1G TPS voltage too high

[GooeyGus]

Today I finally got my datalogger all set up. I'm using TMO with a powered logging cable (I forget the brand... It's three letters, like PPT or something like that) as well as a keyspan serial to USB adapter.

I've had this setup for a long time, but the last time I actually had it installed was about 4 years ago.

My issue is that I can't get the TPS to read correctly at idle. The lowest I can manage is .78V, which correlates to 16% throttle. The TPS has a nice smoothe rise all the way up to 4.99V with no dead spots.

I pulled the sensor off and did notice that the "tracks" inside the TPS are a bit worn. If I turn it by hand with the sensor removed I can get it to go down to .50V.

Is there a fix for this or do I need a new TPS?

Also, could this effect fuel economy? I'm getting horrible mileage in the city, but everything on the logger looks fine.

Thanks!!

PS: I can post some cruising logs if anyone would like to see them. I would post them now but I am not on my PC.

 

[jrohner]

Loggers usually don't show 0% throttle; if I remember correctly I see 13-15% or something. .78V does seem a bit high, but I guess I wouldn't worry about it.

 

[GooeyGus]

From what I've read, I've heard that the tps should read between .48 and .52 at idle. I would assume this correlates to about 10%.

I think the issue is the worn tracks inside the tps. Since there is a bit of slop, it doesn't fully bring the sensor to the closed position, yet functions normally.

As long as this won't cause performance issues, I won't worry about it, my idle is fine, the car just uses too much fuel in the city and I can't nail down the problem.

 

[steve]

Off the TB the TPS should go close to 0v.

On the car if it won't go lower then .7v I'd first make sure that the throttle was actually closing all the way and that I had at least 1mm of slack in the throttle cable and that the TPS was correctly installed on the TB.

Are you still running a 90 TB?

 

[GooeyGus]

Off the TB the TPS should go close to 0v.

On the car if it won't go lower then .7v I'd first make sure that the throttle was actually closing all the way and that I had at least 1mm of slack in the throttle cable and that the TPS was correctly installed on the TB.

Are you still running a 90 TB?

Throttle seems to be closing all the way. I took the idle switch off to see if the voltage would go down a bit more, and I pushed the plate to make sure it was closed, but I think it only went down by .02V or so.

Throttle cable seems to have just enough slack. I can deflect the cable about 1mm before the plate starts to move.

Unfortunately, it is still the 1990 TB. I would love to get a newer one in the very near future.

 

[steve]

This may be the catalyst when you look at what a new 90 TPS costs.

 

[GooeyGus]

Jesus!!! Damn near $200 for a PARTS STORE TPS versus about $50 for the '91+ TPS... that is ridiculous.

Hey Steve, I just noticed that there are two connectors coming off of the '90 TPS. What is the smaller connector for?

Also, how do I manage wiring in a '91+ TPS once I actually change my throttle body? Can I still use my 1990 ISC motor? I think the only difference in the ISC is that the '90 is mounted on the bottom and has a pigtail, so it should mount up, right?

For the price of the '90 TPS I can damn near buy a '91+ throttle body, TPS, and ISC.

Does the '91+ throttle body just bolt right up? Do I need to make any non-electrical changes?

I cant believe I actually just bought ANOTHER '90... the first time I didn't know better, this time I did and I STILL bought it.

Fool me once, shame on you. Fool me twice, shame on me!

 

[steve]

Without a picture I don't remember the connectors. You have three things that connect to the TB, TPS, IPS, and ISC.

I don't know if a 90 ISC will fit. I would get a new black one and o-ring.
You have to hit up the junk yard for the 91+ connectors and splice then either into your harness or onto the existing connectors making an adaptor.

The fuel rail needs to be swapped. the 90 is too long and hits the 91+ TPS. Figure another $20 for one.

 

[GooeyGus]

Without a picture I don't remember the connectors. You have three things that connect to the TB, TPS, IPS, and ISC.

I don't know if a 90 ISC will fit. I would get a new black one and o-ring.
You have to hit up the junk yard for the 91+ connectors and splice then either into your harness or onto the existing connectors making an adaptor.

The fuel rail needs to be swapped. the 90 is too long and hits the 91+ TPS. Figure another $20 for one.

Looks like I'm going to start throwing some parts together and just get rid of the '90 TB once and for all.

Any decent aftermarket fuel rails that aren't ridiculously expensive? I figure I might as well upgrade if I'm taking it off.

I just dont see how they justify charging $175 for a potentiometer with bolt holes.

EDIT: I forgot to add, when I took my TPS off, the o-ring (or at least it looked like an o-ring, between the TPS and the TB. Not the shaft seal) came out in pieces. It was so dried out it was like plastic. Will this cause a leak?

The second connector on the '90 TPS can be seen here:

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[steve]

The single connector is the IPS wire.

If the o-ring (I didn't know there was a o-ring there) was dried out and hard it was already a leak.

Aftermarket fuel rails look nice but questionable value. I guess if you have dual fuel pumps and 1600cc injectors running E85 you might want/need one. Save your money and get rid of the 90 CAS too. If the wires haven't broken yet they not going to last forever.