Strange fuel pressure behavior

sevynos · 07-27-2009, 11:06 PM

Hi,

I have a ford ranger '90 2.9L EFI.

I'm suspecting a fuel pressure regulator (FPR) problem so I made a pressure test. The result is bugging me!

With the key to ON, on the first fuel pump activation I have a reading of 0 (Zero) PSI. To get the needed 40 PSI I had to activate the pump 5 times. And that's not all! If I don't touch anything, the pressure start going down until it reach zero.

Then I started the engine and got a constant reading of about 78 PSI.

With these results, should I consider that my FPR is faulty or a vacuum problem?

Area 52 · 07-28-2009, 06:55 AM

It would be safe to say that the regulator is shot. You are getting full pump pressure. As for the pressure dropping after shutting engine off, the injectors are leaking. Pressure should hold for at least an hour before you start to see any pressure drop off. Time to get some rebuilt injectors. Don't drive it until after you get the regulator changed out...will cause engine damage. After the regulator swap, change oil/filter. The oil will be diluted from the excess gas.

RustedRanger · 07-28-2009, 11:52 AM

sevynos mine acted very similar when my FPR was shot. It would jump up to almost 80 then slowly drop down. I ran fuel injector cleaner in it several times and replaced the FPR and now the pressure reads good and doesn't drop off anymore.

**bobbywalter** · 07-28-2009, 12:08 PM

sounds more like a pump issue to me. or rather a cobination of it...as in the pump check valve failed..but an open injector would do that...the 70 psi though dont jive that..that or the return line is plugged and caused the c/v failure in the pump or something.

without pulling the return line to check for volume i cant really say. i would do that before buying parts.

be very careful when working with the fuel lines, dont want to burn yourself down.

sevynos · 07-29-2009, 01:19 AM

Thanks to all for your replies.

According to your oppinions, some on another forum and people i've talked to, i will replace the FPR since I found an affordable one at CarQuest. Anyway, it won't hurt to get a new one!

bobbywalter: I'm no expert but if it is a pump issue, I think I shouldn't get a 78PSI pressure instantly after startup. Am I wrong?

Again, thanks to all!

**Sasquatch_Ryda** · 07-29-2009, 01:25 AM

Yes but it sounds like the pump is leaking down, and not holding the fuel pressure which is why you would have to cycle the key 5 times like you say you do. All the fuel has drained back out the lines and into the tank.

sevynos · 07-30-2009, 02:12 PM

Thanks all again!

I've got my new FPR. I will install it on next Monday or Tuesday depending on weather conditions. I will post a follow up of the results.

gw33gp · 07-31-2009, 11:48 AM

I had a similar problem with an 89 2.9L Ranger and recently with my 02. Replacing the fuel pump solved the problem. The check valve was not working properly and I would have to cycle the ignition key 4 to 5 times to get the engine to start. The pressure would not build to full pressure when turning on the ignition switch because not enough volume would pump before the pump automatically shut off.

The check valve is not the only thing that causes this problem but if the new FPR does not solve the problem you should take a hard look at the fuel pump. I find the quickest way to check that is; disconnect the fuel filter and connect a pressure gauge to the line coming from the tank. Cycle the ignition switch and if the pressure drops off when you shut of the ignition switch, the check valve is not functioning properly.

warrior24 · 07-31-2009, 11:55 AM

Where do you connect the fuel pressure gauge to?

Psychopete · 07-31-2009, 11:57 AM

Quote:

Originally Posted by warrior24

Where do you connect the fuel pressure gauge to?

The schrader valve on the fuel rail.

Pete

gw33gp · 07-31-2009, 06:58 PM

Quote:

Originally Posted by warrior24

Where do you connect the fuel pressure gauge to?

I connect it to the end of the fuel line. It might take some ingenuity to come up with a good connection with some fuel pressure gauges. I have one that has a tapered fitting that fits inside the line and requires holding them together. That requires a helper to cycle the ignition switch.

sevynos · 08-04-2009, 04:43 AM

Finally I installed my new FPR yesterday.

Truck runs well and startup are much more easier!

Now my pressure reads 37-38 on key ON position. There's seem to have a small leak, in about 5 minutes engine off, I lost 10 PSI. When the engine is running, the pressure climbs to 40 and stay there. It's the opposite of specifications. Anybody have an idea?

And there's now another little issue about the gas! When I hit accelerator, the pressure and engine RPM drops a little to go back up after 1-2 seconds. I've seen this before but I don't remember what it was. Anybody knows?

07-27-2009, 11:06 PM	#1
sevynos New Member Join Date: Jul 2009 Year: 1990 Make: Ford Model: Ranger Posts: 4 Rep Power: 0 iTrader: (0)	Strange fuel pressure behavior Hi, I have a ford ranger '90 2.9L EFI. I'm suspecting a fuel pressure regulator (FPR) problem so I made a pressure test. The result is bugging me! With the key to ON, on the first fuel pump activation I have a reading of 0 (Zero) PSI. To get the needed 40 PSI I had to activate the pump 5 times. And that's not all! If I don't touch anything, the pressure start going down until it reach zero. Then I started the engine and got a constant reading of about 78 PSI. With these results, should I consider that my FPR is faulty or a vacuum problem?
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07-28-2009, 06:55 AM	#2
Area 52 Junior Member Join Date: May 2009 Location: Newport Beach, CA Year: 1990 Make: Ford Model: Bronco II Built: 12/89 3.73 Axle Mitsubishi Trans Engine: 2.9 Class: 4x4 Stock Used For: 95-On/5-Off Road Posts: 94 Rep Power: 9 iTrader: (0)	It would be safe to say that the regulator is shot. You are getting full pump pressure. As for the pressure dropping after shutting engine off, the injectors are leaking. Pressure should hold for at least an hour before you start to see any pressure drop off. Time to get some rebuilt injectors. Don't drive it until after you get the regulator changed out...will cause engine damage. After the regulator swap, change oil/filter. The oil will be diluted from the excess gas. __________________ 1990 Bronco II (12/89)
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07-28-2009, 11:52 AM	#3
RustedRanger Member Join Date: Mar 2009 Location: Farmland IN Year: 1987 Make: Ford Model: Ranger XLT Engine: 2.9L Class: 4x4 Used For: Everyday driver Posts: 825 Rep Power: 10 iTrader: (0)	sevynos mine acted very similar when my FPR was shot. It would jump up to almost 80 then slowly drop down. I ran fuel injector cleaner in it several times and replaced the FPR and now the pressure reads good and doesn't drop off anymore.
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07-28-2009, 12:08 PM	#4
bobbywalter RBV Technical Advisor Join Date: Aug 2007 Location: higgins lake mi Year: 1988 Make: FORD Model: RANGERISH SORT OF THING Engine: BIGGER Class: 4X4 Used For: EVERTHING Posts: 15,307 Rep Power: 49 iTrader: (0)	sounds more like a pump issue to me. or rather a cobination of it...as in the pump check valve failed..but an open injector would do that...the 70 psi though dont jive that..that or the return line is plugged and caused the c/v failure in the pump or something. without pulling the return line to check for volume i cant really say. i would do that before buying parts. be very careful when working with the fuel lines, dont want to burn yourself down. __________________ 88 ranger ext cab low rider 4x4 propelled by 395 cubes of of non turbo SLOBBERIN DIESEL...BLAHHH...motating a 4l80 thats AUTHORITATIVELY turnin a ford 208 spinning 410 open dana 60s and whatever tire suits the mood that day. how ya like me now? Last edited by bobbywalter; 07-28-2009 at 12:12 PM.
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07-29-2009, 01:19 AM	#5
sevynos New Member Join Date: Jul 2009 Year: 1990 Make: Ford Model: Ranger Posts: 4 Rep Power: 0 iTrader: (0)	Thanks to all for your replies. According to your oppinions, some on another forum and people i've talked to, i will replace the FPR since I found an affordable one at CarQuest. Anyway, it won't hurt to get a new one! bobbywalter: I'm no expert but if it is a pump issue, I think I shouldn't get a 78PSI pressure instantly after startup. Am I wrong? Again, thanks to all!
	Tweet

07-29-2009, 01:25 AM	#6
Sasquatch_Ryda Coast Mountain Crawlers Join Date: Aug 2007 Location: Terrace, BC, Canada Year: 1991/1997/2008 Make: Ford Model: Ranger/Ranger/SuperDuty Engine: 4.0L/3.0L/6.4L Class: 4x4 Used For: Play toy/Daily Driver/Grocery Getter Posts: 7,479 Rep Power: 10 iTrader: (0)	Yes but it sounds like the pump is leaking down, and not holding the fuel pressure which is why you would have to cycle the key 5 times like you say you do. All the fuel has drained back out the lines and into the tank. __________________ http://www.coastmountaincrawlers.com 1991 Ranger - one tons, 3 link, air shocks and 40's 1997 Ranger - reg cab flare side, 3.0L, M5OD-R1, 4x4, 4.56 gears, 6" lift, 33" MT's. 2008 F350 - 6.4L Powerstoke Diesel, 35x12.50R18 Procomp Xtreem AT's on 18x9 Incubus Crushers, AFE DPF/DOC Delete pipe, H&S XRT Pro tuner, AFE Stage 2 intake 1967 Mustang Coupe - 289, c4, pretty much stock
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07-30-2009, 02:12 PM	#7
sevynos New Member Join Date: Jul 2009 Year: 1990 Make: Ford Model: Ranger Posts: 4 Rep Power: 0 iTrader: (0)	Thanks all again! I've got my new FPR. I will install it on next Monday or Tuesday depending on weather conditions. I will post a follow up of the results.
	Tweet

07-31-2009, 11:48 AM	#8
gw33gp Member Join Date: Aug 2007 Location: Costa Mesa, CA Year: 2002 Make: Ford Model: Ranger FX4 Engine: 4.0 SOHC Class: 4X4 Used For: Daily driver, towing & off-road Posts: 501 Rep Power: 13 iTrader: (0)	I had a similar problem with an 89 2.9L Ranger and recently with my 02. Replacing the fuel pump solved the problem. The check valve was not working properly and I would have to cycle the ignition key 4 to 5 times to get the engine to start. The pressure would not build to full pressure when turning on the ignition switch because not enough volume would pump before the pump automatically shut off. The check valve is not the only thing that causes this problem but if the new FPR does not solve the problem you should take a hard look at the fuel pump. I find the quickest way to check that is; disconnect the fuel filter and connect a pressure gauge to the line coming from the tank. Cycle the ignition switch and if the pressure drops off when you shut of the ignition switch, the check valve is not functioning properly. __________________ 2002 FX4 - 4.0 SOHC, 5 spd manual transmission & transfer case, 32" ProComp MTs, K&N air filter, Modified air box inlet, Gibson SS cat. back exhaust, Bama flash, Hidden Hitch round receiver, Rear helper air springs, electric trailer brake controller, Line-X bed liner, WAAG bar with KC lights and Wildernest shell.
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07-31-2009, 11:55 AM	#9
warrior24 Member Join Date: May 2008 Location: Surprise, AZ Year: 1992 Make: Ford Model: Ranger SuperCab Engine: 4.0 Posts: 330 Rep Power: 11 iTrader: (0)	Where do you connect the fuel pressure gauge to? __________________ I'm not asking you to fix it, just please let me get it back to the way it was before I touched it. The Technician Prayer
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08-04-2009, 04:43 AM	#12
sevynos New Member Join Date: Jul 2009 Year: 1990 Make: Ford Model: Ranger Posts: 4 Rep Power: 0 iTrader: (0)	Finally I installed my new FPR yesterday. Truck runs well and startup are much more easier! Now my pressure reads 37-38 on key ON position. There's seem to have a small leak, in about 5 minutes engine off, I lost 10 PSI. When the engine is running, the pressure climbs to 40 and stay there. It's the opposite of specifications. Anybody have an idea? And there's now another little issue about the gas! When I hit accelerator, the pressure and engine RPM drops a little to go back up after 1-2 seconds. I've seen this before but I don't remember what it was. Anybody knows?
	Tweet

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