Hiya,

Now I have my techedge AFR meter fully installed I have found that at idle / cruise off boost I have an AFR of about 12.5 which seems too low and I guess might mean my car will fail the MOT. Therefore Id like to build myself a 5th injector setup so I can dial back the EMFPR on the KE Jet and get a better AFR off boost but still have enough fuel on boost to maintain the 11.2 AFR Im getting now.

I have been knocking a few circuit ideas round in my head of how I might drive the injector. Basically I will want it to kick in at a preset boost level so I could achive this with either a MAP sensor (Motorola MPX4250) or a simple pressure switch. Then I'll need something to drive the injector and to be able to vary the duty cycle to hense vary fuelling. To to this I was planning to use a simple 555 timer based monostable circuit which could be driven by :-

a). Another 555 in astable mode so when the boost level got to the "on" pressure a set additional amount of fuel would be provided regardless of RPM.

or

b). I could use the dizzy signal to trigger the monostable so once the injector kicks in the extra fuelling will increase linearly with RPM.

I realise that the engines fuel requirements are not linear but given Im ony looking to run 14 psi max would one of these crude systems be sufficient??.

Alternatively I considered using an LM2907 frequency to voltage convertor IC to give me a way of measuring RPM and allowing me to vary the duty cycle of the drive to the injector with RPM so give a bit more refinement.

Anyone got any views?? - I know its not going to be anywhere as good as an MF2 etc but it might be good enough for my needs??

Cheers

Stu