: Poor gas mileage in aurora 4.0

05-03-06, 05:17 PM
I have noticed that my last three tanks of gas my mileage has been off. According to the computer I averaged 18.5 miles to the gallon and used about 15 gallons of gas. Well, I put in about 17.5 gallons of gas giving me an average of 15 miles per gallon. I checked the fuel pressure regulator and it seems to be working, no gas coming out of it. What could this be, a bad injector. How can I check for a bad injector? I read somewhere to put a guage on it and see if it holds so what kind of guage should I use and where can I get one. Could it be anything else, the car doesn't have a fuel leak and I never smell gas and it just passed emission with flying colors so I don't think it's running rich, could it be the computer? any help is appreciated.

05-03-06, 06:31 PM
18.5 is about right for around town driving.
How long has it been for a major tuneup?
Fuel injector service,plugs,plug wires,O2 sensors

05-03-06, 07:20 PM
The problem is that it says that it is getting 18.5 miles per gallon according to the computer but it is not getting that. The fuel used on the computer is off by about 2 gallons or more everytime I fill up making my average mileage only about 15 no matter how hard or how carefully i drive it. After the first time I noticed it I was very careful with throttle application to improve mileage but im still putting in two gallons more than the on board computer says I should. The o2 sensors are working fine they were just looked at, I just did the plugs, wires and changed 2 coils within the last month so it runs fine but it is not getting the miles per gallon that it should. What is the injector service? Is it something I can do.

05-03-06, 07:24 PM
looked at? your supposed to replace the O2 sensors. When i replaced them in mine it bumped me up over 100 miles to the tank. I now get 376 miles out of a V8, even with a couple 6000 RPM blasts here and there. As i say to the ricers Beat that with your piece of crap 6 bangers.

05-03-06, 07:38 PM
Before two coils went the car was running rich. My first thought was o2 sensors so I had my mechanic took the o2 sensors out and checked the values and they checked out perfectly. i even had them test some new o2 sensors and the values on my originals were the same so it wasn't my o2 sensors. 2 days later the coils blow out which was the main reason the car was running rich. Now the fuel mileage is bad and the gas used is not adding up, any other ideas.

05-03-06, 09:46 PM
Seems as tho the injectors are putting out more fuel than the PCM thinks they are.
Next step is check the FPR pressure to see if its in spec.
injector service is running a high grade fuel injector cleaner thru the injectors at the fuel rail. This is not anything you put in the tank but is dispensed at the fuel rail by specialized equiptment.
Im partial to the 3M stuff.Or you could always replace all 8 injectors.

05-03-06, 10:18 PM
I did the fpr check as outlined in the cadillac tech tips section by pulling the vacuum line off of the fpr and looking to see if any fuel leaks out. Out of curiousity, how long should I have waited to see any fuel come out? should I have revved the engine. I was looking at injectors earlier and they can cost 30 bucks each. I read in the forums that ford 19# injectors from a 4.6 or a 5.4 can work in a cadillac engine, will they work in the oldsmobile. I think they said it had to be the orange top ones, if they will work ill post a link to some ebay auctions cause they are dirt cheap. im also looking at a used aurora set with 68000 miles on ebay. What else can I do?

05-03-06, 10:43 PM
If the FPR is leaking you should see fuel almost immediately. There is also a post in the Tech Tips section for checking to see if the injectors are leaking. A fuel pressure guage will tell you if the system is holding pressure, but if it is not, you are still not sure if it is an injector that is leaking or the check valve in the pump and fuel is leaking back intop the tank.

05-04-06, 04:50 AM
too high of pressure will use more fuel than the PCM thinks it is using.

05-04-06, 11:56 AM
ok, I will look for the leaking injector test and try that but ranger said that that it could then be either the injectors or the check valve in the fuel pump, how do i see which one it is. and how would my car be having too much fuel pressure? what part should be replaced to correct that?

05-04-06, 02:50 PM
A fuel pressure guage will tell you what the fuel pressure is. It doubtfull that it is too high.

05-04-06, 05:08 PM
well i did the fuel injector test by pulling the rail and turning the key to on and seeing if any injectors leak and it was inconclusive. none dripped after a couple minutes but a couple of them were moist at the bottom of them while others were not. I am getting a fuel pressure gauge tomorrow and will see if the system holds pressure. What should the pressur be around when the system is pressurized? what is an allowable amount a pressure to drop before you decide the injectors are leaking, 1 maybe 2 #'s? If the fuel pressure does drop indicating bad fuel injectors will 19# ford injectors work. I have a set of injectors from a 1992 mercury grand marquis with the 4.6 sohc, will those work. I just don't wanna spend an arm and a leg for injectors, the parts store wants 30-40 each new.

05-04-06, 09:01 PM
I believe the fuel pressure should be something like 45-50 psi, but you have already proven that neither the injectors nor the FPR are leaking, so the problem does not lie in the fuel system. Sounds like something is commanding a richer mixture, if infact there is a problem. Maybe is just the calulator that is off.

05-05-06, 12:43 PM
well, ill still check the fuel pressure just to be sure, could the engine computer be this far off? maybe ill try disconnecting the battery and try to reset it, maybe that will work.