Why the TPS relay trick?

[falconGSR]

Why do you want to tell the CPU you're at WOT when you are at part throttle? I understand that at partial throttle, you're in closed loop, and everyone is running
lean. Why does closed loop run too lean? Does the ECU have a limit to how much it will richen the mixture based on the a/f ratio seen thru the O2 sensor on the exhaust?

I would rather leave WOT alone, if there is a way to properly tune closed loop operation @ 6psi.

Joe



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Bone stock GSR

[Holden]

At partial-throttle, if you start boosting, the FPR is trying to richen the mix by increasing fuel pressure.

At the same time, the ECU is still trying to maintain optimum emmisions, so it fights back and reduces the injector duty cycle to keep the A/F ratio bouncing around stoich.

This leads to lean conditions under boost, which can cause detonation.

All this trick does is tell the ECU to get out of the way once boost passes 1psi and let the WOT fuel map rule.

It will have no effect on actual WOT operation.

Greg

[falconGSR]

"At the same time, the ECU is still trying to maintain optimum emmisions, so it fights back and reduces the injector duty cycle to keep the A/F ratio bouncing around stoich.

This leads to lean conditions under boost, which can cause detonation."

Ok this is where i am missing something. I am under the impression that at part throttle, even under boost, you want to run stoich which means you're burning all that additional fuel you're putting in. But you're saying that if the ECU is adjusting for stoich, then you're running lean. Sounds like a contradiction.

But I think I understand why you are saying this. In other words, running stoich under boost will cause detonation, which isint technically caused by a lean mixture, but its bad and you want to fix it by running rich...

Am I getting the picture here? I lost alot of sleep trying to figure this out last nite.


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Bone stock GSR

[Holden]

You got it pretty much.

The reason you don't want to be stoich is that under high load (i.e. WOT or Boosting), you don't want to be lean or stoich. You want to be rich rich rich!

Our problem is that the stock ECU doesn't know about boost and assumes the engine IS NOT under load at part throttle, even though it is if you're boosting.

Greg

[falconGSR]

OK I am starting to get it. What are the reasons for not just changing the o2 sensor voltage to report lean to the ECU, thereby richening your mixture at part throttle?

Is it that you cant get it rich enough like this? Plus you'd be messing with the idle mixture too, then...unless you do something like rjaffey is doing with the pressure switch..

Holden, thanks for following me around while I chase my tail on this. I am just exploring all avenues...



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Bone stock GSR

[falconGSR]

Thanks Greg, its starting to make alot of sense...


Why do you think its not a perfect fix?

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Bone stock GSR

[Holden]

Because the perfect fix would be the ECU having a 3D fuel map (3rd dimension being boost(after RPM and Throttle Position)) like a factory turbo ECU or an aftermarket engine management system.

Greg

[falconGSR]

You mean 3D mapping ZDYNE style? If they can get ODB II systems out some time...




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Bone stock GSR

[Holden]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by falconGSR:
What are the reasons for not just changing the o2 sensor voltage to report lean to the ECU<HR></BLOCKQUOTE>

I don't want to begin imagining how that would be done. However, you'd probably throw codes left and right.

Fooling the TPS is an almost perfect fix for this.

Greg