JamesS

Posted a couple of days ago about an FCD not working.

Have since datalogged voltage into and out of the FCD and it is working fine.

However I am hitting (what feels EXACTLY like) the boost cut when trying to push above about 1.35/1.4 bar and 4000ish rpm. MAP voltage is clamped well below 4volts.

ANY IDEAS??????? Have NOT got a samco intake pipe that might collapse. Only flexi bits are the Samco joins between the HKS pipework and the 90deg elbow at the compressor-out - and these are obviously pressurized!

HKS headers, SS upipe, full decat exhaust, monster K&N filter, APEXI AVC-R, HKS FMIC, UNICHIP, 7B plugs at 0.7mm.......

If there was an issue with wastegate I`d get boost creep or would not be able to make the requested boost? Compressor can easily handle 1.5/1.6 in the mid-range.

Any suggestions welcome! Please, please!

dowser

Be very careful - probably a fuel delivery problem if it feels 'just like fuel cut'. What size injectors do you have? Can you datalog idc's with the Unichip? Did you fit a decent fuel pump yet?

Richard

Claudius

Why dont you just unplug the boost sensor thingy completely if you have an AVC-R and see if that works? Otherwise you may be reaching max inj capacity, but I cannot see how that would cut the fuel off; it would just (ahem) run lean, wouldnt it?

JamesS

I`m using some OEM datalogging kit inc wide band lambda up the pipe.

Car is running fine at 1.3/1.35 bar, except for hitting the cut above this boost pressure. As I say it feels exactly like the std boost cut.

Uprated pump as well.

So fuel is OK, boost control is OK it just won`t go above 4000ish rpm....saturated MAF? I can check IDC on the APEXi.........keep em coming!

...all on a late 00MY UK with 550(?) injectors......

[Edited by JamesS - 1/28/2003 12:11:38 PM]

StephenDone

Get someone with a diagnostic tool to check for trouble codes.
You may have hit an air flow sensor upper flow limit check - the ECU _can_ tell what you are doing ! Trouble codes will confirm or disprove this.

btw, MY00 has 440 injectors unless they've been changed. You've got to be running lean at that sort of turbo+boost unless your injectors have been changed or your fuel pressure upped. My car runs 85% duty at 312BHP, and that's at 1.2 bar with a much smaller turbo. You are likely flowing a fair bit more air than this.

Steve

JamesS

Muuummm, fuelling looks ok; rich at 12-12.5:1, nice rich spike on the tip-in. This is true for top end of 4th.....I thought that the late model 00MY had the 550`s(?) plus one of MarkA`s fuel pumps....

Cut is occuring in the midrange 3500-4000rpm so even if pushing the injectors at the top, they should be ok in this region....

I assume that the MAF is not maxing out either, although I will check voltage level....

Could it be a parity check between the MAF and MAP readings? Too large a difference = something wrong = cut fuel?

Strange no other 00MY seems to have this issue - a certain Mr JB springs to mind!

I cant think of a physical reason for this to happen (pipes, compressor, BoV etc) and it `feels` like an electronic intervention........

EMS

James,

I whould also suggest to read the trouble codes, as I expect something goes wrong somewhere with the Unichip or FCD.

AFR 12.0 - 12.5 is WAY too lean for an Impreza in my oppinion! (if you don´t have WI)

All MY99 and MY00 have 440 cc injectors.

Mark.

john banks

With my FCD I had a working fuel cut at 23 PSI, no problems. Can't explain. Had MAF voltages up to 4.84 V before (on airbox, now 4.54 with APS induction) with no fuel problems.

Mine is making a bit more power at 11.8:1 than it was at 11.2 and 11.4:1. I will probably go to 12:1 without water injection, but with a FMIC. It doesn't seem to adversely affect the det threshold and the EGTS are still about 800C max at the bottom of the uppipe.

JamesS

FCD is working fine.

12:1 is OK IMHO....I`ve followed up the Unichip angle as well. Feeling is that it is very unlikely it is causing it. There is no software in the unichip that would cut/interupt a signal........

At 1.34/1.35 bar all is very well indeed!

StephenDone

>AFR 12.0 - 12.5 is WAY too lean for an Impreza in my oppinion!
>(if you don´t have WI)
>
Ditto. Your engine's likely to expire without more fuel. You only have to get dirt in an injector, on the MAF or the boost restrictor and your engine is history. Richen it up and take it for a rolling road diagnostic check. Anything else is asking for trouble IMO.

[Edited by StephenDone - 1/29/2003 3:46:56 PM]

Claudius

I read somewhere scoobies "like" 12.3:1. How rich would you go and why?

JamesS

Engine has run this way for 30K miles, now on 50K!!. Including 130+cruise for 3000miles round france last summer (admit not all at that speed!!!!!). Numerous rain-water peeing onto MAF events and loads of boost-cut! Throw in a few track days and 320bhp on powerstation rollers (with a TMIC running at 70DegC) and I would have to say that the engine is `fairly` happy with things as they are!!!!! Fuel pump went on same time as FMIC. All steps checked and datalogged.....phew!

Now, granted the unichip was mapped pre-FMIC, but part of the appeal of the unichip is the MAF/TPS based mapping - you pull more air it reads and fuels accordingly. No re-map for every change required (within reason)....but perhaps it could use a little more fuel for extra durability......BUT from the logs so far, it does not explain its reluctance to generate higher than 1.4bar boost!!!!! Not really a big-deal (Just run at 1.3bar as before!!) but now know for sure `something interesting` is happening. I`ve experienced numerous boost cut events (inc the water on the maf story), high altitude events (French trip, going up Route Napoleon), all previously put down to tripping the new higher FCD limit...now I know the MAP voltage is not reaching the clip something else must be cutting in.

Next step I think is the ECU codes, MAF voltage and IDC......