For OBD-1, as the chip is removable, things are easier for him.

This chip he made was similar to mine, as the guy has a 1994 BLAZER like me (not a 1995 as I wrote), levels are :
  • stock S
  • stock F
  • economy
  • towing
  • "wild :D

EGR deleted in any case, and last 3 speed limiter maxed out, tcc staying on with 0% throttle.

I will install mine today on my BLAZER ;)
 
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