Taurus Car Club of America : Ford Taurus Forum - View Single Post - only runs in acceleration mode
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post #1 of (permalink) Old 01-03-2019, 03:10 PM Thread Starter
ddan
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Join Date: Dec 2018
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only runs in acceleration mode

'88 Vulcan 6 won't start or run without pumping the gas pedal. Engine dies when pumping is stopped.

Tried thickening the TPS drive tang with layers of Mylar tape which increased the idle TPS voltage 40% (without increasing the throttle angle--more gas without more air, theoretically). No effect. Still had to be pumped.

Verified continuity from TPS plug to 60 pin computer plug.

Would not start with TPS electrically disconnected. Would not start with TPS electrically connected but mechanically disconnected (unmounted). Would not start unmounted with fabricated plate to hold TPS wiper in idle position or wiper held in higher-than-idle position. (Also tried spare TPS.)

Test light connected to one injector plug blinks at same frequency as spark when gas pedal is not moving (cranking with starter). Test light stays on while gas pedal is going down.

Fuel pressure measures 40psi. Removed all injectors and tested them at low pressure (with aftermarket pump designed for carbureted engine): All squirt fine stream.

Bad MAP?

It seems like the injectors have a fixed on-time regardless of throttle position--unless the TPS signal is increasing--and this on-time is too short for the air coming in, even at idle. Or the on-time is not fixed, but always too little for the air (lean). How big of an air leak would there have to be to negate a 40% increase in idle fuel request?

Meanwhile, engine runs fairly smooth while pumping the pedal. Fuel seems to build up (in manifold) sometimes so that engine can run for a couple seconds without pumping. Runs longer if throttle is closed during this time. Holding throttle open during this 2 second run-on makes engine bog (lean out).

Verified spark in all 6. Compression is 150 +/- 2.5 psi in all 6. Valve timing checks out with air pumped into spark hole. (Probably wouldn't get 150 psi if it was wrong anyway.) No evidence of fuel leakage into fuel pressure regulator.

Again: Bad MAP? Air leak? Senile computer? I presume air in the fuel rails would quickly get flushed back to the tank or blown into the cylinders (no need for bleeding)?
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