Very large duty cycle?! 130+

[MomentFD]

How is this possible? I've read that duty cycle can exceed 100% because of calculations but on my recent test run I hit 100% around 4k rpm. I'm on an S14 SR20, stock turbo, boost around 10psi. This is the stock boost for the JDM trim I believe and my only upgrades are intake, FMIC, exhaust. Also the map is stock so far, just trying to figure out my starting point.

On a side note, my AFR numbers from the LM-1 look good, between 10.5 - 12 for WOT up to redline.

Also, my MAF is reading up to 4.7 volts or so, which also seems near the top limit. From what I've read I really thought I'd be able to get push for more power before needing to upgrade injectors / MAF. TP is maxing out at 120. I definitely need to change that part in the ECU.

Thanks for input guys. Starting out advice always welcome.

[Matt]

Duty is calculated as injection time * RPM / 1200 / 100 %

Here your injection time works out as 24.37ms x RPM at 6525 = 132.51%

That is quite a large injection time which is why the duty cycle works out this high. However AFRs are the main thing to look at here and those seem to be fine.

You can measure the physical injection duty by using an automotive multimeter with duty cycle measurement for an exact representation

[MomentFD]

I read a case where a guy re-wired his fuel pump and that dropped his duty cycle from 90% to 70%.

Does the ECU even have the feedback ability to do this automatically? Could the short/long term fuel trims make up for low fuel pump pressure? It still doesn’t make sense as I thought those values were disregarded in open loop / WOT runs, or is that incorrect?

Either way I have some 550 injectors and an FPR coming in, I’ll get that sorted before pushing the engine anymore. I’m trying to keep the duty cycle as sane as possible.

On a side note, if you have input, I got greedy 2 weeks ago and upped the boost to about 14psi, and the car was pretty dang quick. Anyway I did a pull and around 6k rpm the engine cut power abruptly and it came back around 2k rpm where I just cruised and started worrying about my motor. I’m really hoping I hit the TP load limit, and not something like leaned out and broke something. I wanted to do these recent 10psi test runs to see if my TP was getting anywhere near the limit (140) but they seem to be plateauing @ 121, which is where my TTP max is set. I’m thinking the TTP max of 121 prevents the ECU from logging actual TP values > 121? Not sure, just tryng to take it easy now and learn the ECU and motor. I’m thinking a new MAF is in order too...

[Matt]

Dont think would make any difference from the ECU side of things, at that RPM/injector time it will calculate the same

O2 trims are determined whilst in closed loop and long term trims will affect overall injection. however you should aim to tune the vehicle with the intended mods so the ECU is not trimming

Watch your AFRs when going on boost if you have a wideband fitted. There are TP and RPM limits in the ECU so depends where those were set

Total TP (TTP) limits maximum TP the ECU will calculate. We normally increase this so it does not lean out the tune

[MomentFD]

I'm going to do some more testing to figure this out, but I'm curious, are you saying if TTP Max < TP Load Limit (in my case it is, 121 vs 140), the ECU will never boost cut because it won't calculate TPs > 121?

[MomentFD]

Dropped the boost back down to 7psi and did a few logged runs.

AF Alpha - right at 100
AF Alpha learn - 131

TP MBS comes in right under 121, the stock TTP Max.
Injection time is still coming in hot ~24ms = duty cycle of 115 this time.

I just don't understand how a stock S14 SR with bolt ons is working the injectors so much. My AFRs are still okay (10s), how would hte ECU know to up the duty cycles to acheive this, cause I can't imagine a stock tune relying on 100%+ duty cycles. Really makes me question what happened on my 14psi run, I hope I didn't break something. I'll have a fuel gauge soon to check the pressure.

Happy holidays all, thanks for the support.

[UNISA JECS]

Dropped the boost back down to 7psi and did a few logged runs.

AF Alpha - right at 100
AF Alpha learn - 131

TP MBS comes in right under 121, the stock TTP Max.
Injection time is still coming in hot ~24ms = duty cycle of 115 this time.

I just don't understand how a stock S14 SR with bolt ons is working the injectors so much. My AFRs are still okay (10s), how would hte ECU know to up the duty cycles to acheive this, cause I can't imagine a stock tune relying on 100%+ duty cycles. Really makes me question what happened on my 14psi run, I hope I didn't break something. I'll have a fuel gauge soon to check the pressure.

Happy holidays all, thanks for the support.

WTH 10 AFR's that retarded rich trying fixing the AFR and then see what your duty cycle is cause that's horrible and that will screw up your duty cycle numbers, sounds like your injection multiplier needs to be adjusted.

[MomentFD]

Adjust K on stock injectors/maf? Doesn't seem right to need to do that

Let me see what the fuel pressure looks like, and I may just get these 550s in and see if that clears it up.

[Matt]

Reset the trims and see if that learn goes back to 0. There is a bug in the latest beta version of Nistune with the long term trimdisplay on SR20s so use Display > Raw View

Usually best to resolve existing issues before doing things like upgrading injectors. Yeah K should be factory setting (actually car should run as factory if you have no mapping changes). Check fuel pressure, MAF working properly, no air leaks etc

[MomentFD]

Roger that Matt, I'll have a fuel pressure gauge and boost tester soon.

I still don't understand how the injection times can be so long, why the ECU would even decide to make them that long. Even if I am having a fuel pressure/boost/MAF issue, I wouldn't think the computer can KNOW this and adjust my injection times. I'd think injection times would stay normal and I'd have running issues because of it. Maybe I'm missing something.

Merry Christmas all.

[raddy]

AFM value significantly affect injection time, so if there is any AFM malfunctiom present,it will screw up fueling. If you have high Alpha correction, it can point also to oem lambda issue. For sure,any significant boost leak will result similar way.

[MomentFD]

"Happy new year chaps. Long break from 240 work but I finally got a fuel pressure gauge on. I'm sitting right around 49 psi which is 5-6 psi too high, most likely from the Walbro 190 LPH. Fine by me, I'll take the safety while sorting out this injector thing. Going to try clearing the fuel trims today, and I still need make a shady-tree boost leak tester.

Could it just be that the map that was loaded on the ECU @ Autovaughn has some very high values in the fuel map? I haven't found a good explanation yet on how the ECU could even be doing this. Could a leak or faulty MAF really cause this much injection time to be added on?"


Thanks for the support guys.

[Matt]

Compare the map they have loaded against the factory map for your ECU and use that to compare (use compare button in top panel)

[MomentFD]

I think I cleared the fuel trims, I selected the test and hit the check box then hit the button and it said test started.

After a bit of driving,
AF Alpha ~ 100
AF Alpha Learn ~ 130

How do I know if 100 = 100% or 128 = 100%? If 100=100% I could see why my injection times are so dang high. If 128 = 100%, I'm still looking for my issue.

Think I should just get my new Z32 MAF and 550cc injectors in and see how it looks after getting the K constant figured out? I know having a healthy base is the key to starting a tune properly, but honestly I can't find anything wrong, the car is driving very great, AFs are healthy. I really can't see any mechanical issue requiring 30% more fuel (compared my injection time of 24ms to a stock-ish log I found here w/ injection time 18ms), and I'm really thinking it's just the map

[Matt]

I've put up another release 1.2 yesterday with the fix for AF alpha display. It appears that the ECU uses 100 as the base for AF Alpha (STFT) but 128 as the base for AF Alpha learn (LTFT) despite the documentation from Nissan saying otherwise

If AFRs are fine then I would move onto the modifications