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djkeev
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Location: Reading Pennsylvania
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MarkWard
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 Posted: Thu Apr 15, 2021 6:14 am Post subject: Re: Testing TPS in real time |
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I think the ohm meter might bypass the switch. If you know what the switch is doing, completing a ground or routing power, you could safely add an LED to one leg I imagine.
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djkeev
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Ronzo_volvo_guy
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Joined: December 31, 2015
Posts: 194
Location: Connecticut
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| Posted: Thu Apr 15, 2021 7:58 am Post subject: Re: Testing TPS in real time |
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dj;
Mark has it (partly) right...it is not good to apply an Ohm Meter (or other continuity checking device, which will have an internal power source) to a powered up system (which obviously has its own power source)...at best, the two power sources wont play nice together and the system wont function normally, at worst, damage to the system under test could result (and that is clearly the LAST thing you want!). ...but adding an LED is not the best thing either, as it draws current to light (admittedly not much), but which could still affect the circuit under test, and that is baaad in the world of testing...
...but by pointing out the fact that this input is in a 5V circuit, you have also given your own solution!
Don't check for a Closed Switch (with an Ohm Meter) but check for an Open Switch (with the Volt Meter function!). When the switch is Closed, it will not (CANNOT by definition!) have voltage across it...when the switch is Open, you will measure the Voltage which the active control circuit is applying to the circuit (and which the switch is an input to). Connecting a quality (high impedance Volt Meter, which will highly unlikely affect the circuit under test at all!) cannot cause damage either...(wire it in carefully such that test leads can't pop off or short, from engine vibration, but that is a separate issue of careful test implementation).
I do need to add that if you check the switch function when activated by way of gas pedal, but with engine off (which takes into account any linkages along the way), I don't see much advantage to testing it "real time" with engine running (unless you suspect an intermittent function or condition).
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Wildthings
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Joined: March 13, 2005
Posts: 50338
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| Posted: Thu Apr 15, 2021 8:43 am Post subject: Re: Testing TPS in real time |
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| Set your meter on amps and put it in line with one of the leads to the TPS. Shouldn't affect the output reaching the ECU from the switch or otherwise hurt a thing. |
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a2wolfsburggli
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Joined: October 30, 2018
Posts: 279
Location: WI
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| Posted: Thu Apr 15, 2021 8:48 am Post subject: Re: Testing TPS in real time |
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Alligator clamps and a test light or amp meter in line should do just peachy while running.
Connect up. Start, idle, go to back, trip TPS with a pick or small screw driver, look at the amazing results you've gotten.
Easy peasy.
The mechanical actuation can be checked without the van running.
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MarkWard
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Location: Retired South Florida
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| Posted: Thu Apr 15, 2021 9:09 am Post subject: Re: Testing TPS in real time |
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I believe the reason for testing on the road is to account for real world testing.
After all these years, the throttle plate bushings are worn as well as the OE switch. I recall the spec is .004" throttle movement before the switch disengages. Thats a really tight clearance to attain on a worn throttlebody switch combination.
When the engine is at operating temp as coming off the highway, there's likely enough expansion and play, that the throttle switch may not sense closed throttle adjusted to .004". An automatic may also not always return to the same spot. So, it makes sense to have a way to "see" going down the road.
So, if the switch is passing 5 volts, then I like the idea of a grounded led up front vs trying to extend my meter leads. You'd connect to the switched side of the switch.
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djkeev
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skills@eurocarsplus
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Joined: January 01, 2007
Posts: 16863
Location: sticksville, ct.
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| Posted: Thu Apr 15, 2021 10:46 am Post subject: Re: Testing TPS in real time |
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if you want real world data i'd use a scope
https://www.picotech.com/products/oscilloscope
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4Gears4Tires
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Joined: October 08, 2018
Posts: 3028
Location: MD
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| Posted: Thu Apr 15, 2021 10:53 am Post subject: Re: Testing TPS in real time |
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Have you seen the multimeter scopes on Amazon? I keep thinking about getting one but then I realize I am not too great with electrical engineering so why am I going to buy a tool I don't really understand how to use... https://www.amazon.com/Oscilloscope-Multimeter-LIU...amp;sr=8-3
But they look neat.
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MarkWard
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Location: Retired South Florida
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| Posted: Thu Apr 15, 2021 11:17 am Post subject: Re: Testing TPS in real time |
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Unplug the harness and start the engine. With your meter on dc volts, and the meter grounded, probe both terminals in the harness, the one from the ECU should read 5 volts. Shut the engine off. The opposite pin is the one you’d connect an LED to. The led would be grounded on one leg. With the harness reconnected at idle, the led should be lit. When you open the throttle the led should go out. At full throttle the LED should light. I would get this working before you extend it up front. I’ve never done this and am basing this based on the above post referencing the 5 volts.
Never probe an ECU harness with a 12 volt testlight. It’s possible to damage something due to the draw of the filament. This goes for all ECUs. I have a couple LED test lights just for this purpose. I’m old school and prefer working with test lights vs meters when possible.
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djkeev
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zoti
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| Posted: Sun Apr 18, 2021 12:27 am Post subject: Re: Testing TPS in real time |
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| Our up and coming idle control unit will be able to give indication of TPS position while the engine is running. |
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djkeev
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