[V8] sanity check, what, from a V8Q owner?

Thu Mar 20 19:01:49 PDT 2008

If Cylinder 1 isn't firing, then Cylinder 6 is, when the crank is at TDC.

So, one has to dig up the cap/wires routing to find......

..that cylinder 1 and cylinder 6 are on the same cap.  So the ECU just 
notes where the crankshaft is (0, 90, 180, 270, and how it knows for 
sure, I'm not 100% sure), and then sparks... and since it knows where in 
the rotation, it knows which coil to spark.  The ECU doesn't know if 
it's TDCc or TDCe, but it knows it's TDC, so it sparks Right-Bank coil.  
Right-Bank rotor decides where the spark goes.  That settles that.  The 
ECU probably fires the two cylinders that "may" fire?  My hands are too 
greasy (french fires, not car parts) to dig up the wiring diagrams.

If only 2 injectors are firing, surely we'd get better gas mileage??  
The 944 batch fires 4 cylinders twice a revolution and still manages 
around 25-30 mpg.  The V8q fires... yup.. 8 times a revolution.  Two per 
90º, so yeah, bad gas mileage. 

I think someone out there has done stand-alone engine management?  
Anyone worked up sequential?  I know guys in the 944 world have.  
Sequential gas mileage would (in theory) double mpg?

I babble on about 944's cause they were my lifeblood before 16 months 
ago. ;)

~Scott S.

urq wrote:

>Yes, you can tell from the wiring diagram that there are two injectors wired
>to each driver circuit in the ECU.  What you describe for the 944 is called
>batch mode.  Not many EFI systems even try to time the fuel pulse for when
>the valve is open.  The goal is to get the correct amount of fuel into the
>intake manifold, and assume it will get sucked into the cylinder when the
>valve opens ...
>
>As to the ignition, I don't know that I had ever heard that both coils fired
>simultaneously ... it really sounds like a waste (no pun intended) if it
>were true.  Each coil has a separate connection to the ECU, so I'd expect
>they are fired independently.  It seems to me that it almost has to be this
>way.  I would expect that the dizzys are actually out of phase from each
>other by 1/8th of a turn, and the coils phased to fire one and the other as
>the adjacent cylinders in the firing order hit TDC.  I guess the way to
>prove my theory would be that the cylinder that is at TDC compression when
>#1 is at TDC exhaust would have to be the same cylinder that is 180 degrees
>opposed from cylinder #1 on the same distributor.  The ECU is triggering the
>same coil independent of whether it is #1 or the other cylinder (probably
>#5), and it is the distributor that makes sure the spark makes it to the
>proper place.  If all this is true then the ECU really doesn't need to know
>when #1 is at TDC compression via the Hall Sender.  The thing that will get
>confused without the Hall Sender is the knock sensor feedback, and this
>might well be the reason the ECU decides to back down a bit when it doesn't
>have the Hall Sender input.  
>
>Steve B
>San José, CA (USA)
>
>-----Original Message-----
>The injectors fire two at a time?  So it fires both 1 and 6?   Because 
>either 1 is firing at TDC or 6 is firing?
>
>That being said, how does it time the spark?  Do both 1 and 6 spark?  
>The pin will only tell when 1 is at TDC, so it's either TDC for 
>compression and 1 is firing, or it's at TDC for exhaust and 6 is firing.
>
>I know on the 944s I worked on, all 4 injectors fired at the same time, 
>so the computer only had to know where TDC was.  The coil would energize 
>twice a revolution and the cap/rotor would get it to the right cylinder.
>
>But the V8q has two coils, so how does the computer know which coil to 
>fire?  Or does it fire both coils and one just ends up being wasted?
>
>~Scott S.
>
>Tony and Lillie wrote:
>
>  
>
>>They fire two at a time. That is what the hall sender is used for. The 
>>computer uses the hall sender to determine #1 TDC. Which is one of the 
>>reasons for the slight hesitation if the hall sender is unplugged.
>>
>>As fro wasted spard, you are thinking of a COP setup. With a 
>>distributor, you can only fire each cylinder once per revolution. The 
>>width of the rotor is what gives teh ECU adjustability. But, only a 
>>certain amount. Basically, if the coil fires, the spark is going to 
>>the cylinder that the rotor is pointed at. And, each coil fires four 
>>times per engine revolution.
>>
>>Tony Hoffman
>>
>>
>>----- Original Message ----- From: "Scott Simmons" <indischrot at gmail.com>
>>To: "urq" <urq at pacbell.net>
>>Cc: <v8 at audifans.com>
>>Sent: Tuesday, March 18, 2008 8:56 PM
>>Subject: Re: [V8] sanity check, what, from a V8Q owner?
>>
>>
>>    
>>
>>>Are we saying that the V8 uses wasted spark?  Also, what times the
>>>injectors?  I assume they're batch fire.  Which fire at what time?
>>>
>>>~Scott S.
>>>
>>>urq wrote:
>>>
>>>      
>>>
>>>>For an engine with a distributor and an even number of cylinders it 
>>>>doesn't
>>>>matter whether you're at TDC compression or exhaust, the time to 
>>>>fire the
>>>>coil(s) is the same.  My V8 ran for a long time with a no Hall 
>>>>Sender signal
>>>>code.  Odd number of cylinders, or coil per plug then the ECU needs 
>>>>to know
>>>>whether it is exhaust or compression.  An I-5 will not start if the 
>>>>Hall
>>>>Sender is bad ... the PT in a V8Q will ...
>>>>
>>>>Steve B
>>>>San Jose, CA (USA)
>>>>
>>>>-----Original Message-----
>>>>
>>>>
>>>>so who does if not the Hall sensor? ;)
>>>>
>>>>73
>>>>
>>>>Bastian
>>>>
>>>>
>>>>Scott Simmons schrieb:
>>>>
>>>>
>>>>        
>>>>
>>>>>The ignition sensor pin the flywheel will only tell you if you're at
>>>>>TDC, but not if it's compression or exhaust, BTW.
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
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>>>
>>    
>>
>
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