Question about how SMEC behaves at full throttle

[MopàrBCN]

Hi there,

Upfront: The car is a 1989 Lebaron 2.2 Turbo II GTC. It has a straight through 2.5" Exhaustsystem (with high flow cat). Also I have a BOV and G-Valve installed (currently at something around 10-12 psi (using the Chrysler built in Boost gauge). Whatever it is, it was the preset as I baught it.

For the rest the car is basically stock.

However since having installed the G-Valve I am experiencing a lack of power at full throttle. Remember I run it at its preset level (10-12 psi). It is as if it would be running rich. At all other throttle positions it feels very responsive and performing great.

Now my question: At full throttle, I beleive to know that the Oxygen Sensor is ignored for the fuel delivery. Does this apply for the Map Sensor as well? Or in other words, does the SMEC at Full Throttle always give the max amount of fuel regardless of the boost pressure?

Thanks for letting me know!

[shadow88]

Yes the program involves adding alot of fuel, not everything it has, but alot. The oxygen sensor is ignored, but all the other sensors are still used. You might want to try without the g-valve and see what the power is like.

[GLHNSLHT2]

The ECU gives a preprogramed amount of fuel based on boost level at WOT. So wether or not you have it hooked up to the grainger or to the factory boost control it doesn't matter. Now the ECU runs the car richer at WOT than it does at part throttle so you'll feel the power drop a bit because of the extra fuel but it keeps the valves cool and detonation down.

[turbovanman²]

The ECU gives a preprogramed amount of fuel based on boost level at WOT. So wether or not you have it hooked up to the grainger or to the factory boost control it doesn't matter. Now the ECU runs the car richer at WOT than it does at part throttle so you'll feel the power drop a bit because of the extra fuel but it keeps the valves cool and detonation down.


Yep, its keeps the engineers happy at Dodge so there not warrantying motors every week.

I asked this same question years ago, :thumb:

You have 4 options-

1)Custom cal
2)More boost
3)Use an adjustable zener diode on the map to lean it.
4)Lower the fuel pressure-not recommended.

[MopàrBCN]

Well then, I go for more boost :D :D :D

And thanks for the rapid response time in this community!!!

[TurboBuggy]

Well then, I go for more boost :D :D :D

then your gonna get boost cut, custom cal or recal yourself and thats about the best way you can do it.

otherwise you can mess with mapclamps and fuel pressure.

[GLHNSLHT2]

More boost is not the answer. Since the fuel curve rises with boost you'll have the same a/f ratio as the boost climbs. Unless you eliminate the cutout with a grainger and are boosting over cut out. Then as boost rises the car will start to lean out because the ECU only sees up to just before cutout even though your boost is higher. But if you're just running up to cutout then you won't see any leaning of the boost curve.

[MopàrBCN]

then your gonna get boost cut, custom cal or recal yourself and thats about the best way you can do it.

otherwise you can mess with mapclamps and fuel pressure.

Hi, thanks for your advice. I do know this. When I was referring to more boost I was referring to getting my G-Valve set closer to the SMEC limit of 14.7 psi. And yes, the G-Valve thing is and was a temporary solution. I have set my mind on getting a "trim cal". But before doing so, I want to sort out the basics, and for me those are handling, braking and Engine Tune up. Right now I want to understand what is going on within its limits.:thumb:

[MopàrBCN]

More boost is not the answer. Since the fuel curve rises with boost you'll have the same a/f ratio as the boost climbs. Unless you eliminate the cutout with a grainger and are boosting over cut out. Then as boost rises the car will start to lean out because the ECU only sees up to just before cutout even though your boost is higher. But if you're just running up to cutout then you won't see any leaning of the boost curve.

Hi, this one I do understand as well! I was not expecting to solve the issue by raising the boost up to the smec limit, even though I will do this now, having the comfort knowing that I am rather rich then lean (it was a precaution to leave it rather low until now).

For the time being I will accept this as a "problem" I am having right now. In time to come, as mentioned earlier on I will put in a trim cal and all that goes with it (injectors, fuel pump, regulator etc).

[GLHNSLHT2]

well you are richer at WOT than at part throttle. I wouldn't assume your safe rich without a wideband O2.