If you saw my other thread you know that I just replaced my ICM, Coil and three injectors(out of spec) in order to fix my no start condition now I'm trying to figure out why I'm only getting 13 mile to the gallon with a 3.1 v6 , When I was testing the fuel pressure before I found out that my injectors were shorted I remember that with the key on engine off I had 45 psi at the fuel rail and when I applied vacuum to the regulator It wouldnt move no matter how much vacuum I applied.I even left the gauge hooked up over night and the pressure didnt drop. Now my question is can this be the cause of my bad milege? Do I have to replace the whole fuel rail or can I just replace the regulator? Does anyone have a prefrence as to what company to go with neihoff or bwd?

 

when is the last time u did a tune up. plugs wire cap and rotor?

 

I just changed the plugs 100 miles ago, the previous owner had the wrong ones in it he had bosch platnum 2s form a v8 and to top it off two different part numbers. I put in autolite copper core oem. The cap and rotor look to be in good condition so I did not change them.

 

I have had fprs fail on a few different GM v-6 engines. The rubber diaphragm leaked...thereby sucking gas in through the vacuum line. Yes...mileage did go down.

You should be able to find the leak pretty easily with the fuel pump on...pull the vacuum line and smell for gas.

HTH...

 

Its been awhile but i have an update. I bought a new FPR but before I changed it I decided to check the old one because i cant remember if my above statements about the psi and vacuum were correct or not. Guess what it passed every test I threw at it from mitchell, alldata and even the factory manual so its not the FPR. I just changed the O2 Sensor and now I'm going to look into the egr valve (digital). I heard if these are leaking it will cause the MPG to go down.

 

Fuel milage problems are the hardest things to check for. Unless your engin is in PERFECT condition, your milage will be down. There are so many factors that go into your milage that it's next to impossible to find one thing, unless it is painfully obvious.

The 2 biggest problems with fuel milage are Tire pressure and driving habits. People always post on this site about how they are easy on the throttle and do a lot of cruising, but in a different thread they are wondering how to get more power out of their car. The bottom line is that the stock 2.8/3.1L motors are way under powered for our cars and to make them drivable with other cars, you need to be into the pedal a good amount. I get 18mpg combined with my car. I am meam to it too. To drive it around Santa Clarita, CA where I live and work, I have to rev to about 3500 or 4000 RPM before I shift to stay with the acceleration flow of traffic.

The only way to see if you actually have a problem with how the engine is using fuel is to get a scan tool, hook it up and check out your block learn numbers. Now that you have a good O2 sensor installed, they don't lie. If you ahve a sensor or a leak somewhere causing a rich condition, then the O2 sensor will adjust the block learn all the way down to a minimum. If' it's hanging around 128, then it's a driving style problem.

I'm not saying that this is the case, I just want you to be enligtened and not think that you're going to get 25MPG out of your car. Most of the people on this site that post numbers like that have had that happen once on a full freeway run, it's not regular occurance, I promise.

it does sound like you have something out of whack at 13mpg, so I would start by pulling the plugs and looking at them. What is the mechanical condition of the engine (compression, idle vacuum, etc). This can tell you a lot, even stuff that you didn't want to know. One low cylinder can mess up your vacuum reading at the MAP sensor, causing a false enrichment condition for the rest of the cylinders. What is your fuel pressure now? Start with the basics before you dig very deep, it'll save you a lot of time and money in the long run.

Good Luck