[Gmecm] Injector sense - addendum

[Rob Handley]

Just had another go with the new 'scope.

If I read it right, when the BPW is very short (e.g. sub 1 ms) the injectors 
AREN'T fired every crank revolution, but ARE every 2 (as I thought I saw 
with the old 'scope). This makes sense. Does it stack up with anybody's 
understanding of the code?

This conclusion is based on me changing the relevant contents of the VE 
table, with the engine idling, from 30% to 99%. The ALDL-reported BPW jumps 
from just under 1 ms to about 2 ms.

Interesting.

Robin

----- Original Message ----- 
From: "Rob Handley" <Robin at FuryWorld.fsnet.co.uk>
To: <gmecm at diy-efi.org>
Sent: 03 September 2007 18:43
Subject: Re: [Gmecm] Injector sense


>>> 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?
>
> To answer myself - YES. Just tried a shiny new 'scope and this time I see 
> injector pulses at twice the DRP interval. Phew!
>
> And no sign (on the 'scope) of the big spikes that appear on the ALDL, so 
> I reckon that must be another ALDL artefact.
>
> Thanks again Bill.
>
> Rob