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Optimax stalls above 1200 RPM

J

JGKIII

New member
My 2001 Opti starts and idles fine. At crank the TPS fault shows briefly on the Smartcraft gauge, horns sounds momentarily and then shuts off. Advancing the throttle either in neutral or while engaged causes the motor to run extremly rough, sputter and stall above approximately 1200 RPM. It will motor around without symptoms but moving the throttle above 1.2Kish initiates it. New Racor, motor mounted gas filters, primer bulb, plugs inspected and run on a portable tanks. Same results. Will the TPS cause this problem? What should I check / eliminate to narrow down the problem?
 
Will the TPS cause this problem?
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Since everyone else is still asleep I'll try to help you. The TPS (throttle position sensor) as a rule last a long time...used is auto industry for many years w/great longevity. You may have a bad one but first disconnect the plug to it and carefully inspect it for corrosion on the pins and chafed wires in its harness. It is just a variable resistor or potentiometer. You can test it w/a digital ohmmeter. Unplug it and connect the ohmmeter to the contacts and slowly move the throttle from neutral to WOT. What you are looking for is a slow and steady change in resistance along its movement range. ANY jump or quick change in resistance means it is not working.

There is a method to test the voltage the same way as resistance w/o cutting any wires. You wrap a single strand of 16 ga. copper wire around the variable output pin and attach the plug to hold it in place. One pin is input base voltage...less than 1 volt I think. W/the key in the run position move the throttle as above and observe the voltage change. If the voltage drops to 0 in the movement it is not working. watch this test http://www.youtube.com/watch?v=C8t25GjZ6i4&feature=related
 
> It is just a variable resistor or potentiometer. You can test it w/a digital ohmmeter. Unplug it and connect the ohmmeter to the contacts and slowly move the throttle from neutral to WOT. What you are looking for is a slow and steady change in resistance along its movement range. ANY jump or quick change in resistance means it is not working.<

Excellent! So a TPS failure could account for the stalling as the throttle is advanced if I understand you and electrical theory correctly. At this point I am really stumped as to any other cause for this problem. Thanks for the guidance.
 
You need to get two fuel pressure gauges and hook one to the fuel rail and the other to the air rail. Start the engine and see what the pressures are. Should be 90PSI on the fuel rail and 80PSI on the Air rail. See what the pressures are when the engine stalls. I have never changed TPS on an optimax.
 
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