Curious about fuel pressure

[Jimmy9190]

When the fuel pressure regulator is bad, will it cause you to have less MPG, and will it cause less power from the engine? I had to replace my fuel pump assembly because the pressure regulator was definitely bad, and I had some recent cold starting problems. When I disconnected the fuel supply line on the old pump today, hardly any fuel came out of it at all. Plus I did a pressure test on it last night with a gauge at the fuel rail. Pressure when running was 48.5 to 49 psi, which is well within specs but soon as I turned off the engine the pressure fell to 25 and even less psi in about 3 minutes.

I have to reinstall my tank and everything tomorrow but am wondering whether a new pump/regulator will help increase the MPG and maybe the power too? The old fuel pump was the original one and has 123,000 miles on it.

I have been searching online but didn't come up with much info. Any help here is greatly appreciated.

 

[Petrou]

the likely hood of better mpg is slim, with those new parts. It will start. If i was you i would change the fuel filter as well unless its a filter that is in the tank, then you should have changed that with the fuel pump.
anyway, no probably not better fuel mileage by replacing those parts

 

[Jimmy9190]

Fuel filter is part of the pump assembly. Mounts to the bottom of the pump. The assembly came with all new fuel pump, fuel pressure regulator, gas gauge sending unit and fuel filter.

 

[mechtech2]

There is no fuel filter in the line? Really?
If this is true, it's a dirty trick, and rare!

Is you car equipped with a pressure sensor, or pressure regulator?
Vacuum or electrical lines to it?
Depending on which way it was 'stuck', your future gas mileage may go up , down, or stay the same.

 

[Snafu]

What kind of car is this?

 

[Jimmy9190]

The fuel pressure regulator and fuel filter are both built into the fuel pump assembly. This is on a 2001 Dodge Dakota. I'm not sure when Dodge started doing it that way. The fuel gauge sending unit is part of the pump too. A lot of Chrysler vehicles are the same way.

I dropped the tank and got the pump assembly installed yesterday, finished it up today and the truck fired right up on the first turn of the key. It was a royal PITA R&R'ing the tank by myself on the garage floor but I got it done and I hope I never have to do another fuel pump for a long time. I tried doing it by R&R'ing the bed to get to the pump, but the bed was way too heavy to do by myself. It would have taken 4 guys and a 12 pack of beers to do that way.

I also changed my oil, put on a new serpentine belt, rotated my tires and cleaned & adjusted the rear brakes too. Test drive went very well, truck is running fine and starting like it should. I went and filled it up with gas to check that the gauge was working right, and it is. With the bad regulator the truck would crank for 7 or 8 seconds before it wouuld start. The regulator has a check valve in it that goes bad, which is also a common problem with Dakota's. When I pulled the fuel line loose from the pump, barely a trickle of fuel dripped out so I know the regulator was shot.

I'm just very glad to see my truck back on the ground again, instead of up on jack stands. I am also glad I was able to fix it myself, it runs between 400 to 600 bucks to do a fuel pump on a Dakota, so I hear. Plus I saved 45 bucks with an online purchase coupon sale this weekend on the AAP website. I posted that link in the sales and promotions section here.

 

[mechtech2]

Good work -nice job.
I hope it lasts the life of the vehicle!

But for the future, tell us what type of vehicle it is that needs help!
You'd be surprised how some of us are familiar with specific cars.

 

[The_Jeff]

I'm familiar with dakota fuel pumps, LOL.

At least they use a plastic tank, or did in 92.

My GMC sonoma was a much worse job with a metal lock ring rusted to a rusty tank, and undercoating goo in all the fasteners.

I had the most elaborate maze to monkey around, driveshafts and exhaust parts blocking vision and access. I let my tank drop six inches to do the job.

Kind of a 3-beer job.

Incidentally with my fuel pump failing, spec pressure was 20, 40, something, I don't remember. But the truck would run, make power, and idle on like 5 PSI, and the pressure gauge was fluttering all over the place. On something as primitive as the 92 (3.9 V6) the o2 sensor probably took care of the wonky fuel issues.

 

[Jimmy9190]

I can't imagine trying to R&R a rusted and undercoated tank with all the road salt and slime from up north. That's one more reason I am glad I live in Florida. It really wasn't to bad of a job, just that the tank was heavy and bulky to maneuver around while I was underneath the truck. It was a pretty straightforward job, and I was glad to have enough clearance to get it out and back in OK. Part of the problem was I cheaped out on it and did not buy any gas cans or a siphon to empty the tank. I would have had no use for two ten gallon gas cans after I got the fuel pump done. So I horsed the tank off and then back on the truck with about 15 gallons of fuel still in it.

I didn't check the fuel pressure on the new pump, and I guess there really is no need. Truck seems like it may using a little less gas now, and it is running great so far. It starts right up when I turn the key again too. I need to drive it this week and fill up again and check the mileage. I'm thinking it may take the PCM a little while to re-learn the fuel mix from the new pump. I used 3.5 qts of oil and 18 ounces of MMO in the oil when I changed it Saturday too and the engine really is running smooth and quiet now.

Thanks for the info and help here.