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