Nistune Forums

So I hate asking questions that have similarly been covered before, but this has been giving me issues for over a week now.

I just changed my injectors over to some Blitz 700cc (SARD, DENSO, whatever they are all made by the same people) last week and can’t seem to dial in both my idle and my cruising A/F ratio. I can tune in one, but not both. Currently the settings are as so:

K value: 33625
Latency: 850u

Blitz says those injectors should have a latency of 650u. But to get them to work with that latency is next to impossible.

With the current setting I have perfect cruising (throttle at 8% +) and WOT A/F ratios as per they are mapped, but my idle is stupid off the scale lean, which causes her to idle very rough and almost stall out. If I mess around with the numbers to get a great idle then everything else gets thrown out of whack. It’s very frustrating. I can also get her to have the correct cruising and WOT A/F ratios at a lower K value and higher latency (K: 28000ish, 1050u), but in doing so the idle is stupid rich (11~12:1). When at this setting if I try to drop down the latency to bring up the idle A/F there’s like a wall where it’s either stupid rich or stall out the car lean.

Any insight would be nice.

The engine/ECU is a RNN14 sr20det with a z32 MAF and fuel pressure at 4 bar. And yes, the injectors are low independence as well as the car being wired for it (its stock low independence). For those of you crunching numbers, the GTi-R has stock 444cc injectors.

do you really need fuel pressure at 4bar ? ?
if so, why ?

anyway... have you tried to adjust the fuel map on the idling area ?

You get better drivability at 4 bar because of higher rate of fuel atomization and you car will do better at the emissions station (a big thing here in the States) because of better fuel atomization at 4 bar.

No I haven't adjusted the map because I'm trying to dial in the injectors, not mask whatever issue is happening. In theory you should be able to get the perfect setting of latency and K value to have your injectors firing correctly across the board.

I don't think you'll be properly masking a problem by tuning the fuel map...
plus, those injector are bigger than stock, so at the same pressure/duty they'll flow more... with higher pressure... I guess you see where I'm getting...

just to be clear, I'm talking about fuel base pressure (while idling)... stock it tends to be around 2.94bar without the vacum pipe connected and 2.45bar with the pipe connected... so if you're using a base pressure of 4bar, you're adding 1bar at least, wich is quite a bit...
though on the other hand, if I'm not mistaken, the fuel in the US is of low octane rate so that might have something to do with it... not sure...

anyway, from my understanding, giving the mods you've made, having to tweak the idle area of the fuel map ain't a bad thing, if the rest of the map is good and the AFR's are good accross the rest of the map...

Most of us I know of (if not everyone I know that has the proper add-ons to do it) run 4 bar. Running less is just a waste. You get better gas mileage, a better burn, and better emission numbers. The only draw-back is that you need to be able to adjust your fuel pressure and tune for it. I’ve been running 4 bar on my cars for almost a decade now. Regardless, 4 bar vs 3 is no difference in this issue seeing that you should be able to adjust the ECU to work with the injectors via K value and latency alone. Effectively all running 4 bar has done for the injectors is made them 808cc rather than 700cc. Same goes with the stock 444’s, they are effectively 513cc injectors at 4 bar.

I see what you’re getting at with adjusting the map, but I was hoping someone might be able to give more insight into the fact that they are being beyond temperamental in finding the perfect balance of latency and K value to make the tune work.


EDIT: BTW Matt (or whoever can move things), I just realized I posted this in the Type 2 section. Could you move it to the appropriate (Type 3) forum? Thanks!

Are they single pintle or EV6 style or?

bachig24u wrote:Are they single pintle or EV6 style or?

I'm pretty sure they are a single pintle design.

What is the maximum boost pressure expected at the inlet manifold?
Is the rising rate regulator fuel pres reg giving 1psi-fuel/1psi-boost or greater?
What is the Fuel press reg ratio? does the ratio change at all?

What are the diameters of the sections in your exhaust system?
Where is your Lambda situated exactly in your system? How far from to/from cat/mufflers/resonators etc?
What high pressure fuel pump(s) model are you using?

What is the maximum boost pressure expected at the inlet manifold?
16.5 psi from time to time, but I have a rock solid 12.5psi for daily drive

Is the rising rate regulator fuel pres reg giving 1psi-fuel/1psi-boost or greater?
What is the Fuel press reg ratio? does the ratio change at all?
Not fully sure what you’re asking for right here with these two. My fuel pressure gauge is in the engine bay. I run 4 BAR of pressure(~48psi on vacuum), and does of course change with load, about 1 pound per pound.

What are the diameters of the sections in your exhaust system?
3”, from the turbo all the way to the end. Mandrel bent.

Where is your Lambda situated exactly in your system? How far from to/from cat/mufflers/resonators etc?
About 6 inches from the turbine outlet. There is nothing in-between the sensor and the turbine wheel. So the next thing would be the cat, which is about 3-4 feet from that, then the muffler about 5-6 more feet back. No resonators.

What high pressure fuel pump(s) model are you using?
Walbro 255lph

I’ve been running this setup for over 6 years now. The only thing I’ve changed was moving up from the stock 444cc injectors to the 700cc injectors (because I’m moving up in turbo size soon). I have it set now so the cruising and WOT A/F ratios are perfect, it’s just when I come to an idle now it goes to 11-12ish A/F. I have the dead time set at 960u.

Let the car idle for an extended period, and see if it gets richer by it's self to the point where the car splutters or stalls.

Do you get puffs of black smoke or an unstable return back to idle after stabbing the throttle?

Let the car idle for an extended period, and see if it gets richer by it's self to the point where the car splutters or stalls.
Done that, just to see what she was doing. She sits steady at 11ish A/F, and just produces exhaust that smells of muscle car. She doesn't get richer, just holds as idling very rich.

Do you get puffs of black smoke or an unstable return back to idle after stabbing the throttle?
Nope, no smoke at all and she returns to idle with easy fine. She doesn't idle badly at these setting, just rich.

Sounds like the Fuel pressure regulator isn't leaking.
Just to add to what TM_S13 mentioned earlier re: fuel volume increase,

Bring the Minimum TP's down if not already, adjusting the latency down to its engines lowest smooth running point, drop the Fuel pressure to the point that your Lambda are on 1.0

If you have larger overlap cam installed then I'd bump up the idle speed a hundred or so to increase idle air speed.
You probably will have to bump idle up with the larger injectors also.

If this doesn't work, try adding some timing, if you are feeling dangerous then increasing the coil dwell time around idle to 1000rpm may help emissions. (no responsibility taken, who said that would work!!!).

If you didn't increase the MAF to something larger like a Lighting MAF than your fuel maps AFR's will probably never match the AFR's on the wideband. The translation curve for Z32MAF/Q45 is an almost perfect Match to 450cc

There's not much else you can do to get huge injectors to run well at idle on a small Litre engine.

I suggest to pull "0" across the whole Min TPluse width table when adjusting the Injection Latency ( and Injection Multiplier). When the number in the Injection Latency table is too big, it usually show rich A/F reading on idle, but finally you have to put some reasonable number back in that table.

So I’m starting to run out of ideas with what’s going on. It’s like there is a brick wall when it comes to the latency. I can drop it down to about 950u but once I go lower (940u for example) the car starts to idle very very rough, and the A/F on raises slightly too around 11.5 A/F.

I’ve tried:

Dropping the fuel pressure back to stock 3bar = nothing different
Altering the VQ map down at the idle RPM range = nothing
Changing the TPP min maps to 0 across the board = nothing

I have also noticed that she idles rough during cold starts. The A/F reads 14.0-15.2 when cold and warming up, but she needs some light throttle for about a minute or she idles super rough. This might be some IAC issue that might also be messing with things, I’m not sure. It’s just odd that it was fine and then went bad when I just swapped out the injectors.

I’m starting to think maybe it’s an ignition problem, but I don’t know. It’s really starting to annoy me. And though I can just switch back to the 444s for now, when I upgrade turbos here in a month or two I will need these injectors and I wanted to get this dialed in.

and have you touched the ignition and fuel maps ?