Reall bad MPG on my S14 SR20DET

[K_style]

Hello everyone..

I recently swapped S14 SR20DET and it has

1.1mm Cosworth head gasket
stock bore CP pistons
stock 370cc injectors
Z32 MAF
FMIC
Apexi air filter
Walbro 255 fuel pump
stock FPR
R.S enthalpy tuned ecu
NGK copper spark plugs for SR20DET

I am getting 17 miles per gallon on highway driving
first time I thought it was tune problem.. I contacted RS enthalpy
and they sent me new roms which should help my mpg..
drove 2 weeks after.. nothing seemed changed...

when I used to have S13 SR I used to get 24~25 MPG on highway

one thing though before car is wormed up after reving rpm
Idle get really unstable and try to die...
I was looking for any vacuum leak.. but cant find any...

does idle control valve has to do with gas mileage ?

I was thinking to remove ROMs and put stock MAF and see how it is...

any advise will help.

thanks

[K_style]

need help !!!! I am filling up twice a week.. too much $$$$ =(

[slothonaleash]

Look around for boost leaks

[S14Serge]

Definitely check for boost leaks, and another thought would be check your wiring of the Z32 Maf.... that would answer the bogging down wanting to die at idle.

[lazysk8er2]

i have the same problem on my sr redtop

i upgraded to a 2871r and have 555 inj. z32 maf and enthalpy tune.

for some reason it runs like crap with that set up. but when i take out the injectors maf and enthalpy ecu and put it back to stock the car runs fine.

i have a brand new o2 sensor and coolant temp sensor(maybe you should check yours as you will dump fuel if the cts is bad)

my injectors are brand new tomei injectors and the z32 maf works on my friends car.

well thats my 2 cents and i have changed the ecu 5 times on this car back and forth from enthalpy and says it should work.

good luck

[dongoesby]

before anyone says this first, test your timing.

i'm actually on the same boat except i'm running stock ecu and maf.
i did so many things to help the mpg and idle in the past months, and many things seem to have got involved.

1. boost leak (make sure all hose are tight including brake vaccum hose)
2. iavc and throttle sensor (make sure they are adjusted correctly per fsm)
3. maf ground (i know many nissan mechanics recommend to have an extra ground)
4. aftermarket fpr (if your stock fpr is clogged, that could be the major reason of bad mpg especially while driving local)
5. make sure there is no coolant/water going into your engine (that could yield to bad mpg)
6. check no air in coolant system and replace coolant sensor if necessary
7. that is all i could think of now...

I have gone through many listed above and seems the idle and mpg are getting better and better (painful process).

[Mosaic]

When dealing with ECU issues and mileage, verify if you are going to OPEN loop sooner than u should, I had a similar mileage issue on an SR20VET, turned out the prev. owner had put in an IMPUL Hi Perf. CHIP....which goes WOT open loop at 1800 RPM...so no lean cruise AT ALL. I installed a MAF interceptor that delivered closed loop control up to 3800 rpm UNLESS i went into boost. Got a 20% improvement immediately.