[DML] Re: Scoping out the dwell and RTFM

["Harold McElraft" <hmcelraft@xxxxxxx>]

Page 122 of Technical Information Manual - set the dwell meter to 4 
cylinder scale.

Harold McElraft - 3354


-- In dmcnews@xxxxxxxxxxxxxxx, "drdhdmd" <doctorDHD@xxxx> wrote:
> It was a beautiful almost "Spring" day so I couldn't resist.  I 
> connected my scope to the diagnostic port to "see" what was going 
> on.  According to my calculations the frequency of the signal was 
70 
> Hz which I believe is correct.  The problem is the duty cycle ON 
was 
> only 38.8% with the WOT switch closed.  The manual says 50 - 60.  
> Something did not seem right so I went back to the DeLorean 
Workshop 
> Manual and checked all the "Pulse Ratios" on page D:04:15.  
> Everything seemed to be inverted, that is, the lower part of the 
> square wave pulse signal got bigger when the WOT switch was 
closed.  
> I tried all the test configurations and the all were right except 
> they were inverted.  Attaching a known voltage and polarity to the 
> scope proved that + was indeed up.  I was confused. It was getting 
> dark and I had to close up shop.  Now sitting here something I 
read 
> popped into my head. It talked about connecting the dwell meter to 
> the pinS on the diagnostic plug.  A quick check of the schematic 
> revealed the problem.  I had connected my dwell meter and scope to 
> one pin on the diagnostic plug and ground. (They way we used to 
check 
> dwell on a car with points.)  It seems that the other pin of the 
> diagnostic plug is not ground but rather positive 12 volts.  Thus 
all 
> my measurements were off and I guess I adjusted the CO to around 
60 
> instead of 40.  Now I have a project for next weekend!
> 
> I believe this has been address in the past but none of the 
answers I 
> have found seem to make sense...to me.  When using a DWELL meter 
to 
> measure these "ratios"  What scales and setting do you use?  Since 
we 
> are talking about something that in theory can go from 0 to 100 
> percent, it doesn't seem correct to use even the 4 cylinder range 
> because that maximum is only 90%.  Does anyone have an answer with 
an 
> explaination?  (I know I am asking alot but remember what the old 
> wise man said about giving a fish vs teaching someone how to 
fish...)
> 
> When all else fails Read The Manual.  Fortunately when I was 
> flying Pipers I ALWAYS used my checklists and went by the book 
> carefully.
> 
> Thank you,
> 
> Dave and 6530




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