R34 GTT run off AFM and MAP

[Abo Bob]

666Dan and myself are working on a theory and I think the rest of SAU might be able to help us out.

To my knowledge, when an R33 GTST hits the limit of it's air flow meter it is a harsh thing. As in, boost boost boost bang! No power. Can someone please confirm this before I make any more of a fool of myself?

[Sydneykid]

666Dan and myself are working on a theory and I think the rest of SAU might be able to help us out.

 

To my knowledge, when an R33 GTST hits the limit of it's air flow meter it is a harsh thing.  As in, boost boost boost bang! No power.  Can someone please confirm this before I make any more of a fool of myself?

The standard ECU will go heavily rich and retard when the AFM voltages exceeds 5.1 volts.

On the other hand a Power FC doesn't care, it just keeps on supplying fuel and igntion according to the maps. You can have RPM load points that exceed the AFM load points and so you can have reasonable fuel and ignition. Provided the engine uses air and needs ignition timing in a linear fashion this is not a problem. The only time it becomes a problem is if the engine has a jump in its fuel or ignition requirements after the AFM has reached its maximium voltage. Then it becomes tricky to tune.

That's why you can survive with a maxed out AFM as long as it not too much and the engine's requirements are predictable. Most tuners would reach for an AFM with higher airflow per volt (Z32, Q45 etc) rather than risk the engine.

[RB30-POWER]

After testing on my own car, there is more to it then just hitting 5.1V from what i can tell.

I have installed a DFA unit and after adjusting the input/output voltage to keep all values up to 5.3V input from the AFM to under 4.90V output from the DFA to the ECU.

(I tuned/calibrated the unit up to 5.3v from the AFM signal even though i think 5.12V is the max it can ever give out just to be safe.)

Anyway, what i have found after upping the boost a bit, is that now the extra boost/airflow at lower RPM is triggering the cut or rich and retard.

Even though its showing a max of 4.9V, because its occuring at a low RPM point, it puts the ECU on a map point that is mapped to be retarted timing and rich fuel injection time.

Basically what i think Nissan has done is basically mapped the ECU with good mixtures and timing up to or just over the load point seen by the standard boost/air flow of the RB25 engine. Any load points over this have been mapped with retarted timing and an extended injection pulse to richen it up.

I have found the stock ECU very hard to crack and work around. I now really have to invest in a complete managment system to up the boost, even though i wanted minimal gains.

Because i have the ECU on an RB30DET i am able to get high AFM readings at low RPM.

[666DAN]

OK from what I've found, unplugging the MAP sensor on a GT-T will result in poor acceleration under boost. The e-manage was indicating a pull in timing and increase in injector duty when revs are over ~3000rpm.

Replacing the sensor with a variable voltage supply I found that by mimicking boost (raising the voltage) the ECU appears to change the maps based on load, basically the car ran better by supplying an equivalent voltage to what would be produced by the boost sensor at say 7psi.

The other thing I have noticed is that with the e-manage intercepting the AFM voltage, you don't see the expected change in duty cycle you would expect when changing fuelling over 3000rpm.

So it appears the ECU relies on 2 sets of inputs to deliver fuel at 2 areas of the rev range.

Just a theory

[RB30-POWER]

I can't say i have the map sensor hooked up on the ecu im running (Series 2 RB25DET ECU).

All wiring diagrams indicate that the R33 map isn't connected to the ecu despite speculation on here lately.

I wish i had an R33 to look at and i could test wether its connected to the ecu and what pin, clear the matter up once and for all.

I wonder how different the R34 managment setup really is?

[RB30-POWER]

All that aside, measure what voltage the map sensor is at at say 7psi (map sensor usually work with a 0-5V output)

Wind the boost up until it cuts (just so you know how much boost is required to hit the cut), it would only be a few psi over standard.

Then clamp the map sensor output to what it was measuring at 7psi, take the car for another spin and see if it still cuts at the higher boost level.

The Jaycar DFA would be perfect to modify a 0-5V map sensor output.

[Abo Bob]

I was doing some logging of data with a consult cable connected to my laptop. What I noticed was that I was hitting 5.1V quite easily high in the rev range and accelerating but that this had no effect on the power delivery of the car.

I intend to log it again on a dyno and overlay the data at some stage to see if power keeps increasing with the AFM maxed out.

A japanese tuner told me that R34's don't need z32 AFM's but due to language problems, even though he was nice enough to explain it to me, I couldn't quite understand why.

I am now thinking that perhaps the R34 usees both the MAP and the AFM. Maybe above a certain RPM at full throttle only it switches to the MAP.

This would explain his opinion on Z32 AFM's for R34's and also why we get no big drama from maxing out the AFM. But... I presume that Nissan didn't intend the AFM to max out. They gave it more than enough head room for it's stock application. So why would they bother?

Maybe they just preferred it in WOT conditions.

What do people think?

[666DAN]

Forgot to say that, yes all my observations were under WOT...I fogot other SAU members don't all drive like that

[otto]

sorry to jump in can someone clarify for me ... r33 gtst afm, r34 gtt afm+map. have i got it right??

[Abo Bob]

That's what we are trying to work out. I think so.

[otto]

Are you talking about an actual map sensor or the sensor for the boost gauge giving info to the ecu? sorry for the stupid questions I just always thaught the ecu got all its info (reguarding air) from the afm only.

[RB30-POWER]

Maybe the map sensor is just for boost control which is done by the factory ecu.

What happens to your boost levels with the map sensor disconnected totally?

Does the R34 run a two stage type arrangement like the R33 or is it more sophisticated?

[666DAN]

Are you talking about an actual map sensor

Yes located on the centre of the firewall at the rear of the engine. The R34 also has the sensor for the cluster gauge, that does not give any output to the ECU, as in the R33

Does the R34 run a two stage type arrangement like the R33 or is it more sophisticated?

Yes it has a similar solenoid set-up as the R33, low-boost then high-boost. This is run purely by a switch at a certain rev range...on the N/A the same output controls the baffle in the twin-entry manifold.

[vr4sigma]

After testing on my own car, there is more to it then just hitting 5.1V from what i can tell.

I have installed a DFA unit and after adjusting the input/output voltage to keep all values up to 5.3V input from the AFM to under 4.90V output from the DFA to the ECU.

(I tuned/calibrated the unit up to 5.3v from the AFM signal even though i think 5.12V is the max it can ever give out just to be safe.)

Anyway, what i have found after upping the boost a bit, is that now the extra boost/airflow at lower RPM is triggering the cut or rich and retard.

Even though its showing a max of 4.9V, because its occuring at a low RPM point, it puts the ECU on a map point that is mapped to be retarted timing and rich fuel injection time.

Basically what i think Nissan has done is basically mapped the ECU with good mixtures and timing up to or just over the load point seen by the standard boost/air flow of the RB25 engine. Any load points over this have been mapped with retarted timing and an extended injection pulse to richen it up.

I have found the stock ECU very hard to crack and work around. I now really have to invest in a complete managment system to up the boost, even though i wanted minimal gains.

Because i have the ECU on an RB30DET i am able to get high AFM readings at low RPM.

The worst part is if retard not enough but it also richens the mixture which also causes retard by adding extra fuel you see when you add more fuel what you are doing is making the fuel burn slower which in turn retards the timing so in reality its like a double retard

Edited October 23, 2006 by vr4sigma

[Beer Baron]

adam, it's not unusal. as SK explained. you are running a PFC, yes the AFM maxes out but car keeps making power as there still good numbers there, and it will still move to different poitns on the map as RPM increases (it'll just be pinned at the end of the airflow axis). same thing in my GTR. AFM his max voltage but the car keep running nicely, and making more power right to redline. but mine doesn't even have the MAP sensor connected any more. I really doubt the 34GTT ecu switches to using the MAP sensor as a load axis. and even if the stock ECU did, your PFC isn't. but you can tell easily. when doing a run, look at where it reaches max AFM voltage, if it the map trace then moves further down on the load axis then it's using something else, but I'm quite certain it isn't.

[mad082]

to be the first to answer the actual question that was asked, yes. when it hits the limit it is like somone has switched the key off.

[Abo Bob]

You might not have noticed the date of this thread but that doesn't invalidate your post.

I have now run pfc with stock AFM maxing out and in this case I could feel the point at which the AFM maxed out. When I had the stock (chipped) ECU I could not feel the change over.

[Abo Bob]

to be the first to answer the actual question that was asked, yes. when it hits the limit it is like somone has switched the key off.

Woot!! Only took a year and 4 months.