Why are TPS's so danged expensive?

[rocketwheels]

I have narrowed down my crazy "miss" that has no rhyme or reason. It must be the TPS. Just recently, the truck had a high idle issue, it would hang in a higher rpm range. I would shut off the engine for a few minutes and the idle would return to normal. This doesn't happen very often. This along with the miss makes me look at the TPS.

 

Previous problems was the erratic miss while holding highway speeds. Changed out everything in the ignition one by one. It did run much better, but the errant miss is still there,but only while trying to maintain 55-70 mph. It idles fine, rolls up to 45 mph fine, and doesn't miss a beat when you flog it. Sensor must be worn at that "freeway speed" range of movement.

 

shopped around (including O'reillys where I work part time) and have to special order this TPS for the '87 4.0/ Man Trans....around $70-85 bucks ! Any idea where I might find it cheaper? (there are other TPS listed but they are for the 4cyl and 4.0 / Auto Trans...and some of the listings are incorrect showing the wrong part for my application).

 

I guess I'll pony up for the TPS when I can, just not in a place financially to do it now.

[foreman1063]

Test it, it could be a ground or connector problem. A quick test will tell you for sure if it has a dead spot and if it needs adjusting. Pretty easy to do with a multimeter and a couple of paper clips. Plenty of write ups floating around to guide you through it. Might save you some money.

[Geonovast]

www.rockauto.com has one for $30, it's a 2-plug for an automatic, but will work with a 5 speed.

[cruiser54]

Just buy the one for the auto and be done with it. Way cheaper and bolts right on and plugs right in.

 

I mentioned it here:

 

 

RENIX TPS ADJUSTMENT

 

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.

It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

 

IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector

of the TPS . The letters are embossed on the connector itself.

Touch the black lead of your meter to the negative battery post.

If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be

necessary. The harness repair must be performed before proceeding.

I can provide an instruction sheet for that if needed.

 

MANUAL TRANSMISSION:

 

RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.

This manual transmission vehicle TPS provides data input to the ECU. The manual transmission

TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.

 

Wire "A" is positive.

Wire "B" is ground.

 

Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..

Note the voltage reading--this is your REFERENCE voltage.

 

Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your

OUTPUT voltage.

Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For

example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If

you can't achieve the correct output voltage replace the TPS and start over.

 

AUTOMATIC TRANSMISSION:

 

RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-

wire connector, same as the manual transmission vehicles have, and it is tested the same as the

manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.

 

However, the automatic TPS also has a square four-wire connector clearly embossed with the letters

A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.

 

Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your

REFERENCE voltage.

 

Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT

voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.

For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.

If you can't, replace the TPS and start over.

 

So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and

the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire

connector side of the TPS. If you have ENGINE issues check the three-wire connector side of

the TPS.

 

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is

stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

 

Revised 11-28-2011

[cruiser54]

Be sure to do the sensor ground test as outlined in the beginning. That can really screw with things it has high resistance. C101 connector cleaning on an 87 is always a good idea.

[carnuck]

I spray mine down with NAPA electronic cleaner before throwing in the towel on them.