TPS short

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Trump
Experienced MS/Extra'er
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Joined: Fri Oct 15, 2010 4:41 pm
Location: Sydney,Australia

TPS short

Post by Trump »

I have fitted a MS3X (upgrade from MS2). Fitted multi TBs. Had the car running and took for quick test. Unfortunately I had not tied down the TPS wires (temporary install) and all three contacted the exhaust and melted the insulation. they then shorted on the exhaust and the engine shut down.

Now the engine will not start and I can not get the TPS to calibrate. When cranking. the pulse width goes to over 60 but no fuel is injected.

I assume I have managed to cook the board. It is not the 5v ref as IAT, Coolant and MAP all seem to be working OK.

I have tested the TPS itself and it appears OK.

Any suggestions on where to look?

Attached is a log of an attempted start.
Triumph TR3A. MS3X, IBT, Fully Sequential Injection, Wasted spark, 60-2 crank wheel.
jsmcortina
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Re: TPS short

Post by jsmcortina »

Measure the voltage at the TPS plug - is the 5V there?

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DaveEFI
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Re: TPS short

Post by DaveEFI »

There is a polyfuse - F2 - between Vref and the DB37, so check the 5 volts at DB37 pin 26.
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Trump
Experienced MS/Extra'er
Posts: 232
Joined: Fri Oct 15, 2010 4:41 pm
Location: Sydney,Australia

Re: TPS short

Post by Trump »

Well, tried both suggestions and found that there was no Vref at the TPS.

I fitted a spare V3 board (this is a MS3X) that I had and loaded firmware 1.3.1 and tried again. No luck, Throttle position still showed 32% and would not calibrate. If there was damage in the TPS circuit I would have thought that a change of board would have fixed it. Could the Flood Clear Mode setting cause no fuel to be injected? It is set at 70%.

I checked power at the CPU socket and found V ref between pin 1 & 2, 20 & 19, 31 & 32. Also had V ref at pin 26 on the DB37. AD3-1 showed 1.4V regardless of TPS (Stim-old style) position.

This all said to me that I had a wiring problem but a continuity check showed no problems. Also I would have thought that the engine would still start, even without a TPS. Is that correct?

Remember that this all started when the insulation on the three TPS wires was melted on the exhaust and all shorted. The engine stopped dead.
Triumph TR3A. MS3X, IBT, Fully Sequential Injection, Wasted spark, 60-2 crank wheel.
DaveEFI
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Re: TPS short

Post by DaveEFI »

I can't see the input circuit being damaged by this short, so if the 5 volt supply is there the problem would most likely be in the TPS or wiring to it. If it is possible, probe pin 22 or R9 with a DVM and measure the voltage to ground while the throttle is slowly opened. It should smoothly increase from about 0v to 5v.
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Trump
Experienced MS/Extra'er
Posts: 232
Joined: Fri Oct 15, 2010 4:41 pm
Location: Sydney,Australia

Re: TPS short

Post by Trump »

After reviewing all the data, I came to the conclusion there was a problem between the TPS and ECU. Continuity check on loom showed no problems. When removed, the TPS tested OK. However, when removed I found that there was an issue with the leads into the TPS itself. I found that you could cause he connection of the ground lead to fail. This is a new good quality unit. These connections are sealed in the TPS housing. With a bit of jiggling I could get the TPS to function correctly. That problem is now solved. Now a new issue and new thread.
Triumph TR3A. MS3X, IBT, Fully Sequential Injection, Wasted spark, 60-2 crank wheel.
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