Terrible gas mileage ~12mpg!! What's wrong

[robomatic12]

I have a freshly rebuilt twin turbo engine in a 2+2 with rebuilt stock turbos by a garret distributor. I have cleaned the MAF, air filter, new spark plugs when engine rebuilt, recent oil change. I have a Kakimotor ECU and a greddy boost controller set to 10psi for street. Tire pressures are set to factory. The only things I can think of are the 02 sensors and the TPS being bad. Anyone else have any ideas? I'm getting about 300-330km per a tank in a 2+2 and I'm not heavy on the throttle just getting to school/work. That's terrible!!!

[Zwicked]

Have you run ECU diagnostics including the o2 sensor test? This is the first place to start.

Definitely something wrong from your mileage.

-does it idle smooth?-is it responsive and has lots of power?-have you tested for vacuum leaks?-have you checked the timing?-what injectors are you using?

[robomatic12]

-does it idle smooth? -idles really smooth and running on all 6 cylinders-is it responsive and has lots of power? -gobs of power but seems a little slow down low in the rpm range, like its slow to rev up-have you tested for vacuum leaks? -not yet, im guessing boost leak detector? or a propane sniffer thing-have you checked the timing? - last time i checked with a light it was at 15 degrees but i will check to see if it moved. i used the front left cylinder (looking at engine bay) but i will use the ptu loop if it makes any difference.-what injectors are you using? - should be stock injectors but really it is unkown, could be different?

[Zwicked]

Only other thing I can think of is the chip you have. Are the exhaust tips really black?

[robomatic12]

Unfortunately I have silencers in so it's hard to say but they don't look like crazy rich dirty. Looks normal to me and doesn't smell super rich besides not having cat's installed. Just checked and Im getting a code 55 all is okay. I'm going to run an o2 diagnostic next time the car is warmed up just dont feel like wasting gas letting it idle in my driveway.

Is there an easy way to check if the injectors are stock? They still use the old style metal clip connectors.

One thing I can say is lacking that it feels slow to respond to throttle input. When I'm trying to blip the throttle on downshifts or rev up it seems slow.

[HellHamer]

you could try tightening the throttle cable right under the throttle body cover, my NA was idling rough and that was suggested to me and it worked and it still idles at 750

also the slow acceleration does it feel like its delayed?

cant you look on your ECU cover to see what CC they are?

[robomatic12]

It's all Japanese =) It just says "Kakimoto Racing ECU" plus some other characters in Japanese.

Yeah it feels delayed like hmmm.... waiting.. POWERRR

[robomatic12]

Just did the 02 sensor diagnostic, both sides are blinking consistently. The right side does blink slightly faster than the left but both meet the 5 times within 10 seconds. Can I rule out the 02 sensors?

[Zwicked]

I'd say they are fine. All signs are pointing to the chip in my opinion, although it seems they have a good reputation

http://www.nengun.com/kakimoto-racing/

[robomatic12]

It seems like my last option is the TPS, which could solve my power loss issue at certain rpms while crusising. Apparently that can kill gas mileage

I'm also going to re-check my timing

Thanks Zwicked

[JDMZ32]

I had sluggish power at one point due to my coolant temp sensor (to ECU). $20 replacement. I replaced it, the connector, and the water temp sensor (for gauge) and it ran a lot better. I've also had a ton of coil pack issues, but you said you're sure you're on all 6. I'm not the best mechanic, but if what I said helps at all, good.

Edit: You would've got a CTS code had that been the issue. Nevermind. Still some good info I guess. Good luck...

[Zwicked]

You can easily test the TPS before spending money unnecessarily. When you set it up, just open the throttle slowly and watch the multimeter. Easy to see if there are any dropouts along the path of it opening. Also, do test the coolant temp sensor as the other person mentioned. Sometimes they can go out of spec and not throw a code but does affect performance. In the manual in the EF&EC section somewhere around page 178 it shows how to test it. I've had one go bad like that.

By the way, what do you mean you have silencers in your exhaust???

[robomatic12]

I get uneven readings from my multimeter, seems like at points it will go back to a previous voltage while I'm still opening it more and it's jumpy. I also tried doing it with ohm's and there is a point that it reads infinite.

I will check the coolant temp sensor!

It's a Kakimoto exhaust and ends in something like a 4-4.5" tip, there is a little donut you stick in the tip which has some sound deadening material inside of it and reduces the opening to 2". It makes it alot more "street legal".

[pintovit]

I had a bad TPS and it was always cutting out the engine while trying to maintain speed... Didn't notice a huge improvement on mileage when I fixed it though...

Do you smell fuel? Fuel leaks can hurt mileage (obviously!)...

[txQ45]

If you had a wideband you could watch it and be able to tell more..
For instance if your about to shift and it goes rich you have a boost leak..
A consult , blazt, nprobe, or Nistune would tell more....

[NISMOlvr]

Id check TPS,Check MAF voltage at idle ,Mid throttle and WOT.Spark Plug Gap and timing,Coolant Temp sensor,Last you may have a thermostat that opens too early,(low temp )and engine is not getting to normal operating temp quickly.

[evildky]

heavy right foot? I had as low as 9 mpg with lots of boosting, think of boost as a gas leak

[NORCAL300ZX916]

ha im constantly at 13 or 14 mpg given im NA 2+2 and i would say my driving is 70% city also. but yea i thought my car was having a problem so i was taking it easy for a while and OH MY GOD 17mpg lol just from shifting a 3g. but F that i smash around if i wanted good gas milage i would have turned im my balls and bought a HONDA!

[es.biggs]

Hahahahaha damn. I think I get around 17 mpg in my NA...Haven't done the math yet though. Maybe it's time lol

[NORCAL300ZX916]

so far with the headers and ecu flash and remap i have been smashing around(probably harder than usual) and gettin a consistant 16mpg w more power HELL YA and thank you DRIVENAUTHORITY/MATTZGARAGE

[DokkTekk]

Mine was the same thing, a bit sluggish upon acceleration. The TPS is within spec. I was getting a code 54 (rightside O2 sensor). The O2 diag shows both sides blinking as well (at least 5 times within 10 sec). But when I checked for resistance on the O2 sensor, it read 1 ohm. It's suppose to be 3-1000 ohms. Changed the O2 sensor, and she's running alot better. My MPG improved dramatically, acceleration and power was restored.