98 4.0 Ranger cuts out for a second.

[cookieboy_03]

Hi all!

I have a 1998 Ford Ranger XLT 4.0 5 speed with 112k miles, that cuts out for a second at cruising speeds of around 50-60 mph under light throttle on level ground.

The whole truck jerks, like the engine has quit for a second and then restarts or something. Its kinda scary on slick roads. I have replaced the coil pack, plugs, wires, and I think the fuel filter, but may replace it again to make sure. No CEL. I shall check the fuel pressure, but doesn't seem to bog or anything under load, takes throttle well.

Been doing this for a while, but seemed like on this very cold January day today that it was worse. It did this randomly three or four times in a span of 10 miles or so.

But believe it has done it on hot days too.

It runs fine otherwise, and doesn't seem to do it when under load or at any other speeds.

Any ideas would be much appreciated!

 

[nitrofan1]

Does it seem like an engine stumbling or loss of power (voltage)? Being OBD II have you have a scan tool diagnostic ran yet? Even though there may not be a service engine light on a scan tool will show a lot of information on the current state of the truck: voltage, injector pulse etc.....

 

[Andy D]

It sounds like a bad connection to me. The cold shrinking stuff isnt helping . I would start at the battery. Just a WAG, clean up the contacts on the fuel pump relay. I wouldnt start replacing parts. I think it is a bad connection

 

[TwoTon]

I know you aren't getting codes for it(when you almost always will/should), but have you checked your oxygen sensor plugs? trace the wires back from the oxygen sensors to the plugs and make sure it's a TIGHT fit... had a loose connection once and my motor would hesitate all the time. plugged it in and she ran like a top.

 

[RonD]

The only couple of fuel issue that would fit, one would be the injectors being shut off then turned on, a fuel supply issue(pump or filter) would tend to last longer.
All the fuel injectors have 12vDC power when the key is on, each injector is activated by grounding it, the engine computer(PCM/EEC) grounds the injector for the period of time it wants it to open.
So either the power(12v) is being intermittent or the EEC ground is, grounds near the EEC would be where I would look.
The other thing could be the Throttle Position Sensor(TPS), this tells the computer how much fuel to give each cylinder, i.e. the position of the gas pedal.
The TPS is like an old style light dimmer, you rotate the knob to give the light bulb more or less power, if you rotate the knob to a now dead spot light can flicker or go off until you move knob slightly one way or the other.
The TPS is very easy to test with a volt and/or OHM meter.
http://www.therangerstation.com/Magazine/winter2009/throttle_position_sensor.htm
You rotate the throttle(TPS) with meter hooked up(engine off), you are looking for dead spots or jumps in voltage or OHMs, it should be a smooth increase or decrease, no sudden jumps or drops, rotate it very slowly.
Dead spots or "weak" spots occur at your average gas pedal position, just wear and tear.
The dead spot makes the engine computer think your foot is off the gas, and on fuel injected engines if RPM is above 1200 and you take your foot off the gas the computer cuts fuel completely until RPM drops to 1000-1100RPM and then restarts injectors for idling, this saves on gas while coasting.


There are only a few things that can cut spark while driving, obvious thing is the power and control wires to the coil, also the coil's ground.

The engine computer "knows" engine is turning over(starting) or running from a signal from the Crank Position Sensor(CPS or CKP), each rotation of the crank sends a signal to the computer, if signal stops then spark, and fuel injectors in some cases, are stopped until signal returns, the sensor itself rarely "breaks", but the 2 wires going to it are very exposed, they run from the wiring harness on top of the intake down past the t-stat housing around the front of the engine to the sensor next to the crankshaft pulley.
The CPS generates AC current when "tab" on crank passes it, this is a weak signal to start with so any slight defects in either wire can drop it below the EECs ability to detect it.
T-stat replacement, water pump replacement pretty much any engine work can damage one of these two wires, these are also easily tested with an OHM meter, there is no power in these wires even with key on, the the CPS generates its own power from the spinning of the crank.
You hook up the OHM meter and then move the wires around, see if the meter changes.