Bucking

[Grace2]

I'm sorry that my first post has to be a question, but I've searched and had only one person on here with a similar problem.

My 93 Ranger 3.0 has developed a very annoying problem this month. I was coming down a hill one day and heard a slight ping/rattle come from my engine. It has now turned into a buck/missfire/stumble but ONLY on deceleration. I have no drivability issues in acceleration. The problem happens only when I take my foot off the gas. I've got to put the clutch in or put the shifter in neutral when coming to a stop or slowing down. Gas pedal down and no problems. Take my foot of the gas, and my engine bucks. I've replaced my cap,rotor,plugs,air filter and ran fuel injector cleaner to no avail. My old plugs only had some white residue(lean condition?)

I want my good old reliable Ranger back. I'm afraid that I'm doing some damage to the engine. Any help or suggestions would be greatly appreciated !

Thanks,
Grace

 

[Rearanger]

Does your truck have a TPS Throttle Position Sensor?

 

[Grace2]

Yes, it does. I hope that's the problem. Funds are a wee bit tight being a single Mom; so I don't want to start throwing money at sensors. I also forgot to mention that my Ranger doesn't have a CEL popping up.

Thanks. I'll report back soon if the TPS replacement helps.

 

[Rearanger]

The TPS has a zero signal adjustment that tells the computer when the throttle plate is closed and to initiate idle. If that adjustment is off or the TPS has a dead spot then the engine may be hunting for idle. I'd check the adjustment as well as the TPS. You'll need an OHM meter.

 

[Bob Ayers]

The TPS has a zero signal adjustment that tells the computer when the throttle plate is closed and to initiate idle. If that adjustment is off or the TPS has a dead spot then the engine may be hunting for idle. I'd check the adjustment as well as the TPS. You'll need an OHM meter.

She will actually need a volt meter, not an OHM meter. There are 3 wires going to the TPS. With the KEYON, measure the voltage between the BROWN/WHITE and GRAY/WHITE wires. The voltage should be close to 950mV,
with the throttle closed.

 

[Rearanger]

Bob, your test tests the connector side of the TPS. For adjustment of the idle position (throttle closed) would it not use an Ohm meter on the TPS side connector to measure continuity off/on? Your test seems to confirm power to the TPS, but the connector side does not determine idle position. My experience with TPS testing is with non-Ford, but the tests should be pretty much the same.

 

[Bob Ayers]

Bob, your test tests the connector side of the TPS. For adjustment of the idle position (throttle closed) would it not use an Ohm meter on the TPS side connector to measure continuity off/on? Your test seems to confirm power to the TPS, but the connector side does not determine idle position. My experience with TPS testing is with non-Ford, but the tests should be pretty much the same.

No, the Ford TPS is a potentiometer, and as the throttle is opened the voltage will increase approaching 5V. So, the
correct way to set the idle position is to measure the wiper voltage with respect to GND, and it should be 950mV.

 

[Rearanger]

the Ford TPS is a potentiometer,

Yes, they're all potentiometers.

and as the throttle is opened the voltage will increase approaching 5V.

Yes, increase from zero (idle position) to 5v, WOT.

the correct way to set the idle position is to measure the wiper voltage with respect to GND, and it should be 950mV.

That would be with the connector hooked up, KEYON, how would she measure that, with a pin in the back of the connector? There should be an instruction in the Ford manual that says at what throttle position the voltage is zero. There'll probably be a throttle plate adjustment screw that is factory set with a clearance measurement. I guess 950mv on a Ranger is as close to zero or no continuity on an Ohm meter as they get.

Anyway, we're probably confusing the OP so full TPS test instructions from the manual would help and I don't have one to quote from.

 

[Bob Ayers]

Yes, they're all potentiometers.



Yes, increase from zero (idle position) to 5v, WOT.



That would be with the connector hooked up, KEYON, how would she measure that, with a pin in the back of the connector? There should be an instruction in the Ford manual that says at what throttle position the voltage is zero. There'll probably be a throttle plate adjustment screw that is factory set with a clearance measurement. I guess 950mv on a Ranger is as close to zero or no continuity on an Ohm meter as they get.

Anyway, we're probably confusing the OP so full TPS test instructions from the manual would help and I don't have one to quote from.

No, the 950 mV is there for a reason. If it was set a 0V, there would be a hesitation when the throttle was cracked open. A voltage measurement is more accurate, because this is what the comparator in the PCM measures, not OHMS.