I have just fitted a set of 550cc injectors to my 94 WRX, what fuel pressure should I now be running if I'm running 1.3 bar boost.

Since fitting the injectors the engine will not rev over 4,000 rpm, I set the fuel pressure reg to 3.5 bar ( vacum hose disconnected ) but I don't know if this is too high. My air / fuel ratio gauge is reading rich, but not excessively. Everything appears to be reconnected. I presume the car was running ok before but it hasn't been driven since October.

Cheers Colin.

 

your car would need to be re-maped if you have fitted bigger injectors

mikee

 

You have set the fuel pressure higher than std, also fitted 25% bigger injectors so its choking, as Mikee says it must be remapped in some way.

You can mitigate by reducing fuel pressure, std is about 2.5 bar at hot idle with vac pipe on, revert to that and then see. ECU is in limp home as it thinks something is wrong (which it is of course)

Why did you think you needed bigger injectors ?

bob

 

I have recently fitted 550cc injectors to MY96 UK Turbo and as the others have already said you will need to remap as you will be choking the car mid-upper range as the ECU is mapped for the standard 380cc injectors. I custom mapped my own ECU with input and advice from various sources (You know who you are )

 

If you want the car to run at all prior to a remap then you will need to lower the fuel pressure to around 2.3 bar above manifold.

I finally spent some time custom mapping my own car (after doing everyone elses) and was horified at how rich it was at around 1 bar. I have an uprated pump and pressure regulator, but even them removed 25% of the fuel to get the AFR correct.

Your best bet is going to be either a replacement ECU with custom mapping or remap the factory ECU. THe misfire you have is due to overfuelling as mentioned above, and will not be good for the engine in the long term.

If you drive off boost you will by more or less okay, but you need to get it sorted. You should also consider an uprated pump (and regulator would be nice too) if you're to make the most of the injectors.

Paul

 

Cheers for the replies guy's, I did realize I was going to need a remap but I was hopeing it would run well enough to get me somewhere to have the remap carried out.

Bob the reason for uprateing the injectors is that I was already running 319bhp and 320 lbft on 380's and to say they were maxing out was an understatement. The rest of spec is listed below :-

HKS induction kit,
HKS iridium plugs,
HKS FCON 5 ECU with additional GCC fuel controller,
HKS EVC 3 boost controller,
HKS downpipe,
HKS hyper TI tip exhaust,
LP fuel pump,
LP fuel pressure regulator,
Blitz 550cc injectors,
HS up pipe,
Apexi IHI RHF5 hybrid turbo,
Apexi front mounted intercooler,
Apexi dump valve,
Lightend and balanced flywheel 7kg.

Moving to 550cc injectors was the next step towards 350 + bhp. The HKS FCON 5 is running an STI 3 base map at the moment designed for 440cc injectors so I would of expected less problems than running the standard ECU designed for the 380s. Bob are you able to map the HKS unit as it would behandy as I'm only in Southampton, the nearest places I know of that can map it are G Force and TD. I have no problems with G Force but I'm not sure about TD as they can't even seem to supply me with the correct parts I have ordered, so I don't hold a lot of hope about getting a decent remap

I was planning a remap after changing the turbo again to a straight entry turbo with possibly a different down pipe and a set of headers, and also fitting the Bosch MEC 723 coils and Magnecore leads that are sat in the shed.

Cheers Colin.

 

Nice spec, the HKS is a stupid setup where only authorised dealers (or someone with the dealers software) can remap, silly really.

If it's set up for 440s at 3bar fuel pressure, then theory suggests 1.92 bar fuel pressure would give you the same flow with 550s. I would er on the side of caution, but you should be able to make it driveable to get it remapped.

Paul

 

Yes it is annoying that it can only be mapped by an authorised dealer. I know good results can be achieved with this management system as Jun have proved on their Scooby's in Japan and also Abbey motorsport on their Skylines. But it's all down to the person mapping at the end of the day. I have even considerd asking Abbey Motorsport if they would be willing to give it a go.

Colin.

 

If Abbey can map it, and you don't mind the expense of putting on their dynapak hub dyno, then I would say it's definitely the best way to go.

Paul

 

Hi Paul,

Adjusted the fuel pressure today to 1.95 bar atmospheric, spot on Just very slight det at 1.38 bar at approx 5,000 rpm which disappeared with a tweak of the HKS graphic control computer, I'm only running on Optimax at the moment so with octane booster added it should be fine.

I'm at Tuning Japanese on Saturday for a rolling road day so I will see how well it's set up on their rollers before I play any more.

Cheers for all the advise Paul,

Colin.

 

Nice one M8