Need some input on Injection Latency and Multiplier

FlawleZ · Post by **FlawleZ** » Mon Oct 20, 2008 6:27 pm

So we're tuning a Z31 with 650cc RC Injectors and a Z31 MAF. We're having a very hard time getting consistent afrs regardless of how close we get on the values. Based on the chart provided in the sticky, the RC 650cc injectors are rated at .41@14v and .54@13v. However, I'm a bit confused as to how this translates into the NIStune latency.

Any advice on a good starting point for these?

Thanks!

kenbam · Post by **kenbam** » Mon Oct 20, 2008 7:41 pm

If your talking about the values in the fuel table (A/F ratios). they will never be spot on across the range. They are meerly a starting point. Trims will alter them slightly. Get your multiplier close to the mark (mid map rpm, low load) and then set your latency at idle.

FlawleZ · Post by **FlawleZ** » Tue Oct 21, 2008 2:12 am

kenbam wrote:If your talking about the values in the fuel table (A/F ratios). they will never be spot on across the range. They are meerly a starting point. Trims will alter them slightly. Get your multiplier close to the mark (mid map rpm, low load) and then set your latency at idle.

Actually, I was referring to the K and latency values. We can't seem to find a working compromise between the multiplier and latency. If the idle is set well so that fluctuation is only within ~.5 or so, driving conditions even under light and moderate load are extremely lean. When setting the multiplier at cruising speeds under light load, the idle then returns to a 1.0-2.0 fluctuation.

Bernardd · Post by **Bernardd** » Tue Oct 21, 2008 2:59 am

1SIKZ31 · Post by **1SIKZ31** » Tue Oct 21, 2008 5:16 am

Bernardd wrote: set your entire fuel map to 14.7 and then set the k value for best results in the 2.5k to 3.5k off boost. reset fuel map to 12.5 and do it again. at this point the wideband will tell you if the latency needs to be changed in the idle - lower rpm ranges. after you have the idle set up, increase your ttpmin to the point where it starts to richen up the idle, then lower it a bit at rpm you idle at.

Why would you set the K @ 14.7 and then completely change the K again by setting the whole map to 12.5? Whats the point? Why not just start out with 12.5 til you get the K right?

Also... You said increase your TTPMIN to the point where it starts to richen up idle, and then lower it? Please explain in detail.
The post you made is absolutely 100% informative to a great extent but some points you kind of skimmed on instead of explained in full detail!

I don't know about Flawlez but im getting problems getting my IDLE (TPS ON) AFR's to read anywhere NEAR the fuel table! ... Im running WAYYY to rich @ idle, I have to set the Fuel table to -17 (Raw values) to get the idle to be @ 14 AFR's!
If I adjust the Latency down till I get closer to a Raw value of 0 to get 14:1 @ idle, the car will start mis-firing because the Latency is SO low! (mid 700's) and if I try to adjust the K lower to make the lower RPM's read more correctly then it makes me run some abnormally Lean AFR numbers in the fuel table to get it running anywhere near what I need it and by the time I richen it I run out of resolution to run any richer! (raw value 127)

Example... RIGHT now I have my K set to 250, and my Latency set @ 700, Raw values in the first 4 columns regardless of RPM are set to 0, I am getting 13.5-14.5:1 AFR's which is perfectly fine but I am having to set the Raw values under 0 boost and above to like the 100's and I basicaly run out of resolution because 127 is the farthest it will allow to go!
Advice???

GZ@hybridka · Post by **GZ@hybridka** » Tue Oct 21, 2008 8:45 am

If your RC injectors are spec'd with an opening time of .41-.54 mS, set your nistune latency around 400-500 uS (or 900-1000us with earlier nistune versions). Nissan injectors are usually spec'd around 700 uS.

You are adding around .2ms to the total injector opening time (unnecessarily) which is requiring that you set a lower K number in order for you to get proper idle, it is not helping you out any as far as fueling up top either.

Latency/injector opening time should not cause your engine to misfire at idle, it is simply a static amount of time added to the total injector pulsewidth so that the injector has a chance to fully open. If your engine was misfiring, leave the latency alone (if you have already adjusted it for your injectors) and change the K number instead.

TTP min can be a bit confusing. What you should do to start with is just zero out the entire TTP min and start tuning your car. Once it seems to be tuned out right, idle good etc.... You can raise the TTP min numbers back up until they start adding fuel at idle, and then back them off just a bit (so that they dont).

TTP min is just as it is described, a total theoretical pulsewidth limiter. It comes in handy as a feature to prevent the injector pulsewidth from dropping too low in certain conditions, but does not have to be utilized.

hope this wasnt confusing...

GZ@hybridka · Post by **GZ@hybridka** » Tue Oct 21, 2008 8:55 am

Oops, looks like I got the posts confused a bit.

Info should still be relevant.

1SIKZ31, which injectors are you using?

And also, what maf/ecu hardware modifications for the maf?

1SIKZ31 · Post by **1SIKZ31** » Tue Oct 21, 2008 9:39 am

Yea sorry about that I hope I didn't thread jack!!!!

Im using:
DSM 450cc Injectors
Z32 MAF (BLOW-Thru!!!)
Walbro Fuel pump
Aeromotive A-1000 FPR (set base pressure @ idle to 40psi)
87na ECU with Nistune

a LONGGGG time ago (last year) matt told me to use "1390uS" as a good starting point for the injector latency, is this true? Or do I need to use half of that number?
I have found that if I am idling, If I have my Latency at like 1150uS, the idle is CRISPY AS HELL, around 800 its still pretty smooth but I around the 700 range you can feel little misfires here and there... Obviously when I say this I am talking 14.0:1 AFR's @ idle, regardless of latency.

Maybe a log would help someone to help me out?

GZ@hybridka · Post by **GZ@hybridka** » Tue Oct 21, 2008 10:21 am

Partly at least, I think some of your problems could be attributed to using a low impedence injector (I assume with a resistor pack).

The dsm ecu uses the resistor pack and those injectors, along with a 690us opening time. But, I do not know how the current coming from the dsm ecu injector driver compares with the nissan. This is important with low impedance injector because it requires a certain current profile for it to operate correctly (peaking and then holding current for the duration of pulse).

When you use low impedance injectors on a high impedance (saturated) type injector output (along with a resistor), sometimes it is necessary to increase the opening time well beyond spec. It simply is not getting the current "peak" to open quickly like it is supposed to.

Now, that said, I have tuned dsm 450's personally on a bunch of hondas and a couple nissans that use saturated injector output, and they seem to perform properly for their rated size throughout the entire range, but again I do not know how the current out of the injector output (honda) compares with the nissan.

In order to properly open low impedance peak&hold injector with the nissan ecu you must use an external peak and hold injector driver (theoretically anyways). The need will increase with the larger aftermarket high performance peak & hold injector also, the opening times are going to be really long if you try using only a resistor pack.

Or, you can just switch to a saturated injector of similar size. Series 5 rx7 are nice, they have modern sealed connectors.

I think that would eliminate a lot of the discrepancies you are finding with the tune. It could also have something to do with the MAF/VQ setup....

GZ@hybridka · Post by **GZ@hybridka** » Tue Oct 21, 2008 10:23 am

I believe Matt has corrected the Nistune setting for latency in the later versions, but I am not sure how it may interact with your specific firmware. You would have to ask him.

1SIKZ31 · Post by **1SIKZ31** » Tue Oct 21, 2008 11:07 am

I have a low-impedance driver in my ECU. 88 and 89 were the high impedance!! (not using any resistor packs)

So I have low impedance injectors with the low impedance drivers!

I think you have mistaken.

Matt · Post by **Matt** » Tue Oct 21, 2008 5:55 pm

so what is the impedance then on the injectors used with the ECU that you have (1984-1987 UDSM)?

how does that compare to the impedance that you use currently?

yes latest versions - halve the original latency values posted here

1SIKZ31 · Post by **1SIKZ31** » Wed Oct 22, 2008 2:06 am

I am using Impedance of 700 at the moment.
K value is @ 245 I Believe.

I am getting NICE and consistent AFR's cruising (value of 0 in the first 4 load columns regardless of RPM) and im getting 14:0 AFR's across the range EXCEPT low LOW loads and idle!

@ idle im getting 12.8-13.5 AFRS (Fluctuates)
@ 20 inches of vacuum IN GEAR im running VERY rich (11:1) and this is a problem which I cannot fix?

I really like the way the car is driving right now, cold start has NEVER been so damn SMOOTH, and driving in gear the AFR's are fairly consistent and are not flying all over the place!

Any ideas of changing the Idle AFR's and the LOW lite load AFRs? I REALLY would like not to touch my K and latency much because im afraid to lose the consistency im getting right now!!!

Heres my Tune (see attached) if someone can give me some advice!!!