Massive sudden Lean-out RB20DET

[Rex_Kelway]

Hi Lads,

Lets not hear any non-sensical "Toyota (insert car here) is the BEST car EVER!!!! kind of talk" just because Rex's query regards His Nissan.

Had His 'R31 KingPinny $2500 Mr1G smokes pole Dript-Barge hack' on the Dyno the other day for its post-build, pre-thrash checkup. It makes respectable grunt with AFR's sticking nicely between 12.3 and 11:1 for the whole run.

However at the top of the run just prior to limiter (perhaps 500rpm) the AFR suddenly makes a dead vertical up past 15:1 which is where the operator jumps off the acceleratix. We repeated the run three times, peak power was within 2-3rwkw and the same massive sudden vertical leanout condition.

The dyno was done as a favour so no fault finding was performed, Rex was thinking that perhaps the AFM may be faulty (NIssan's are renowned for them) causing the ECU to basically drop the injector duty cycle right off.

The engine R32 RB20DET and is basically stock, along with the ECU and turbo etc. Only modifications are filter, exhaust and intercooler setup. Boost is unmodified but up to 11psi due to the pipework etc. The car makes an indicated 190 odd rwkw, but the stock AFM should still be able to map up around there.

Anyone seen/heard similar problems?

Thanks Lads

Rex

[Grega]

been a while rex....fuel pressure perhaps?

[oldcorollas]

either AFM is goign spack, or the injector duty cycle(what was it?) is at the point where opening and closing becomes unreliable.. ie, 80-90%...

otherwise.. not boost related fuel cut? not revs related fuel cut?

for the afm, you could stick on a multimeter, and then manually move the flap (iof it has one.. is it hot wire?) and check the resistance at all positions....

[gianttomato]

Perhaps Rex should check AFM voltage to see if it has peaked (I think it's 5 volts) - PFers suggest that 5V is good for around 190 rwkW.

Timely PF thread. GT suggests Rex ignore all the bullshit about who can tune what and read the only handy bit of tech in that thread at post 6.

Also, what is happening to manifold pressure as the lean out occurs?

[Rex_Kelway]

Yep, has been a while. but havent really had much to say.

Shame there's no intrest rate on +rep...

Fuel pressure He ruled out, because if the pressure drops off the AFR would gradually climb, something like a 45deg trend on the line. To climb vertically it would have to be the sudden removal of all fuel pressure, which is highly unlikely.

The AFM is a wire type. Maxing the injectors would explain it, but they should be good for that, am double checking right now.

Boost cut is 14psi, boost peaks at 12psi then drops back to a solid 11psi, and the car never made rev limiter because it deemed was far too dangerous to do so.

Rex just thought of something, maybe He'll grab the multimeter on peak/hold to see if the thing makes it to 5V (maxed out) or if not, where it peaks. Then test another AFM back to back.

Mmmmm

[Rex_Kelway]

Rex just thought of something, maybe He'll grab the multimeter on peak/hold to see if the thing makes it to 5V (maxed out) or if not, where it peaks...

Posting at the same time is fun.



Thanks GT, that was a tid-bit i was after... But Rex knows not what the boosty boosty guage was doing.

Should've paid more attention.

[Hen]

...Thanks GT, that was a tid-bit i was after...

...We repeated the run three times...

First person twice in 1 thread. Old Rex you must be out of practice.

Hen

Please excuse the lack of constructive input.

[Rex_Kelway]

God Damn it!!!,

Rex usually has to double check His posts for silly anti-Rex grammatical errors like that.

Out of practice He must be, and now its on record...

He wonders is that is worthy of a negative rep ???

[gianttomato]

GT looks the other way whilst Rex edits his post.

Also reports Hen for immediate banishment.

[Rex_Kelway]

Its no point, Rex's momentary lapse in self identity is forever highlighted in Hens quote. He obviously minds not that he is killing the dreams of the children.

Anyhoo, some indepth interweb research indicates that 190rwkw is roughly the accepted for the RB20's AFM to max its 5.1 volt range and KingPinny's peak was 192.6rwkw to be exact.

But until He can check it for sure on the morrow, Rex is left with an unusual dillema...

How does one modify an engine to produce approximately 5 - 10 less Kw?

Funny thing though, people doubted the cars ability and the accuracy of the dyno-sheet, but a maxed AFM is kind of proof - smoke pole, pole smokers!!!

[gianttomato]

Is it possible for Him to use a different AFM - like the 1UZ 7MGTE swapparoo?

[ViPeR_NiPPleX]

is it the Z32 maf that you swap in or something? bah, it's a nissan.

[Rex_Kelway]

Its the Z32 one, it uses a wider tuning band or whatever. The problem is that it needs the ECU to be calibrated to suit the new AFM's band. Thats why its usually associated with the Power FC.

But in all honesty it doesnt need any of that shit, Rex just wishes to pull it a few kw off the stock AFM's max.

Its not that He set out to build 'some sick RB', It just kinda happened unexpected like...

[oldcorollas]

hmm, if it was a flap type, you could physically limit the flap a bit, but being wire...

isn't what the dodgy boys do, a kind of zener diode trick? so it breaks down and flows current at a fixed voltage.. like.. 5V.. so that maxes the voltage out?

maybe ask teh Witzl/Mos for clarification?

may not be perfect, but if you are not in danger of going too lean by a little bit in those last 2kw... it's better than going stupidly lean when the AFM goes spack...



ie, voltage limiter ftw

[takai]

Maybe a revlimiter. Although that could be a pain to create.
Other suggestions which come to mind include:

• Inlet Restrictor
• Exhaust Restrictor
• Boost Controller (more bleed valves y0)
• Zener Diode dodgy mod
• Ditch the RB and put a JZ in (like all the hekt1c Cefiro boyz do)