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Renix CPS adjustment per Cruiser54

G

GregGA

87 Laredo Galloping Ghost
Location
Woodstock GA
87XJ/AW4/NP231 107K

I had some issues yesterday: stalled, hard restart, chugged on what seemed like 2 cylinders, restart and to 3000 rpm.

5-90 suggested a vacuum leak and I found the IAC screws loose, with some movement. Tightened them up. Thanks 5-90:thumbup:

I had adjusted the engine TPS several months ago, but figured, what the heck do it again.

I used Crusier54's method this time. I found the resistance at .7 ohms.
Good.

Checking the flat 3 wire connector, I got 4.86 volts. Using his formula,
I needed .826 volts from connector C. I had .37 and no high idle. Ah ha I said and adjusted to .82 volts. Restart, RPM to 2000 and no drop. I kept dropping the volts until I got a no high RPM start. I could only get to .58 volts.

I am curious: why is this the max voltage when his instructions call for .82?

Thanks all!

Greg in Georgia
 
According to my info you should be using the square tranny connector on an AW4, setting the voltage at B-D to 82 % of the voltage at A-D. That always worked for me, with the added note that even a little bit high setting made it stumble coming off idle, so I would set it a tiny bit below the calculated amount. I'm not sure that this was a universal trait, or just a glitch in mine, which had constant harness and connection issues, and the voltage wasn't very consistent.
 
Matthew Currie said:
According to my info you should be using the square tranny connector on an AW4, setting the voltage at B-D to 82 % of the voltage at A-D. That always worked for me, with the added note that even a little bit high setting made it stumble coming off idle, so I would set it a tiny bit below the calculated amount. I'm not sure that this was a universal trait, or just a glitch in mine, which had constant harness and connection issues, and the voltage wasn't very consistent.
Click to expand...

You can use either one. The calculation is just different. Use the flat one for engine/driveability issues and the square one for trans/shifting issues. They are independent of each other on Renix even though they're in the same sensor. Two different ribbons.

I suspect a faulty TPS.

BTW, what resistance was .7 ohms? The sensor ground circuit?
 
Cruiser54,

I sent you a PM with the driveabilty issues, so I adjusted the flat connector and the volts are no where close to .83. Why are they not
.83 or there abouts? I think I adjusted the square on last time.

I am confused, but it seems to be running in the garage ok. Will drive it tomorrow.

Thank you!

Greg

Ohms were per your write up.
 
Sounds to me like the TPS is bad on the "engine side". That's why I advocate checking both sides. If you have a driveability problem and check the trans side of the TPS, you could mistakenly believe the TPS is good when it isn't.
 
Ok, so if I'm not getting .83 on the engine side(I'll check the trans tomorrow) and the trans side is ok, I should replace the TPS? If so, go to NAPA?

Thank you!
 
Here's a dumb question: the trans square connector runs to the flat 3 wire connector and to the TPS. How does the TPS have a "bad side" if they both run to the TPS?

I am sorry, but I am just trying to gain knowledge.

Thanks,

Greg
 
There are 2 ribbons inside the TPS. One for the ECU, one for the TCU. Bust your old one open after you get a new one from Napa and you'll see what I mean.

Post a pic if you can.
 
Thank you Cruiser! The new one should then read to your specs on both the square side and the flat side, correct?

Thank you.
 
GregGA said:
Thank you Cruiser! The new one should then read to your specs on both the square side and the flat side, correct?

Thank you.
Click to expand...

Yes, it should. This is PRECISELY why the instructions were written as they are. Almosr everywhere else the instuctions advocated checking the TPS on an auto equipped Jeep at the trans connector only. I think you see now how that cold send a guy off on a wild goose chase.
 
Matthew Currie said:
According to my info you should be using the square tranny connector on an AW4, setting the voltage at B-D to 82 % of the voltage at A-D. That always worked for me, with the added note that even a little bit high setting made it stumble coming off idle, so I would set it a tiny bit below the calculated amount. I'm not sure that this was a universal trait, or just a glitch in mine, which had constant harness and connection issues, and the voltage wasn't very consistent.
Click to expand...

87 & 88 FSM said to use the flat 3 pin side of the TPS, and to use .80 and .82 Volts setting for idle respectively. The 89 said to use the square 3 pin connector using the specs you mentioned.

I found the need to test and verify BOTH SIDES!!!!!! If either one will not come close to locking in the other sides settings, the TPS needs to be replaced if the two input voltages and the two grounds are good. Both grounds need to be good and the input voltage on both grounds need to be close to 5 volts (about 4.75 V seems to be OK).

IF a setting of .82 gives a high idle, try 3 restarts to see if the idle changes. IF the idle is still high, look for a fuel leak, FPR to vacuum line, or a vacuum leak. There are all sorts (dozens!) of quite little possible vacuum leak places that yield a high idle. A stick IAC can cause a high idle (not likely in this OP case, based on his test data!!!!). A bad gound on the sensors can cause a high idle. A bad IAT, Intake temperature sensor can cause a high idle.

Setting the TPS below .82 is not a solution to the high idle.
 
GregGA said:
Here's a dumb question: the trans square connector runs to the flat 3 wire connector and to the TPS. How does the TPS have a "bad side" if they both run to the TPS?

I am sorry, but I am just trying to gain knowledge.

Thanks,

Greg
Click to expand...


Each connector has a 5 volt input from the ECU, an independent ground wire and a return output voltage wire back to the ECU. Each 3 wires, and single connector pair is connected to a separate sensor mounted inside the TPS assembly. The only connection between the two sensors inside the TPS is physical, not electrical. The two sides share a common shaft connection to the throttle assembly on the throttle body and move as a common sensor. EITHER side can bad in various ways, that lead to different symptoms and issues!!!! The sensors are carbon brush variable resistor that does wear!!!! and thus does wear out. Just like an old style radio volume potentiometer control that gets noisy near its end of life.
 
Ecomike said:
Each connector has a 5 volt input from the ECU, an independent ground wire and a return output voltage wire back to the ECU. Each 3 wires, and single connector pair is connected to a separate sensor mounted inside the TPS assembly. The only connection between the two sensors inside the TPS is physical, not electrical. The two sides share a common shaft connection to the throttle assembly on the throttle body and move as a common sensor. EITHER side can bad in various ways, that lead to different symptoms and issues!!!! The sensors are carbon brush variable resistor that does wear!!!! and thus does wear out. Just like an old style radio volume potentiometer control that gets noisy near its end of life.
Click to expand...

Well stated. He's gonna bust the old one open and post photos. I hope.......
 
If you can find a very sensitive analog meter, you can test the resistors for glitches or dead spots, either with an ohmmeter on the disconnected sensor, or with a voltmeter connected Connect the meter, and run it through its range, and watch the needle. A worn one will jump or drop on bad spots.

Unfortunately a digital meter won't do this, and even the ones with analog bar graphs, etc. probably won't respond quickly and delicately enough.
 
Well, it's been more than a week, and I finally bought a spankin' new TPS from NAPA, made in the USA. I even ran two independent grounds, one to the TCU side, one to the ECU side:.2 Ohms on each.

Input voltage to engine side was 4.87 x .17= .87.9. Set it, started it, and
right to 2500 RPM and stayed there. Just like the old TPS. I've got it down
to .68 without an idle flare on start up. I'll let it sit and see what happens.

There were really no engine issues on the old TPS, I just didn't understand why it couldn't meet spec, so I bought a new one. I was going to cut the old
one apart and post pics, put I might as well keep it as a spare:spin1: UNLESS Cruiser54 or one of the Renix guru's can figure this out:worship:
 
It is not having idle flare at .60 volts. Almost exactly like the old TPS.
That is where I am going to leave it. Trans side is about .80 of input voltage.
Oh well, I do have a new TPS:looney:
 
Sounds like you are miss adjusting the TPS to fix a non TPS problem. Check the vacuum line to the fuel pressure regulator, FPR, for any sign of a fuel leak into the vacuum hose. If you find gas, replace the FPR.

Then disconnect one fuel injector electrical input at a time, and see if the problem goes away, or if there is NO CHANGE, maybe a leaking fuel injector.

Also test the MAT, manifold air temp sensor, to see if it meets temp versus resistance specs. Any of those can cause your problem!!! My money is on the FPR or MAT from what you posted so far, assuming you did not miss a vacuum leak. But the fact that the TPS setting affects the issue, makes me thing FPR or MAT.

Check the Vac line to the MAP as well!!!
 
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