SR20DET tuning issues

[Mr. Invincible]

I'm having a problem with my SR tuning correctly.
There are two distinct things happening.
I have adjusted my MAFS and Injector sizing maps and have tweaked the latency a smidge to achieve a pretty steady idle but I'm stalling after accelerating beyond 3k rpm and letting the throttle close instantly.

The other thing is that I'm cutting out when boost starts to build. Like at about 3500 rpm.

The background info is as follows.
I have 800cc injectors and a T3 Turbocharger, AR70 with a 4" inlet. I'm running the Z32 MAFS with the setup. I run a large wastegate set at about 10PSI stock and do have a fully functional BOV on the hot side of the innercooler.

I have heard that the location of the MAFS in relation to the turbo spool has a lot to do with tuning headaches like mine and think this may have a lot to do with the problems I'm having. My top mount turbo inlet is 4" turned directly on a 45 degree elbow right as it reduces and turns into the 3" that connects to my Z32 MAFS. I'm concerned because of the turn and the reduction being so close to the turbo, etc. and want to see if anyone has had the same issues with this type of setup and maybe get some decent suggestions on how to correct this if possible.

I will attach a pic of the setup for reference when I can.

Please help and any ideas are welcome. Thanks, >Chase.

[skylinegtrhr]

I had same symptoms on one car because of very small boost leak on one connection, also reset TPS to be around 0,5 V it's help stabilizability of idle I notice that when mounting JUN intake manifold on SR20 and also ignition must be set correctly and CAS must be in good condition (also have problem with CAS on one S14) so start with this basic checks.

[Mr. Invincible]

I had same symptoms on one car because of very small boost leak on one connection, also reset TPS to be around 0,5 V it's help stabilizability of idle I notice that when mounting JUN intake manifold on SR20 and also ignition must be set correctly and CAS must be in good condition (also have problem with CAS on one S14) so start with this basic checks.

Hey, I appreciate the input. I've looked for boost leaks and have none that I know of. I also have checked the timing and it's on the mark. 15 degrees btdc. I'm still looking into the situation and will update here if I find out a solution. May check the TPS angle too. I adjusted it once and got some mild improvement but don't want to change it too much.
Thanks again.

[skyline_stu]

4 things I can think of.

1) Do you have a vent to air blow off valve ?
2) Is your base idle speed set correctly?
3) Have you corrected your TTP min to suit
4) Have you reset your TP max

Remember to start out with LOW boost pressures when tuning - you may well find you will need to rescale your maps accordingly with such large injectors and airflow meter

Attach a log of the cutting out - it helps a lot to be able to replay things.

Stu Cornall
Nistune Specialist & Calibration engineering

[Mr. Invincible]

4 things I can think of.

1) Do you have a vent to air blow off valve ?
2) Is your base idle speed set correctly?
3) Have you corrected your TTP min to suit
4) Have you reset your TP max

Remember to start out with LOW boost pressures when tuning - you may well find you will need to rescale your maps accordingly with such large injectors and airflow meter

Attach a log of the cutting out - it helps a lot to be able to replay things.

Stu Cornall
Nistune Specialist & Calibration engineering

Stu, first and foremost, I appreciate the response to my issue and would like to thank you for taking out your time to try and help.
I will try and give you some more info at this time and see if that helps for the next time I get a chance to adjust some things.
The answers to the previous questions:
1)Yes, my BOV is vent to air and not a recirculating unit. It's been tested to be good.
2)The idle was set correctly on my last setup I used with 555cc injectors and the engine ran perfectly. I've adjusted it a little on this setup with the screw on the manifold to try and keep it from stalling on decel, but that has not helped, it has only raised the idle after it stabilizes. I have not had any positive results changing the idle setting in Nistune but that could be that I'm not sure what I am supposed to be changing. Just alterning the figures slightly in both directions achieved nothing useful.
3)I Have not corrected my TTP min to suit yet. I have made no adjustments to those figures yet whatsoever because I wasn't sure if that effected this and didn't want to make a crucial mistake.
4)I Have not corrected my TTP max to suit yet either. Same ordeal. Not sure what to do to get the right results.

Also, I have just used the resize injector and the change MAF feature to get the general map settings I'm running and have done minor latency changes from there and a few on timing at idle. It seems to me that it should be to a point where I can go through the RPM range at low boost to be able to look at things but being that it's cutting out so bad, I don't want to run it up like I should be able to.

I will be extending the MAF position in relation to the turbo to see if that makes any change and will also look into TTP max and min and see if it does anything positive.

Thanks again, I'll be on here to report within another day or two.

[chris2712au]

just read your post... do a log of the data especially from the maf sensor.. it would seem that reversion is the problem that when you are transiting to boost and if you have your BOV on the cold pipe or bov spring too tight.. it can be that some air is reversing and this tends to null the maf reading out.. and a null maf reading will stop the injection pulses.. no injection pulses will stop the engine.. you can keep your TTP min up a little which could help and look into the fuel cut / recover tables.. but it will depend on what the maf voltage is doing..

theoretically if you raise the TTP min it will start injecting too much fuel for the maf voltage reading.. which should inturn start making the idle mixture rich as long as you have the feeback turned off.. but if you raise it just beow that maybe it will be enough to hold the fuel up till the maf sorts itself out..

Maf voltage is flow through the maf.. on the Z32 it doesnt care in which direction not like the stock Sr unit.. as it has a seperate chamber flute setup for the sensor airflow.. someone should look at designing a bigger version of it..

[skyline_stu]

Chris,
I see an error in your suggestion - reversion ?? As the car transitions onto boost total airflow will increase, even if the BOV is leaking or not fully closed - this is why we always suggest a recirculating valve be fitted (it stops the ECU 'gaining' airflow). I suggested TP max (which is LOAD limit) be checked for his cutting out issue (this tells me he's going for gold if hitting the airflow cut or a HUGE intake air leak [and not creeping up on the tune]). On the SR MAF some air would still pass through the sample tube due to the significant area change in the reverse flow direction ([venturi effect] but no where as bad as the Z32). The BOV on the cold or hot side should not radically affect the metering, unless the intercooler is far to small for the volume of air being passed (posing a restriction). TTP min would need adjusting, in the real world, due to the 800cc injectors fitted.

Your MAF will not 'null' out as suggested - it may reduce the output voltage but should never achieve close to 0 (a DTC would be set at that time also). Oscillation of the airflow wil produce a rapid change of the MAF voltage, the ECU would attemp try to average the value when it comes off decel fuel cut. I'd expect a changing voltage which the ECU may well think there is a corresponding airflow change and try to provide additional fuel enrichment (as long as your not in decel fuel cut). Some serious reworking on the VQ table often fixes this. I realy dislike tuning a vent to air valve on MAF equiped vehicles, you can easily spend hours getting it correct. Often you find the fuel consumption is higher as the ECU is always changing the AFR correction to compensate for leakage air under closed loop conditions. I've made bigger SR maf's before, with the overall cost involved it's cheaper to use a Z32 and tune correctly.

Chase, check your TPS is set correctly too - you should have a fuel cut under deceleration from higher RPM - your AFR meter should show very lean mixtures when under fuel cut. I didn't mention TTP Max because you should set that on the dyno as you rescale the fuel tables (don't forget to rescale the IGN tables too, otherwise you'll loose tuning resolution!)

What DOES your mixture do when it's about to stall? I suspect it goes bulk rich. And as stated earlier, send in a log !!

with
1) RPM
2) MAF V
3) TPS V
4) AFR

If possible include a log with TP value instead of MAF V too.

Oh, and be cautious with that turbo - looks like a chinabay spec turbo, not very reliable or durable in my experience when worked hard- They're cheap for a reason. (super shiny compressor cover, ID plate and rusty exhaust housing give it away).


Stu Cornall
Nistune Specialist & Calibration Engineering

[skyline_stu]

Oh and Chase, get a decent air filter!! those dry foam style elements only stop house bricks and small children entering your turbo.

Stu

[chris2712au]

I have a bov fitted to my s15.. when on the gass and you back off it lightly flutters and messes up the afm reading.. as for the recirc bov.. they are ok but as long as the reversion charge is pointed at the compressor wheel... otherwise same happens the air comes back out the air cleaner.. the larger the volume between compressor and throttle the larger the reverse charge..

My stainless mesh cleaner doesnt help the matter..

when the throttle is closed.. the pressure has to go somewhere if not back from where it came through the compresure blades aka flutter.. back through a recirculating BOV or dumped out.. reversion is unavoidable.. you wont see it on a dyno though..

From my experience the Z32 maf is way more sensitive to this issue far more than the sr20 number as I have had both on my s15...

http://www.plmsdevelopments.com/sr_setu ... #7.z32_afm

an extract from petes web page.. I have experiened the same..


the z32 will not care which direction the air is going.. as you said simply gaining air.. I can see where you are headed and it does make sense.. but I never experienced it with the sr20 item.. If only I had a log of the z32.. still.. you could see the wacky afm readings I was getting.

I disagree with the venturi effect of the sr20 afm.. there is stuff all flow in the reverse direction for it to go through the sampling port and there is little to no pressure drop across it at that time when the throttle is closed to be a problem..

[Mr. Invincible]

Guys, thanks for the help and suggestions.
I didn't have time to mess with it over the last couple days. (Daddy+family stuff) But, I will try and save a log of what is happening and post it once I lengthen the intake pipe and retest. Not sure it will help but am trying that first just in case.

And yea, the turbo was cheap and was sold as China junk, but it's big and I have a friend that owns a turbo rebuild shop. The internals are all that matter and when this one wears out, which should take no time, it will be built with the best bearings, shaft and seals. Just about any housing and set of compressor wheels will do their job so I'm not worried about that.

Also, the foam filter elements are all I'll use. I know they don't filter as well as paper/cloth but I clean them often and foam always produces more power. Hell, I see more people not even running a filter than are on most over the top applications. I just want to remain steetable, etc.

Will be in touch, tyvm - Chase.

[skyline_stu]

And yea, the turbo was cheap and was sold as China junk, but it's big and I have a friend that owns a turbo rebuild shop. The internals are all that matter and when this one wears out, which should take no time, it will be built with the best bearings, shaft and seals. Just about any housing and set of compressor wheels will do their job so I'm not worried about that.

You'll find that the thrust bearing will eat itself up in no time when under 'reasonable' boost, this will then munch out the dynamic oil seal surface - filling your intake piping/cooler with oil and totaling the comp cover/turbine housing. The dynamic balance job is often sub par as well. I wish it was as easy as a rebuild, the wheels/bearings don't match up to anything close to garrett parts, thus you end up with a nice shiny door stop I see this here all the time. It's better to replace it with a genuine quality item. I've had excellent results with Turbonetics turbo's, they have the best industry warranty. Got a client here with a GT2871R running regular high 11's. Be wary if you have a cheap manifold too, the welding has, in 99% of all cases, been done incorrectly (not back purged) and rough chunks dislodge, often killing your current and/or repalcement turbos. Not trying to scare you off, but it happens very frequently to my poor clients vehicles ( i don't fit those manifolds myself at all unless I rework them - which takes plenty of time to do right)


I'm waiting for your logs
Stu

[Mr. Invincible]

Okay guys, great news!

I added about 4" of length to my suction piping and have had positive results correcting the issues I was having. The idle now stabilizes and the engine is not cutting out apon hight RPM acceleration now. I guess my hunch was correct about the 4" to 3" reduction and then immediately turning into a 45 degree angle was somehow spiking the values to the MAFS and causing the reading to be way off.

Anyways, I will be trying to tune it out now that the manners are more correct and will be in touch if I need further assistance.

Thanks a lot, -Chase.

[skyline_stu]

That's great news. Now time for your tuning

Cheers,
Stu

[s13_silvia_redtop]

do you think you can include another picture of what your intake setup looks like now? i was having the same idling problem too and my intake looked extremely close to yours, i hope this works for me too