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Renix TPS - Technical

GSequoia

Everyone says I'm a jerk.
NAXJA Member
Location
Torrance, CA
Okay, so I'm diagnosing some odd stuff and right now my guns are pointed at my TPS, here is what I've gathered, I just want verification on this and any ideas.

The Auto trans. TPS has two connectors, one three wire (same as the manual) and one four wire for the TCU. The adjustment procedure uses the automatic four wire connector (actually only three wires in that) and you adjust it to (at closed throttle) where output voltage is 83% of input. Optimum would be 5 VDC input and 4.15 VDC output.

According to my FSM a manual is adjusted exactly the same, meaning 80%, however if I pretend I have a manual (test via the three wire connector that goes to the ECU, meaning it's the same as on an auto) I cannot get this.

I looked at alldata and it says that input should be 5 VDC and output 0.8 VDC, or 16% of the input voltage. Is the FSM wrong here?

If I adjust the TPS so that the ECU feed is at it's proper 16% the TCU side will not be at 83%, I would imagine that they should both be adjusted to the same point, am I correct?

Tonight I adjusted it to 16% on the ECU side, ignoring the transmission. Right now if I start the Jeep it runs to about 2500rpm and sticks there. If I disconnect the ECU TPS feed the Jeep starts, idles, and revs (no load) normally. I have not had a chance to test drive it like this as my dash is torn apart.

At this point I want the ECU to be spot on, I can deal with the transmission being off a bit at the moment.

If you have a Renix system that you know is in good shape could you test the voltage on both the TCU and ECU feeds of the TPS? I would like to see if you're getting the 83%/16% values that I'm thinking are correct. Also if you just happen to know the way it should be let me know. I'm going to work on this a little more tomorrow as well, I will keep the board updated on my findings.

Sequoia
 
Hey Sequoia.

I saw this discussed on a board once and if I remember correctly, the manual and automatic setups are different in that with the auto, the Renix ECU gets it's TPS data it uses to manage the engine from the TCU, while on the manual version the ECU gets throttle position straight from the sensor. Or something like that.

Anyhoo, the upshot was that the circuit/voltage behaves differently on the auto TPS than on a manual, and therefore it's not useful to compare them. Just set it as per the manual using the four-wire connector. On my '90 my base voltage is 4.76v and with the output voltage set to 3.95 volts (.83) it idles at dead-on 700rpm and shifts correctly. I'll be happy to check the voltage at the other connector if you want, but I can't do it until after I get home this evening.

:revolver
 
The FSM is wrong... somewhere there is a TSB (technical service bulletin) that gives the correct way to set the TPS....

I'm sure it's posted on the internet somewhere....
 
revolver said:
Renix ECU gets it's TPS data it uses to manage the engine from the TCU

In looking at the wiring diagrams in the FSM I cannot see this anywhere. Also if you look at the TPS you'll see the two sides of it (the four wire connector vs. the three), the manual TPS only has a three wire connector. As basic as the Renix ECU system is I doubt it's sharing any data with the TCU, mainly because you can completely cut power the the TCU without causing any issues with the ECU (I've done it).

Digger87xj said:
The FSM is wrong

I'll look for the full thing but thank you for letting me know!

Sequoia
 
revolver said:
the Renix ECU gets it's TPS data it uses to manage the engine from the TCU, while on the manual version the ECU gets throttle position straight from the sensor. Or something like that.

That is incorrect. the TCU uses the 4 place connector, the renix ECU uses the 3 pin
 
I forgot what the base and ouput voltages were on my '90 but after the math it ran and shifted best at .83. The manual I had said the value should be .82 but the shifting was a bit off at that.
 
would like to see if you're getting the 83%/16% values that I'm thinking are correct.
Sequoia, the voltage reading on the ECU side goes up as the throttle is advanced, and the voltage goes down on the TCU side. That's why the different specs in closed throttle voltage readings, on the different plugs-ins.

I can't get an accurate reading on either one of my TPS plugs, because of a constant 1/2 volt on the ground wire. This is with both the key off or on!!!???

I also get a constant 14mA draw with the key off, that's going through the ECU and TCU. The Renix was either designed this way, or it starts bleeding current as it ages.......?

Why don't you check for voltage on the ground wire, with the key off. If you've got some, that'll explain why you can't get the signal readings to coincide on both plugs.
 
In looking at the wiring diagrams in the FSM I cannot see this anywhere. Also if you look at the TPS you'll see the two sides of it (the four wire connector vs. the three), the manual TPS only has a three wire connector. As basic as the Renix ECU system is I doubt it's sharing any data with the TCU, mainly because you can completely cut power the the TCU without causing any issues with the ECU (I've done it).

Well I apologize, apparently I don't remember something correctly. I did some serious searching on this board and others last night to see if I could find where I'd read this but unfortunately I couldn't find it. The only thing I do remember clearly is that there is an actual reason the various service manuals instruct taking the readings off of the TCU connector.

Anyhoo, my daughter barfed at school this morning so I had to get out of work early to go pick her up. She's comfy and happy on the sofa watching Cartoon Network, so if you're still interested on some TPS readings just tell me exactly what readings you'd like and I'll run outside and do them. My '90 is an automatic by the way, the TPS is a year old and the engine runs pretty well I'd say.

:revolver
 
Runnin'OnEmpty said:
Sequoia, the voltage reading on the ECU side goes up as the throttle is advanced, and the voltage goes down on the TCU side. That's why the different specs in closed throttle voltage readings, on the different plugs-ins.

I can't get an accurate reading on either one of my TPS plugs, because of a constant 1/2 volt on the ground wire. This is with both the key off or on!!!???

I also get a constant 14mA draw with the key off, that's going through the ECU and TCU. The Renix was either designed this way, or it starts bleeding current as it ages.......?

Why don't you check for voltage on the ground wire, with the key off. If you've got some, that'll explain why you can't get the signal readings to coincide on both plugs.

I believe the "floating sensor ground" to be designed this way because my diagram shows a sensor ground input to the ECU. The little I know about ECU/computers tells me that for some reason the designers chose to keep sensor ground in control of the ECU and somewhat isolated from vehicle ground. Maybe this allows for more accurate voltage swing and reference measurement in certain conditions? I dunno but I've seen something like this before in an industrial PIC and I just know to measure TPS through that ground and not vehicle ground.

Dunno what connector is actually for ECU/TCU but I suspect it's the 4-plug square with only 3 wires used. Adjusting is not a big deal if the device is constructed properly and you get a good "reference" adjustment on the thing. Backprobing connectors can be hard to get a good contact and try to look for anything funky as the voltage/resistance swings across the device.

Yes, I have read/seen something about KAM or "keep alive memory" but I have no idea how much, if any Renix should draw during key-off condition? I'm kinda curious and interested about ECU rebooting and all that too so maybe I'll insert amp meter and see what my '89 shows?
 
XJXJ, I'd be interested what your current drain is with the key off. My 14mA is split between the ECU and TCU; 7mA each. I unplugged each module to check it. This seems excessive to me, I figure more in the range of 1-2mA would be normal....? (Mine is also an 89)

I don't know if the Renix has KAM or not, since it's such a rudimentary system. Maybe it does, since the ECM is constantly powered, and not switched.....?
 
The procedures are different for Auto and Manual, your FSM must be incorrect, what year FSM is it?.
I have the 1990 FSM and in the Electrical Volume section 8D p 32 there is a flow chart for testing the Auto. Trans. TPS which states input voltage=5.0 (pins D & A), output voltage=4.15 (pins B & D).
On the next page is the flow chart for the Manual Trans. TPS which states input voltage=5.0 (pins B & A), output voltage=0.85 (pins C & D).
I know that the numbers above are nominal values and adjustment of output voltage is based on a percentage of actual input voltage but I can't find that procedure right now.
 
A couple of things to look at, don´t really know the significance, but seemed unusal enough to take notice. And a few WAGS (wild assed guesses).
I believe there is a capacitor in both the TCU and ECU. There is some resistance to ground through both.
The TCU and ECU seem to have different input voltages (tested on 2 ECU´s and TCU´s), to the dual sides of the TPS (sensorS). The ground resistance in the control units (either a capacitor or a same function circuit) May be to deal with voltage spikes, in the vehicle charging system. Could just be the third leg of an amplifier also.
I check for standing voltage, the TPS grounds to vehicle ground, as a quick check for connector resistance. There is gonna be a little because of the control unit ground resistance, but should be close to the same for both control units.
One of the ground connectors (dipstick holder) on mine was crimped (corroded) and not soldered, had a good bit of resistance ( I soldered a ground from the TCU/ECU wires at the dipstick holder to the firewall and from the battery to the front clip as insurance). There is a TSB, about changing the location of the TCU and ECU ground connectors to the opposite side of the battery ground cable. Also found some resistance in some other connectors, a little here and a little there that added up.
Many of the TPS (TCU) imput voltages (measured to TPS/TCU ground) that I have heard of, are often in the 4.60-4,65 range. A 86% setting seems to work well most ways. Close to 4 volts, seems to be a good starting point, tranny seems to work well (shifts just at a touch higher RPM than the 83% setting). You can then make some very small adjustments, to accomodate the voltage imput differences on the ECU side of the TPS. I ended up with a compromise, that seems to work well (about 3.9 volts).
Do believe the voltage settings are, a base line for a variable curve for the control units. Or in other words, if they are close, the control units will make adjustments anyway. Close is good enough.
I have an extra wiring harness that I lay on the floor, when troubleshooting the wiring in my XJ. Sure makes tracing wiring, finding all of the connectors and good points to test much easier.
Have fun.
 
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