Well I got my manifold on and the car is running WITH THE 87MM TB!

See my build thread: http://forums.maxima.org/all-motor/6...ttle-body.html


And here's a video of the throttle body being controlled by the stock ECU with no special signal altering devices...it's hooked up directly.



There is a problem though...as soon as I started the car with the throttle body on, the ECU went into DBW limp mode (won't allow for more than a certain percentage of throttle). I cleared the code with my Blazt cable while the car was running, and I was able to drive the car normally. (Somewhat normally I should say; if I revved it up too high, it would stall out upon returning to idle)

Something interesting to point out is that the ECU has no problem making the engine idle even in limp mode. There is no high idle problem or anything.


Now here is where I need help:

I need someone to measure both of the TPS signals (there are two) at idle AND at closed throttle (aka key on, in gear, foot off the accelerator) on their stock Maxima with DBW. I need to compare these TPS readings to what my TB is putting out.

So far, my plan is to put a dual channel op amp in front of the TPS outputs of the TB. I will apply a gain factor (and the inverse of that for the other TPS) and hope this fixes the problem. I'm guessing that the TPS values are slightly different for each throttle body and this is messing up the control loop that the ECU uses.

If anyone has any knowledge on this kind of thing...please speak up. My car is a PITA to drive right now.

 

A few mods (see sig) but with stock TB. May or may not help you.

Idle, taken in drive on a cold start (idle probably 900+, didn't bother to look) :


Key on, in gear, not running (I hope thats what you meant) :


Max throttle, in gear, not running :


Maybe I need a Sprint Booster

 

THANK YOU SO MUCH. I appreciate the quick reply man. I'll report back tomorrow morning with results from my op-amp theory test.

One thing that is weird is that the values you have for TPS1 and TPS2 look to be almost the same. Normally, TPS1 goes from 0-5volts and TPS2 goes from 5-0volts. Hmmm

Edit2: I bet Cipher just subtracts the actual TPS2 value from "5" to give you an easier reference to go by. Either way, this data is what I needed.

 

OK...I tested mine.

At "idle" (same as key on, in gear, engine off), I'm reading .842V.

At WOT with engine off, I am reading 4.23V.

This tells me I need to subtract ~.158V across the board (and add ~.158 for the inverted sensor).

 

In for updates!

 

I seem to have messed up my ECU. It started throwing a code about ROM failure. I think because it kept failing to learn the closed throttle position. I got a new ECU and threw the stock TB on for now. I haven't given up though

 

SG ran into the same problem when they ran their LS2 and had to clear the code every time they started the car.

It's been proven a larger TB/intake will go a long way NA.'

Good luck!

 

Yikes!


Larger DBW TB goes back to tuning on these cars which is very limited!


Ive got some ideas how to make it work, but .000001% of Maxima people would spend what it really takes.

 

I will do what it takes. Lets hear your ideas.

I messed up my ECU trying to make it work. Here was my theory:

The ECU sends the TB two PWM signals (open and close) that are inversely related to each other in terms of duty cycle. The servo uses these to sanity check itself. The same process is used on the TPS output from the throttle body (two inversely related signals, 0-5 and 5-0). What I am unsure about is if the ECU uses the readings from the TPS as a feedback mechanism to correct and monitor the throttle position, or if the ECU just sends a certain duty cycle on the PWM motor input for a given position.

When I first put the throttle body on, the car actually started and ran FINE! It was a little hesitant when blipping the throttle, but it seemed to idle OKAY for the most part. The car would stall when the rad fans kicked on or the AC (the ECU couldn't respond fast enough).

After the second time starting the car, it threw a code for the TB. The car was in limp mode. I then had to clear the code while the car was running to be able to drive it.

I discovered that the stock TB produces a voltage of .68 when closed (thanks to the help of Reizy). The LS2 TB was producing a voltage of .89 volts when closed. Both measurements taken from the TPS that goes from 0-5.

So I made a circuit that would subtract .2 volts from the TPS circuit that goes from 0-5 and it would also add .2 volts to the circuit that goes from 5-0. This would have the effect of fooling the ECU into thinking the throttle plate is closed more than it is (or in the normal position for that matter).

This circuit seemed to work until I got greedy and tried changing the .2 volt subtract/add value to .3. After I did that, the ECU threw a code "P0605 ROM FAILURE". I put the stock TB back on but the ECU kept throwing this code. It would go right into limp mode as soon as I started it unless I kept revving it. It was also throwing an ETC TP Closed code. My hypothesis here is that the ECU learned the default throttle closed value of when I had the circuit on there, and that value was out of range. Now, the ECU keeps failing to relearn the closed throttle position (due to it already being in a failed state). After a certain amount of failed attempts, it probably throws that P0605 code.

What was weird was that the code would go away when I took the circuit off, but as soon as I connected just one wire to the ground, it would come back. Maybe I fried something, IDK. But I honestly think it was some sort of a freak accident.


As far as making the TB work, Relentless RPM did it with the Titan. They sold a kit which included a little converter box. I looked at the wires that they had running into the box, and I discovered that the motor drive (open and closed) wires DID NOT GO TO THE BOX. (Power, GND, TP1, and TP2 all did however). This means that they were doing something to the throttle position sensor readout.

There couldn't have been anything too complex in that little box. I'm guessing it was either an addition/subtraction circuit or a gain/attenuation circuit. Those are pretty much the only things you can do to a signal with an op-amp. I doubt any filtering was involved.



I'm interested in anyone's input here as long as it doesn't involve "get a full standalone and control the TB with that" lol

 

I haven't had my coffee today and am slightly hungover but could you leave the stock TB in the engine bay sending the signals back to the ecu and also send the signal for open/close to the 87mm TB that is actually hooked up the in manifold? Use a diode so the signals from the 87mm never go back to the ECU? This probably doesn't make sense.

I really hope you get this to work as it will really help those looking for MAX hp out of a 3.5.

I will agree that there is nothing fancy inside that box the titan guys used. too bad they sold so few kits, otherwise you could ask someone to open up the box and show you what is on the pcb board.

 

I actually tried that. I had the LS2 tb hooked up to the manifold, with the original throttle body's TPS signals being sent back to the ECU, but for some reason, when I started the car, the engine went right to redline. I stopped messing with it at that point but this seems like a very viable option. The fact that the RPMs went up indicates that there is a feedback loop going on there.

The ECU can run both TB's at the same time.

 

Hmmm couldn't you use diodes and make sure nothing gets sent back from the LS2?

What if you convert to a wire driven TB and just leave the stock TB inside the engine bay?

A 4'' intake with a 90mm TB should have some great gains. Now we just need someone to make a log style intake manifold that will accept a ls2 tb...I got a quote for just under a grand from a local shop.

 

Lol see what i mean?

 

lmao dag.

A cable driven TB is out of the question for a few reasons. One being that I don't want to modify my pedal assembly and the other is that the ECU will go into limp mode if it detects that it has no control over the throttle.

 

No way to leave the pieces connected but to have them not have them control anything? Like the TB sitting in the engine bay just opening and closing but not connected? Same with the pedal assembly? I am guessing the answer is probably no...

I hope you make this work! should be some great gains for those pushing the whp limit. These engines are definitively starved for air.

 

update?

 

I ended up just getting an 09 TB. I don't have the time to mess with the LS2 TB anymore but I haven't given up. As soon as I get time between school and work, I'll look back into it. I am also on the lookout for other cars with similar TB's that may be bigger. I have recently been looking into the BRZ throttle body but haven't found too much info on it.

 

09 TB will not dissappoint. Trust me!

 

I went from a stock 70mm TB to the 09 75mm.. It's definitely not a seat of the pants mod..