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What does it mean if fuel pressure drops quickly after shut off?       #: 834
 Moderated by: Mike69, MaDMaXX
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 Posted: Thu May 3rd, 2018 10:06 pm
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wh23g3g
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I've got a P0171 code that has popped up in the past couple of days. My 98 2.5 has been running good, finally with good idle after battling some idle issues for the past few months that turned out to be a leaking EGR vacuum regulator. In that time frame of diagnosing the idle problem all sensors and ignition components had been changed over to new Motorcraft parts to rule out lower quality aftermarket parts. Even had the timing and compression check twice. It now runs good. It does take a few extra cranks to start up usually. I attribute that to the quick fuel pressure drop. I've checked the static fuel pressure today and the running fuel pressure. It's hard to get a static reading because the pressure leaks down as soon as you cycle the key. It starts fairly easily just an extra second or so to get it to fire up. At idle running in Park it's right at the Ford limit at a steady 58 PSI. I believe the limit is 56-72 PSI according to the Ford manual. So what would it be that is causing the pressure to bleed down so quick after shut off? Is there something on the fuel pump assembly that controls that. I was told on another forum that an injector leaking down wouldn't likely cause such a drop so quickly. I replaced the injectors with remanufactured Bosch injectors about a year or two ago. The only difference between now and back months ago when I was still diagnosising the idle problem is that I've been using the A/C a lot. It still drives good and has as much power as a stock high mileage 2.5 should have. The engine was replaced at 228,000 and is now probably close to or at 200,000 itself. I've got a pump assembly under warranty but I want to make sure if I need to check anything else first. It was also replaced a year or two ago and from the beginning the sender never worked right. It's close to a 1/4 off.



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 Posted: Fri May 4th, 2018 12:50 am
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CBB9M
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Focusing on the question which is the title of this thread.....

*Could be the check valve in the fuel system

*Could be an injector(s) bleeding down

**When I skimmed alllllll the text following the title, there was no mention of odor or a puddle of fuel so it's probably not leaking.



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 Posted: Fri May 4th, 2018 01:50 am
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My guess would be the pump.

Again it is a guess.



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 Posted: Fri May 4th, 2018 01:56 am
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I would think the check valve like Billy mentioned. Is it in the pump on the Ranger? Same exact thing on my daughter Jeep, bad check valve would let the gas leak back into the tank. Some extra cranking and it would start. New pump, fixed.

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 Posted: Wed May 9th, 2018 05:56 am
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wh23g3g
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I finally had enough extra money to order another pump from Rockauto. I've warrantied the Airtex out already twice because of failing pressure regulators. So they told me to order another brand and they would refund the Airtex I ordered originally. Well I only had enough to get a Spectra SP2207H and when I looked at it there was a Spectra label on top of the pump that was covering an Airtex label. So I guess Spectra bought Airtex. It probably won't last more than a year or two again. The clear tube going to the regulator won't stay in the cheap plastic clip that's made into the module hold down clamp. I had to zip tie the tube in there. Is that ok? I can't remember but I think I had that problem last time too. I remember the last time I put the Airtex pump in the fuel gauge is off about 4 gallons. I don't know if it was a bad sending unit card or we installed the pump wrong. Does the pump sending unit arm need to be in a certain position when installing the pump down into the tank? 



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 Posted: Wed May 9th, 2018 12:14 pm
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wh23g3g wrote:
I remember the last time I put the Airtex pump in the fuel gauge is off about 4 gallons. I don't know if it was a bad sending unit card or we installed the pump wrong. Does the pump sending unit arm need to be in a certain position when installing the pump down into the tank? 


For any given year, there may be as many as three different Ranger fuel pump assemblies because there are three different tank sizes. The pump must match the fuel tank or it will not read correctly. To get the correct pump, match it to the year and wheelbase of your Ranger. Within any model year, wheelbase determines which tank it will have. 

Unfortunately, there is no guarantee that the listing of an aftermarket pump is correctly matched to the tank. Maybe, maybe not. The only brand I would trust 100% is Ford/Motorcraft but you would definitely pay a premium compared to aftermarket.

So be sure that you have the right pump and be sure that the arm did not get rebent during installation.


  • Something else to consider. When the gauge reads near empty and the low fuel or check gauge light illuminates, there is about 3 gallons or roughly 50 miles left. This is how Ford does it and, if that's what you're seeing, it is normal for Rangers.



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 Posted: Wed May 9th, 2018 02:43 pm
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wh23g3g wrote:
................... So I guess Spectra bought Airtex. ......... I had to zip tie the tube in there. Is that ok? I can't remember but I think I had that problem last time too. .
* Airtex has been around for years (and still is) and is a supplier for both OEM and aftermarket auto products. Most likely Airtex slapped a Spectra sticker on it and now it's sold under that brand name.

* If I were confronted with that situation, I too would use a few sturdy zip ties.



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