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17L/100kms with RB25 - solution?


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Just filled up the rb25 silvia ive got and found out its doing over 17L per 100kms. This is just gentle driving around the suburbs, no highway, so that could partially explain it, but its still off the scale.

Would a dyno tune help diagnose the problem?

Possibly oxygen sensor? Is it possible to test the o2 sensor without just buying another and seeing if it works better?

Considering the silvia weighs a couple hundred kilos less than a skyline, fuel consumption should be even better one would assume, so im keen to try and work out what the problem with this is.

91 Silvia Q's with Rb25DET (from '96 R33 afaik)

RB25 gbox

2.5" exhaust

Boxed pod filter

Running 10psi vis bleed valve

FMIC (600x300x65)

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ill check the fuel pressure hopefully sometime next week.

as for o2 sensor, ive read different places where you can get cheaper ones (from falcon or something?) that work just as good?

also ill reset the ecu tonight - didnt think of that till now, but it may help?

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EL Ford O2 sensor, from petroject cost me $80. The plug is different, as are the pins, so you need to swap them.

I couldnt get the solder to take to the OEM sensor wires, so had to remove the pins from the plug, cut the wires and solder directly to the pins.

Either that or $184 from nissan.

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I went from 250ks to a full tank to 350ks odd (i got 380 once) by changing the 02 sensor

its only supposed to last 40,000 ks according to nissan. i had mine replaced at 95,000 (odd) and it was the factory unit still. so i had 55,000 odd ks of a dead o2 sensor and bad fuel economy

the sole purpose of the o2 sensor is to give feedback to the ECU so it can lean out the fuel mixture

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Geez, I'm starting to feel a bit better now (I'm not the only one)!!

I presume you're running the standard ECU. I'm running a similar setup to yours in my R33, with the addition of a Microtech LT12.

Up until a couple of weeks ago, I was consuming about 20.5L/100km driving it like a hurse!! Had it in my head that it should be returning more like 11-12L/100km.

Had some fine tuning done on the dyno last week and tonight I've returned 16.1L/100km with quite a few WOT blasts. Am pleasantly relieved that it's improved, but I'm not sure whether I can realistically expect much better at this stage. My car is currently putting out about 165rwkw, so I guess that this rate of consumption is not so unreasonable, it's just not what I'm used to.

However there are blokes out there running much higher outputs and claim to be running better economy than this!? What's the story guys? How is it so?

I definitely thought that a standard ECU would return much better economy than mine as the Microtech doesn't have a "closed loop" circuit to reduce consumption at idle and on steady throttle.

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perhaps the dyno tune helped reduce it, but a new o2 sensor may help more?

does consult on the ecu (brother who works at nissan thinks they may have consult computer thingy) tell u much, eg would u be able to tell from it if the o2 sensor is dead?

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this is readout from consult. are ECU's made as either MT or AT? if so, i think i may have a AT ecu

ticket reads:

SYSTEM: A/T

DATE: 07/11/2004 17:50:37

P/#: 31036 - 52F00

SELF-DIAG RESULTS

DTC RESULTS

THROTTLE POSI SEN

T/C CLUTCH SOL/V

LINE PRESSURE S/V

OVERRUN CLUTCH S/V

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turns out my o2 sensor had short circuited or something internally (resistance ~ 8 ohms), and melted the insultation off one of the wires, then melted the wire.

so guess ill be needing a new o2 sensor

does the EL Ford one fit the same thread? if so does anyone know how it's wired up?

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im not sure, it seems that most people are of the opinion that if the ford el sensor (3 wire) fits the thread, then u can use it.

try unscrew urs, then put it back in (not too hard) then go down to repco, unscrew it (bring wet cloth), and take it to the counter and compare it with the el ford one?

btw my fuel consumption is down to 13L/100kms from 15 and 17 last two times i filled, was hoping for less though. i think my ecu might be an auto one so perhaps something to do with that?

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