j_martin

I got tired of trying to resurrect failing TPS sensors, and it's against my religion to buy a cheap potentiometer in a special genuine plastic box or $250 - $300, so I decided to fix it.

I made an adapter plate and drive coupling adapter for a TPS found on many 91 - 93 Chrysler gas products, available at junk yards for $5 with the connector, or $22 - $45 brand new at auto supplies. The range of said TPS is a little short, so I changed the 5V drive supply to the 8V CPS supply in the same harness. I tested that supply circuit and found that adding the TPS to it would make no difference at all in the CPS function. It takes a dropping resistor to get the adjustment in range, with the bonus that selection of that resistor gives you options, like all out performance, or conservative shifting.

The only alteration to the original setup is removal of the original TPS and drive coupling, and changing the connector.

What do you think?

feets

Looks good.

Can you tell us what kind of resistors you were talking about?


There is a similar post in the Sticky.

j_martin

Just an ordinary 1/4w electronic resistor in series with the supply wire. TPS's vary around 5200 ohms plus or minus 10%. For example, a 5.2K TPS, with an 820 ohm resistor, set at 1.0V idle, would be 3.9V at WOT. That's a slight bit over range, and shifts at full throttle at 65 mph, 2300 rpm into a tight TQ. Light throttle shifts into OD at about 35 mph. A different TPS. or a different desired adjustment range would be attainable with a different resistor.

Differences between this one and the one in the sticky.
1. Original bracket remains in place. An adapter is added.
2. The original drive coupling is not used, and can be saved unmolested if you want to go back to original, or sell it. A new and simpler coupling, better adapted to this TPS is used.
3. The wiring change allows it to be even more adjustable than factory.

ChrisLib

pics of said coupler?
oh...and NICE work, love outside the box thinking. I have a pot on mine but it was a $5.00 radio shack deal I wired up myself. it was a cheap enough fix but lacks the variable o/d capability of a real tps...which I prefer, I find with the pot it`ll hunt in/out of od/ more than I like at a given setting.

j_martin

The hunting is because the throttle on these things is actually the governor setting. When it shifts, you normally back off the throttle a bit, and that sets the tps lower, lowering the shift down rpm's. A pot doesn't know the throttle setting, but only the manual shift point setting.

Here's the mount and coupler installed:


And the parts kit:




One thing I need to do different is make the drive coupler more like a screwdriver. That is to compensate for an unlikely but theoretically possible stuck TPS sensor. Keeps it from jamming the throttle.

samiam4

Not following the resistor need and the change in voltage from 5V to 8 volts?

j_martin

From the original post
If you install a gasser tps in the original wiring, set the idle point at 1.0v, the full throttle point will be somewhat less than 2.5v as expected. To get the proper range, the voltage across the TPS needs to be increased to a higher voltage. There is 8v available in the same harness going to the CPS, so that voltage can be used provided it is dropped to 6v with a series resistor. Testing shows that taking the small current from that circuit won't affect it in the least.

The value of the TPS itself will vary from 4680 ohms to 5720 ohms, with an average value of 5200 ohms. I have to map out some pots to determine the series resistor value needed. As I noted on the experimental one, I got a slightly high range with 820 ohms and a 5200 ohm TPS. It works perfectly with my custom tranny. As you can see, this item is highly variable.

Just got back from vacation a week ago, and am digging out from a nasty snow/slop storm. I'll be back.

samiam4

Thanks Jim for the clarification. I've got a bunch of resistors @ home. I will tweek to match operation range as you have noted.

Got to make the bracket first.

MIchael