BAD GAS MILEAGE!!

xbn377 · Post by **xbn377** » Wed Apr 08, 2009 7:04 pm

It is an automatic and i used to get about 18 but not only 13-14 in the city. I am starting to think that the timing is off, the belt that is. I believe that one of the previous owners may have put it back on wrong. I will be doing an oil pump this summer and will double check that it is correct. It idles high so im going to try to make sure everything is sealed up but I am hopeing to get an wrx intercooler and then work on the leaks. Also i noticed that i am missing a nut for the turbo-downpipe so i need to pick one up. It is old but I dont blow smoke or anything. I did upgrade the fuel pump to a 255lph pump over stock and found out the oem pump was actually good but i have a bad ground that i am dealing with. Bad chunk of wire. Could a bad ground cause this or a higher capacity pump cause it? I mostly noticed it after I did swap the pumps. Any ideas on this would be greatly appreciated. Any suggestions are appreciated. Thanks Guys

PhyrraM · Post by **PhyrraM** » Wed Apr 08, 2009 7:34 pm

First step is to fix any current problems that you know about. You had quite a list there. I would do all of them before any mods, not after or during.

Mileage is most commonly the O2 sensor, TPS or vaccuum leaks. It can be others though, especially when you know you have multiple issues. They kind of play off of each other.

My suggestion is to go back to square one and deal with everything you currently know about. Then deal with any codes. Troubleshoot and fix your mileage problem. Then, start your upgrade process. You will be time, and money, ahead in the long run.

xbn377 · Post by **xbn377** » Thu Apr 09, 2009 12:39 am

Like i said i got the cel to go off finally. I did not change the tps though. I am actively searching for vacuum leaks. So as i didnt not think that the new fuel pump would cause it to start sending excessive gas but i do not know for sure.

PhyrraM · Post by **PhyrraM** » Thu Apr 09, 2009 1:23 am

If the regulator is bad, then a new pump would raise the fuel pressure. This would dump extra fuel anytime your not in closed loop.

asc_up · Post by **asc_up** » Thu Apr 09, 2009 1:25 am

Sounds like it could be a bad O2 sensor. When was the last time it was replaced?

xbn377 · Post by **xbn377** » Thu Apr 09, 2009 1:29 pm

PhyrraM wrote:If the regulator is bad, then a new pump would raise the fuel pressure. This would dump extra fuel anytime your not in closed loop.

I have had suspicion that the regulator may not be working correctly, is there anyway to test it or do you just replace it. I would imagine vacuum testing it would be a solution? As I understand it that even if the pump flows more the regulator would do just that, regulate it, and send the excess fuel back into the gas tank.

asc_up: I actually just replaced the oxygen sensor in this string of getting sensors replaced. It has been about a month and a half.

Thanks for the info.

PhyrraM · Post by **PhyrraM** » Thu Apr 09, 2009 2:34 pm

Put a fuel pressure gauge on it. If it's out of spec (service manual is around here for D/L somewhere), either the pump is too big or the regulator is bad. Could be a blocked return line also.

A O2 can go bad very fast if the car is not running right. Both too rich or too lean OR a bad O2 heater circuit can crush an O2 sensor.

xbn377 · Post by **xbn377** » Thu Apr 09, 2009 7:35 pm

PhyrraM wrote:Put a fuel pressure gauge on it. If it's out of spec (service manual is around here for D/L somewhere), either the pump is too big or the regulator is bad. Could be a blocked return line also.

A O2 can go bad very fast if the car is not running right. Both too rich or too lean OR a bad O2 heater circuit can crush an O2 sensor.

Thanks for the information i will search for that manual. I will report when i find out information from this. Thanks again.

xbn377 · Post by **xbn377** » Fri Apr 10, 2009 2:37 am

Ok I put the a gauge on the fuel line and it read 35 psi at idle and i revved it up and it showed about 45-50. I thought that fuel injection was around 32 psi but the Chiltons manual says it should read 2.6-3.3 psi. Thats really low i would think. What am I missing here? Bad fuel pressure regulator?

PhyrraM · Post by **PhyrraM** » Fri Apr 10, 2009 2:55 am

Idle seems OK, but I don't think it should jump that much when revved. Could be wrong though. What does the FSM say about off idle pressure?

Fuel pressure should rise 1 psi for every psi increase in manifold pressure. Vaccuum included, so "less" vacuum is seen as 'more' pressure to the regulator.

ericem · Post by **ericem** » Fri Apr 10, 2009 4:48 am

At full BOOST it should be around 50psi.

xbn377 · Post by **xbn377** » Fri Apr 10, 2009 9:26 pm

Ok good info. I noticed the vacuum line to the regulator came off and i put it back on and zip tied it to hold it. This may help a lot I will update if I find a difference as there should be a huge difference. The only thing is that it didnt really make a difference in the vacuum on the gauge or the boost. Which is weird.

xbn377 · Post by **xbn377** » Tue Apr 14, 2009 1:12 pm

Well no luck yet! Still crappy mileage. Now where? It is like I am leaking gas but I am not...URGH!!!

xbn377 · Post by **xbn377** » Thu Apr 16, 2009 6:43 pm

Ok I got bored and smacked the Catalytic and it seems to run different. Last I knew the cat looked clean inside. I am starting to wonder if it is plugged up a bit and is causing backpressure and also resulting in bad gas mileage. Still now CEL though. Sound like a good direction, look for a dp?

ericem · Post by **ericem** » Thu Apr 16, 2009 8:53 pm

I wonder what the life of a catylistic converter is. Like miles or years ?

xbn377 · Post by **xbn377** » Tue Apr 21, 2009 2:24 am

Yeah im wondering that too...I did do seafoam through the intake and it definitly cleaned things up it runs smoother and blew out all kinds of carbon build up. I found my two leaks bc of the smoke too...I have one where my BOV mounts on my intake and also one small one on the turbo to downpipe gasket because i need a new nut to go on the stud bc it was missing found one but it didnt seal it as i dont believe it was the right nut for it. I will be puting on a intercooler and getting the proper mounting adapter and that should take care of the bov leak since its just bolted to the factory pipe where the bpv used to be.

xbn377 · Post by **xbn377** » Tue Apr 21, 2009 11:10 pm

I just filled up the tank and calculated 16 mpg instead of 12-13!! Headed in the right direction....next up that pesky vacuum leak.

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BAD GAS MILEAGE!!

BAD GAS MILEAGE!!