SKiDaZZLe

Both Tim (t32gzz) and I have had problems with the car running into limp mode when we are boosting above 8-8.5lbs.
Basically the car will go into limp mode, but there will be no MIL (check engine light) commanded on. There also are no OBD2 codes stored... but, if you clear the engine codes with an OBD2 scanner, the limp mode goes away.

The experience is very similar to what happens when a MAF sensor dies on you... there is no revving past 2500, car idles rich enough to make your eyes tear!

We both noticed this happening when we are boosting on the highway... Tim's happens to do it much much more often than me, though.

So, we both go to Jotech to get some testing of his car done on the dyno. We get a couple runs in (5.6lbs, 7lbs, 7.5lbs), and then on 8.5lbs, the same limp mode is achieved.

I start to mention it sounds airflow related... so we do some more passes while looking at the Super-AFC2 for Airflow %..

This is what we noticed:

When the car sees 100% airflow before 4500-4700, the car will go into limp mode. We did this many times it can be duplicated every time.

So, we went home, keeping our boost set to 7.5lbs, and all was well. For the last week, we have been trying to figure out how to get better numbers on what is happening...

Well, today we decided to get more details and facts on what is actually happening...

Here is what we did:
We did some runs at 5.6lbs, 7.5lbs, 7.7lbs and 8lbs.
What we looked at was the following for each boost setting:
1) Max Airflow %
2) RPM @ Max Airflow %
3) MAF Sensor voltage
4) OBD2 Input of AirFlow

Here is what we got:

MAF Sensor output to the ECU is a 0-5v range.
The Voltage of the sensor when the AFC2 says 100% is 5.115v
This corresponded to a MAF reading of 33.872 lbs/min on the ECU.
This is all the air the stock MAF/ECU combo can meter.

At all boost settings, 100% airflow was reached.

Here is a breakdown of the RPM where 100% airflow was reached:
5700 @ 5.6psi
5100 @ 7.5psi
4900 @ 7.7psi
4700 @ 8.0psi (Limp mode achieved)


Now, here are some thoughts:

Seems like the ECU does not like to see Airflow hit 100% before 4500rpm (maybe still in closed loop?!?!). Also, ECU does not seem to care if the number is 100% over 4500rpm... This is why it is critical to have a boost dependant fuel delivery system (like emanage, or DFMU)... The stock ECU just cannot deal with boost!


No one besides Tim and I have seen this, because I think we are the only TT guys running well over 7.5lbs of boost...
You might ask "What about the ATI S/C guys...? They got up into 8 and 9 lbs..."
Well that answer is easy... those centrifugal S/C's do not reach that boost level until they are well over 4500RPM. In fact, those kind of S/C reach max boost at redline.
See, a turbo'd car can reach max boost at 3500rpm...


What's next?

The next thing we need is to see what an N/A car with a Super-AFC2 reaches as MAX Airflow... I wonder if its even close to 100%.
The other thing to get is an OBD2 logged N/A car, and see what the MAX Airflow (computated by the ECU) is...

Tim should be making a post in the general engine forum, asking for help on that.

Only option I see is to clamp the MAF sensor voltage to something like 4.7v... This way the ECU will never see 100% flow. Since we have a boost dependant fuel delivery system, I do not necessarily care if the ECU sees true airflow above what an N/A car would see.

Here are links to clamping MAPs (which is the same idea):
http://www.thedodgegarage.com/turbo_map.html
http://minimopar.knizefamily.net/perf/mapzener.html

As a side note... it would be better to put the diode before the Super-Afc2, as opposed to after it, as then you can still increase the voltage to the ECU by raising the Air correction % in the fuel maps. If you put the diode just before the ECU, it will never go above the diode voltage...




Questions/Concerns?



PS: Props to GaryK, in first trying to convince us all the MAF sensor was ill-equipped for F/I on the car.

JeffR116

Kudos on the dyno researching. At least you already know what is causing it.

That's really interesting...

Chebosto

iTrader: (43)

Michael-

please reiterate, this is only happening sparringly, correct? or is it everytime you are 8.5+psi.


If you're stating that the MAF at WOT @>8.5psi is 5.115V, thats it. game over until you can get a broader operational voltage of the MAF.

Not sure if Tim told you or not, my N/A car saw 4.78v STOCK.

TS is working on the issue- to see if its feesible to adapt another MAF to the Z.... or to trick the MAF into reading something else... i'll report our findings when we turn up the boost higher-


-Cheston

toykilla

iTrader: (1)

wow, that is some good findings.. keep us updated!

fluidz

hmmm........I had the same problems with LIMP MODE after I put on my CAI for about a week......sometimes it would just go into limp mode........I was like wtf.......the I unplugged my MAFS and battery, and tried again and a day later did it again.......so then i unplugged the battery only and did it again limp mode.......then I unplugged both and plugged the battery in and 10 minutes later plugged the MAFS in......it did it again, then I took off the INJEN metal tube off the throttle body and put the OEM plastic black tube on in replace of the metal injen tube, still with CAI and 5 months later has never done it again. Runs perfect......just a experience ive had.

Nathan

Why not try removing the sensor section of the MAF (its only held in by 2 screws) & install it in a larger diameter pipe similar to what the new Nismo S1 combined intake MAF pipe is like.
Make up a temporay one for testing.
With the same volume of air the larger pipe will have less air speed.
Will it work ? Dont know, but I'd give it a try

JonathanG35

dont hate if this post reveals i am on crack.

the jun turbo z was making 600-800 hp so they either solved this problem or the jdm ecu does not have the problem?????

since there is obviously a market for their solution maybe jun would have the info we want or would develop and sell a product that would address the needs??

ether

something tells me they ripped out the ecu..

azrael

JUN wasn't using the stock ECU.

The stock ECU just isn't a good solution for a boosted Z. Realistically, t32gzzz and Skidazzle both have put a bunch of band-aids around the stock ECU to try and force it to spray enough fuel for the boost, but this is a hack. We really need a full replacement ECU with a MAP-based fuel table. The MAF just won't cut it.

SKiDaZZLe

cheston: happens everytime if >8-8.5# is present before 4500RPM.
i think i am gonna try a zener diode to see if this solves it... atleast until TS comes up with a flash to solve it... dont know what woudl do it, though....

fluidz: sounds like yours might have been excessive vibrations on the MAF sensor causing it to freak-out. the experience is similar

nathan: that could work also, but you still need something to compensate for the extra air the ecu is not seeing (some kind of fuel delivery based on boost)

jonathan: jun had to have thier own stand alone ecu.. just the fact it was running soo much boost... probably used a 3-bar MAP sensor, with the ECU running air/fuel maps off of it.

ether: you are right.

azreal: you too

g356gear

iTrader: (12)

You can oufit the e-manage/e-o1 system with an optional MAP sensor and then base you're fuel maps off of that instead of the voltage from the MAF.

03_ppw350z

iTrader: (4)

isnt there a way to jus remove the maf and use a vpc like the supra guys do with a map sensor? somone has got to figure it out for our cars.

SKiDaZZLe

vpc no longer made. that was my first thought..

even if they still made it, we would need one programmed for the 350Z's MAF and ECU specs.

i love speed density

LiqTenExp

Time to get yourself a zener diode.

http://www.digikey.com/scripts/DkSea...=31862&Site=US

GaryK

Sorry, I have to come out of lurk mode to say this...but this is what I said long ago and coincides with what I found on a stock ATI kit. Too bad the idiots had to ruin the thread back then. Back into lurk mode....

I told you so!

jesseenglish

People don't like being told they're wrong.

Chebosto

iTrader: (43)

Michael-

Thanks for those voltage readings. those were extremely helpful-
since our Z is hot-wire MAF'd.. i'm suspecting swapping out to a larger maf (ala GT-R) shouldnt be too hard-, or finding another company'd A/F with a wider band of measurement--

Tadashi is out seeting up for the D1 races this Saturday- i emailed him your specs and RPM readings. i gave him a call too and he said he'll take a look at it first thing tomorrow morning. maybe even taking up my Z currently to 8.5 to see if we can replicate the problem in house...

what size is your itake piping for the MAF? its still in the black housing that came in the car, right?

perhaps relocating the sensor itself, in to a larger diameter pipe would allow the hot-wire to cool down slower, since the velocity of the air in the tube would be moving slightly slower... worth a shot-

i m going to look into the manufacter of the stock Z MAF sensor.. my A6 friends have been telling me that BOSCH mafs have a little more sketchier than say, Hitachi brand MAF.. maybe just swapping over to another MAF sensor should be ok...

the remapping of the ECU is another possibility, but i wouldnt know that until TS can take a look at it-

--Cheston

SKiDaZZLe

LiqTenExp: probably would want 1W of dissapation... just to be safe


cheston:

my MAF is in the stock housing.
its located right after the i/c.

larger pipe still means you need ecu compensation. what would be 2.5v is not what the ecu thinks it should be... and being more specific... the ecu would think its LESS air than it is, causing it to run lean. i think clamping the output of the MAF with a zener is the trick.. i mean since I am running with piggybacks to worry about boost. people with just larger injectors, and a new air/fuel map flash would benefit more from an ECU related solution..

i will let you know.
m

LiqTenExp

LOL, I wasn't trying to actually say what I chose was the correct component for this car. In fact I would never rig something like that to correct such a huge problem. It was more of a joke. You could always do some signal conditioning with basic op-amps and scale down the output of the MAF using negative gain.

DynoDon

forgive me if this sounds ignorant, becaus I'm still new to the Z's and how things are setup. However, when we ran into this with OBDII Mustangs we simply had a chip burned, don't know if anyone out there can get around all the things in the Z that we could in the Mustangs. We could turn off or up rev limiters, adjust A/R at different RPM's, deactivate knock sensors, bypass the anti theft system, and a whole lot more.

Would an aftermarket MAF that's bigger help? I know that's been mentioned, but if someone knew enough you could probably have it setup to read correctly (properly). I always went through a company called Pro Flo, they make MAF's for just about anything, probably could make one for a Z if they haven't already.

Just my .02, none of it may matter at all.