So one of my stock injectors decided to die and it just happened that I had a set of 600cc injectors lying around that I bought from forum member Arvin. Anyway after installing the new injectors and swapping of the plenum I had dressed up and installing 58mm throttle bodies. I connected Nistune and used the function that changes your K value by injector size, K value was 288 and after punching in the new injector size it went to 177. Started the car and it ran but idle was sitting at around 2000 RPM when at running temp, after speaking to the tuner he advised me to remove the 58mm Throttle Bodies as I was not at that stage yet, even thou I have 2 1/2 inch intercooler set up with HKS bigger turbo's. Anyway I swapped them back over with the stock ones and the idle at cold seemed to be ok but once it was warm went back up to 1500 to 1700. Took it to the tuner and he was unable to bring the idle down either. So back in the garage at home I pulled all the idle control gear off the back of the plenum and it passed all the normal test except for the Air Con idle up, no big deal as it is a normally closed anyway, reassembled and started the car and idle now was fine. sorry for the long winded story but find it better to give history. Anyway from there the car now idles fine but seemed to be slightly lumpy at idle and now it has a back fire on rev down if you give it a good rev, so I checked timing and found that it was at 25deg both on Nistune and with the timing light, so I adjusted timing back to 15deg readjusted Idle and now it idles smoothly but still has the backfire on rev down. So before I take it to the tuner I need to know is if this is because it still needs to be tuned or could it be another issue? also noticed that Nistune still shows timing at 25deg and so does ECU talk is that normal?
You should put your timing back to 25 at the pulley, the ECU uses a pulse from the CAS to know where the crank is and then based on that signal tells the coils when to fire. The timing you see being sent from the ECU is when the ECU wants the coil to fire. If your car is an auto to manual conversion that will explain the extra 10 degrees of advance from the ECU at idle because the automatic neutral switch is missing. The previous idle problem was probably just a vacuum leak which you fixed when you put it together again. The current idle problem is probably to do with injector latency and triming the K value which your tuner should be able to fix up, better to do this with proper AFR data.
timing So I adjusted timing back to 25deg and readjusted idle and dropped K value down to 148 seems to idle nicely but if you give it a good rev it occasionally still backfires on rev down?? still seems a bit fumie / rich?? the 148 K value is what the tuner had it set too when it was on high idle. And yes it is a Auto / Manual conversion
What brand injectors? Someone here might be able to help out with what the latency and K value should be. I'm not a tuner so you'll want someone else to help you fix up the overfueling, you'll need a wideband O2 sensor/s if you're going to DIY. The ignition timing is right though, there's been a bunch of threads on here about it in the past for manual conversions and my car was like that when I got it. You can probably turn off a setting in Nistune somewhere so that it idles at 15 to avoid confusion.
Get a proper tune , from what your explaining it sounds as though you are running rather rich. What position is your CAS in? Do you have a picture or description just to varify
Tune up (injector leak?) OK picked it up from the tuner today, it still idles slightly rough and is hard to start if you leave it for 15min or so, he thinks it has an injector that is leaking? I bought these from forum member pennyarve - Arvin so one would think that their ok? so he got the K value sorted and it is currently pulling 287KW with a standard Nistune 300zx bin file with a modified K Value. He stopped it at that point until I have the Injectors flow tested / leak tested? any thoughts would hate to think that I have wasted my money on these injectors off a valued forum member?
Sorry, what? That is wrong on so many levels. I hope you meant hp not kw How much did you pay for this tune?
287kw 287KW Has HKS turbo's, ported Manifolds, 2.5" Piping with bigger intercoolers, HKS boost controller ect, so was chasing 300KW with a proper tune. His dyno should be that far out as my mate has a new 317KW clubbie and after a couple of miner upgrades and a tune it pulled 294KW on that dyno. Oh I haven't paid a cent yet as we still need to sort out this issue. currently running 17PSI Boost
boost leak test No not yet, but unlikely as I have double checked every connection and am using the heavy duty SS clamps on the 2 1/2 inch piping.
maybe luck maybe just luck? was pulling reasonably hard on the stock injectors and stock bin file before.
hmmm, stock injectors shouldn't have supported that power, was it running less boost before? what fuel pressure regulator does the car have? if the fuel pressure has been raised that would explain why its running richer than you'd expect. Although I guess its possible the injectors did handle it and you were lucky enough that it didn't lean out. Have you had a look at the spark plugs? if one or a few of the injectors are leaking you'll be able to tell from the plugs in that cylinder being covered in more soot or perhaps visibly wet with fuel. If all the plugs look the same I would be guessing its more of a fuel pressure problem, I don't know Arvin but I've never seen a mention of him providing problem parts or services before so I can't imagine all the injectors are shagged. Can someone else confirm that o-ring leaks on sidefeed injectors don't result in leaking into the cylinder? Only installed injectors once and didn't pay that much attention. I know with topfeeds o-ring leaks can be responsible for overfueling.
I still have the stock set still in the rails, I will have a look. You could be on to something as I did remove one of the 600CC injectors out of the rail to have a look maybe I pinched the O ring when I re installed it.
Perhaps you should have mentioned that small detail PRIOR to questioning Arvins reliability/skill/knowledge/trustworthiness.......?
Injector leak Sorry my bad, first to admit I stuffed up. Yes it was the lower O ring seal on number 1 injector. Thanks for all your help. Will post results after the tune next week.
