Need a bit of a point in the right direction :)

vn_luke · Post by **vn_luke** » Tue Jun 10, 2008 11:27 am

Well, after almost 2 years, I've finally got my car to the stage where it's ready for some tuning! - exciting times!

Just some related info on the car:

- VN commodore
- Nissan RB30 Motor
- gt3582r (.82 rear, .5 front)
- N/A VL commodore ECU (fitted with nistune, obviously)
- siemens 3145's (750cc) injectors
- stock rb30 pressure reg
- 'draw through' stock vl commodore AFM (for the time being), mounted about 20cm from the turbo
- turbosmart atmospheric BOV

And now for my questions:

- I've calculated the new K value using the 'injector resize function' (came up as DEC 189)

- I also did a bit of a search on the net for latency values for these injectors, here are the specs:

Flow CC/min: 756
Flow LB/Hr: 72
Ohm: 3
10v: 1.41
11v: 1.21
12v: 1.03
13v: 0.87
14v: 0.76
15v: 0.68

- As such, somewhere on these forums I read that you have to multiply specced values by 2 in order to get the correct value to insert into nistune (although I DO undestand that these values may not be 100% correct)... In either case:

- my latency @ 14v is set to DEC 1520uS
- my CHANGE rate/volt is set to 220 (although I just noticed that this is in milliseconds? - so should this be somewhere around 0 DEC? - this could explain my 'thermo fan comes on - engine dies problem!, but that's another story all together)

I'm getting idle AFR's of about 14.5 - 14.9ish with a coolant temp of 80degC, and it seems to start & idle very nicely.

if I bring the revs up slowly with the gas (either on/off the converter), it seems to maintain AFR's very close to what is in the fuel map.... = good.

my main problem at the moment, is that if I let go of the gas (not even anywhere near boost), the afr's go to 9-10:1 and the engine wants to stall.... = bad.

I have two theories for this:

#1) the AFM measures air coming in, but when the throttle shuts, there is still a cooler and piping worth of air that the engine is expecting, but hasn't gotten, and as such would be overfuelling.

or, a very similar theory

#2) The throttle gets shut, the turbo is still spinning a bit, and causes enough pressure in the piping (and difference in pressure between the plenum/cooler piping) to open the BOV a little, and let the measured air out, resulting in the same scenario as theory #1.

I've tinkered with the 'fuel cut' map (i.e. raised the RPM) in hope that as soon as it detects a shut throttle, it would cut fuel and I wouldn't have this issue, but this didn't really seem to change anything at all. (do I have the right address for these? I'm using the VLT address file)

I'm happy to switch to a plumb-back setup for the BOV, but it would be nice to be able to vent to atmostphere and get non-pre-warmed air entering the turbo (if there's an easy way)

I'd like to avoid sticking the MAF in the cooler piping (i.e. a blow through setup) as I eventually intend to be running low-mid 20's psi, and don't really trust the plastic MAF to hold this kind of pressure. (even if it is eventually a Z32 maf)

Has anyone dealt with a similar issue before? or have I just missed something simple?

Cheers and thanks in advance,
Luke

Matt · Post by **Matt** » Tue Jun 10, 2008 12:54 pm

Luke - Please see this thread. Similar issue

http://www.ibconceptions.com/nistune/vi ... .php?t=601
http://www.ibconceptions.com/nistune/vi ... .php?t=606

Options currently seem to be
(a) recirculating blow off valve
(b) plumbing into the cooler piping
(c) trying moving AFM further away from the turbo

vn_luke · Post by **vn_luke** » Tue Jun 10, 2008 2:29 pm

Thanks Matt - it's as I suspected really.

I was hoping to be able to 'hack/tune' for this with the fuel cut - but it seems to have no effect.

Just to be absolutely positive - if you could confirm that the addresses for the fuel cut/recovery tables in the VLT ECU address file should work on the N/A VL Ecu, that would be great.

I've brought the fuel CUT right up to approx 4krpm and recovery to about 1krpm, in hope that I won't be getting excessively rich mixtures upon backing off, but nil difference. (and the tps switch works :p)

I'll experiment with plumbing back and moving the AFM a bit further away from the turbo over the next few days, and report back! Thanks!

Matt · Post by **Matt** » Tue Jun 10, 2008 8:15 pm

With the fuel cut, it will only come into effect around the desired temperature cell you modify with the desired RPM and when TPS is idle (light in guages window is red when active) until the recover RPM is reached

If you are backing off the accelerator but not completely, then unfortunately the table wont be used and fuel still injected

The VLT fuel cut/recover tables are the same as CR31/VL except for the first value (which is limp value used when no temp sender is connected)

vn_luke · Post by **vn_luke** » Tue Jun 10, 2008 10:28 pm

I relocated the MAF about a foot further away from the turbo, with a bit of success! but unfortunately it still wants to stall a bit when the bov opens. Over the next few days I'll try a plumb back arrangement and hopefully resolve this issue!

In regards to the fuel cut, I was trying with the accell completely off, i.e. red light on... and had modified the whole table, rather than just one rpm point - but was still overfuelling when throttle completely off (after a rev, obviously) - I'll re-try the experiment again a few times and see if I'm doing something wrong.

vn_luke · Post by **vn_luke** » Thu Jun 12, 2008 11:24 am

Still haven't tried re-circulating, but have gotten pretty happy results so far with increasing the volume between the turbo and the MAF even more-so. (although I can see the surge(s) of air when i back off on the logs!)

In theory - would it not be possible to use another AFM on the outlet of the BOV, and somehow 'mechanically' (i.e. in the wiring) subtract the value of the reading of this one from the reading of the 'main' AFM? (though it would be a fairly ugly setup, I guess :p)

iaredam · Post by **iaredam** » Thu Jun 12, 2008 12:53 pm

You could always change the setup for blow-through. Just put the maf sensor in between the bov and the throttle body, you shouldn't have any issues with an open-dump bov this way.

vn_luke · Post by **vn_luke** » Thu Jun 12, 2008 5:53 pm

This would work - but I just don't trust a plastic AFM under that high pressure, I don't know if anyone's had problems with them blowing apart? (25psi?)

RB30-POWER · Post by **RB30-POWER** » Sun Jun 15, 2008 2:45 pm

Check the other thread as posted by me and I now have pics to prove this, as you can also seen in your logs.

An atmo venting bov is the same as no bov when it comes to airflow meters and big turbos.

The standard factory turbo is small and has convulated inlet piping to help dampen the effects when the car was originally designed, but once its modified, seems a recirc is going to be the only way to fix drivability, because this ecu/car does not have a throttle sensor only a basic throttle switch, which is only activated if you fully back off.

My only question now is, is a single bov going to move enough air with big compressors or is it going to need atleast two of them.

The GTR uses two so it might be an indication.

I will try one and check the logs for any further spiking.

Regards
Mick