Pre95

Everyone points towards the hitachi injectors... yes they do suck, but there is a larger problem with MPI once you start to dig thru some wiring diagrams. It seems on the same power circuit that the automatic timing and air/fuel mxture is on, also lies the heating/AC control, and automatic fan switch (ever notice when the fan kicks on the idle adjusts?). This happens because when the fan kicks on it draws enough power thru that circuit that the injection looses enough power to affect your idle. Now you think.. meh... just enough to screw with idle but at speed its not a problem.

Well heres what happens when your cars modified. When the heater kicks on, or a/c or soemtimes the fan can be a big enough jolt, but when it kicks and ur idle adjusts, it can be enough of a surge to actually default out the injection (i.e. resets to factory on the air/fuel mixture and partially on the timing!) So if you have a cold air intake and exhaust (thus needing more fuel) your car will run a touch lean until the MAF amd O2 sensor reset the air/fuel mixture (which soemtime scan take up to an hour for it to get it properly set!).

The way to fix this problem is to run MPI on its own power circuit, or tap it to a lesser used power circuit (or less jumpy atleast). I do have access to wiring diagrams that show hwo to correct the problem but dont have a scanner right now. I'll definately post up about them when I have them scanned.

Now the injectors themselv's still are not the greatest in the world (tho they are ALOT BETTER with the wiring fixed) but I still suggest getting some bosch replacements (youll need bosch adapters). Infact, benchflow tests show 20v 7A injectors actually run a touch rich! The proper amount of flow rate should be more like 299cc/min not the stock 300-360cc/min (info collected by word of mouth from out-of-US bench flow testing, I havent tested this myself yet but I will)...

Any insight greatly appreciated.

Johnny

Zzak

I'm looking forward to seeing the re-wiring diagram & write-up. Good info!

Zzak

Hey is it just me or does 300cc seem like a hell of a lot of flow for 170hp?

Pre95

Considering the zo6 corvette runs 299cc/min ... hence the benchflow testing haha. Ill keep you posted when this dumb scanner gets up n running again.

Just Paul

Aren't the two injectors tested at different threasholds? This would account for the different flow numbers. There is extensive discussion of this on the CQ forum at Fortitude. Someone has developed an adaptor kit to put Bosch injectors on the hitachi rails.

So are these cars wired this way stock? I have noticed a power surge with the A/C, I always thought it was because of the drag of the compressor not a change in fuel flow.

Pre95

Audi simply kept a blind eye to it because on non modified cars the owner truley wont notice any difference with the surge's in place.

Zzak

I was playing around on this site <a href="http://www.rceng.com/technical.htm">RC Injector Sizing</a> and used:
Desired H.P. = 167
Number Injectors = 5
Fuel Consumption = 0.5
Max Injector Duty Cycle = 0.5
Rail Pressure of 4.2 bar / 0.069 = 60.87 PSIG

and came up with 299cc/min at a test pressure of 43.5 psi(299Kpa) so maybe Bosch 280 150 357 for 300cc/min would work (which surprisingly enough is what the one person I've heard of who got this to work is running)

so for 200 H.P. you need 358cc/min or maybe Bosch 280 155 009 for 346 cc/min would work.

Ah Theories =)

Regenmeister

Way rich! RC Engineering claims to have an injector which equals the specs of the Hitachis. All you need is the adapters from Patrick Carlier.
The wiring schematic interests me.

Zzak

That's becuase I fubar'd the math. 300cc@3.8bar is 266cc@3bar so 300cc@3bar is rich for &lt; 200hp

Regenmeister

to use on these engines if you could locate a supplier of Bosch injectors?