Too cold of air inside the intake manifold ?
 

Hey guys,

This is a problem that I'm not sure how to get past. My setup for far is Fuji racing ITB's, racing beat side draft intake, and a pretty neat heatshield from ReSpeed. Prior to the heatshield installation, my intake temp were probably around 45*F, but now with the heat shield on and even if its a 95*f day my intake temps are probably closer to 30*F. My manifold gets pretty darn cool. The problem lies when I'm doing WOT runs, where the temps probably dip down even cooler than that from the rushing air and more fuel inside the Manifold. When i go back down to idle, it won't idle, it would just spit and sputter, unless I hold the rpms around 1500-2000 to let it re-warm up a bit and then my idle would be fine. Any clues on what I could do to prevent this. I'm running a standalone so I can control any injector things.

Sam

Sounds like your air temp sensor is bad. You will never seen lower than ambient air temps inside your intake manifold with your setup.

^ what he said. It's physically impossible to run 30 degree intake temps with an ambient temp of 95, unless your using a dry ice box etc.

I don't have a temp sensor inside the manifold only at the opening, but if its not getting that cold, how do you explain the intake manifold forming frost ontop of it sometimes, most of the times it is cool to the touch. at WOT there's usually moisture forming on top of it. Wouldn't the fuel be cooling the air charge quite a bit?

My Weber DCO carbs used to ice up even on a hot summer day. I dont remember specifically which tuning element eventually reesolved that, but I have it now to where it will get pretty cool to the touch but will not ice up. Ultimately, it was tuning related as now that I have it properly jetted and timed the problem went away.

How confident are you in the current tuning?

Indeed, the fuel can cause a cooling effect. All in all I don't think there's anything bad about it, other than it seems to be causing a tuning issue. You'll need to re-tune it to avoid this issue, and it may be worthshile to relocate the temp sensor further downstream to help it see the effects of this more.

I know the tunning is a bit off and I'm in the process of tunning it bit by bit which is why asked about this. At WOT i'm seeing around 12.2 AFR at idle closer to 13's. So its not like I'm running excessively rich , I'm pretty much where I want it to be.

As was stated by others, air temp will not be cooler than the available ambient air unless something else is being introduced into the airstream to remove the heat (fuel, NO2, chilled intercooler etc). Were do you have the Air temp sensor? If it is down stream of the fuel discharge then it needs to be moved to an area before the injectors, as it appears from what I see from your discription, the air temp is being effected by fuel evaporation cooling, and is giving false readings to your ecu and once off throttle the chilled temp sensor is causing an over rich condition until the sensor normalizes... if this is the cause, retuning would only move the problem...

my temp sensor is not after the fuel, it is sitting at the opening of the ITB's. The numbers that I gave are a guess of what it is because i think its making the manifold too cold. The air temp isn't compensating for anything.

Exactly the problem.

You are running a race induction system with many of the compromises for driveability deleted for simplicity and power.

OEM would heat the intake manifold with coolant and leave a rough cast surface to fight the fuel condensation problem.

You could run the megasquirt so rich at idle that you still get enough fuel when the manifold is cold, raise your idle rpm so it is in the smooth 1,500-2,000 rpm range all the time or do some real work adding a manifold temperature correction table to richen it up when manifold is cold.

I have this problem to a much smaller degree from polished stock based manifolds and have just tuned it for worst case scenario with the haltech. Yes, this means running rich at idle always to cover for when manifold is cold, but the rotary will happily idle at 10:1 AFR so, meh- let tailgaters eyes water.