RB25 Holset HX35 problem during acceleration

[MATTs14]

Ok i got my car running and moved the maf back to the turbo instead of doing blow through. Still idles s***ty but drives pretty good.

The problem i'm having is that at idle its between 15 and 16 AFR and when cruising its around 12 and 13 until it gets to about 6 or 7 pounds of boost. WHen i get to that 7 pounds it goes completely rich and starts to backfire and pop and bog down. I'm running a Walbro 255, a Nismo FPR, stock injectors, and an RB25 MAF.

My diagnosis of the problem is that the ECU senses that the injectors are maxing out so it dumps fuel at it. Let me know what you guys think. THanks

[krayton]

how much boost are you running.

and i think your a lil off with the theory of injectors maxing out so it dumps fuel at it....

but your thinking, and i like that.

[krayton]

oh and just read your title. what are you using to tune.

please tell me something good. and your running low boost. otherwise i dont like you anymore

[MATTs14]

Yes i'm running low boost and I'm using a Power FC but no tune on it. I'm just limping around until i can get to my tune next week. I'm just wondering if it in fact is my injectors maxing out or if the problem is deeper. I don't really wanna show up at the tuner and have a whole different set of problems.
Modified by MATTs14 at 1:36 PM 8/30/2009

[Carryl]

Check for boost leaks, make one of those boost leak testers and see if a leak shows up under boost.

[rb25drag]

I dont think its an injector issue. If so you would lean out not go rich.

Since you have not tuned the PFC im going to say your fuel map is no were it needs to be.

When you are in and out of boost the ecu senses a different map kpa, which puts it in a different fuel bracket and if the ecu is not tuned correctly in those different kpa brackets the car will do different things as for fuel.

Get the pfc tuned and you will be fine.

[MATTs14]

I highly doubt this is a boost leak. I'm not even getting to very high rpm's

[MATTs14]

rb25drag, I see that you're in tennessee as well. Where could i get the PFC tuned? I don't have a hand controller so it will need to be somebody that has datalogit.

Another thing, if its on the stock map, why would it be doing funky things? Wouldn't it like you said, lean out when boost hits instead of going rich? I ran the stock ecu and it did the same thing.

[crazyandevil05]

Check coilpacks? or spark gap?

[MATTs14]

I'll check both when i go back. They appear to be the stock plugs so that could be a problem. I guess timing could be off as well.

The coilpacks and plugs do sound like a reasonable option. I guess when the computer start to add more fuel the plugs and coils could fail to keep up and cause it to go completely rich.

[rb25drag]

I don't know alot on the pfc. I dont know if they can be tuned or not without a hand controller. Im sure they can tho. But I personally use A-Z Performance for my dyno time. There located in Soddy Daisy just out side of Chattanooga.

I also Tune my own car with the Megasquirt ECU so I dunno about how well there tuner is.

From what I have heard and read in the pass the PFC Stock map tune is crap and also with you having a Bigger turbo than stock its going to be way different with the maps.

From what I have heard of the Holset turbo's is your prob picking up boost somewere in the 3k range and On a stock ecu. The stock turbo is not even close to spooling yet, So im sure in the PFC map they did not account on the EARLY boost and prob have it way rich down low. Thats why when your cruising around its dipping into the rich mode,

Now your coils and plugs could be an issue also. You can easily check those and change them. Also be sure to go with a COLD spark plug, It gives you a little more tuning ability.

If you happen to have a Coil pack issue or think you do. I have my Stock coils laying here at the house your welcome to try. I know there GOOD. I went 14psi on them with no issue's.

But Im pretty sure its just your tune.

[MATTs14]

Ok thanks for laying all that out there. That really helped me to figure it all out!

As far as the coils go, I'm going wasted spark this week so I won't be needing them, thanks for the offer though! I appreciate it

Also you suggested a colder spark plug, which one do you suggest? I have the Power FC from a friend just kind of doing a trial run, but i'm considering going with Nistune as a cheaper, yet affective alternative. Any input on this?

[rb25drag]

I run an AutoLight racing plug. There like 2$ a piece. Ill have to see what the part # is. its been a while.

Also I have not messed with Nistune stuff either. I personally LOVE the Megasquirt and wastedspark LS2 coil setup.

Megasquirt Gives you full capabability of everything IMAGINABLE on a car.

So far I have had alot of sucess with the megasquirt.

You can call DIYAUTOTUNE and give them your setup and they will build you an ECU for around 530$

They send you a wiring harness thats labeled and easy to install. You may have to change a Couple of wires in the plug for the coil setup and if you do a launch control setup ETC.

If you really wanna learn to tune your car your self. Megasquirt is the way to go IMO!

You can check out my setup here in this Build thread!zer...age=1

[crazyandevil05]

another plug option, and the one i've always used throughout my flogging is NGK bkr6e or bkr7e would be one colder. any parts store should have them. they're pretty cheap, i think $3ish. and gapped to .8mm from the boxes i've gotten.and let up know how the wasted spark works out

[MATTs14]

Thanks for all the pointers rb25drag and I'll definitely look into the megasquirt option. Do i have to do any more wiring or will it be plug and play??

And thanks for the plug tips crazyandevil05, i looked at those once already so I'll probably end up running the bkr7e so i have some room to grow on. And as far as the wasted spark, this will be my second time doing it so I'm sure it will go smoothly but could post up some pics if you'd like.

One other thing, rb25drag, how does the wasted spark setup you have differ from the buick grand national coil retrofit, which is what i planned on doing for the 2nd time.

Thanks all!

[rb25drag]

The megasquirt is no plug n play. There is alot of wiring and a few mods you would have to do. BAsically your staring from scratch on the wiring. Which leaves a CLEAN result under the hood.Also you will have to do a 36-1 trigger wheel with a vr sensor as the stock cas will not work as a trigger on the megasquirt.There is alot of info on Diy's website you need to checkout and research.The Ls2 coil wastedspark vs the buick wasted spark is like the new zr1 vette vs a honda accord. Bigger, better, faster and no competition lolThe ls2's have a built in ignitor which the buicks do not. Also if your using a megasquirt it open the option of launch control,flat shifting, and rev limits, U also have the options of setting the dwell.The ls2 coils are as powerful as they come. And usually cheap. I picked up a set of 8 used on ebay for 96$

[MATTs14]

Is there any writeup on doing the LS2 coil swap??

[Cjmartz2k]

You can NOT do a real tune with a hand controller. You need dataloggit or something similar. You can't even begin to trouble shoot with out a tune. That's the problem now I'm sure, but you might find there are more problems like plugs or coil packs or something else later. What size injectors are you running?

[placham]

You can NOT do a real tune with a hand controller. You need dataloggit or something similar. You can't even begin to trouble shoot with out a tune. That's the problem now I'm sure, but you might find there are more problems like plugs or coil packs or something else later. What size injectors are you running?

^ he mentioned stock Inj at top, what are they like 370cc side feed for RB25's right. and 270cc top feed Rb20, and obviously 444cc for Rb26

[Cjmartz2k]

Ah, just re-read that. Probably not causing your problem, but you'll need bigger injectors for sure for that turbo.

[rb25drag]

I have not seen a write up on the ls2 coils. I may of missed it tho. But I know darius just done the ls2 coil swap using the pfc. Might get in contact with him.

[Cjmartz2k]

I finally read that all the way through. You are maxing out the MAF, the computer is freaking out, and it's dumping tons of fuel into the motor and pulling all the timing in hopes of saving it. Some people call it "boost cut" even though it has nothing to do with boost. What's you MAF voltage when it goes rich and pops? I'll bet it's close to 5v. You need a z32 maf and a tune (and bigger injectors).

[WhatsADSM]

OP, first things first you should really check for boost leaks. Any boost leaks you have will show up as a rich condition under boost.

As for the LS2 coil thing (although I actually don't think that is the underlying issue):zerothread?id=353832http://forums.nicoc ... ?id=435099

[MATTs14]

Yea thats what i was thinking which is why i didnt flog it at all. As soon as any pop or backfire started.

Cjmartz2k, thanks for your diagnosis. I didn't realize that this turbo would be able to max out the MAF and injectors so quickly. The spool on this thing is crazy! It spools like my stock turbo rb20! Also if you still have that Power FC i think i'll go ahead and buy that from you. I planned ahead and bought the z32 maf so i'm good there. I won't go any lower than an injector in the 740cc range. What do you guys suggest as far as brand? I have heard mixed things about Deatschwerks, which i considered getting.

At any rate, thanks for all you guys help, i feel stupid that i let it happen so early but now i know

[l0nestar]

I would max out the stock AFM and stock 25 turbo at 0.8 BAR / 10psi.

Upgrade to a Z32 AFM. The 'base' tune on the PFC is horrific. It's designed so that you can get the car to start, then you are supposed to take it immediately to an authorized PowerExcel tuner to be tuned.

[MATTs14]

I'm contemplating what engine management to use. I've heard nothing but good things about Nistune but a local buddy swears that Megasquirt is the best there is. Any input?

[l0nestar]

NisTune = PlugNPlay

MegaSquirt = complete re-wire & all new sensors.

[RustspecS13]

I didn't think they had a nistune program for the rb25 though, because its a much harder to crack ecu.

But you can get a Z32/j30 ecu and run it with a rb25 map and a short jumper harness or a quick repin.

I'm a huge fan of nistune and I'll be buying for my rb20 soon. One huge benefit of using the OEM ecu (or in your case a OEM ecu from another nissan) is reliability. Its made to start in the extreme cold and hot and start every time. That and the starting maps for all different weather is already done for you, and that's a huge tuning process for megasquirted cars.

Both are easy enough to tune, but if you put a lot of miles on the car or use it as a daily Id lean to using nistune/z32 setup. I like megasquirt as well, and its a great option for a lot of people.

~Alex

[MATTs14]

Yea i think I'll go nistune for sure. Anybody know exactly how to repin an ecu harness?? I tried it on my F3 plug but to no avail. And exactly which z32 ecu do i need? I read through all the Nistune threads and couldn't find exactly which one. Can i use the auto? Can i use the N/A or the TT or both?

[l0nestar]

Yea i think I'll go nistune for sure. Anybody know exactly how to repin an ecu harness?? I tried it on my F3 plug but to no avail. And exactly which z32 ecu do i need? I read through all the Nistune threads and couldn't find exactly which one. Can i use the auto? Can i use the N/A or the TT or both?

Any Z32 ECU, preferably the older (93-pre) since it is the 8-bit.