Silly Fueling Issue - Type 3 Board S14 SR20DET

[Jont]

Hi all!

I am new here, this is my first post. I am also new to tuning and NIStune.

My intentions are to map my current S14 to the level I want, but we'll see how it goes

I started up a couple of weeks ago, Ive been getting the gear working etc, and doing various test runs.

Before I decided to start doing my own tuning the car was already running a type 3 board with a map done by a well known chap from the UK. My first action was to start fresh with one of the OEM maps from the nistune ROM_PACK. I used "S14_SR20DET_75F00_MT_NATS_EDM.bin".

I have started by keeping things simple with some cruise tests. I have noticed with the above OEM map at cruise with O2 Feedback switched off I am averaging 11A/F at the wbo2 sensor. This is strange as surely it should be around 14.7, as the car has standard injectors/MAF etc. So this evening I adjusted K const right the way down to 25,000 from the original 33,000. This did in turn give me the desired 14.7AF at cruise. (as a consequence the car would no longer idle without stalling, but not too bothered about that now as Im just testing)

So my question is - why on a more or less standard car have I had to reduce the injector output by 25% to achieve a normal working AF? Surely if this is the oem map, then it should just work fine without any changes. I was only expecting to have to change the Injection multiplier once I installed my larger injectors.

(it gets more strange when I see that the aftermarket map that the car came with has a k const of 39,000! No idea why that is... but it seemed to work weirdly)

The car is:
1994 S14
SR20DET 90k miles
All the usual low level mods (FMIC, Walbro 255lph, Straight Through Exhaust etc)
Stock MAF/Injectors

I have performed all of the pretune checks as described in the NIStune manuals (maf clean, 15º timing etc)

BTW - I know that I am huge newb at this and have probably done something stupid, but any feedback appreciated.

Thanks

[johnus]

hi welcome to nistune,
the fact that the k was changed to 39000 suggests that its been modded more than you thought what was the latency on that tune? If you know who the tuner was it might be worth giving him a ring ,he might remember the car and tell you why he tuned it that way. Also before doing any tuning i alway clear self learn ,this clears the long term/ short term fuel trims

[bachig24u]

the Walbro specs aren't same as stock.

[Jont]

Johnus - Thanks mate. The previous tuner's map latency was 580, the same as the OEM map. Infact when I compare the tuner's map to the OEM the only difference is 1) Load Cut rise 2) K Const rise 3) Main fuel/Ign maps at the top end. 4) DTC knock sensor, DTC boost sensor flags removed.

Also this comment "Also before doing any tuning i alway clear self learn ,this clears the long term/ short term fuel trims". This sounds important, what does this mean please? I may have missed something somwhere. Thanks! EDIT - Oh did you mean the O2 closed loop?

Bachig - yeh but with the stock ful lines/rail/fpr I assumed rail pressure would be the same as standard? 3bar or what ever it is.

There is one other thing, the car is costantly firing two errors at me, please see below:


The boost sensor is just becuase I removed the stock sensor/solenoid I guess. Still trying to diagnose the knock error, I guess faulty sensor/wiring/noisey engine, it fires constanly even on idle. Either way I assume neither of these errors are causing my fueling irregularity.

Thanks guys

[PL]

I'd be checking fuel pressure before anything else. You wanna see 43psi at idle with hose removed from fuel pressure reg.

PL

[bachig24u]

comment: - yeh but with the stock ful lines/rail/fpr I assumed rail pressure would be the same as standard? 3bar or what ever it is.

no, it's not correct to assume that the regulator will regulate to the same pressure if a higher rated volume vs pressure pump is installed.

[Jont]

OK thanks guys that makes good sense.

I'll check the Psi at idle.

Ive just installed Nismo 740cc/m injectors, so we'll see how she performs with these. Wish me luck