Help point me in the right direction for my poor MPG
05-17-12, 04:40 PM
#26
actually i played with a sender unit once and the sender is actually pretty accurate, when you have it outside the car, half way on the sender is actually half way on the gauge, and etc etc.
i had tweaked the float on this car, hence the messing about, but i notice that the gauge isn't linear partly because the float hits the top of the tank before its 100%, so it doesn't get its full travel. (it may have been the other way around, it was a long time ago)
i rebent it, however use with caution! i actually got each quarter of the S4 gauge to be about 4 gallons, which is fine, but when its on E its out! the stock way gives you 3-4 gallons on E, and we're used to that.
i had tweaked the float on this car, hence the messing about, but i notice that the gauge isn't linear partly because the float hits the top of the tank before its 100%, so it doesn't get its full travel. (it may have been the other way around, it was a long time ago)
i rebent it, however use with caution! i actually got each quarter of the S4 gauge to be about 4 gallons, which is fine, but when its on E its out! the stock way gives you 3-4 gallons on E, and we're used to that.
Everytime I'm on the interstate I get concerned at how quickly the gauge drops from full to 3/4, but it slows slightly after that and pretty much stops moving for 50 miles within a needle width of 1/2. After that it does the opposite on the way down.
I too bent my sender arm slightly when I installed my FD pump, it actually reaches "F" but that 15-20 mile reserve capacity after "E" is definitely a thing of the past lol. Of course that wouldn't be so much of an issue if the FC didn't have the stupidest design for a low fuel light on earth and any of them still worked...oh well.
05-29-12, 10:18 PM
#27
OK, still getting bad milage here.
I replaced the secondary rail with another for the change in FPR (S5 intake on S4 car), and am getting 32 psi w/ FPR vac line plugged in, 40 w/o. Still doing high 13's on milage when dividing miles driven by gas to fill!
I'm at a loss here- from my original thread it-
-New tires, and allignment
-New brake master & properly bled brakes
-Injectors were removed & cleaned, then re-installed
-Engine hasn't been in the car more than 1500 miles. It's a used S4 engine, but was rebuild 2 years back. Fires right up everytime, but do not know the compression figures.
-New O2 sensor, confirmed operation of closed loop with checker light
-Not pulling ANY trouble codes w/ code checker (was pulling an O2 sensor, but it has been replaced & no longer comes up)
-New thermostat & radiator installed with engine, and full shrouding. Temps are normal
-Rats nest removal, vac routing is identical to the 88
-Main cat is replaced with a straight pipe, 2 pre-cat casings still there, no cats inside though
-Properly timed, and idle properly set, as well as TPS, to FSM spec
-No exhaust leaks, no fuel leaks
-Good condition used spark plugs. I disassemble lots of these engines in the junk yard (cordless impact FTW), and always take the plugs if they're near new.
-New E8023 Airtex brand fuel pump and fuel filter (pre & post pump)
-Water temp sensor:Checked by FSM and is reading proper voltage range relative to temperature
Here are the few things I now think it can be, after fixing the FPR & confirming the water temp sensor & it's respected wiring is good.
-Clogged or too small diameter mufflers/piping. Vs my 2 FC's with all stock exhaust, & my other w/ RB system, it just sounds, funny. Maybe there's an excess in back pressure. I guess the way to check would be remove both mufflers & drive, & see if there's an increase in performance & mpgs?
-Gear drag. Car had a bad rear wheel bearing, I replaced that. However, the diff &/or trans makes a harmonic wummm wummm wummm noise going down the road. It coasts fine, but maybe when loaded it's sapping engine energy? I can't see it being bad enough to rob several MPGs though...
-Leaky brake booster- there's a hissing when I shut the car off, and the pedal is immediately hard to press to the floor, so there's definitely a vacuum leak from this.
Any other ideas?
I replaced the secondary rail with another for the change in FPR (S5 intake on S4 car), and am getting 32 psi w/ FPR vac line plugged in, 40 w/o. Still doing high 13's on milage when dividing miles driven by gas to fill!
I'm at a loss here- from my original thread it-
-New tires, and allignment
-New brake master & properly bled brakes
-Injectors were removed & cleaned, then re-installed
-Engine hasn't been in the car more than 1500 miles. It's a used S4 engine, but was rebuild 2 years back. Fires right up everytime, but do not know the compression figures.
-New O2 sensor, confirmed operation of closed loop with checker light
-Not pulling ANY trouble codes w/ code checker (was pulling an O2 sensor, but it has been replaced & no longer comes up)
-New thermostat & radiator installed with engine, and full shrouding. Temps are normal
-Rats nest removal, vac routing is identical to the 88
-Main cat is replaced with a straight pipe, 2 pre-cat casings still there, no cats inside though
-Properly timed, and idle properly set, as well as TPS, to FSM spec
-No exhaust leaks, no fuel leaks
-Good condition used spark plugs. I disassemble lots of these engines in the junk yard (cordless impact FTW), and always take the plugs if they're near new.
-New E8023 Airtex brand fuel pump and fuel filter (pre & post pump)
-Water temp sensor:Checked by FSM and is reading proper voltage range relative to temperature
Here are the few things I now think it can be, after fixing the FPR & confirming the water temp sensor & it's respected wiring is good.
-Clogged or too small diameter mufflers/piping. Vs my 2 FC's with all stock exhaust, & my other w/ RB system, it just sounds, funny. Maybe there's an excess in back pressure. I guess the way to check would be remove both mufflers & drive, & see if there's an increase in performance & mpgs?
-Gear drag. Car had a bad rear wheel bearing, I replaced that. However, the diff &/or trans makes a harmonic wummm wummm wummm noise going down the road. It coasts fine, but maybe when loaded it's sapping engine energy? I can't see it being bad enough to rob several MPGs though...
-Leaky brake booster- there's a hissing when I shut the car off, and the pedal is immediately hard to press to the floor, so there's definitely a vacuum leak from this.
Any other ideas?
05-30-12, 11:48 AM
#29
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,796
Received 2,574 Likes
on
1,830 Posts
its actually easy to check the backpressure, just tee a boost gauge into the 6 port vacuum line.
on my 87 GXL, i was seeing around 0psi, up to about 4000rpm@wot then it starts to climb and i think it was about 3.5psi@7000rpm WOT in 3rd.
you need about 2.5-3psi to open the 6 ports.
the other thing i'd look at is the sensor on the bottom of the radiator, it does something with closed loop, so when its non functional the car runs fine, but it won't pass smog and mileage is down. the wires for the switch get pinched under the battery.
on my 87 GXL, i was seeing around 0psi, up to about 4000rpm@wot then it starts to climb and i think it was about 3.5psi@7000rpm WOT in 3rd.
you need about 2.5-3psi to open the 6 ports.
the other thing i'd look at is the sensor on the bottom of the radiator, it does something with closed loop, so when its non functional the car runs fine, but it won't pass smog and mileage is down. the wires for the switch get pinched under the battery.
05-30-12, 04:06 PM
#30
J9fd3s-
I'm running the 5/6 ports as well as vdi (s5 inake) from smog pump air & using rpm switches/solenoids to send the air. So sadly I can't easily check the backpressure
Switch is intact and working, as I've confirmed closed loop with a blinky LED inside the car
I'm running the 5/6 ports as well as vdi (s5 inake) from smog pump air & using rpm switches/solenoids to send the air. So sadly I can't easily check the backpressure
Switch is intact and working, as I've confirmed closed loop with a blinky LED inside the car
05-31-12, 06:54 PM
#33
Measure the dynamic chamber sensor voltage, it was within spec. Also pulled vac on the boost sensor as per FSM & it was within spec as well.
So still could be the leaky booster, drain from bad trans/diff, did not check the atmospheric pressure sensor behind pass kick panel.
Could PS be causing the drop? My other car has a manual rack. I just can't see it going that much lower when it was rated around 17 city from the get go, w/ PS.
So still could be the leaky booster, drain from bad trans/diff, did not check the atmospheric pressure sensor behind pass kick panel.
Could PS be causing the drop? My other car has a manual rack. I just can't see it going that much lower when it was rated around 17 city from the get go, w/ PS.
05-31-12, 08:37 PM
#36
Aws is removed, it does rev up cold using the BAC to rev it. I've just capped off on the dynamic chamber where the aws would attach.
I use the odometer too, its needing fill up, typically around 12.4 gal at around 185 miles. Sorry its not metric! Haha
I use the odometer too, its needing fill up, typically around 12.4 gal at around 185 miles. Sorry its not metric! Haha
06-01-12, 02:37 PM
#41
613nn
Join Date: Mar 2010
Location: orlando
Posts: 65
Likes: 0
Received 0 Likes
on
0 Posts
Has your air flow been tampered with? I've seen people open them and "adjust" It. Massive change in a/f when this is screwed with.
And what size tires are you running? I lost about 5 MPG changing my tires from a 205 front, 245 rear - to a 245 front, 275 rear.
And what size tires are you running? I lost about 5 MPG changing my tires from a 205 front, 245 rear - to a 245 front, 275 rear.
06-01-12, 03:57 PM
#42
Unconventional
iTrader: (1)
Join Date: Apr 2010
Location: Visalia, CA
Posts: 329
Likes: 0
Received 0 Likes
on
0 Posts
I get like 15mpg out of my 88 GTU. All stock (for now) except for streetport.
I was told I'd get like 20+ after my rebuild, but it's unchanged.
Nothing to contribute, just following your progress hoping to cure mine.
I was told I'd get like 20+ after my rebuild, but it's unchanged.
Nothing to contribute, just following your progress hoping to cure mine.
06-22-12, 11:18 AM
#43
Still getting between 13 & 15 on every fill up. Floods everytime on a warm start up. AFM checked, wasn't tampered with. Thinking maybe there's a short somewhere in the wiring harness, sending a bad signal to the ECU- going to probe all the pins & check the readings the next free chance I get.
06-23-12, 02:00 PM
#46
Still getting between 13 & 15 on every fill up. Floods everytime on a warm start up. AFM checked, wasn't tampered with. Thinking maybe there's a short somewhere in the wiring harness, sending a bad signal to the ECU- going to probe all the pins & check the readings the next free chance I get.
06-23-12, 05:30 PM
#48
Injectors have been cleaned.
Did a poor mans comp test, even pulses around 100 on the front, & 85 on rear. Not GREAT but not power robbing by any means.
I honestly think there's a short in the wiring harness somewhere, I'm going to back probe all the pins @ the ECU as a start
Did a poor mans comp test, even pulses around 100 on the front, & 85 on rear. Not GREAT but not power robbing by any means.
I honestly think there's a short in the wiring harness somewhere, I'm going to back probe all the pins @ the ECU as a start
