R33 Not Running

[lui]

Have just put the engine back into the car, it starts then instantly dies, when I unplug the afm, it starts and runs, soon as i plug the afm back in, it idles high for about 3 secs then dies.

Its a r33 with s2 engine. Have just installed the following:

-Gt35 turbo

-front facing plenum

-z32 afm

-555cc nismo injectors

-nistune (stock tune with z32 and 555cc injector changes)

-fmic

-040 pump

-timing belt, water pump, spark plugs (7 heat, 0.8mm gap)

Not sure what the problem could be, any ideas? What can I check? Thinking it could be a vac leak, may something to do with aac valve, dont know.

[R31Nismoid]

If you plug the AFM in, and the car dies... And you take it out and it idles...

Tried another AFM? Is the AFM throwing a fault code/sensor?

Might be a VAC leak but it'd have to be a rather large one. Sure you've sealed the plenum correctly?

[lui]

Yeh its throwing up afm code, but im guessing thats cause its not plugged in?

All the bolts on the plenum are tight, even put gasket silicon on plenum.

[Hadouken]

Derrrr... Plug afm in car dies, unplug afm car idles good.

Try a different afm then report back!

[Mitcho_7]

I know when Dvs Jez was tuning my car with the nistune z32 ecu base map for r33's and just updated the afm and injector settings for 555's and z32 afm, it wouldn't really run. He had to fiddle with a few settings to get it to idle properly.

[DVS JEZ]

I know when Dvs Jez was tuning my car with the nistune z32 ecu base map for r33's and just updated the afm and injector settings for 555's and z32 afm, it wouldn't really run. He had to fiddle with a few settings to get it to idle properly.

Correct. Its not as simple as selecting the afm and injectors and drive away.

K const needs to be adjusted to get it running

[lui]

Thing is I bought the nistune 2nd hand, it already had a tune and running on a r33 with more or less similar mods (different turbo and injectors), was having this problem, so I had the base tune loaded and adjusted for 555 injectors, still same issue.

[GTSBoy]

Yuh, as Jez said, it is not just "change AFM and injectors" in Nistune and drive away. The K constant will need a fiddle, and if it needs a big enough fiddle, the car won't run with the AFM connected.

[lui]

why would that be? if the stock tune is loaded to nistune, it would run just like it would with the stock ecu plugged in. is the K constant to do with the injectors, as in if injectors arent set up correctly, car wont run at all (not even rich or lean)

[GTSBoy]

Dopplepost

Edited May 18, 2012 by GTSBoy

[GTSBoy]

A Nissan ECU measures the AFM voltage, and uses the VQ curve to convert that to an amount of air flowing. The ECU then calculates the injection time by multiplying the revs by the air flow value by the K value (basically). If you put bigger injectors in, you need to reduce the K value, as you don't want to the bigger injectors to pulse as long as smaller ones. If you change the AFM (physically), then you change the VQ map in Nistune to reflect the different voltage-flow relationship and you have to adjust the K again.

The built in functions for resizing injectors and AFM in Nistune do this for you by simple ratio calculation between known (assumed) sizing of injectors and known (assumed) performance curves of the air flow meters. But such simple maths does not capture the fuzzy edges of the differences between things you change, and worse, with injectors the latency can be quite different, which is not automatically updated when you use the resize functions. End result, it is more normal to have to manually tweak the K value to get it to run properly, fairly common to need to adjust K to get it to run at all, and almost unknown to be able to swap stuff around without needing to touch the K value at all.

[lui]

Is there any set K value I can use, or does it have to be specific to my setup? I just wanna get the car to the dyno for a full tune.

[GTSBoy]

That's the point....it is very specific to your setup. Here's my tip. In Nistune, with the basic changes for AFM and injectors done, increase the K value by 10% and see if that makes it better. If not try +20%, +30%, maybe even higher. If none of that helps, try -10% and so on. When you find a change that makes it better, then try 5% changes around that.

[Zoidberg1]

Hi All,

I'm a noob so I'm not sure if I'm on the right thread or not, but here goes..

Last night I did the mod where you ground out the boost solenoid on an R33GTSt.

Well I read the entire thread on that before attempting it, & then did it as specified.

When I went to test it on my way to work this morning it would not rev over 2500rpm, just kept coughing until i dropped the revs below 2500.

I freaked out (i only just got the car), & put it back to standard, but it still wont rev over 2500rpm..

Have I broken something? Can I fix this?

So far I have reset the ECU as specified (disconnect batt & pump brakes)

I hot wired the solenoid to see if it works (it does)

& I tried running the car with the solenoid grounded & ungrounded.

Still only 2500 rpm..

Please HELP!!!

[scotty nm35]

Did you unplug the AFM? Check the plug is in, if it is then you have most probably damaged the the AFM internal connection, its a common fault. Can you borrow another one to try?