Hi. I bought a scantool recently and noticed my TPS was 13.73v at idle and 90v WOT. I thought it was totally normal until I found posts here saying it should be around 0.45v at idle and 4.60v at WOT.

WTF

My idle has always been a bit on the high side (also recently found out it idled at 1000RPM) but it always felt and sounded very healthy and my LS1 always went good/hard, never hesitated... so I thought "it's all good".

So I immediately lowered my idle with the idle screw on the throttle body and re-scanned my TPS. It then measured 11 something volts so I kept going.. screwing in the idle screw more and more. Well after doing it and re-checking the TPS volts 20 times and running out of threads on the idle screw, I got fed up and completely removed the idle screw (so that my butterfly/shaft tab/stop thing is resting on the T/B stop - not the screw). It still reads 3.92v on idle!!

I've done the TPS/idle re-learn thing 5x. Didn't make a difference.
The only good news is it now idles at 800RPM (smoother into gear, less noise, less fuel consumption) and I got it down from 13.73v to 3.92v (not like that's helped in any way).

Btw I have an aftermarket throttle body and the instructions say the idle screw should be sticking out about 6mm above where it screws into the throttle body. (It's now at 0mm obviously after I removed the screw)


So yeah, don't know where to go from here and am going nuts trying to figure this out Need your help.

 

Something is way wrong somewhere. Your battery only supplies 12V. There is no way you're actually getting 90V off your TPS. If, for argument's sake, 90 V was getting back to the computer, your motherboard would have shorted out and blown the copper traces out of the silicon.

Either your computer is reporting way wrong to the scan tool or the scan tool is way off.

 

Thanks for your help/thoughts.

I thought it might've been a faulty TPS reading on my scantool too, but after thinking about it.. I doubt it.
The reason why I think my TPS signal on my scantool is accurate is because I've lowered my TPS volts (adjusted/closed my butterfly) by a sh*tload to where the idle v's is "ALMOST" in the normal range, and my throttle body butterfly hasn't fully closed yet as far as I can tell/feel.
A fully closed butterfly should read 0v (and should be a bit "sticky"), right? Well if mine's still a bit open at idle (though I can't seem to close it anymore from the outside), then 3.92v might be "normal" for the amount of angle the butterfly is at.. right?
So could the problem be the butterfly somehow? Might remove the intake and check it out tomorrow. How the hell can it not be fully closed without the idle screw??? It's like my butterfly stop tab/arm thing which usually rests on the screw is bent or something, but it isn't.
Actually no..... if it should be around 4.6v at WOT, then my butterfly flap can't be THAT open at idle (3.92v). Something else is going on. F*ck, I don't know

Could it also be a vacuum or PCM ground problem??




Another thing I don't understand is you guys who (very commonly) talk about drilling holes in your butterflies and elongating the 2 holes on the sides of the TPS because your TPS volts is out by like a tiny 0.15v. What the hell. If I can lower my TPS volts by about 10v with just the idle screw, then why do you guys need to drill and elongate holes for just 0.15v? Why don't you just turn the screw a little bit? Probably wouldn't even make 0001RPM difference to your idle.
And I've heard people say the PCM fully controls the idle, you can't mechanically adjust it. So then how did I lower my idle by 20% with just the idle screw??

 

What car is this? What brand sensor are you working with?

It's simply not possible to have 90V in that system, it doesn't work that way. You need to realize that fact before moving forward.

 

Okay, thanks. So TPS signal on my scantool then is indeed inaccurate?? Could my TPS be f*cked? Isn't there a way of checking it with a multimeter to see if it's okay?

My car is a C IV Vette. The sensor should be the one that came from factory. I can tell you the brand tomorrow. Do you guys want other readings of other sensors or something?

 

I think either your computer or scan tool is F-ed. I don't see any other likelihood unless your car runs on a 120V electrical system. If you divide your readings by 25, they are believable.

You can jumper a terminal to 12 V and read with a voltmeter but drawing s blank on the pinout.

 

Did a little bit of searching for you. Read this thread ---> http://www.corvetteforum.com/forums/...dle-speed.html

For electrical testing I much prefer a good set of back probes, but the methods listed on that thread will work. A DVOM is what you're looking at using here, preferably a decent one.

 

Thanks. I'll message the guy who made the scantool software and ask him if the TPS signal is accurate and to check the reading on his own LS1. My A/F ratio doesn't really seem believable too, though everything else seems fine.

If I divided my readings by 25, it still wouldn't fully make sense because my WOT still shows about 90v even after lowering the idle volts from 13.73 to 3.92. Shouldn't the WOT volts have dropped from 90 to say 30?

I have no idea what you mean by "but drawing s blank on the pinout".. (Edit: oh, "drawing a blank", right?)

 

Thanks for going out of your way a bit to help me, but I don't see what TPS/idle info for 80's L98's and LT1's have to do with me I have an LS1 and an LS1 problem. The vehicle it's in pretty much means nothing. Or is all that L98/LT1 TPS and idle info identical to LS1's?



(Am I the only one who gets pc problems with this forum - pages freezing, getting "Recover Webpage" messages....? F-ing hell.)

 

One thing I'd like to add..

My scantool knows the TPS is very high because the gauge is maxed out even at idle / engine off.

 

I missed the LS1. That's even easier. They're are many pin out diagrams available for that TPS. Get a DVOM and start testing. It's all 5V reference stuff. You don't have 90V. Maybe .90V.

I still can't fully understand what, if any, problem you have... besides a malfunctioning scanner. You stated it was running fine.

 

I guess I want to know exactly why my scantool is showing such extreme TPS volts (wouldn't you and anyone else?), if all my scantool gauges are accurate, if I can improve things without a $1,000 tune (like I already have by lowering the idle)...


So what's the easiest way to test the TPS with a multimeter?
- Ignition on
- Negative lead from multimeter to negative battery or earthed to engine
- Stab positive lead from multimeter through TPS Signal wire???

Quick TPS pinout google search says:
Pin.....Wire Clr.....Function
A.......Gry...........5v Reference
B.......Tan...........Low Reference / Ground
C.......Dk.Blu.......TPS Signal

 

No, dividing by 20 or 25 would be about right. The TPS only has a range of 0-5 V. That means any reading over 5V is errant. At idle you should about .4-0.7 V 13/25=0.52. Closing the blade completely would be close to zero V. 4/25=0.16. 90/25=3.5, which is about where WOT should be. The only three possibilities I see are bad scan tool, bad computer, or decimal/calibration error.

 

For it to be 100% accurate & calibrated & going by what you're saying..
Idle would have to be divided by 8 (3.92v / 8 = 0.49v)
Wot would have to be divided by 19.5 (90v / 19.5 = 4.6v)
So it's a little out of balance. Bit more than double the difference between idle and wot.



Soooo,
what's the easiest way to test the TPS with a multimeter? Anyone?
- Ignition on
- Negative lead from multimeter to negative battery or earthed to engine
- Stab positive lead from multimeter through TPS Signal wire???

Quick TPS pinout google search says:
Pin.....Wire Clr.....Function
A.......Gry...........5v Reference
B.......Tan...........Low Reference / Ground
C.......Dk.Blu.......TPS Signal

 

Yes.

Your signal voltage should be .5 at idle and 4.6 at WOT.

Measure this by preferably back probing the connector or gently breaking the insulation on the wire. Care must be used to not damage the integrity of the wire, I don't recommend a "stabbing" motion

 

Either of 3 ways:

1. back-probe: you carefully insert the needle-like probes in from the rear of the connector (along the wire, between the wire and the wire seal, until it touches the terminal).

2. piercing probes: these pierce the insulation (you have to fill it in with lacquer when finished, not RTV; don't leave it unfilled in).

3. test subharness (male connector at one end, female connector at other end, with either loose "fly" test leads, or you pierce the test subharness wires) (you can either buy one or make one).

NOTE: do *not* stab the wire with the DMM lead probe, this will cause wiring damage.

 

Thanks a lot fellas. Will back-probe test the TPS now and let you know what readings I get.

 

Typical. The wire colours are different.
Okay, I just found a TPS wiring diagram which suits my engine.
2 other things I noticed about my TPS cables:
- There doesn't seem to be a way to back-probe as the wires are flush with the back of the TPS - no gaps around them to slide a probe in.
- There is a small cut in the insulation of my TPS ground wire 1mm from the TPS. If only it was the Signal wire..

Hm, I'm just gonna make a small cut in the signal wire, get a reading and tape it up.


(Get this. I just had insulation tape delivered to me which I ordered about 2-3 weeks ago from China. I was all out of tape.)

 

Good news (kind of)
I just read 0.27 at idle and 4.55 at wot.
So yeah, the problem was my scantool after-all
Pretty weird that my TPS volts are near spot on when I have no idle screw.
Gonna screw the idle screw back in at its lowest setting and see if I can get the #'s perfect.. then email the guy who made the software..

Thanks again everyone

 

It was fairly obvious the scan tool was giving false reading, Ohms Law doesn't lie when dealing with DC circuits

Sounds like everything on the TPS side of things is good to go... Congratulations