gas mileage
Thread Starter
Intermediate
Joined: Oct 2003
Posts: 42
Likes: 0
From: San Lorenzo Ca
gas mileage
It seems that in the last few weeks my car has all of a sudden lost gas mileage. I'm lucky to be geting 10-12 in the city. My engine is 600 miles new on a lot of mod's. Bigger cam, hypertech chip, shaved heads, 30 over pistons, crank and bearings...etc. is this normal. Also, it does seem to idle a little rougher than before..any and all suggestion PLEASE. THANKS !!
Burning Brakes
Joined: Sep 2000
Posts: 1,199
Likes: 1
From: NewCastle IN. USA
Re: gas mileage (89blkvet)
probably the O2 sensor, unless its running so rich the ECM can't adjust enough to compensate.
when cruising around, the O2 sensor is monitored by the ECM and the A/F mixture is constantly adjusted to give best performance/gas mileage.
however the ECM can only adjust so far, so something like a leaking injector can put it past the limit.
vaccume leaks and exhaust leaks can also effect what the O2 sensor is seeing (if the O2 see's a lean condition it adds fuel, possibly making it richer than it should be).
If you have any exhaust or vaccume leaks I'd start there.
if not then get a fuel pressure gage and see if the pressure drops quickly after shuting off the engine (it should hold pressure for a good 10 minutes or more).
If thats good then I'd try a new O2 sensor (or get someone to hook up a scanner and check things).
since you have new mod's and a new chip then those things may be involved, a chip can be too rich (if it was running fine with this chip before the gas milage problem happened then its probably OK, but if the problem has been going on ever since the mod's and chip then it could be an issue).
before throwing a bunch of money at it or pointing fingers at the chip maker I'd check for trouble codes and or get it scanned. it could be something as simple as a burnt O2 wire.
RJ
when cruising around, the O2 sensor is monitored by the ECM and the A/F mixture is constantly adjusted to give best performance/gas mileage.
however the ECM can only adjust so far, so something like a leaking injector can put it past the limit.
vaccume leaks and exhaust leaks can also effect what the O2 sensor is seeing (if the O2 see's a lean condition it adds fuel, possibly making it richer than it should be).
If you have any exhaust or vaccume leaks I'd start there.
if not then get a fuel pressure gage and see if the pressure drops quickly after shuting off the engine (it should hold pressure for a good 10 minutes or more).
If thats good then I'd try a new O2 sensor (or get someone to hook up a scanner and check things).
since you have new mod's and a new chip then those things may be involved, a chip can be too rich (if it was running fine with this chip before the gas milage problem happened then its probably OK, but if the problem has been going on ever since the mod's and chip then it could be an issue).
before throwing a bunch of money at it or pointing fingers at the chip maker I'd check for trouble codes and or get it scanned. it could be something as simple as a burnt O2 wire.
RJ
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: gas mileage (89blkvet)
You can use the ECM's diagnostic mode to see if it's going into closed loop; the method is on my site (see sig. below). If it isn't going into closed loop the problem is with the coolant temp sensor or with the O2 sensor.
But, since it's also running rough, you might look for ignition problems. In this case pull the plugs for inspection and check the wires for arcking.
But, since it's also running rough, you might look for ignition problems. In this case pull the plugs for inspection and check the wires for arcking.
