300zx's ELX work log

[bomdoutscort]

what does the car idle at??

[KAinjection]

Its around 800-900 RPM

[bomdoutscort]

try 1000 and see if it still shuts off.

[KAinjection]

I messed with the VAF idle mixture screw and leaned out the idle some. seemed to take care of the issue enough to be livable.

So I adjusted the VAF 5 clicks CCW from its pre-rebuild setting to add more fuel and see how it runs. Just went and test drove it and it made absolutely no difference in the A/F ratio at WOT.

I also noticed this thing will stumble in the low end if you go wide open too fast. The A/F ratio will spike at 17:1 and then drop down to 14.5. If I ease into it before WOT it will give me 15:1 and then settle at 14.5.

I am thinking I maxed out my injectors from watching my fuel pressure gauge since its reporting as high as 50psi when I snap the throttle and 30-40 most other times.

Anybody have any suggestions or ideas? IDK what the Kia injectors are rated at but I though it was slightly more then the standard BP ones.

[crazycanadian]

Proper tuning is needed. You should get at least a 10psi spike in fuel pressure when you snap the throttle. Thats normal.

[KAinjection]

Proper tuning as in a MS? Thats obvious but is my lack of change in WOT fuel ratio an indicator of the injector not delivering enough fuel?

I know when I adjust the VAF its adding fuel because my idle will get richer but WOT is not changing.

[crazycanadian]

Proper tuning as in a MS? Thats obvious but is my lack of change in WOT fuel ratio an indicator of the injector not delivering enough fuel?

I know when I adjust the VAF its adding fuel because my idle will get richer but WOT is not changing.

Wide open throttle is an open loop operation... I can't say for sure since I don't know everything about how the PCM has been programmed but most likely the VAF is being ignored and the PCM is reading off set tables...

Bigger injectors might help, then you can try tuning the VAF to get your mid throttle happy.. IT's going to take some playing around to find the optimal set up where you can make everything happen..

[KAinjection]

I would then wonder if the stock ecu could handle bigger injectors properly. I have emissions coming up in november and I really feel the vaf tuning is not going to be able to help much. if the ecu is only looking at tables then anything I try is just going to be a hack and patch with this old system.

I wish I still had that set of gtx injectors, I would put them in and try it out just to see if it would work.

I have been looking today at buying a diypnp megasquirt from diyautotune. Seriously considering going this route......

[bomdoutscort]

Do you have an untampered with U code? I'd try that first.

[CODY004WD]

I'm pretty sure from my experience that even at WOT the ECU still references the VAF. I was able to lean and enrich WOT AFRs quite a bit, with just VAF adjustment.


James, I would try an AFPR first of all. I had great success tuning with the AFPR and VAF. I was running E85 on a BP26 ECU with the A-code and 460's, without the AFPR, I'm sure that combo would have been a no-go.

[KAinjection]

Do you have an untampered with U code? I'd try that first.

I do have one, but I feel thats just taking a step backward.

I'm pretty sure from my experience that even at WOT the ECU still references the VAF. I was able to lean and enrich WOT AFRs quite a bit, with just VAF adjustment.


James, I would try an AFPR first of all. I had great success tuning with the AFPR and VAF. I was running E85 on a BP26 ECU with the A-code and 460's, without the AFPR, I'm sure that combo would have been a no-go.

I dug through some old threads from naprotejay and he built a similar setup to me, but a little different a few years ago. Long story short he was running a B-code and as best as I can tell the stock N/A injectors and he was getting the exact same problem as I am, but I am running bigger injectors then him and getting worse lean spikes then he was. He "fixed" it by putting the U-code back on the engine, but after thinking about it the only reason it worked for him was because the added restriction of the smaller VAF was like a restrictor plate and reduced the air flow into the engine causing his A/F ratio to richen up at WOT. Thats why I say its like taking a step backward to put the U-code back on.

This engine wants to breath but its not getting enough fuel for its full potential, so I am borrowing a set of GTX injectors to test out from azgtx on monday. If this works then I will have to find my own set of GTX or similar drop ins and purchase a MS to unlock the full potential. If it does not work then I will have to look elsewhere like the pump is not flowing enough (which I doubt) or the VAF is bad.


BTW I was looking at the a MS 2 DIY PNP and was wondering what is the difference between it and just getting the regular DIY kit with a Nippon Denso 76pin connector? price?

[crazycanadian]

If it does not work then I will have to look elsewhere like the pump is not flowing enough (which I doubt) or the VAF is bad.

IF the pump was bad or not flowing enough you would be loosing fuel pressure as you reved out at WOT... At WOT if you are maintaining at least 10 psi over your base fuel pressure at idle then your fuel pump is good..

Remember its not just how big your injectors are, but how long they are programed to be open as well...

[KAinjection]

So if the pump was not flowing enough then it would more then likely be getting leaner as the revs go up. If I apply the same logic to the fuel injectors, that would possibly mean the tuning is the only thing this needs. I will have to look again, but I think my A/F is steady at 14.3-14.5 all the way to redline.......

[CODY004WD]

I.E. Try an adjustable fuel pressure regulator.

The Aeromotive one I had acted just like the stock regulator, meaning the rate would rise and drop with boost/vac. I could adjust the VAF to the point where the car would no longer Idle, then I would adjust base fuel pressure to bring it back to an Idle. Then I would take a run, log my AFR's with my camera phone, pull over, watch the run a few times, adjust the vaf, fix Idle with the AFPR, and do it again. I was leaning the Vaf, and adding fuel pressure BTW.

It took like 8 "runs" to dial-in E85, 10PSI, and 18*base timing advance, on a stock ECU without any piggybacks... And it Idled at 850RPM smooth and steady. I'm sure you can make your setup work without megasquirt. Although In your application, there is a lot to be gained by deleting the VAF. They are restrictive no matter the size.

[KAinjection]

Problem solved!

Installed some borrowed GTX injectors from another member today and thats exactly what the car wanted. More fuel. It now revs instantly from an idle with zero hesitation. Stabbing the throttle from idle now gives 12:1 approx where before it would go to 17:1. I also returned the VAF to its pre-rebuild setting and then going about 3 clicks leaner then that. Idle is no longer buttery smooth like before, but I kind of expected that with a N/A ECU controlling GTX injectors.

Because of this new development a MS 2 or 3 is in the future along with some DeatschWerks 350cc injectors, a brand new intake setup and an experiment I want to try with the exhaust. After that it will be ITB's

Unfortunately I cant do a test drive because my water pump just started to make a lovely scraping noise, so I will change that first.