Question on TPS from EFI



Hey hometowns, I'm feelin' a little looney here...

Just found out TPS stands for 'throttle position sensor' and here's my question.....

My final reading at WOT reads 66.7, I'm using WinALDL. Is that percentage? Because I know that the pedal kit I have does not allow me to go full throttle. It's a cheap one from Clifford. (It worked great for the carb, but not for this TBI). It makes sense to me but if someone can correct me, that would be kewl...



I think it's time for a Lokar system cuz if I'm doin' what I'm doin' with only 67% throttle... :shock:
I'm not positive off the top of my head, but it seems to me that the TPS numbers are just arbitrary numbers between 0 and 255 that relate to the throttle position. This is how my Holley ECU is setup and I think the GM TBI computer is the same.

I wouldn't worry about it too much, because it's not the absolute value that's important, it's the rate of change of the value. Remember the TPS gives the ECU a chance to do what an accelerator pump would do in a carb. The ECU just waits for a fast change in the TPS and then adds more fuel for a few revs.

I think I may have the actual numbers in a book I have. I'll check when I have a minute.

Yo C-town,
I busted out my "How to Tune and Modify Chevrolet Fuel Injection" book, I am assuming you have GM EFI. On page 82 it has instructions on how to test the TPS and it says the range for GM TPS is usually from .65V (throttle closed) to 4.0V (full throttle) I know AutoZone can test em for you if you take them off and bring them in. Its has some decent instructions for testing the part in the book also I could give you if you need it.

I think you posted it before the board died, but what type of EFI are you running again?
What did it come off?

Sup hometowns...

Thanks 292C10

I have a GM 560cfm 2 barrel TBI system. I'm way off I believe. Using WinALDL, there is a pop-up window that measures kpa, tps, O2, rpm and speed. At idle, the tps reads 2.1! I know when I initially put on the system, I was having trouble with idle. I found out I had to fiddle with the throttle stop screw. I had to jump the ALDL with a paper clip. I'm wondering if I did it right. The hometown from Howell told me I had to do it with the engine on. But there was no way I could do it. Without the IAC connected, it reved like mad. I couldn't keep the throttle open long enough to adjust the screw. Fuking scary! I'm serious! I did it with the motor off....

Luckily for me, there is this cool cat I met at who lives down the road some, but close enough to cruise...My BLM #'s are averaging 108 when I'm near idle. He's gonna begin the process of fine tunning the eeprom for me. In the meantime, I will learn from him and go about it someday on my own so that I can be the tunner of my own rod...
WinALDL is a decent program, but you should do baseline voltage readings first. The # (66.7) should have been % of throttle- 67% ain't good for WOT, especially if that's what your ECM thinks (it will be referencing the wrong fuel map).

As Coupeboy siad- check to see if you get the full movement from .65 to 4VDC. You can do this with the key ON, and the engine not running. Also- running your engine without the IAC keeps the stepper effect of the IAC out of the picture, so you'll get nearly the full air-gap at the IAC's pintle. Consequently, it will also screw up your BLM #s a little.

Have you ever checked out the DIY_EFI page? They have all the GM ECM's decoded and everything- and have most of the tricks sorted out (your Howell system is two steps ahead of someone running a stock ECM).
I'm working on getting a lokar pedal kit. Also, I just recenlty met this fella who is a moderator at He'g gonna tune the eeprom and I assume he will be testing the voltage. I don't have any testing equipment. Is the testing equipment a cheap deal like the boys, or something more expensive like snap-on and the like?

Thanks again HOMETOWNS...


ps- I thought the DIY-EFI page was just a list of emails?? I'm gonna check it out in more detail...