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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
I recently rebuilt the Quadrajet on my 86 LG4. It's running much better, but I still need to get the air bleed adjusted, and set the TPS properly.
When I measure the TPS voltage when warm and the throttle on the stop I only get 0.010 V. If I push down on the plunger or open the throttle it does increase, but to get it to 0.48 V per the spec I have to have the throttle at about half open.
So something isn't right.
The TPS signal seems steady, and the plunger moves up and down freely in the bore. Is it possible that I'm missing a spacer or something under the TPS? I'm pretty sure the spring is back under there. I didn't replace the plunger during the rebuild, just cleaned and reinstalled it.
I didn't know which way to adjust the screw, so I pulled it all the way out with no change. Then screwed it in as far as I could with still no change. If I shove a small pick down the adjustment bore I can get the Voltage reading to increase, but then it looks like the plunger isn't actually touching the TPS. Here's my adjustment tool, I used a butt connector (the size with the blue cover).
So does it sound like a bad TPS? I would rather not pull the top of the carb off, but if I have to I will. I could at least test the TPS vs a new one and see if they are radically different.
I've had a TPS that was gunked up enough, or the spring too week, so that the spring below it wouldn't keep it at the top of its bore. the whole unit would drop with the plunger with similar voltage readings to what you are seeing. fixed it by installing a second spring underneath-just let them wrap themselves together.
only way to know for sure it to take the top off and observe the TPS body as its plunger is pushed in.
I've had a TPS that was gunked up enough, or the spring too week, so that the spring below it wouldn't keep it at the top of its bore. the whole unit would drop with the plunger with similar voltage readings to what you are seeing. fixed it by installing a second spring underneath-just let them wrap themselves together.
only way to know for sure it to take the top off and observe the TPS body as its plunger is pushed in.
could be a bad TPS too.
A weak spring makes sense. If the spring isn't pushing the TPS against the plunger it won't read anything. I will pull it off and check the spring and tps plunger and see if I can make it work. If not I will buy a new one.
Well, chalk it up to a rookie mistake. I forgot to put the spring back in. Doh! Thankfully I have learned not to throw anything away for a while. Or ever.
I made a quick adjustment and got it to 0.479V. It's super sensitive!
I left my probes in so I can warm it up and double check it in the morning The neighbors probably don't like me idling it at 8:00 PM with the loud exhaust.
Hopefully tomorrow I can dial in the TPS, adjust the dwell and call it done! And move on to exhaust, interior, suspension, etc.
01-06-2019, 04:09 PM
