| Rich Z |
02-26-2013 02:09 AM |
LS2 throttle body issues on a LS1/LS6
This is one of those "gotchas!" I think that is pretty obscure, so I figured I would copy the details of what I've just read here for future reference.
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Now if only someone could get the 90mm TB electronics working properly with the 03 and up PCMs!
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Apparently, the only one(s) that claim to achieve 100% physical throttle opening with the LS2 90mm swap are those with 02 PCMs. Even though the 02 TAC module is also installed as part of the swap. With my LS2 TB, 02 TAC module and 04 PCM I am only seeing about 85% physical opening when 100% TP is commanded. I believe the correlation is off at the closed end also(affecting idle tuning).
The TP sensors of the LS2 TB operate on a slightly different voltage range than those of the 78mm. The LS2 sensor output at 85% TP is equivalent to that of the 78mm at 100% TP. I don't know how only the 02 PCM adapts to this. I do know that the stock TP sensors on my 04 both move in the same direction(voltage increases as TB opens), while the LS2 TB's sensors move in opposite directions. Hence the need for the swap to the 02 TAC module which operates similarly to the LS2s. Although the TAC is built into the PCM on the LS2s.
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I am only referring to ETC vehicles with the LS2 90mm swapped in to replace a stock 78mm. This is not relevant to cable actuated TBs. As far as I know this issue has only been seen on 03 - 05 vehicles. 06 doesn't work at all with the swap. The swap may work OK on earlier vehicles. I have seen pics of a 02 TAC/PCM setup where the TB was fully open. Logs will look OK (i.e logged TP will match commanded as per the pedal position/TP table) but if you actually take a look at the TB it will not be at 100% physical opening.
This is what I see happening. Let's say that sensor1 on a 78mm TB puts out 3.8V at WOT while sensor1 on the LS2 TB puts out 4.2V at WOT. Because the setup was engineered to expect 3.8V at WOT it will not actuate the throttle blade beyond that point. So the LS2 will never achieve full opening. Because this is programmed into the TAC module rather than the PCM we have no way of addressing it with EFILive.
There may also be some difference in the way that the throttle actuator motor is driven by the PCM(both use pulse width modulation). Someone would have to compare a stock 78mm setup to a stock LS2 setup, looking at the PWs at WOT.
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Source: http://forum.efilive.com/showthread....-needed!/page3 |
