SAFC2 TPS problem.
 

I just installed my SAFC2 last night. Every sensor seems to be reading properly except my TPS. I have the SAFC set to 4 cylinder arrow pointing up. When I have the gas pedal down about 40%, it will read 100% throttle. If I am in the sensor check mode, at 40% throttle, my voltage will max out. Any help will be appreciated, thanks!

That's correct behavior on a S4 (which is what your sig would imply you have).

The TPS is a short range TPS. It pegs out around 1/4 throttle, and is just used for idle and low throttle operation.

The best solution is to tie it into your boost sensor instead of the TPS. Then the SAFC is reading actual engine load, and can be tuned to respond to boost/manifold pressure, which is what you'll most likely want to use it for.

-=Russ=-

^^^^^ Thats sounds about right

i hooked mine up to the pressure sensor and i have alot more accurate reading on what the engine is doing . i even try to rig up a few things and the map sensor works the best so far

I see what you are saying. However, if you splice it into the boost sensor, you have your key on(engine off) and you are in the sensor check mode, it will read 0% correct?

I followed this (http://www.1300cc.com/howto/how2/safc.htm) article. I woulda been nice if he had addressed that. Well, I suppose writing the article was nice in the first place.

You need to understand how the boost sensor works, and manifold pressure. I believe the arrow needs to be set the opposite way (rising voltage = rising "throttle position") from using the TPS.

The boost/pressure sensor gives a 0-5v reading. The NA unit is close to 5v at atmospheric pressure, and the TII unit should be somewhere around 2.5-3v at atmospheric pressure (with 5v occurring under boost, not sure exactly what PSI).

On my NA, it reads 100% throttle with the engine off, 20% throttle or so at idle, and only goes down to 0% throttle when at high RPM closed throttle (max vacuum). I expect a TII would read somewhere around 50-70% with the engine off, 10-15% at idle, 100% under full boost, and 0% again at high RPm closed throttle.

-=Russ=-

Based on the info in Paul Stokes' DIY FCD article, the TII's 0-5V MAP sensor reads from about -14psi up to +16psi. If you connect the S-AFC's TPS input to the MAP sensor those pressures would give a 0% and 100% "throttle" readings respectively. At atmospheric pressure (engine off) you should see about 45% (2.3V); idling at 16inHg vac you should see 20% (1.0V); and at 8psi boost you should see 75% (3.7V). You'll never see higher than that because you need an FCD to get over 8.6psi, and the FCD should hold the MAP sensor output at ~3.7V to avoid fuel cut.

So you need to set your low-throttle and high-throttle set-points to suit the narrower range of readings you'll get from the MAP sensor compared to the TPS. You'd need to compress 0-100% into 20-75%. If you decided to use throttle position settings of 30% and 70%, with the MAP sensor you'd need to set them to 37% and 59% instead to get the same effect.*

Personally I'd use 30% (~10inHg, cruising vac) and 50% (~1psi boost). :)

Depends on where you put the FCD. If the signal goes from the MAP sensor to the SAFC-II, *then* to the FCD, the SAFC-II can see the higher range.

-=Russ=-

True, but most people with FCD's have an aftermarket one that plugs into the MAP sensor. If you build an FCD yourself and wire it in at the ECU (like I did) then you won't have this issue. :)

I've one home made FCD on one car and one RB on the other car. Both located in the engine bay where they belong and both wired to SAFC from the plug on the boost/pressure sensor. Gotta run a wire from the boost sensor to the SAFC to make it work. Big deal.

yep, unless the FCD is built into the boost sensor then there will be a 0-5v feed wire coming out of it which you can patch into for the SAFC.

Where they belong? :confused:

IMO the FCD is much better off in the cabin by the ECU where it can't be affected by underbonnet temps. Paul Stokes even mentions this in his article. There's no reason not to wire it in at the ECU. The stock boost gauge will work normally (for what it's worth) and if you do wire an S-AFC to the MAP sensor you don't need to run extra wires...

I wrote that to annoy someone from NZ (and I succeded). But ..........I've had no adverse effects from having it in the engine bay. If I do have problems with it I'll be sure to let you know. The ones from RB are meant for the engine bay and plug and play to the boost sensor and I've yet to read even one thread about how there is/was a problem with the FCD.

I think the point here is that while there is no *problem* with putting it in the engine bay, there are *advantages* to putting it near the ECU in terms of getting an un-clamped signal to assorted other things that can make use of the actual signal.

-=Russ=-

I put in a switch to experiment with both ways.

The ones from RB aren't cobbled together in your garage either. Maybe I'm wrong but I'd imagine RB have taken steps to protect the circuitry from high temps and moisture, rather than just slap them into a cheap plastic box from an electronics store like I have. ;)

Stoaks says, "Set the output voltage a little conservatively as variations in temperature can change the behavior of the boost sensor and your FCD. You need room for a little error." I'd rather reduce that room for error by removing the large temp variations you see in the enigne bay. Plus I'm trying to tidy up my engine bay a bit. I'd rather not add yet another little blank box. :)

I have a RTek7 1.5 which includes a FCD, what should i do then...?

Thanks for all the great replies

The RB ones are *potted*, so monkey see monkey do....I potted my homemade one with clear RTV as the potting compound. Packed it with clear RTV. Rattle free, moisture free outfit. The pot screw is accessable though if I want to play.

I'd bet the RTEK does not clamp the voltage ......so you can just wire it like a regular SAFC. Since it's obvious I don't know about RTEK you might turn the key to ON, put a MittyVac on the pressure sensors input nipple and apply zero to ten plus psi to it. Monitor the output brown/red wire with a meter and see how high the output voltage gets. Memory here, but if it gets over 2.65vdc, say closer to or above 3vdc, then all's well with the RTEK/SAFC.

This answer might be called suspect since I've little knowledge about what the RTEK does or how. I got your post back on top though.