2004 explorer won't rev. idles good

[cjben]

Not even sure what to check for.2004 4.6 140,000 miles. No check engine light and no codes stored. Engine starts up great,idles good,maybe a little rough but not bad. When you step on the gas,even floor it,the rpm's jump to 1200 for a second then back to idle speed even though my foot still has the pedal on the floor. Keeps doing this as long as the pedal is pushed down. Of course it is totally undriveable like this. Any help would be great!!

 

[imp]

Not even sure what to check for.2004 4.6 140,000 miles. No check engine light and no codes stored. Engine starts up great,idles good,maybe a little rough but not bad. When you step on the gas,even floor it,the rpm's jump to 1200 for a second then back to idle speed even though my foot still has the pedal on the floor. Keeps doing this as long as the pedal is pushed down. Of course it is totally undriveable like this. Any help would be great!!

@cjben If the 4.6 uses "drive by wire" throttle body (4.0 does, but not sure of 4.6) there may be something wrong with the throttle body mechanism. Should throw a code, however. The throttle plate is driven by a small electric motor, opened by the motor, closed by a spring load, through a gear train. If a gear broke, or jammed at a certain point, it could account for the throttle not opening properly.

If you remove the inlet air rubber duct from the throttle plate, you will see the plate inside the opening, and can push it open with your finger. It should move freely, all the way to full open, and return almost closed, but not quite, by the spring load. At closed position, you will see if you look very closely, it closes down with about 1/4-inch of gap. You can push it fully closed to close that gap, and it should then spring back itself to 1/4-inch. That provision allows the PCM to "prove-out" operation of the throttle and Throttle Position Sensor. Each time the key is turned to ON, PCM momentarily pushes the plate closed and allows re-open, while checking TPS output.

If you have a cable driven throttle plate, cable from the gas pedal, check that the cable is operating the throttle plate. It may be loose, broken, fallen off, or something. imp

 

[cjben]

@cjben If the 4.6 uses "drive by wire" throttle body (4.0 does, but not sure of 4.6) there may be something wrong with the throttle body mechanism. Should throw a code, however. The throttle plate is driven by a small electric motor, opened by the motor, closed by a spring load, through a gear train. If a gear broke, or jammed at a certain point, it could account for the throttle not opening properly.

If you remove the inlet air rubber duct from the throttle plate, you will see the plate inside the opening, and can push it open with your finger. It should move freely, all the way to full open, and return almost closed, but not quite, by the spring load. At closed position, you will see if you look very closely, it closes down with about 1/4-inch of gap. You can push it fully closed to close that gap, and it should then spring back itself to 1/4-inch. That provision allows the PCM to "prove-out" operation of the throttle and Throttle Position Sensor. Each time the key is turned to ON, PCM momentarily pushes the plate closed and allows re-open, while checking TPS output.

If you have a cable driven throttle plate, cable from the gas pedal, check that the cable is operating the throttle plate. It may be loose, broken, fallen off, or something. imp

yes,it is dbw. thanks for the info. I will check it out tomorrow.

 

[TechGuru]

If its idling good it might be the sensor at the pedal and not the TB actuator.

 

[imp]

If its idling good it might be the sensor at the pedal and not the TB actuator.

@TechGurru Good Point! Ford did a lot of homework, beyond the Japanese cars which ran away throttle and wound up with quite a few piling up. Ford uses a variabler double-resistance in parallel and programs the PCM to look at the voltage balance between the two wipers. If it ever fails to go in the same direction, it shuts down the engine, possibly to idle first with "Forced Engine Idle". If that happened, there would be absolutely no throttle response, but cj said it went as high as 1200 rpm. There are several codes throwable for pedal sensor failure.

I got the forced engine idle once, while sitting in my shop, fortunately. Gas pedal did absolutely nothing, started and idled normally. imp

 

[TechGuru]

Since mine is a normal throttle cable I don't know much about these and don't want to, lol.

 

[imp]

@TechGuru Don't blame you one bit. Add to the complexity this: in 2008, all vehicles sold new in the US MUST incorporate "Permanent Digital Trouble Code" ability. This sets DTCs which cannot be erased. Only the vehicle itself can clear them, after it has had the cause for the codes repaired. So, what happens with those multitude of questionable codes and/or intermittent, near-impossible to repair issues? Or some like, "Forced Engine Shutdown"?

I'm thinking of going back to carburetor btechnology. imp

 

[cjben]

well,I checked the operation of the throttle body butterfly. it opens and closes freely and shuts and opens a little as it should when the key is turned on. Any other tests I can do? Today for whatever reason,the engine will rev to about 1800 before it stops revving,idles rough then dies. starts right back up and idles fine after that. Thinking it could be a something clogged in the exhaust? how hard is it to remove the o2 sensors to check and see if it runs better?Where do they disconnect from the wiring harness? really thinking about drilling a hole in the exhaust pipe to see if it runs better,looks easier then taking o2 sensors out. lol

 

[imp]

well,I checked the operation of the throttle body butterfly. it opens and closes freely and shuts and opens a little as it should when the key is turned on. Any other tests I can do? Today for whatever reason,the engine will rev to about 1800 before it stops revving,idles rough then dies. starts right back up and idles fine after that. Thinking it could be a something clogged in the exhaust? how hard is it to remove the o2 sensors to check and see if it runs better?Where do they disconnect from the wiring harness? really thinking about drilling a hole in the exhaust pipe to see if it runs better,looks easier then taking o2 sensors out. lol

@cjben If the 4.6 is similar to the 4.0 setup, which I expect it likely is, there are two cat converters each having an HO2S at their inlet and outlet. The harness is secured by plastic and rubber pieces inserted in holes in cast-on ears above the exhaust system, above the crossmember and there are various metal heat shields in the way. My hands looked like hamburger by the time I got all 4 disconnected. Even thought about lowering the rear crossmember and mount to get at them, but that would only give one inch, at which the driveshaft would rest on another crossmember which holds up the gas tank. Shaft would have to come out, I opted for getting the supporting pieces loose and pulling the connectors downwards. I replaced all 4 sensors at 153K, they were original.

It seems unlikely that both cats would clog equally, unless over really high mileage use. If one clogged more first, exhaust gas backup should throw a too rich code, as the downstream sensor saw too little volume. What might be tried is to stick two pressure gauges in place of the oxygen sensors on one cat at a time, and see how much pressure drop is occurring across the cat. It ought to b e very little. That's pushing the limit a bit, sorry.

Did you try cycling the T.B. with it opened up, key on, by depressing the gas pedal, or only observe the close-reset? imp

 

[cjben]

I will try cycling the TB with it opened up,depress the gas pedal,key on tonight when the wifey comes home to help. But if I remember correctly,the throttle plate wouldn't move by hand as long as the key was on. I will do it again and see for sure what it does. Wish there was a way for the common person to operate the throttle on these damned dbw systems from under the hood like NORMAL vehicles!!

 

[cjben]

ok,took me longer then I thought to get back to work on the explorer. I think the throttle motor is working as it should. I had my son work the throttle while I watched the throttle body,seems to work as it should. Can hear the motor running and see the butterfly moving when he moves the gas pedal. Not real sure what to check next.

 

[cjben]

Any other suggestions? really need to get it fixed and sold.

 

[imp]

Any other suggestions? really need to get it fixed and sold.

@cjben

We might have missed one important thing. Unless checked for codes using a "CAN supported" code reader, you would have missed ABS codes. The ABS Module generates it's own codes, separate from the PCM. Check for ABS code and I suspect you may find "Forced Engine Idle". This is thrown in the case of failed ABS Module. imp

 

[TechGuru]

FYI, ForScan pulls ABS codes and even does tests and ABS pump bleeding.

 

[imp]

FYI, ForScan pulls ABS codes and even does tests and ABS pump bleeding.

@TechGuru

So I've heard, but I still haven't figured out what-all I need to use it! Computer illiterate. imp

 

[cjben]

how can I tell if my code scanner is can supported? I have an actron obd2 autoscanner cp9175. If it isn't can supported,is there another way to test for ABS codes?

 

[imp]

how can I tell if my code scanner is can supported? I have an actron obd2 autoscanner cp9175. If it isn't can supported,is there another way to test for ABS codes?

@cjben
It appears CP9175 as originally sold did not view ABS codes. It can be determined whether it was updated with C19D software, which enables CAN protocol. Follow below procedure.

CP9175 OBD II AutoScanner
The most current software version is C19D. This software version is compatible with OBD II and CAN vehicles up to the present day

To determine the software version in your tool, follow these steps:

1. Plug the CP9175 into an OBD II vehicle and turn the key to the ON position
2. From the Diagnostic Menu arrow down to System Setup and press ENTER
3. Arrow down to Tool Information and press ENTER

I have an Actron 9550 which led me on a wild run-around, simply because it did not read ABS, which I didn't know, and assumed there were no ABS codes. In fact, the damned ABS Module was shutting down my vehicle! imp

 

[cjben]

@cjben
It appears CP9175 as originally sold did not view ABS codes. It can be determined whether it was updated with C19D software, which enables CAN protocol. Follow below procedure.

CP9175 OBD II AutoScanner
The most current software version is C19D. This software version is compatible with OBD II and CAN vehicles up to the present day

To determine the software version in your tool, follow these steps:

1. Plug the CP9175 into an OBD II vehicle and turn the key to the ON position
2. From the Diagnostic Menu arrow down to System Setup and press ENTER
3. Arrow down to Tool Information and press ENTER

I have an Actron 9550 which led me on a wild run-around, simply because it did not read ABS, which I didn't know, and assumed there were no ABS codes. In fact, the damned ABS Module was shutting down my vehicle! imp

 

[cjben]

ok,my scanner does have the 19d software. There are no transmission codes in the scanner. Do I need to do something different with the scanner to get tranny codes to show up?

 

[cjben]

I meant ABS codes,not tranny codes