Can a throttle potentiometer be manually calibrated?

[Jetter]

A buddy who is a mechanic suggested they used to do this with trucks after changing a pot. He suggested something like disconnecting battery for a bit and hooking it back up. Then turn on key and do 5 up and downs with throttle. Turn key off again and see if it manually calibrates the new pot with the ECM.

Has anyone ever heard of this with a boat or do I just need to take to a marine shop with the computer?

[ChrisSnow]

Which ecu do you have?

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[Jetter]

I have a MEFI 5. We got the spec sheets from Marine Power and all they say is check voltages off the white and black which should output 5 volts. We get 5.01 so pretty much bang on. Then it says to check the low or idle position. This is where the "calibration" comes in. Basically the TPS has to be outputting a specific voltage in neutral. In other words the arm must be turned a very specific amount. The reading off the black and blue wires is supposed to be between 0.95v and 1.0v . We have it at 0.975 volts. Couldn't get more exact.

ECM is still reporting TPS out of range errors on sensor #2. I don't know what sensor 2 means. We are at a complete loss.

[ChrisSnow]

There is two independent pots in the unit. It's complaining about the second one. There is 6 wires IE two sets of 3 I think the signal is opposite on the second.

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[IDBoating]

I just had a very nice phone conversation with Jetter about this topic. He's off to measure signals at both ends of the cable for BOTH pot sections of the TPS. From the clues, my guess is an intermittent connection related to the second pot in the TPS.

The reason he didn't understand about the second pot in the TPS is because apparently the documentation he received from Marine Power only covers the wire color codes for one of the two sections. I got the impression he and his mechanic were basically left in the dark about the whole second section. We had a good talk about how pots are built, how the two sections relate to each other (whether in phase or opposite), how the element voltage comes from the ECU and the wiper voltage goes back to the ECU, etc. Jetter is definitely competent with a multimeter so he's going to dig in and report back on what he finds so everyone can benefit from the knowledge.

By a happy coincidence, it turns out that Jetter and his family often vacation at a lake not five miles from where we live! They rent a cabin on one of the other lakes quite close to us in our area. Hopefully they will be back soon and we'll get a chance to meet in person.

[Jetter]

Just spoke to mechanic quickly. He says computer is showing a voltage of .95 for pedal position 1 and a voltage if 1.05 on 2. Since the acceptable range for a neutral position is between 0.95 and 1.0v I'm going to assume these are too far out of range. He is not getting what I'm trying to explain to him so I am going to have to go out there tomorrow and test myself.

Question is how to get the two pots to match voltages. I have to believe pot is stable so I guess it means running new wires.

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[Jetter]

Ok so... mechanic says computer attached to ecm says sensor 1 at .96 and sensor 2 at 1.0. Both in range. Error codes still won't clear.

He is now thinking faulty throttle body motor. But the motor works when you turn on ignition. Flap moves up and down quickly like it's supposed to.

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[IDBoating]

You said the text in the error message coming from the diagnostic tool said something about "erratic". It's possible the voltage you're seeing is *generally* there, but if one of the connections to that pot section is intermittent you could be getting spurious voltages that the ECU doesn't like.

Does your mechanic have an oscilloscope? It would be really nice to actually SEE the signal coming back from both wipers. Meters give a coarse idea, but a scope is the proper tool for something like this.

Also: "ECM is still reporting TPS out of range errors on sensor #2" (your comment above) would not be caused by a throttle body MOTOR problem.

[Jetter]

I think we may have found the issue. If the part from Napa here locally does not match tomorrow, Marinepower has one and I'll have it shipped overnight.

The problem was the error codes returned by the Rincom Diacom were Throttle Position Errors. We automatically assumed given the history of the TPS sensors in these boats that it was a TPS error. Meaning the throttle position sensor behind the throttle handle. In actuality there are 4 voltages that get reported. Two from the TPS which the software calls Pedal Position Sensors and two from the throttle body itself called the throttle position sensors. As you can see from the screen captures below, the one voltage from the throttle body reads 0 volts. The other voltage reports correctly and fluctuates when you press the brass flap on the body up and own. The voltage that shows zero should be fluctuating as well.

I will update once a new throttle body is installed. Here's hoping!

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[ericinmich]

Correct, on a car and boat, the driver request is the pedal position sensor. On both, the throttle blade on the engine is attached to the throttle position sensor.

Many people still say that they are stepping on the throttle.... that went away once the cable connecting the two went away!

[IDBoating]

Yes, that rotten naming convention has caused all sorts of confusion in the past - and it's done it here again. When the industry says "Throttle Position Sensor" they should really be talking about the THROTTLE (the thing on the engine), not the user control. Yet what do they call the dual pot that senses the user control? The TPS (Throttle Position Sensor)!!!

Can you just replace the sensor on the throttle body, and not the entire throttle body (as your post suggests)?

Hopefully this will resolve the problem. How frustrating....

[dom w. forte]

They call the shifter sensor a PPS because it is hooked to the pedal in a car or truck , the ECM looks for a request for excelleration from the PPS 1& 2 and intern moves the motor on the throttle plate and looks for a signal from TPS1 & 2 to confirm that the engine is turning proper RPM per request , there redundent sensors for safety.

[ericinmich]

They call the shifter sensor a PPS because it is hooked to the pedal in a car or truck , the ECM looks for a request for excelleration from the PPS 1& 2 and intern moves the motor on the throttle plate and looks for a signal from TPS1 & 2 to confirm that the engine is turning proper RPM per request , there redundent sensors for safety.

A couple things that aren't correct in what you said... maybe nit picking, but engine control design/dev was my job for a few decades so I can't not reply!

- The pedal isn't requesting acceleration. In these system's it is requesting a throttle blade position (a non-linear lookup). In autos, it started the same way, but systems now are requesting airflow or torque, depending on the design of the controls.

- The system doesn't look at TPS1&2 to confirm that the engine is turning. They are used to confirm that the throttle actual matches throttle request. If they don't codes get set and safe modes are invoked.

[dom w. forte]

A couple things that aren't correct in what you said... maybe nit picking, but engine control design/dev was my job for a few decades so I can't not reply!

- The pedal isn't requesting acceleration. In these system's it is requesting a throttle blade position (a non-linear lookup). In autos, it started the same way, but systems now are requesting airflow or torque, depending on the design of the controls.

- The system doesn't look at TPS1&2 to confirm that the engine is turning. They are used to confirm that the throttle actual matches throttle request. If they don't codes get set and safe modes are invoked.

Agree I was only speaking in laymen terms to simplify.

[Jetter]

Happy to report boat is finally fixed! My throttle body needed replacing so it definitely was the throttle position sensor #1 in the throttle body. MarinePower was great at helping me out. They sent me a throttle body for 40% of the original price I was quoted. Then it arrived and it had the wrong wiring harness configuration. They sent a return UPS label and overnighted the new throttle body to me. Just so happens my year of boat (08 Z1) GM changed the wiring harness 1/2 way through the production year. I had 50/50 chance. They are all 6 wire. Mine was three over three and the other config is six in a row.

So to sum up if anyone has similar issues: The Rinda Diacom software which should be used by mechanics to pipe into the MEFI 5 engine will report 4 voltages in regards to throttle. It calls the redundant voltages coming from the BEI TPS (throttle position sensor potentiometer) Pedal position sensor 1 and 2. This TPS is located behind your throttle arm. It must be "calibrated" so at neutral it sends between 0.95v and 1.00v to the ECM. That is the tolerance the ECM is looking for or it will report an error and go into limp mode. In the throttle body mounted to your motor under the flame arrestor, there are two more redundant sensors in the plastic housing. The Diacom software calls these Throttle Sensor voltage 1 and 2. They should show voltages between 1 and 5 volts depending on your throttle position. If you manually move the brass flap on the body with the ignition on (but not running of course) you can see the voltages go up and down on the computer.

Hopefully nobody goes through what I just did - it's been a long two weeks. Now to get some surfing in!

Jetter