fuel pressure ?

olgentdc · Aug 11, 2017

My 98 gran Marquis has been laid up awhile, it just dont want to take fuel ,
keeps sputtering out ,,.today ,i was told by my nephew ,"the new fuel pump is
malfunctioniong" .he claims it only carries 40 or so lbs of pressure, and
should have 90 lbs???..DOES ANYONE KNOW WHERE I CAN FIND CORRECT INFO ?
.personally .i dunno, but that seems like alot of fuel pressure to me , but i
could be wrong and my good hearted nephew may be rite , he done ok getting this
far on his own research in his spare time while working a real job .... well at
least the car is running and i think i can take it to another more qualified
shop ...

David G · Aug 11, 2017

I thought the fuel pressure was controlled by the regulator mounted near the intake manifold.

Duner Wi · Aug 11, 2017

Here is chart for you. Looks like you are in the neighborhood at least. Look under Ford Motor Company
http://jameshalderman.com/links/book_aepd/s_and_c/Fuel_Pressure_Specifications.pdf

jimg.allentown · Aug 11, 2017

Fuel pressure is a nominal 52 psi across the injectors. This is regulated by the fuel pressure regulator located in the fuel rail. Normal should read about 38 to 50 on a gauge. At idle, about 37 to 40 psi which is gauge pressure plus the 14.7 psi nominal atmospheric pressure. Your fuel pressure is correct.
If it is unresponsive, it is most likely a different problem. Like a plugged exhaust. Since it is an OBD2 vehicle, a scan should reveal at least the major problems.
I would suggest starting with a vacuum gauge, and see what the vacuum is at idle. Should read in the vicinity of 27 to 30 inches of mercury. Then crack the throttle and see where it goes. At a slight throttle opening, it should increase slightly, and then go back to the reading you had at idle. If it rises all the way to 10 inches or less, you have a plugged exhaust.

Steve@Advance · Aug 11, 2017

David, I saw that too, all I've seen returned excess to tank.

How else would it regulate with the regulator at the opposite end of the rail???

gab · Aug 11, 2017

40 lbs. sounds a lot closer than 90.

olgentdc · Aug 11, 2017

i did not think there would be 90 lbs of fuel pressure on rubber lines ! tank pump must be good ,,.. you Guys are a great help , ,.. so wonderful getting knowledgable help , many thanx ,..

used red MN · Aug 12, 2017

Take it to a local parts store and have them read the codes for you. That is assuming it has a light on and some codes have been stored. Kind of sounds like it's acting like some GM I've seen with bad mass air flow sensor. Good luck.

Texasmark1 · Aug 12, 2017

The rail on my Dodge trucks was spec'd at 40. Sure about the pressure, not too sure about the vehicle but it was current production, multiport fuel injection with a "rail". After saying what I said pretty sure it was one of my Dodge ? ton pickups.

cool hand · Aug 12, 2017

Educate me just a bit. I'm not familiar with the term "rail" as applied to a fuel system. What is it?

Kellyss · Aug 12, 2017

Normal fuel pressure ranges about 40 psi to 60 psi. You also need to have the correct fuel volume when under load to keep it running.

Bob · Aug 12, 2017

(quoted from post at 08:06:37 08/12/17) Educate me just a bit. I'm not familiar with the term "rail" as applied to a fuel system. What is it?

Here's a "fuel rail" for a basic port-injected 8-cylinder Ford gasoline engine:

The individual injectors connect to it, as well as the fuel pressure regulator.

54836d1225930936-1995-mustang-gt-fuel-injectors-fuel-rail-need-help-0900c152800694fe.gif

RWT · Aug 12, 2017

My 08 F150 uses a fuel pump driver module. There is no return.

It modulates the speed of the fuel pump to set the pressure. The main ECM tells it what pressure it wants and the module sets it.

I had some trouble last week when the gravel roads took out the power feed wire. I noticed after I got it running the ECM was asking for 39 PSI and it was getting it. My info says it will run with 20 PSI and I have evidence this was correct.

My Vantage Pro says the pressure should be 48 to 70. From my previous comment I don't think this is right.

I've also seen an 02 Explorer 4.0L that had a returnless system but it is different. I think it has a bypass in the tank.

RT (Just some thoughts)

fuel pressure ?

olgentdc

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David G

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Duner Wi

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jimg.allentown

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Steve@Advance

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gab

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olgentdc

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used red MN

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Texasmark1

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cool hand

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Kellyss

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Bob

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RWT

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