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TPS voltage won't go low enough?

Old 05-20-2017, 09:24 AM
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TPS voltage won't go low enough?

I checked the TPS voltage on my Qjet and found it to be 1.11v at base idle.

I measured it using two strands of thin copper wire folded into the lower two (B&C) connections of the TPS connector, and then connected it back up so I could read the voltage across the two exposed copper wires with everything connected up and switched on.

When I tried to adjust the TPS back down to 0.48, I couldn't reach the required voltage before the screw bottomed-out at about 0.88v. When I started the car it ran quite poorly, loaded up and stalled. Does anybody know what's going on? For now I've set the voltage back to where it was and the car runs ok, but it still feels like it wants to stall.

Many thanks for any help!

ND
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Old 05-20-2017, 08:11 PM
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Re: TPS voltage won't go low enough?

How old is the sensor? The 2 or 3 times that happened to mine was when the sensor went bad.
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Old 05-21-2017, 02:53 AM
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Re: TPS voltage won't go low enough?

Thanks for the lead! Although it's a relatively new (1 year old ish) reman carb so theoretically it's a new TPS... Is there a way to check it before I source a new one and open up the carb to replace it?

Cheers,

ND
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Old 05-21-2017, 10:01 AM
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Re: TPS voltage won't go low enough?

Only other thing i can think of is the small hook on the air horn, that pushes on the top part of the TPS could be hung up on the air horn gasket, but you'd have to at least loosen the air horn & partly lift it to see if the hook is going past the gasket & down onto the TPS.

Spmetimes i would buy a TPS & simply connect it outside the carb, to see if the voltage reading was normal.This way if nothing changed i could return the TPS.
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Old 05-22-2017, 07:48 AM
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Re: TPS voltage won't go low enough?

Interesting you should mention that - I went to look at the car yesterday and found the TPS plunger stuck fully down.

That explains the hard starts - if the TPS was advancing the timing as though the carb was at full-throttle. It also explains why it seemed to use so much fuel while just idling! Flicking the TPS plunger with a thin screwdriver made it ping back up, back it got squished back down the pump arm and got stuck again.

I'll prise off the airhorn when I get a chance, and maybe replace it with the TPS from my old carb and see if that helps. I'm glad I found it as it explains a lot about how the car was behaving!

I'll keep this post updated as I find things out
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Old 05-22-2017, 07:59 PM
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Re: TPS voltage won't go low enough?

You mean the steel pin coming out the top of the air horn? It pushes the TPS down as throttle is applied, a spring under the TPS pushes everything back up.Possible the TPS body has warped or swelled a bit.Had that happen once too.
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Old 05-23-2017, 01:50 AM
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Re: TPS voltage won't go low enough?

Ok, I'll look out for that - my strongest suspicion is that I got the TPS hooked in the gasket when I last put the airhorn back on... D'oh!
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Old 06-17-2017, 09:17 PM
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Re: TPS voltage won't go low enough?

The green TPS plunger is aluminum, check seal and retainer for that plunger. The seal can cause plunger to bind. Check the spring under TPS sensor as posted, I have seen them loose tension over time. Look at the external linkage and lever, the back side wall for roll pin for being pushed over towards center or broken off.
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Old 06-20-2017, 04:36 AM
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Re: TPS voltage won't go low enough?

Ah, sorry - thanks for reminding me to update this thread!

I opened up the carb and found the TPS had become wedged in the body of the carb, which meant it wasn't responding to being prodded by the little adjuster-arm on the bottom of the airhorn. When I pulled it out, the TPS casing kinda came apart. I opened up the old carb, tested the old plunger, which worked perfectly, and installed that instead. Adjusted perfectly.

I fixed a thing!

Thanks for all the advice and help, everyone!
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