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SOHC - 2.3L & 2.5L Lima Engines Discussions and Topics specific to the Lima 4 cylinder engines

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Old 10-24-2016
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OK - My Grandson and I are working on his '97 Ranger, 2.3 SOHC, MT w/AC and PS. Problem is rough high idle, especially at gear change. Have checked the timing, cleaned T/B (replaced gasket), AIC (replaced gasket), EGR (replaced gasket), replaced Air Filter, Fuel Filter and O2 Sensor. Unable to find any vacuum leaks (with propane). EGR valve opens with vacuum pump attached. Sometimes throws a P1121 code. What are we missing?
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Old 10-24-2016
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P1121 is "Throttle Position Sensor Inconsistent with Mass Air Flow Sensor"

With a carburetor air flow through the carb sucked gasoline out of the Jets, the Jets were sized to get as close as possible to the 14.7:1 air:fuel ratio needed for a gasoline engine.
And a carb also had an accelerator pump, when you pressed down on the gas pedal the accelerator pump would squirt some extra gasoline into the carb throat because extra air was added when throttle opened and the Jets would take a second or two to catch up.

Fuel injection doesn't use Jets like a carb did so air flow into the engine needs to be monitored, that is done by the MAF(mass air flow) sensor.
Ford MAF sensor is a heated wire, as air flows past it the wire is cooled, how much it is cooled tells the amount of air flowing.
Fuel injection computer uses that MAF data to add the correct amount of gasoline to get 14.7:1 ratio.
O2 sensor is used to fine tune the 14.7:1 ratio by "reading" oxygen levels in the exhaust, computer adjusts "Fuel Trims" based on O2 sensor data
FYI: 14.7:1 is a WEIGHT ratio, 14.7 pounds of air to 1 pound of gasoline, or 14.7 ounces of air to 1 ounce of fuel, not a volume ratio

The TPS(throttle position sensor) is like the accelerator pump, TPS tells computer when driver steps on the gas pedal so it can add extra fuel so there is no delay from when you open throttle plate and MAF reads more air(like the delay in the Jets).

P1121 means either the MAF sensor is dirty, you can clean MAF sensor wire with electronic cleaner, NOT carb cleaner.
Or TPS is showing the wrong voltage for the air flow MAF shows.

TPS is on opposite side of upper intake from throttle cable linkage
It will have 3 wires
Top wire will have 5volts
Center wire will have .69 to 4.8volts depending on throttle position

Get a sewing pin and volt meter
Turn key on, engine off
Use pin to piece center wire
Ground meter and test pin voltage
.69 to .99 volts should be seen, under 1 volt with throttle closed
Now open throttle slowly, voltage should slowly and steadily go up, no jumping or dropping.
At WOT(wide open throttle) you should see above 4.5volts, 4.5-4.9 volts
TPS is like a light dimmer or volume control, a variable resistor, so can wear out, jumping or dropping volts means replace TPS

MAF is a main sensor, so that would be where I would start, clean it
Google: Clean MAF sensor

Easy vacuum leak test is to warm up the engine and let it idle, then unplug the wires on the IAC(idle air control) Valve, IAC Valve will close and idle should drop to 500, or engine may even stall, either is good it means no vacuum leaks.
If idle stays at 700 or higher there is a leak

Last edited by RonD; 10-24-2016 at 09:51 PM.
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