1990 240sx - I had the faulty EGR. I blocked the tube from exhaust to EGR and changed the front O2 sensor. I also blocked the vacuum lines. The car has been drinking gas since then. I checked the vacuum lines and no leaks. The spark plugs are fine: no carbon deposits so car is not running rich. Injector no. 1 leaks outside so I guess it could be faulty FPR. But it is a minor leak. The gas mileage is really bad. I checked the timing too. Set it around 17degree. For the O2 sensor, the wiring harness was short. So I put external wire from sensor to ECU. But it didn’t affect the gas consumption. Any suggestions…?
If the car is guzzling gas, then it is running rich, unless that injector leak you mentioned is much bigger than you think.
If the O2 sensor is fine and so is the wiring, then the next thing you should check is the Coolant Temperature sensor. If that’s bad, your car will be running rich all the time even when it’s fully warmed up.
Thats one of the reasons my car wont pass etest!!! From what I know, Its supposed to be around .6v at normal operation. But mine wuz reading around 1.3 constantly! could be some corrosion there or it could be disconnected as well!
ur say ur timing is set at 17 degrees…are u running 91 octane? u know 15 degrees is stock for a sohc
I have the same issue with my car. It runs realllly rich. I’m gonna try a few things. Next spring im replacing the O2 sensor, im going to run some injector cleaner to see if i dont have clogged injectored and im replacing my air filter. I’ll also look into the coolant temp sensor, because my car seems to have the symptoms that lith was mentionning (ie: running rich even when fully warmed up)
same shit here, lith I changed the coolant temp sensor, uhhu same shit, i only get 400k on a full tank, 400 vs 600 from before, thers gots to be something else, now im looking into a fuel presure regulator,
trinituner, how many liters of gas do you usually pump when you fill up? If it’s 40L, then it’s right on… if it’s 55L, then you are is really running rich 
Another thing is, it’s a lot cooler outside right now, so you are getting more oxygen to your engine, therefore more fuel is being sent as well… however, I never found this to make a big difference really… only a slight one.
the most ive ever run was 440km to the tank few weeks ago… when i first got the car i got 300-320km at most… but thats because i stepped on the throttle from light to light like a fool.
I am running on 87 octane. Car was running fine before EGR f***ed up everything. Now is just drinking gas. If the car is running rich spark plugs should be black with carbon. But they are clean. I just don’t know where the gas is going. I checked the Coolant temp sensor too. ok(Within spec. Ohms). Checking it at ECU pin is a pain. I just don’t have anymore time to figure out problem.
I’m still trying to figure out why mine runs so rich, but unlike you guys, my gas mileage doesn’t seem to be affected. I’m running some STP injector cleaner in hopes that it will help, and i’ll be replacing the 02 sensor in the spring and fixing an exhaust leak.
ok well driving my car on average to 4000rpm all the time im driving and i will have to put 20 a day some times more for about 200 km maybe less. i had to put 30 in 2 days ago and i was on empty by the end of the day i might have my o2 sensor in the wrong place or something it burns alot of gas
coolant temp sensor, o2 sensor, timing, leaky injector, spark plugs, coil pack, pretty much anything spark or fuel related.
i would check Coolant temp sensor first, then o2 sensor, but the o2 doesn’t really play much of a roll until the car is at operating temp.
on a side note, i used to drive from kitchener to bala(outside gravenhurts) and back every week on 1 tank of gas, and still have 40-50km to drive around on.
Works out to almost 550-600km per tank…400 seems ok