mpowers

iTrader: (7)

You pabaly all ready know this but those codes mean no O2 sensor activity. Holding the gas at a steady 2k the voltage should fluctuate around 1.5 volts. If you need the diag work sheet pm me a fax number to send it to. It may help discover the problem. But if you are running to rich I could see this causing the problem. I wonder if hks can detune their injectors a little a would solve the problem. Hope this helps,
Mike

APS

Hey guys,

All 350Z coupes with a build date later than 10th month 03 (and all roadsters after 5 th month 03 build production date) have the LEV2 computer, we have tuned these engines/computers without any problem, I don't understand why you guys are having any trouble.

Peter

APS

G3po

iTrader: (8)

FYI G35C dates pretty much also follow the 350Z dates as well.
For example I have a G35C built in October 2003 and it is still
ULEV1. It was about the very last ULEV1 batch built in Japan.

Sharif@Forged

iTrader: (92)

My car is a Nov03 Build date, and not ULEV2 compliant..its the old style ECU.

Speedracer

I don't think there would be a real problem per se tuning to the new ULEV2 ECU (at least I hope this is the case) In the case of HKS, it is just the fact that all the R&D was done on a non ULEV2 vehicle. Same with Greddy. I'm hoping HKS can just make some adjustments and send me a newly programmed F-CON S unit.

Speedracer

Can you tell me why running too rich would be interpreted as no O2 sensor activity? What is the ECU's esponse to this?

Also, shouldn't I be going into limp mode? My car is anything but limp!!!

APS

That's interesting and I just checked the build date of my Z car (build date 12 month 03) and it's definitely ULEV2 spec computer, so maybe Nov 03 was the very last of the old computer.

Thanks

Peter

APS

Ok well that makes a lot more sense to me now.

Thanks

Peter

mpowers

iTrader: (7)

Oxygen sensors interpret rich and lean conditions with a voltage that is sent to the ecu. Running rich would cause the oxygen sensor to read a low voltage. In you're Z case this is anything below 1.5 volts. Typically the oxygen sensor should fluctuate around 1.5 volts.
Seeing your ltft and stft suggest the computer is doing this for some reason? The lower the precentage the richer the computer is adjusting for. So a 75% stft the computer is trying to make the car run rich. While ltft is at a perfect 100%.
The oxygen sensor gave you a code of p1271 and p1281 which is easier to diagnose than jumping all over the place. Confirm the O2 are good and reading properly and go from there.
What one would expect to see is the stft to be the opposite of what it is adjusting for.

Speedracer

What kind of time frame does the stft look at compared to the ltft. I guess I'm a little confused as to why one would be normal and the other one abnormal.

mpowers

iTrader: (7)

I will have to look up the exact time frame but roughly stft is instant in a closed loop. And long term is a much longer period of time. Example of a timing chain would stretch throwing the timing off over a period of time the computer reads this with the cam and crank position sensors and adjust the timing as necessary to keep the performance of the car up.

teh215

iTrader: (8)

Couldn't you just use an older ECU and swap the O2 sensors or is there more to it than that? Kinda glad I have a very early model now.

mpowers

iTrader: (7)

Speedracer I made my last statement incorrectly, Yes the low Stft reads rich but it is shortening the injector pulse thus the ecu trying to adjust for to much fuel.
Check the duty cycle of the injector the higher the duty cylce the richer the fuel will be as well. Shorter duty cycle it will make confirm the ecu is trying to lean out the A/F.
While refreshing my memory of ecu's, the ltft is at a perfect 100% which is to perfect, the car is operating in fail safe.
Go ahead and follow the diag sheet for the O2 to confirm they are operating correctly. Once confirmed this would show that the only way to correct the problem is have the HKS unit add less fuel to the system. Another words morethan likely the whole problem is the HKS control for the additional fuel is way to rich.
How much flexablity does the HKS fuel system have? Can you tune it or only some one with the software?
Let me know what you find I help any way I can.
Mike

mpowers

iTrader: (7)

Oh and by the way even if the car was an 03 with a 75% A/F it would throw a check engine light.

Speedracer

Mike,

I suspected from the start that the HKS F-CON is adding more fuel than the ECU can "adjust" for. According to info I got from the Service manual, the DTC's 1271/1281 do, in fact, correspond to "no output" from the A/F sensors. This condition will occur at around an A/F of approx 11.2:1, according to the accompanying graph that plots sensor output voltage vs. A/F ratio. A 75% lean condition corresponds to an A/F of 11:1 assuming that the ECU tries to regulate to stoichiometric. (There is a line on the graph at stoichiometric 14.7:1, indicating that this will generate a 1.5 millivolt signal).

Looks to me that if the HKS F-CON is programmed to run at this rich A/F, it needs to send a "dummy" signal to the stock ECU so that the stock ECU doesn't see such a rich signal. Alternatively, if the system can be tuned leaner, I hope it will still be safe from a detonation standpoint.

In any case, I will be doing some data logging with my new Digimoto to see what kind of oxygen sensor voltage I am actually generating.

And...if I am operating in fail-safe mode as the 100% ltft would indicate, the car actually runs great in this mode with the SC. Just don't want to do any long term damage and I want o pass OBD based emissions, although that my be possible since I can clear all error codes with my Digimoto.

What do you make out of all of this?

mpowers

iTrader: (7)

Yes the car would run fine because it uses base values from the rom memory in the ecu.
Clear the codes and go for a drive in theory it should throw a dtc the first time the car is driven. This should allow you to view what the O2, stft and ltft is reading before the code sets.

The ideal situation is to either fool the ecu to thinking the O2 is reading properly or lean out the HKS system which we know will not work for the forced induction.

Let say the O2 sensor reads .3 to.5 volts at a steady 2k rpm. If we could add and additional 1.2 volts to what the O2 is sending to the ecu it would work for fooling the ecu into thinking everything is fine. This is where we need someone with a better background in electronics than I have. As well this would still allow the ecu to make minor adjustments that are positive.
HKS could still lean out the system a little which would help as well. How does the HKS system know how much fuel to add to the system? Is it vacume based or is it reading the O2? Or other such as a given map.
One last thought if the O2 is given the addition voltage where it would not throw a check engine light seting the car into fail safe, the ecu will not go back to the "safe" rom memory which is probably set to run a little rich from the factory, would more than likely give you a safe boosted performance and the fuel mileage would increase?
Does this make sense?

Speedracer

Mike,

Two things.....first......when the codes were cleared by the dealer, I had to drive almost 150 miles with about 10 start-ups before the SES light returned. I have cleared the codes again and driven twice now with no return of the SES light, and no DTC's according to my Digimoto. I'll take a few more drives then check for codes again.

With regards to how the HKS system adds fuel, I am not certain, but it looks like it is based on Manifold Absolute Pressure. The MAF is located pre-supercharger, so I am assuming it is left to function normally. The manifold pressure is picked up by a seperate sensor that feeds into the piggyback computer.

I'm going to do some serious data logging after Thanksgiving when I have some time. I'll then send that info plus the contents of everything that has been discussed on this forum to HKS.

Z1 Performance

iTrader: (564)

VJ - other thing you can try (if you did not already), is going back to a stock plug - that should help "lean" your mixture out a bit as well

Speedracer

Adam,

I'm doing okay for now. Car is garaged most of the time now anyway. The car runs well in fail-safe mode and I am able to clear codes with the Digimoto. I need a long term fix, however, as will anyone installing this kit on a ULEV2 car. If you have read a few earlier posts, I think I have pretty much diagnosed the problem.

The missing piece of the puzzle is to find out from HKS what is the exact air:fuel ratios they used to tune this kit. Based on that we can figure out exactly how much the A/F sensor output voltage will need to be manipulated to feed an "in spec" signal to the stock ECU.

The real issue here, however, is that why should I have to be doing all this work to figure it all out. While it is rewarding in a certain way that I am able to piece things together, I have still spent $9500 (all parts and install included) for an outdated piece of programming. A company with the reputation of HKS should have been on top of all this.

Z1 Performance

iTrader: (564)

Also, where in the manual does it say 100% LTFT is fail safe...makes no sense whatsover to me. On every car I have ever datalogged (regardless of maker), 100% stft and ltft corresponded to the car running the way the ecu wants it to. Any number below 100% was the car running slightly richer than stock, any number above 100% was the car running slightly leaner than stock. I remember this from back trying to get my VPC to play nice with my SAFC on my Galant VR4. A stft of 75% would throw a CE light on that car too (it's a '92!), and the car would run like doo doo. If you leaned the SAFC out, you could literally watch stft trim eek back towards 100%.

VJ - try logging just 02, one sensor at a time, one bank at a time, and post here what it does at idle (once the car is warmed up), under cruise and under WOT. Do the same thing for each sensor in each bank and post what you find. Would also be interesting to see what fuel pressure is at idle as well. Remember, the HKS setup has an upgraded pump but no return system