TPS voltage check/adjust carbed engine
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TPS voltage check/adjust carbed engine
I got an 86 305 computer controlled carb. My check engine light is on with code 21- TPS and code 32- pressure differential. I tried checking the TPS voltage today and instead of it reading close to .5 V, it read 3.36 V! what could cause this? I tried drilling the small plug out where you adjust the TPS but I couldn't turn it (no slot in the head), is there something else?
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From: Northern CA.
Car: '82 Z28
Engine: 350
Transmission: TH400 4,000 stall
Axle/Gears: Currie 9", 4.56 gears
What did it read when it was at full throttle? Here's something I found on adjusting the TPS. It isn't 3rd gen specific so use the specified voltages for your car.
Adjusting the Throttle Position Sensor (TPS):
On the top of the carb, towards the front on the driver's side you'll see the lever that activates the accelerator pump. Right behind and tothe side of the pivot point of this lever is the adjustment for the TPS.The adjusting screw is normally covered by a small metal plug.
Drill a small hole in the plug (be careful not to run the drill bit very far through the plug so as not to go into the adjusting screw itself), thread a sheet metal screw into the plug, and pull it out with a pair of pliers.
Next you'll have to find something to fit the tiny hex head on the adjusting screw. They make tools for this which is a 2.5mm hex driver, but I'm cheap so I used a small copper tube (actually the innards from a ball point pen) which I crushed witha pair of pliers so that it just fit.
Find the TPS connector on the driver's side front of the carb. It's a 3-wire "weatherpak" connector. You need to tap your digital voltmeter into two of these wires, but they need to stay plugged in at the same time. If you can't figure out how to do that, you can make a pigtail connector like I did from two extra weatherpak connectors and some alligator clips.
Hook your digital voltmeter between the middle pin (ground) and one of the other pins. Turn the ignition switch to on, but don't start the car. Get about 5V? Wrong pin, switch. One pin is ground, one is 5v, the other is TPS output. You want ground and TPS output. You'll be getting less than 1 volt unless you're way out of adjustment.
Adjust the TPS adjusting screw until you get as close as you can to .48 volts at idle. Open the throttle slowly and verify that the value increases smoothly all the way up to at least 4.5V when at WOT. If it doesn't goup to close to 4.5V, you need a new TPS.
Open the throttle wide open and close it again a few times to make sure it returns to the proper voltage. You may have to readjust a few times to get it to return to about 0.48 each time.
Turn the key back off, disconnect everything, and then disconnect and reconnect the battery (only has to be for a second) to reset the computer (don't forget this part!).
On the top of the carb, towards the front on the driver's side you'll see the lever that activates the accelerator pump. Right behind and tothe side of the pivot point of this lever is the adjustment for the TPS.The adjusting screw is normally covered by a small metal plug.
Drill a small hole in the plug (be careful not to run the drill bit very far through the plug so as not to go into the adjusting screw itself), thread a sheet metal screw into the plug, and pull it out with a pair of pliers.
Next you'll have to find something to fit the tiny hex head on the adjusting screw. They make tools for this which is a 2.5mm hex driver, but I'm cheap so I used a small copper tube (actually the innards from a ball point pen) which I crushed witha pair of pliers so that it just fit.
Find the TPS connector on the driver's side front of the carb. It's a 3-wire "weatherpak" connector. You need to tap your digital voltmeter into two of these wires, but they need to stay plugged in at the same time. If you can't figure out how to do that, you can make a pigtail connector like I did from two extra weatherpak connectors and some alligator clips.
Hook your digital voltmeter between the middle pin (ground) and one of the other pins. Turn the ignition switch to on, but don't start the car. Get about 5V? Wrong pin, switch. One pin is ground, one is 5v, the other is TPS output. You want ground and TPS output. You'll be getting less than 1 volt unless you're way out of adjustment.
Adjust the TPS adjusting screw until you get as close as you can to .48 volts at idle. Open the throttle slowly and verify that the value increases smoothly all the way up to at least 4.5V when at WOT. If it doesn't goup to close to 4.5V, you need a new TPS.
Open the throttle wide open and close it again a few times to make sure it returns to the proper voltage. You may have to readjust a few times to get it to return to about 0.48 each time.
Turn the key back off, disconnect everything, and then disconnect and reconnect the battery (only has to be for a second) to reset the computer (don't forget this part!).
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I was using my hanes manual to check it and it didn't say anything about moving the throttle. The 3.36 volts was on the bottom two wires like the book said and was at closed throttle. I think I'll try it again using the instructions you posted and see what I get.
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Ok I tried the voltage check again here's the results: looking at the plug from the driverside with meter connected between the bottom and middle wires 3.35 volts, meter connected between the top and middle wires .01 volts, with meter connected between top wire and bottom wire 5.10 volts. Also with meter connected (in any one of the 3 tests) voltage does not change at all when throttle is moved to full throttle and back. what could cause this or where do I need to look next?
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From: lakewood colorado
Car: 84-92 firebirds
Engine: 2.8/3.1
Transmission: auto
If the readings are'nt changing when you move the throttle, the TPS is probably history. BTW- to adjust the TPS screw you need either a 2.5 mm or 3/32" hex driver. I bought a set of precision screwdrivers at Home Depot that had the 3/32 hex drive included.
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The TPS itself is a little cylinder inside the carb. It has a little spring-loaded shaft sticking out the top (moving this shaft in and out changes the TPS voltage). On top of this shaft is short, round pushrod that connects the bottom of the accelerator pump arm to the top of this shaft- you can see it from the outside if you look closely- it's near the accelerator pump arm fulcrum point. Somewhat complex system (especially to reassemble correctly for a novice).
Either the TPS itself is bad, or somebody left out this intermediate pushrod when they were monkeying around in the carb before you (a common mistake), or your accelerator pump arm isn't connected to the throttle arm. That's about all it can be.
Either the TPS itself is bad, or somebody left out this intermediate pushrod when they were monkeying around in the carb before you (a common mistake), or your accelerator pump arm isn't connected to the throttle arm. That's about all it can be.
Last edited by Damon; Jun 15, 2006 at 01:12 PM.
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Originally Posted by Damon
The TPS itself is a little cylinder inside the carb. It has a little spring-loaded shaft sticking out the top (moving this shaft in and out changes the TPS voltage). On top of this shaft is short, round pushrod that connects the bottom of the accelerator pump arm to the top of this shaft- you can see it from the outside if you look closely- it's near the accelerator pump arm fulcrum point. Somewhat complex system (especially to reassemble correctly for a novice).
Either the TPS itself is bad, or somebody left out this intermediate pushrod when they were monkeying around in the carb before you (a common mistake), or your accelerator pump arm isn't connected to the throttle arm. That's about all it can be.
Either the TPS itself is bad, or somebody left out this intermediate pushrod when they were monkeying around in the carb before you (a common mistake), or your accelerator pump arm isn't connected to the throttle arm. That's about all it can be.
'
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From: Northern CA.
Car: '82 Z28
Engine: 350
Transmission: TH400 4,000 stall
Axle/Gears: Currie 9", 4.56 gears
Here's a pic showing the parts for the TPS. It's sometimes a pain in the butt to line up the TPS plunger and the rod that pushes down on it.
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Car: Now Camaorless
Originally Posted by EvilCartman
Here's a pic showing the parts for the TPS. It's sometimes a pain in the butt to line up the TPS plunger and the rod that pushes down on it.
Looking at that drawing it's very possible that I didn't get it lined back up right. I've been in older quads many times but this was the first electronic one.
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