RB25 + custom 880cc injectors = terrible cruise and idle

[Decs]

Im pulling my hair out a little with this one...

RB25
GT3076r
sidefeed 880cc injectors in stock rail at stock pressure. overkill i know.
rb20 ecu
walbro pump
98ron ulp
blow through bosch z32 afm (brand new)
camtech drop in's

I've tuned similar setups with 840cc deka's with no issue, rb20 with 780cc denso's with no issue, rb25 with ID1000's and also no issue. up untill now i've never had a problem making large injectors behave. I've got the exact same injectors in my rb25 running e85 and it runs like a dream.

i started with the usual, resize injectors, adjust latency to 750us (as supplied injector specs state), change maf, turn off o2 feedback, start up, k constant to a happy medium under load and idle.

i've got it idling at 14.5 (most of the time), its happy as larry under boost. no matter what i do it cruises on 10.8:1. I've gone over every single constant and table i can possibly adjust 15 times and the only thing that has any effect is lowering the k value. problem is if i do that it starts bucking and carrying on as soon as you approach the boost transition. without putting crazy figures in the fuel map i can't tune around it.

the transition from rich to stoich is very sudden. for example with a tp value of say 22 its at 10:1 and on 23 its on 14:1. it hasn't even moved over a load cell on the map. its using inj pw's of around 3ms when its rich as hell and similar numbers when its good. problem is i can't get the pw's to drop at all where its rich.

im starting to think maybe the afm is naffed but it seems unlikely because once you get on boost its all tuneable and consitent. plus its brand new.

any thoughts?

maybe i'll have to go down to 550cc injectors.

[Eric]

Sometimes these weird problems happen when an 'incompatible' ROM-image is used.
Reflash the Nistune board with the ENT image that the ECU originally came with and see if it behaves better.

[skylinegtrhr]

blow through bosch z32 afm (brand new)

Do You have some custom tube for Z32 AFM as OEM plastic under boost can't hold very long and boost leak then become problem?

[Matt]

With the RB20 ECUs since they are all JDM based there seems to be no issue with incompatible images (like seen with the Z32 ECUs which have those problems)

Since you are controlling an RB25, make sure you are using the R32 image in the folder:

Documents\Nistune\ROM_Pack\Type2\ECR33_RB25\ENT\HCR32_FOR_RB25_11U00_MT_v4.ent

This will add code to allow TPS idle to work on the RB25 TPS. The RB25 doesnt have a switch which the RB20 ECU is looking for when hitting idle

If I programmed the board I write 'V4' on the board to indicate it has this modified firmware

[Decs]

blow through bosch z32 afm (brand new)

Do You have some custom tube for Z32 AFM as OEM plastic under boost can't hold very long and boost leak then become problem?

its runs perfectly fine under boost. its cruise (vacuum) thats the issue. so i doubt thats an issue.

With the RB20 ECUs since they are all JDM based there seems to be no issue with incompatible images (like seen with the Z32 ECUs which have those problems)

Since you are controlling an RB25, make sure you are using the R32 image in the folder:

Documents\Nistune\ROM_Pack\Type2\ECR33_RB25\ENT\HCR32_FOR_RB25_11U00_MT_v4.ent

This will add code to allow TPS idle to work on the RB25 TPS. The RB25 doesnt have a switch which the RB20 ECU is looking for when hitting idle

If I programmed the board I write 'V4' on the board to indicate it has this modified firmware

I programmed the board with that ent file ages ago. I then tuned it with stock turbo, injectors and afm. no issues. tps idle works fine.

This time round i've pretty much just plugged in and adjusted from where i already had it.

[PL]

Hey Decs,

So that TPS Idle flag definitely isn't coming on accidentally at light cruise??? Cos that would explain it...

Have you taken a log of the problem happening? Be interesting to have a look at what the figures are doing.

PL

[Decs]

I tested another new afm today. it made no difference. so that at least rules that out.

im starting to think the injectors might simply be too big and/or poor quality. really small changes in pw make huges differences to the fuelling.


Pete, no the tps idle flag is behaving perfectly fine.


Here's a datalog i did today with my wideband in the exhaust. There's a good example of what it does around at the 1:00 mark. goes from 10.6:1 to 15.2:1 with a tiny increase in throttle position. Also notice that for whatever reason the airlow voltage actually drops slightly when i open the trottle.

I've done no fine tuning of the maps yet, just trying to get it in the ball park first.

[PL]

Hey Decs,

I reckon you might be right. From what I can see in that log we're seeing a very small change in injector pulsewidth causing major AFR changes.

Around 1:10 we can see AFM = 2.1V, inj = 2.8ms, AFR = 15:1, then a couple of seconds later at 1:12 we see AFM = 2.2V, inj = 3.1ms but AFR = 10:1!

So a 0.1V increase of AFM voltage increases inj time by 0.3ms. Which is probably fair enough. But the question is - should an increase in injection time of 300us cause AFR to go from 15:1 to 10:1? I suspect under normal circumstances it wouldn't. But with big squirters maybe it will. They're not the dreaded "high flow" drilled out injectors are they?

I reckon with some very careful tuning and possibly adjustments to VQ map around this area you may be able to improve things if the injectors are performing consistently.

PL

[Matt]

I've gone over every single constant and table i can possibly adjust 15 times and the only thing that has any effect is lowering the k value. problem is if i do that it starts bucking and carrying on as soon as you approach the boost transition. without putting crazy figures in the fuel map i can't tune around it.

The only things which are going to affect injection time here are K, injection latency and the fuel map. Other tables wont help here (as you found out)

for example with a tp value of say 22 its at 10:1 and on 23 its on 14:1.

When you are at 0.33 and same at 0:53 when you take your foot off the throttle the injection time dives from 4ms to 0.75ms resulting in the AFRs going massively lean. At 1:00 I see your throttle increasing and injection pulsewidth and AFRs richening up

At this point I would suggest increasing your TTPmin so it doesnt lean out so much and also perhaps double check the injection latency and bump this up to avoid going too lean

As pl mentioned at 1:02 from 3.3ms to 3ms and such an AFR drop. Injectors seem suspect here to drop that much from 10:1 to 15:1 AFR. ECU is commanding not much difference but the results are huge

[Decs]

Yeah Pete they are modified stock jecs bodies. Not my choice but they fit peoples budget which is the problem.


Matt, I tried playing with the ttpmin and max as usually i can iron out all kinds of issues with ttp min. Everything I did made it waaaaaay worse.

The flow data supplied with the injectors states latency of 750us@ 14v. I also tried upping the latency but it just made the rich spots 10x worse. I tried dropping the latency but it made the lean spots even worse.

Im going to rip out the injectors and put them aside for an e85 project. I have the same ones in my 32 on e85 and its fine. Probably because your using about 40% more fuel.

I'll wak in some good quality 550cc items and see how it goes.

Thanks heaps for the input!

[Decs]

more hair pulling...


I got a set of VERY nice denso 550cc injectors. They look like a work of art in comparison.

didn't change a thing. still runs like shit!


more annoyingly, I tuned an almost identical car today. same 880cc injectors, pump fuel, rb25, rb20 ecu, z32 afm. it worked fine.

im going to try another ecu. its all i can think of.

is it possible for the physical pw output from the ecu to differ from the displayed output in a datalog?

[Matt]

The output PW from the ECU matches on a scope what consult is reporting inside Nistune (Injection time)

The only time it doesnt match is momentarily during cranking where crank ms is used instead

[Decs]

bugger...


well i tried another ecu. same deal. tried starting again with the map. same deal.

had it running almost ok while limping to a petrol station... then i put fuel in it. runs like shit again.

gonna have to start looking at the fuel system again. i'll check the pressure isn't up shit creek for a start. only thing that isn't brand new is the reg.

[dark_180]

Hey i am having the same problems as yourself but i have a ca18det, where under boost its fine but on crusie in light load it just goes to 10.8. I have also tried a new ecu with out a nisetune board and chipped it with other software and uploaded a working map from another car with same mods just diffrent injectors. I still had the problem. Have you had any luck.

[bachig24u]

Have any of the problem setups still utilizing the Fuel Pump Controllers?