gotmud7

I may be an idiot, but exactly how do I adjust the TPS sensor on my 1986 Iroc? 305, automatic.
I have a book that says how to do it in theory. But need another book to see the value to what to set it to. (SD-100)

So far this is what I have done. During the rebuild I lost the metal cylinder that pushes on the TPS sensor. My NOS tps kit had a new one, but was much longer. I had to adjust the TPS adjusting hex head screw to make it fit. Then I found the original pin and put it back in. The directions state to: "Connect voltmeter from TPS connector center terminal to bottom terminal. Make jumpers"
I used a piece of copper wire jammed up into the connector and wrapped it around the voltmeter terminals.
" With ignition on, engine stopped, turn screw to obtain specific voltage at specific throttle position. Refer to AC-Delco SD-100 for specifications."
My readings were all over the place. I have ordered that book and should have it soon.

I could not find a video on youtube showing how to do it.
Seriously, someone must have done this before and can give some advice. Again it sounds easy on paper, but I'm either not getting it or there is some type of trick to it. Thanks!!!

NoEmissions84TA

iTrader: (1)

The stem (plunger) of the TPS is VERY easy to bend and break while installing the air horn.
I use common pins pushed into the wires in front of the carb leading to the TPS connector.
1 in the center wire, 1 in the ground wire. Use alligator test leads between the pins and your meter leads.
IIRC, my 1984 LG4 305 TA called for .48v at idle.

Saxondale

iTrader: (2)

I had my carb apart three times in the past week, therefore have some first-time learning familiarity with the components. Based on that I'd say the TPS is not adjustable. It is preset to function within the required voltage range.

NoEmissions84TA is correct about getting that pin to line up with the TPS plunger during assembly. There is also spring beneath the TPS cylinder that needs to be in place.

Doesn't answer your question, but because the air horn has been off it is relevant.

Thanks.

gt4373

NoEmissions84TA

iTrader: (1)

Actually, there is an adjustment. There is a very small soft metal plug installed over the adjustment screw. The screw sets the position of the TPS potentiometer in its cavity so that the ECM knows where the throttle position is. For my 84 TA LG4, it calls for .48v at idle. Since you never touched yours, it might be fine without touching anything. I will search to see if I can find a pic of it.









https://www.autozone.com/repairguide...00c1528004781a


https://www.hemmings.com/magazine/mu...e/3720231.html
(pic #3 shows the location exactly)

Saxondale

iTrader: (2)

NoEmissions84TA

iTrader: (1)

wrong spot

naf

iTrader: (7)

remove the adjustment screw cover as shown above

if you do not have the proper wrench to fit the adjustment screw just use an appropriately sized roll pin and tap it over the screw. you'll be able to turn it by hand

measure voltage at middle and bottom wires. you'll have to slide a needle or equivalent conductor in there as the voltage must be measured with the connector on and the engine in 'run'. the motor does not need to be running.

look for 0.40V to 0.50V at idle and near 4.0V at WOT. if the reading jumps around while the throttle position is moved, the TPS is likely bad. it should change voltage linearly at the throttle is depressed.

if, as the throttle is opened, and the plunger is pressed down onto the TPS and the voltage doesn't increase to near 4.0V, the spring beneath the TPS may be worn out OR the TPS may be gunked up with varnish. this lets the TPS move up and down with the rod instead of the rod moving the TPS plunger within the TPS body.

The original TPS plunger should be green (or mostly so-it may be worn). it's coated in teflon so it won't stick to the bore of the airhorn. replacement ones are not coated (at least the one's I've seen). use your original if it still looks good.

when installing the airhorn, a dab of grease can hold the TPS rod in the airhorn.