Hey guys and gals, have a problem im hoping you might be able to shed some light on. I have a megasquirt pnp, with a bmw e30 vtps conversion. When the car ignition is on and running, the vtps works correctly, the throttle position and ADC is read correctly when i change the actual throttle position. However as soon is the car is running, the throttle ADC and position in megasquirt fluctuates wildly even when the throttle is closed.

any thoughts? dont think its the tps because as i said it works correclty when the igntion is on but the car is not running. im lost....

cheers

justin

 

My first thought is a grounding problem. When the engine is running, there's a lot of pulsating current running through some of those wires.

My second thought is that the TPS has some mechanical problem in which the engine's vibration causes movement of some internal part.

 

Yeah thanks Joe. Thought maybe grounding,but as it sourcing its grounding through the ecu? then i would have expected other problems from the ecu i would have thought. Might buy a replacement one and see how it goes.

 

Where is it sourcing its grounding through the ECU? TPS should receive the 5v reference signal and the signal return wire from the ECU, and should share a ground common with the other sensors (usually on the TB or intake manifold).

 

tried grounding the body of the tps directly to the body of the car to see if it was a grounding issue, no luck. it just seems really odd that it works fine with ignition on but car not running but as soon as the car is running it fluctuates wildly.

 

i have the same problem but im using a 96 motor in a 90 miata

 

well i just checked the miata red cable with the ignition on. I'm only getting .36v. I thought i should be getting 5 volts? am i wrong in that assumption?

 

It depends on how you have everything hooked up.

If you connected the Vref pin of the MS (pin 26) to the red wire at 1N, and you connected the TPS pin of the MS (pin 22) to the green/white wire at 2L, and also assuming that these wires are connected to the correct terminals at the TPS itself, then yes, you should have a steady 5v on the red wire and 0-5v on the grn/white wire.

Disconnect the TPS and test the red wire again. If it goes to +5, then you have a problem on the TPS end. If it does not, you have a problem on the MS end.

 

Hey joe, thanks for the info.Sorry should have said that I Disconnected the TPS and had 0.36v at the red cable.

I bought the car from someone recently so will have to pull the MS out and see how it is hooked up.

Will keep you posted

 

Hey joe,

Info helped out thanks. Turns out for some reason i'm not getting the 5v from the ref wire from the megasquirt. I spliced in a 5 volt regulatore, took 12 volts from a nearby source and powered the tps with the 5 volt regulator. Worked a treat for the TPS ADC. have a range of 35 to 255 at wot. (the megasquirt apparently had the VTPS mod done to the board by diyautone, only thing i can think of is that over time something has gone amiss in the board? as all the other connections work fine, i.e. ground and signal wire.)

megatune picks up the TPS ADC a treat too. but now the throttle position gauge in megatune doesnt pic up throttle position (dont know how thats possible as id have thought the throttle position % was based on the tps ADC?). but having said that it appears that megatune only takes inputs from the TPS ADC not % of throttle so i think i should be fine without that. Anybody care to inform me otherwise? do i need throttle position %?

Justin

 

You did recalibrate I assume? I had an issue with megatune before, a power cycle of the ecu usually fixed it and the TPS gauge was working correctly again.

 

Yeah I recalibrated. Power cycle of ecu? As in disconnect battery? Or is there a reset button somewhere ?

 

No, just turn the ignition off and on again. Not sure if it's absolutely necessary, but it solved some silly issues with mine.

 

Hey Oscar. You were spot on. It's all good now and I have a fully functioning tps. Don't you just love fault finding?