The RenX Files: High idle problems

[Ecomike]

I will post all the data and details later tonight when I get back. I took extensive ohm readings on three TPS sensors.....turned out the TPS that I posted data on below, yesterday, the one that was on my 87 XJ, the one that turned out to be part of my Transmission problems seems to have a pair of wires flip flopped internally in the TPS :shiver: on the TCU control side of the TPS based on the test results I got. I have swaped it out for a used one I have, that I also tested, one that based on the test results, should work a lot better for engine power and for transmission shifting. I have new one on order.

Details in about 4 hours. GTG.

 

[8Mud]

7.5 Volts!:gag: How the hell are you getting that at the ECU/TPS input? The books all says 5 volts input!??????

Checking my records I am starting to think my TPS is a junk yard part, but its been over 1 year now and my older records are not as good as I am keeping now. I started keeping meticulous records about 9 months ago so I could go back and see what I did when, and what effect it had. These beasts are just too complicated to depend on memory after a while.

Where does that fuse link start at?

I am sure my ECU is working, but if that B-7 is for maintaining ECU memory only, with the key off, like the TCU (I am guessing that line D-14 is power for the memory) that may be possible. I wonder if a prior owner decided to disable the memory on both????

Can you tell me any more about tracing those lines and the splice for B-7 and D-14 and for the fuse link location?????

I was shocking (shopping, LOL) for a TPS late yesterday, and found at least 5 different manufacturers brands with prices running all the way from $59 to $150 for two connector 87-90, auto transmission TPS, including Borg warner, Wells, Airtex, AC Delco, and Standard.

The best deal I found was $34.95 for an OEM TPS from Teamgrandwagoneer.com (I think it is www.teamcherokee.com that I started at).
arty:

I am still puzzled about that residual volatge shpwing up on the brake line "C10 read 0.5 to 2.0 volts with the brake OFF", which should be reading zero volts!

I am starting to wonder if I don't multiple wiring harness issues that I was previously unaware off.

Sorry about the decimal point should read 0.75 volts.
I always wondered if the ignition switch power in and the constant power in to the ECU power circuits were segregated. I was never curious enough to try and find out exactly what each powered up. The power line from the fusible link is fairly robust (the larger wire of the two power sources).
I have an extra harness in the garage, I'll look tomorrow and see if I can't locate the splice for you.
There is a 1.2 k resistor wired between the ignition power in circuit (D-16) to the TCU and the brake switch circuit. I've noticed it before, the resistor is not far from the inline fuse for the ignition power in circuit (behind the glove box). The one I noticed was on the outside of the harness tape.
The fuseable link is on the stater relay near the battery. I sure can't tell you which is which. But every time I trace one out, I name and mark it.

 

[8Mud]

Sorry about the decimal point should read 0.75 volts.
I always wondered if the ignition switch power in and the constant power in to the ECU power circuits were segregated. I was never curious enough to try and find out exactly what each powered up. The power line from the fusible link is fairly robust (the larger wire of the two power sources).
I have an extra harness in the garage, I'll look tomorrow and see if I can't locate the splice for you.
There is a 1.2 k resistor wired between the ignition power in circuit (D-16) to the TCU and the brake switch circuit. I've noticed it before, the resistor is not far from the inline fuse for the ignition power in circuit (behind the glove box). The one I noticed was on the outside of the harness tape.
The fuseable link is on the stater relay near the battery. I sure can't tell you which is which. But every time I trace one out, I name and mark it.

The path is from the battery to the starter relay, through a fusible link to red wire to the flat six pin connector (near the 3 or 4 relay block) to a splice about ten inches down the harness. The two red wires that go towards the firewall from the splice are the ECU and TCU constant power. The three red wires coming from the connector (towards the battery) are the power into the splice from the fusible link, power to the A/C relay and *the red power wire to the diagnostic plug/only middle pin* which would be a good spot to check for power.
It should be easy to follow the red wire back from the flat six pin connector to the fusible link. The flat six pin connector is labeled F E D C B A (the first six letters of the alphabet right to left) on my harness or my dyslexia is acting up again..

 

[Ecomike]

All of my fuses are good, and all my fuse links are good and I have power on both sides of all the fuse links. I will check the 6 pin connector next.

I discovered a few notable things about the TPS sensors. For instance, The upper and lower limits of the resitance readings are wider, broader, for the uninstalled TPS than they are for an installed TPS. Makes sense (not limited by the installed throttle plate limits), but affects test procedure development.

For instance the bad TPS I just replaced read 6660 ohms (idle) to 4280 ohms at WOT on the ECU side. Uninstalled at max range upper to lower (i.e not limited by the installed throttle plate limits) it read 7700 ohms to 3340 ohms.

On the TCU side of the bad TPS, pin A to pin B, it read 990 (idle) to 1100 (WOT) ohms from A to pin B, while one of the used spares I had read 2300 (idle) to 6610 (WOT) ohms on the TCU side from Pin A to pin B (and the second used spare was close to this so I am asuming this is what it should be).

What was really interesting is that the bad one, TCU side, read 4280 (idle) to 2150 ohms (WOT, uninstalled) from pin A to pin D, So it seems that the 2 wires going to pins B & D on the bad one I just replaced, which have the right colors on the outside when compared to the other 2 I have, must have gotten wired backwards at the factory in this TPS when it was made!:shiver:I am only now dscovering this since I have always been testing and calibrating the ECU side of my TPS, and ignoring for the most part the TCU side ot the tps.

So my conclusion is that we should be testing the pin to pin resistance of BOTH sides of the TPS before installation before we bother to install these, even new ones, and we should be testing unknown ones as an isolated part on the Jeep as well, just to verify that the TPS is properly wired and has the right upper and lower resistance ranges to have a chance at working properly before calibrating them with power on voltage settings.

There is still the issue of worn ones developing bad spots in service where the resistance jumps around, up and down, noisy operation, that cause random high idles, surging, hesitation, stumble, and other erratic engine speed behavior. That test seems to require an analog meter and a steady hand to test for noisy operation.

Here are the readings I got on the used one I just installed. Also these values were close the readings I got on the second used spare, and both were working pulls.

TCU Side:
Pin A to B: 2300 (idle) to 6610 ohms
Pin A to D: 4320 to 4320 ohms, constant
Pin B to D: 6620 (idle) to 2400 ohms

ECU side:
Pin A to B: 4360 to 4360 ohms, constant
Pin A to C: 6580 (idle) to 2200 ohms
Pin B to C: 2330 (idle) to 6550 ohms

Lastly the bad TPS I just replaced read 6510 ohms (idle) to 4230 ohms (WOT) pin A to Pin C uninstalled (7700 to 3300 installed) , while the spare I later installed read 6580 ohms (Idle) to 2200 ohms (WOT) uninstalled, so the old bad TPS only went from Idle to about 1/2 of WOT as far as volatge ranges go, to the ECU, due to the higher resitance and limited range of the bad TPS. As A result my ECU never saw more that 50% throttle aplied to gas peddle, something I could feel using MY seat of the pants dynomometer, LOL!

 

[mattbred]

I'm looking at buying that automatic TPS from teamcherokee.com for my manual transmission jeep. Would I be able to set the 3 prong connection to register 0.8 volts at idle and up to 4.8 volts at WOT? Or is it the other way around for autos?

 

[Ecomike]

I'm looking at buying that automatic TPS from teamcherokee.com for my manual transmission jeep. Would I be able to set the 3 prong connection to register 0.8 volts at idle and up to 4.8 volts at WOT? Or is it the other way around for autos?

According to langer 1 below:

langer1 My Renix, 87 FSM does not list a different TPS voltage setting for Manual transmissions,

It should, they operate exactly in reverse. The % are also slightly different.

Based on that I would say no! In fact from what he says you should be setting the idle to the high voltage setting, reverse of what I have been saying, as mine is automatic. perhaps some one else can confirm this?

If it is reversed on the Manual transmision version, then it should be possible to swap wires A and C (I think) and get an automatic TPS to work, unless the resistances are also different for the manual version!!!!

5-90 has a manual transmission, maybe you can get him to check his, and verify the correct voltage at idle and the resistance range???? I say this because I have run into enough backwrds stuff that was wired backwards, that I would want a second check to confirm that Langer 1's is not some kind of weird backwards factory error???? His post below is the first time I heard of the manual transmission version TPS being the reverse volatges of the automatic transmissions.

 

[mattbred]

I just tested my TPS I had laying around with a multimeter, pins A & C and when completley sprung (Ie less than idle, 0 volts etc etc) it gave a reading of 6.69k.

When I fully extended it, past what the TB arm would be, it was at 2.185k

Looking at your automatic TPS, they work the same? If this is correct, an automatic TPS WILL work with a manual ECU.

 

[8Mud]

I just tested my TPS I had laying around with a multimeter, and when completley sprung (Ie less than idle, 0 volts etc etc) it gave a reading of 6.69k.

When I fully extended it, past what the TB arm would be, it was at 2.185k

Looking at your automatic TPS, they work the same?

The TCU (half) TPS (auto) starts out at a low resistance between the Blu and Gry wire and the resistance goes up as the throttle is applied. Between the Blu and Blk wire it starts at a high resistance and goes down.
The ECU (half) TPS (auto) starts out with a high resistance between the Blu and Gry wires and the resistance drops as the throttle is applied. Between the Blu and Blk it starts with low resisitance and the resistance increases as the throttle is applied.
The halves are mirror image of each other.
I guess theoretically you could pick up another three pin connector, remove the pins from the four pin connector (I'm guessing that's what a stick has, I've never owned one) and swap the Gry and Blk wires and have an extra TPS for emergencies.
If I'm full of it,somebody please set me straight. Does the stick have a single three pin connector on a normal TPS?
My eyes are poor (old people problem) I really can't see the pin letters very well.
On the three pin connector A is gray, B is Blk and C is Blu. On the four pin connector A is grey, B is Blu and D is Blk. It's easier for me to sort out the colors than the letters.
If you look where the wires go into the auto TPS, you can see where the gray and black wires are swapped in position, between the two halves (the two TPS's sandwiched together). If you were to swap the wires back at the connector and change the connector to a stick type connector, you would in all likelihood have an extra stick type TPS, for emergencies. The resistance values may not be exact, but likely near enough.

 

[mattbred]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.

From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

 

[8Mud]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.

From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

If the connector on the stick TPS has female pins, it may. The wire colors for the auto ECU TPS harness end connector are.
ECU input, yellow with a Grn stripe to pin C/ to blue on the TPS pigtail wires.
5.0 volt supply is Lite Blue to pin A/ to gray on the TPS wires
Ground is Blk/with a Wht stripe to pin B/ to black on the TPS wires

The wire colors may actually be the same for the stick harness. The connector may be the same and/or have the same lock. I've seen way to many different kinds of connectors, even between different year Renix's not to mention a stick shift, to be sure of anything.
This would be a really good puzzle for 5-90 to sort out.

 

[mattbred]

Middle is ground, rest are input/output. Looks like you could swap an auto right in.

 

[8Mud]

Middle is ground, rest are input/output. Looks like you could swap an auto right in.

Looks the same to me.
Remember what I said about picking up another three pin connector at the junk yard and trying to rewire the TCU half of the connector as a spare ECU TPS if you install an auto type TPS. You can buy the pin removers for the connector, I have a set that really didn't cost much.
You can see here where the gray and black wires are switched in position as they enter the back of the TPS.

 

[mattbred]

Heh I think I'd just stay with the 3 pin connector. If the connector wears out, I think your TPS itself would have wore out as well.

Im still not sure if the TPS is my problem tho I'll keep looking.

 

[Ecomike]

Heh I think I'd just stay with the 3 pin connector. If the connector wears out, I think your TPS itself would have wore out as well.

Im still not sure if the TPS is my problem tho I'll keep looking.

Don't know about the connector wearing out part, but once one side of the 2 part (Auto) TPS wears out, the other side may not be far behind, if it didn't aleady go bad!

 

[Ecomike]

This is a STICK TPS Sensor. It has 3 prongs coming out of it, and at idle it starts at a high resistance, and at wide open throttle, it has a lower resistance.
From all of these diagnoses, I fully believe an automatic TPS can be used with a Manual ECU.

Based on that I'd have to agree, looks like a direct swap. Now I am REALY wondering about what Langer 1 has since he says his works backwards???

 

[Ecomike]

Well after 2 years of !!!1 (At least it was starting to look that way) I have solved the last of the power problems in my 87 XJ, Wagoneer, 4.0. It was the TPS as described below. I seem to have full power restored. It is amasing how much a TPS can affect the power output of the engine and Tranny on an automatic 4.0. Anyway the used TPS sensor solved all the remaining problems as far as engine power and transmission shift points were concerned for me. Now its time toarty:

All of my fuses are good, and all my fuse links are good and I have power on both sides of all the fuse links. I will check the 6 pin connector next.

I discovered a few notable things about the TPS sensors. For instance, The upper and lower limits of the resitance readings are wider, broader, for the uninstalled TPS than they are for an installed TPS. Makes sense (not limited by the installed throttle plate limits), but affects test procedure development.

For instance the bad TPS I just replaced read 6660 ohms (idle) to 4280 ohms at WOT on the ECU side. Uninstalled at max range upper to lower (i.e not limited by the installed throttle plate limits) it read 7700 ohms to 3340 ohms.

On the TCU side of the bad TPS, pin A to pin B, it read 990 (idle) to 1100 (WOT) ohms from A to pin B, while one of the used spares I had read 2300 (idle) to 6610 (WOT) ohms on the TCU side from Pin A to pin B (and the second used spare was close to this so I am asuming this is what it should be).

What was really interesting is that the bad one, TCU side, read 4280 (idle) to 2150 ohms (WOT, uninstalled) from pin A to pin D, So it seems that the 2 wires going to pins B & D on the bad one I just replaced, which have the right colors on the outside when compared to the other 2 I have, must have gotten wired backwards at the factory in this TPS when it was made!:shiver:I am only now dscovering this since I have always been testing and calibrating the ECU side of my TPS, and ignoring for the most part the TCU side ot the tps.

So my conclusion is that we should be testing the pin to pin resistance of BOTH sides of the TPS before installation before we bother to install these, even new ones, and we should be testing unknown ones as an isolated part on the Jeep as well, just to verify that the TPS is properly wired and has the right upper and lower resistance ranges to have a chance at working properly before calibrating them with power on voltage settings.

There is still the issue of worn ones developing bad spots in service where the resistance jumps around, up and down, noisy operation, that cause random high idles, surging, hesitation, stumble, and other erratic engine speed behavior. That test seems to require an analog meter and a steady hand to test for noisy operation.

Here are the readings I got on the used one I just installed. Also these values were close the readings I got on the second used spare, and both were working pulls.

TCU Side:
Pin A to B: 2300 (idle) to 6610 ohms
Pin A to D: 4320 to 4320 ohms, constant
Pin B to D: 6620 (idle) to 2400 ohms

ECU side:
Pin A to B: 4360 to 4360 ohms, constant
Pin A to C: 6580 (idle) to 2200 ohms
Pin B to C: 2330 (idle) to 6550 ohms

Lastly the bad TPS I just replaced read 6510 ohms (idle) to 4230 ohms (WOT) pin A to Pin C uninstalled (7700 to 3300 installed) , while the spare I later installed read 6580 ohms (Idle) to 2200 ohms (WOT) uninstalled, so the old bad TPS only went from Idle to about 1/2 of WOT as far as volatge ranges go, to the ECU, due to the higher resitance and limited range of the bad TPS. As A result my ECU never saw more that 50% throttle aplied to gas peddle, something I could feel using MY seat of the pants dynomometer, LOL!

 

[Steve_Moore]

Good to hear , Mike. Mine's going to a mechanic again Monday .

 

[bn6339]

I have a question....has anyone ever replaced their TPS with a MOPAR unit, rather than an aftermarket, and without all other issues (ground, etc) still possessed problems? I have a 1990 XJ (4.0 auto) which sometimes experienced high idle, I planned to replace the TPS, and bought a MOPAR replacement. I then repaired some other things (intake/exhaust manifold gasket, oxy sensor, CPS, etc) and added a huge ground cable from the cylinder head to chassis....haven't experienced high idle for some time...

 

[Ecomike]

I have "New TPS" Test DATA for new, OEM, loose unmounted TPS sensors! party1:

This is for 87-90 Renix TPS with automatic transmission (has 2 pigtail connectors), tested on the 3 pin, ECU side only:

Loose unmounted, Brand New TPS tested on the ECU side itself, disconnected from harness is:

B to C - 2.360k ohms at Idle
A to B - 3.740k ohms at idle
A to C - 6090k ohms at Idle

Loose unmounted, Brand New TPS tested on the ECU side itself, disconnected from harness is:

B to C - 6.130k ohms at WOT
A to B - 3.740k ohms at WOT
A to C - 2.420k ohms at WOT

Do not confuse this with mounted TPS test results!

Also for the TCU side of the TPS, Loose unmounted TPS:

Pin B to D: 6060 ohms (idle) to 2340 ohms (WOT)
Pin A to D: 3770 idle to 3770 Ohms WOT.
Pin A to B: 2340 ohms (idle) to 6160 ohms (WOT)

 

[Ecomike]

Well pin D14 to my TCU which the manual says should be hot, 12 Volts from the battery all the time, was dead all the time on mine. I am sure it is a keep alive memory for the TCUs operating history (like TPS sensor data) memory.

I am guessing that it's being dead may severly affect gas mileage and I know it affects shifting performance as the manual describes a training period and directions to follow for that training period so that the TCU gets properly familiar with things like a new TPS sensor.

So I ran a new 12 volt battery wire to it today. But I went one step further and added a panel switch so I can turn it off and erase the TCU memory at the flip of a switch any time I want to. I plan on experimenting with it on multiple trips, and gauge gas mileage after training it differently.

Since I have everything else on this 87 working perfectly, finally (almost everything is brand new), this is a perfect oportunity to determine if this was one of the gas mileage problems I was I having (no TCU memory), or if it was just the bad TPS killing the mileage. Keep in mind I found a bad ground to the TCU, a bad TCU side of the TPS, and the missing memory power to the memory of the TCU all at the same time.

So now I want to know which one was limiting my mileage so severly ( I am expecting my 10 to 15 mpgs to increase substantially now). It may be the answer for dozens of others here who have experienced the same poor mileage when compared to others here with the same OEM Renix jeeps that have reported 20 to 25 mpgs.