Boost cut

chris2712au · Post by **chris2712au** » Sat Feb 21, 2009 7:22 pm

When you upgrade to Z32 is there still a fuel cut ? and is it voltage driven ?

or

Can we find out where the boost cut is in terms off MAF voltage.. and make it adjustable ? or set a max TP so you cant run off your maps and outside the range of your injectors ? or cut spark after 100% duty cycle on the injectors ?

Just asking cause it would be hard to max out a z32.. And should I put this on to finish off the intake I would be concerned about running out of fuel.. cause of over boosting ?

Or should I get a turbo fuse ? what do you do to protect against that ? could be as simple as your actuator line coming off ?

chris2712au · Post by **chris2712au** » Sat Feb 21, 2009 7:41 pm

maybe petros was onto something here ?

Legionnaire wrote:I think i'll post here.

First of all i would like to thank you for all your boost control research and all that time you spent figuring out BC capabilities and posting results in here.

Second, about boost spike on the first gear - I think that events are happening and environment is changing a little too fast on the first for stock boost control system to keep up with it. You can try making your map load dependent in the spiking area - this may help. I don't have any first hand experience with BC on s15's, but i do with er34's and even with different boost controlllers, including AVC-R and the such, and even with the fastest feedback speed set on them i was unable to eliminate 1st gear boost spike completely without resorting to some measures like two stage boost/lowered solenoid start duty. But i think that it is not a major issue - like Pete said you can not load up your engine enough to damage it and VE is dropping after peak torque RPM point anyway, so i would not bother.

As for hitting fuel cut - have you removed it from TP limit vector? I'm asking this because when i did it to my r34 and then found that fuel cut was still there when i reach 1-1.05 bar IMP, i was shocked. I thought that i had missed something or done something very wrong. It came out to be pressure referenced cut, not MAF voltage cut.

Cheers, Petros.

Matt · Post by **Matt** » Sat Feb 21, 2009 10:30 pm

the TP cut is based from load which uses AFM as an input and comes out of a calculation. There is no specific voltage, only TP/256 in the tp limit table

as for the boost pressure sensor cut on ER34 we dont know where this is accessed on that ECU but I think stubbing out the boost pressure sensor may be one option used

chris2712au · Post by **chris2712au** » Sun Feb 22, 2009 9:46 am

cool, so if it tries to go over the tp limit it shuts down..

Legionnaire · Post by **Legionnaire** » Fri Feb 27, 2009 11:39 am

Sorry for not being here, Chris.

I actually have a very limited knowlege in this regard. What I know is mostly skyline-related, and my info is mostly from a manual written by a japanese guy for Z32's, It can be found on cherrypicker.tripod.com if i'm not mistaken.

There he says that it works like this (we'll use RB20DET as a good example):
- you look at your so-called "TP-limit" vector. For RB20 it is filled with 128's.
- when you interpret this value as a hexadecimal, you get 80h. You can use standard calc program integrated in every version of windows to convert values back and forth.
- then you take the next value in your "TP-limit" vector and also convert it to hex. Since in our example it happened to be 128 again, we get one more hexadecimal 80.
- then you put those numbers together and get 8080h. Now you convert this back to decimal and get a 32896. This is the value that is compared to the value that has just been recieved from MAF sensor and passed through VQ map. For RB20 with standard 22680-02U00 green labeled MAF this value corresponds to the flow that suits between 4.08v at MAF (31936 VQ value) and 4.16v (33918 VQ). When airflow through MAF is such that returned VQ value exceeds TP limit, ECU begins to take countermeasures to eliminate this unwanted situation.

This is the summary of the section of manual related to so-called AF cut. Maybe this guy is wrong, Matt definitely has more info on the subject.

You see, it was an R34 where I first met this "problem". R34 are unusual here, TPs are not very limited, so to speak. In other words the maximum value of each TP limit entry is 255. R34 have this TP limit vector full of values that are either already 255 or close to 255, so it is not a very typical example. I'm not sure why exactly is this, maybe MAF is close to its flow limit with 25DET Neo. I have DBD9 limiting value at high revs, that is 56281 decimal and is ~4.9v @ MAF sensor. So it is more like the last line of defence against engine overflow.
I tried to increase boost pressure using stock turbo to see what can I get from it. Every time pressure exceeded ~1Bar, the car behaved like very rough traction control was activated - it virtually stopped accelerating. I talked to people and one of SAU members said that he had solved the problem by soldering standard spec diode inline with stock MAP sensor. This causes a voltage drop in MAP signal and *possibly* renders stock boost control useless. Maybe, if we solder trimming resistor instead of diode in there, we can control boost by simply adjusting the voltage drop. This is the area of further investigation.

Sorry, that was not of much help.
Petros.

Matt · Post by **Matt** » Fri Feb 27, 2009 6:05 pm

Now that I've aquired an ER34 of my own to play with we will be having a look on it once bigger turbo is installed...

chris2712au · Post by **chris2712au** » Fri Feb 27, 2009 8:27 pm

Thanks for the info.. it is definitely something we should look into for a last line of defense..

That diode probably is a zenner (signal) diode and he is using a clamping circuit to clip the voltage from the maf to not exceed a certain level... maybe 5v.. I have seen some circuits that use pots.. you simply turn it down to where you want the signal to stop rising..

Problem is that you have to be extremely careful with these things as you are then running in an uncontrolled state.. the engine thinks that the load is not changing and still throwing out the same amount of fuel.. things only get leaner...

Also for the GTR there are some circuits to manipulate the traction control circuit.. I just love my DIY's.. I went in a high power gtr and loved it felt alot safer than a 200..

This guy Julian has some interesting write ups..

As always thanks to the Authors and designers of the system in the zip..

Matt · Post by **Matt** » Fri Feb 27, 2009 9:07 pm

sounds promising... if you were to upgrade to the Z32 AFM then this problem wouldnt be as noticeable until you start hitting the limits of the Z32 AFM

Legionnaire · Post by **Legionnaire** » Fri Feb 27, 2009 9:41 pm

well, hm, i'm unsure - why do you want to put a diode into MAF signal - when airflow exceeds certain amount, MAF's voltage stops rising anyway and the only mean you have to still control the process is to tune against RPM - because calculated TP is rpm dependent.

what i meant is that ER34's have MAF to manage the engine and also have a MAP (actaully, TBAP - because pressure line goes from throttle body instead of intake manifold). It is located at the end of the engine, just above sixth cylinder. From my experience, this pressure sensor is used to control boost via stock boost control solenoid and is also used to cut the engine if pressure exceeds certain level, about 1 bar. By putting diode in MAP's signal line, I shifted the level of the boost cut by ~0.4 bar. I think it is not a good idea to do pull off this stunt on an engine that still uses stock boost control, but since the car this mod was done to has AVCR instead of stock solenoid to control pressues, it is a safe thing to do.

To my knowledge, among all pre-2001 nissans, this layout with both pressure and massflow sensors is only used on ER34, others just remove AF cut by setting all the values in TP LIMIT table to 255.
The latter method - with 255 in TP limit table - I dont like it because i dont know if my MAF is still reading something or is already out of scale. So I like to set this limit to a value between 4.98v and 5.06v or between 5.06v and 5.12v, so the cut lets me know that I'm running out of measurable flow with this particular MAF.

Pedro · Post by **Pedro** » Sat Feb 28, 2009 4:54 pm

in the R34 address file there is two TP limits the first I believe is for the AFM but unsure what the second one is for

also I have spoken to ashley from classic performance dyno centre about this exact thing and he told me he hasnt had the problem of the boost cutting and he has run over 1 bar thru his r34 (19psi he has run thru it ,maybe more)

check out his thread here viewtopic.php?t=816

from memory he has only changed the tp limit (AFM)

hopefully he will log on and tell us more

Pedro

Matt · Post by **Matt** » Sat Feb 28, 2009 7:26 pm

he would be running Z32 AFM though so probably why he didnt have that problem

Legionnaire · Post by **Legionnaire** » Sun Mar 01, 2009 9:43 am

Pedro wrote:in the R34 address file there is two TP limits the first I believe is for the AFM but unsure what the second one is for

also I have spoken to ashley from classic performance dyno centre about this exact thing and he told me he hasnt had the problem of the boost cutting and he has run over 1 bar thru his r34 (19psi he has run thru it ,maybe more)

check out his thread here viewtopic.php?t=816

from memory he has only changed the tp limit (AFM)

hopefully he will log on and tell us more

Pedro

Hmm... I have just re-read that thread - he uses stock boost control solenoid. Now that is really interesting.

standard boost control valve with modified restrictors

What is his WG spring stiffness? Where are restrictors installed?

I do not deny his great results or his experience, but on the other hand I have my own tests, where the car was hitting boost cut at ~1 bar, but when I detached a pressure line (that feeds pressure to the MAP sensor, I may have some pics of it) and blocked it off, the cut at 1 bar was gone.
When I tried to disconnect MAP sensor electrically (disconnect its plug) car would not start. This was done on a sII RB25DET Neo.

Pedro · Post by **Pedro** » Sun Mar 01, 2009 4:09 pm

could the zenner diode work ???

one that would limit the voltage flow to 4.4v or there abouts

when using the emanage ultimate in my r34 i had to clamp the boost voltage
at around 4.4v

it would give it plenty of standard ecu control up until around the 14psi mark
then you would have to tune after that to keep it safe

but on the other hand if its using the MAF voltage against the boost voltage to work out if its overboosting then surely adding a z32 AFM would throw out the calculations and allow you to run more boost

Matt · Post by **Matt** » Sun Mar 01, 2009 9:46 pm

personally i would be very careful with using zener diodes for this kind of stuff on the MAF

reason is that you are going to top out the read voltage sooner and then when there is more air than it is actually reporting its going to lean out

Pedro · Post by **Pedro** » Mon Mar 02, 2009 9:14 am

I mean a zenner on the boost sensor so it clamps it at 4.4v