[Gmecm] Injector sense

[Rob Handley]

> Yes,  just leave them open for saturated injectors.

Many thanks.

> And yes,  the 727 and 749 schematics are the same,  the 727 doesn't have 
> the 2nd injector installed I believe.

Thanks. I've read that the 730 only has one; so, as the 727 and 730 are 
reputed to be identical inside, I guess this means the 727 only has one as 
well. But 2 sets of pins are used to 'spread the load'.

> And yes,  they're all fired at once in batch mode,  once per crank 
> revolution,  plus the asynchronous pulses.

This is the bit that worries me. My tests with the oscilloscope in the 
garage yesterday indicated that the injectors were being fired once every 4 
DRPs - because my (4 cyl) engine was idling at about 800 RPM, with ALDL 
correctly reporting a DRP interval of ~38 ms. The 'scope was showing ~130 ms 
between pulses - which is _roughly_ 4 x 38 (although disturbingly not close 
enough for my liking!). I would expect to see 2 x ~38 = ~76 ms if they were 
firing once per crank revolution.

I'm not _100 %_ sure that I'm reading the 'scope right as I haven't used it 
before and there's no manual (it was thrown out from work), but the same 
scope showed an idle injector pulse width which agreed with the ALDL BPW 
plus the ~0.5 ms battery offset.

BTW: My code ($58) is set for 4 cyl, I've set the max async PW to zero, and 
my MemCal has the leg of the chip at CAL56 desoldered - which I think 
selects 4 cyl TPI mode. I've read that the number of DRPs between injector 
pulses differs whether this pin selects TPI mode or TBI mode - but I'm not 
clear how many DRPs between pulses in TPI, and how many in TBI.

Have I got something wrong?

Thanks Bill,

Rob

----- Original Message ----- 
From: "Bill Shaw" <b.shaw at comcast.net>
To: <gmecm at diy-efi.org>
Sent: 03 September 2007 02:35
Subject: Re: [Gmecm] Injector sense


> Yes,  just leave them open for saturated injectors.  And yes,  the 727 and 
> 749 schematics are the same,  the 727 doesn't have the 2nd injector 
> installed I believe.  And yes,  they're all fired at once in batch mode, 
> once per crank revolution,  plus the asynchronous pulses.
> hth,
>
> Bill
>
>
> Rob Handley wrote:
>> Sorry to bring up old stuff, but I've been trawling through my personal 
>> archives and doing Google searches for hours and haven't found a 
>> definitive answer.
>>
>> I wanted to be sure what to do with the injector sense lines on my '727, 
>> when connecting 4 high impedance (saturated) injectors in parallel.
>>
>> The Corvette wiring diagrams on the diy-efi site just show injectors 
>> connected in parallel, and have the 2 injector sense pins (that are shown 
>> on the quadplugecm cross-reference) listed as 'not used'. From this I 
>> deduce that I don't have to worry about the injector sense lines. I'd be 
>> grateful if somebody could confirm.
>>
>> Robin