**URGENT HELP** engine revs up to 1200, then down to 1000, then below

[azrangerman85]

I have no check engine light, and this happens mostly in idle now this week. My truck is a 3.0 Auto ford ranger 1998 4wd. The engine revs at 1000 which is its normal idle, it goes up to 1200, then down to 1000, and then suddenly it will randomly drop below 1000, almost stalling then suddenly it decides to rev back up , and go back to 1000. My air intake sensor is fairly new, my throttle sensor is fairly new, Whats happening? Im probably at 3500-4000 since my last oil change . I dont appear to have any vacuum leaks. This is scary.... I did have a corroded battery terminal , my battery is 3 years old and is due for a change but my alternator reading is at 14 volts consistent while running, on the battery terminals. Im so confused by this , there is no check engine light. When Im driving at 40-50 miles per hour nothings wrong, and suddenly I feel a yank, like the engine wants to bind or its like a jerk /skip. What the hell is happening?

 

[franklin2]

Have you cleaned the throttle blade area and the idle air control valve and it's passages? Sounds like the idle air control valve may be sticking but I would try cleaning that area and the valve first.

 

[azrangerman85]

I have a brand new IAV , I found a tiny bit of gasoline in the vacuum line boot to my fuel pressure regulator. would that stall my truck?

 

[Dirtman]

I have a brand new IAV , I found a tiny bit of gasoline in the vacuum line boot to my fuel pressure regulator. would that stall my truck?

Unless its a Motorcraft brand IAC valve it's probably faulty out of the box. And as for your second question, yes. There should be no gas in the vacuum line from the FPR. The presence of gas there means the regulator has failed. That vacuum line is only there so that when the regulator fails it leaks into the engine and not ON the engine. Gas spraying inside the engine = OK. Gas spraying onto the engine = BAD.

 

[Bgunner]

Idle should be 700-850 rpms btw, the a/c compressor kicking on and off will also change the idle speeds but no where near as bad as you say you are getting.

Unplugging the iac valve should result in a drop of rpms and potential stall the engine. If it does not drop or stall then the iac is sticking and needs replacing. If memory serves it should drop to around 500 rpms.

 

[adsm08]

That vacuum line is only there so that when the regulator fails it leaks into the engine and not ON the engine.

No, the vacuum line is the throttle input to the regulator. Low vacuum to the regulator (WOT) makes high fuel pressure. High vacuum (idle) lowers the pressure.

 

[Uncle Gump]

Good chance you have more then one problem... but you have to start with the fuel pressure regulator. As adsm08 stated.... the FPR will vary fuel pressure based on engine load. The FPR does this with the engine vacuum line attached to the port. At no time should there be fuel in the vacuum line. If there is fuel in the line... the FPR is bad... and needs to be replaced.

Start the repairs by replacing the FPR... then see how it runs. If the idle is still wandering.... I would first check for vacuum leaks.

 

[55trucker]

I have no check engine light, and this happens mostly in idle now this week.

Is this situation occurring open loop or closed loop?
The PCM will not set an idle rpm code unless the rpm is more than 300 rpm out of range and stays that way for at least 45 secs. So if the rpm is *hunting* continually passing thru the proper rpm range a code will not set.

 

[Rummie]

I have no check engine light, and this happens mostly in idle now this week. My truck is a 3.0 Auto ford ranger 1998 4wd. The engine revs at 1000 which is its normal idle, it goes up to 1200, then down to 1000, and then suddenly it will randomly drop below 1000, almost stalling then suddenly it decides to rev back up , and go back to 1000. My air intake sensor is fairly new, my throttle sensor is fairly new, Whats happening? Im probably at 3500-4000 since my last oil change . I dont appear to have any vacuum leaks. This is scary.... I did have a corroded battery terminal , my battery is 3 years old and is due for a change but my alternator reading is at 14 volts consistent while running, on the battery terminals. Im so confused by this , there is no check engine light. When Im driving at 40-50 miles per hour nothings wrong, and suddenly I feel a yank, like the engine wants to bind or its like a jerk /skip. What the hell is happening?

Very similar problem resolved when I moved heater/ac selector OFF defroster. Seems it uses ac compressor from time to time. Stalling--I got nothing.

 

[azrangerman85]

I discovered my problem . My Fuel Dampener in my 1998 3.0 4wd , it is leaking fuel through the diaphram into the vacuum port/ line . Im now in a a jam. SOB's dont make the part anymore!! I ordered one that said it was for my truck but when I went to hook it up , it has a threaded end and my hard fuel rail line has a ford spring lock connector. Now Im trying to figure out if I can use an inverted female union to connect another spring lock port to then connect the hardlin spribglock . I need help urgently on what parts to use or change . What a SOB of a problem because these moron companies dont make such a simple part . I bought part FDP20. the original part FDP22 is no longer available. I think this is a 3/8 threaded male end ( it has a concave tip for a flanged union ( inverted??)

 

[azrangerman85]

saved more photos of the oem part on my truck that is failed. I can't find FDP22 . See the spring lock connector? Whoever designed these ac lines and fuel lines with spring locks are SOB s !!!!!!

 

[55trucker]

What I see in your photo of the replacement item is a 4l fuel pressure regulator, not the 3 L item, the 3L pressure regulator has a barbed end not a threaded fitting.......

Now I've not had to replace mine so I've never paid much attention to it.....what you require is this?

 

[franklin2]

For the one above with the barb on it, I am coming up with a Herko PR4156. But it says it's for a 3.0 ranger 1999-2001. Yours is a 1998. For a 1998-2000 ranger they are calling for a Herko PR4029, which looks exactly like the one the parts store already gave you.

You may have a half-year model, Ford is famous for changing things mid-year if you think the later one would work better. But I was studying the pictures in this link https://www.amazon.com/Automotive-Pressure-Regulator-PR4029-Explorer/dp/B06Y6G7NPM/?tag=959media-20

I am suspicous that the one you bought takes some sort of o-ring type fitting. I would pursue taking your original one apart. Try unscrewing that end that matches the threaded end on the new one and see if it unscrews.

 

[azrangerman85]

saved more photos of the oem part on my truck that is failed. I can't find FDP22 . See the spring lock connector?

For the one above with the barb on it, I am coming up with a Herko PR4156. But it says it's for a 3.0 ranger 1999-2001. Yours is a 1998. For a 1998-2000 ranger they are calling for a Herko PR4029, which looks exactly like the one the parts store already gave you.

You may have a half-year model, Ford is famous for changing things mid-year if you think the later one would work better. But I was studying the pictures in this link https://www.amazon.com/Automotive-Pressure-Regulator-PR4029-Explorer/dp/B06Y6G7NPM/?tag=959media-20

I am suspicous that the one you bought takes some sort of o-ring type fitting. I would pursue taking your original one apart. Try unscrewing that end that matches the threaded end on the new one and see if it unscrews.

That wont work. Im two steps ahead and stuck. My oem is completely different and no longer in production as in NOT anywhere. I need to know what fittings to use to adapt to the spring lock connector

fpd22 is unavailable . Ive scoured the internet , its impossible to find and everyone says the same

 

[azrangerman85]

For the one above with the barb on it, I am coming up with a Herko PR4156. But it says it's for a 3.0 ranger 1999-2001. Yours is a 1998. For a 1998-2000 ranger they are calling for a Herko PR4029, which looks exactly like the one the parts store already gave you.

You may have a half-year model, Ford is famous for changing things mid-year if you think the later one would work better. But I was studying the pictures in this link https://www.amazon.com/Automotive-Pressure-Regulator-PR4029-Explorer/dp/B06Y6G7NPM/?tag=959media-20

I am suspicous that the one you bought takes some sort of o-ring type fitting. I would pursue taking your original one apart. Try unscrewing that end that matches the threaded end on the new one and see if it unscrews.

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this is my progress solution, I need help. I need anyone knowledgable with modifying or using adaptors on fule lines . I need a -06 AN ( army navy) adaptor that is 3/8 inverted female union. Im also unable to confirm if I neee the top of the female union to be inverted also . Im assuming both flanges of the female union would be inverted to marry the adaptor and the regulator .https://shop.advanceautoparts.com/p/dorman-inverted-flare-fitting-union-3-8-in-785-316d/11910802-P