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C1 air intake temperature

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Wednesday, 31 March, 2010

C1 air intake temperature

While driving to work today, I did some checking on the intake temperature on my Citroen C1. Intake air temperature is very important. The ECU determines the amount of fuel to inject based on 3 important variables:

  • Pressure in the intake manifold
  • Engine speed (RPM)
  • Intake air temperature

If the intake air temperature is hotter, the air contains less oxygen. Fuel and air should be mixed in fixed proportion to get best combustion. The ECU regulates this continuously. So when the intake air is warmer, less fuel is added and the engine will produce less power.

So today the outside temperature while driving to work was about 15C. While looking at my scangauge I saw the intake air temperature.

It was 34C. Which is quite a lot higher then the outside temperature. This could mean 2 things. Either the air being sucked in to the intake track is warm or the air gets heated up while in the intake track.

I already ruled out the first one. I added a hose to the point where the engine picks up air and routed it to the gril. No difference in air temperature.

So when arriving at work, I removed the air filter cover, and used my IR thermometer to check the temperature of the valve cover directly underneath the air intake:

45C

So I think that explains the higher intake temperature. This is a shame, because power is wasted by the increase in air temperature. Every 7C rise in temperature costs more then 1% power. Adding over 15C to the air temperature equals to more then 2% power loss. Sounds like something worth fixing.