[DML] Re: RPM relay (was I think my fuel pump...)
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[DML] Re: RPM relay (was I think my fuel pump...)

I was relaying (pardon the pun) what I have heard. I will at some 
point open up a couple and try to figure out what the circuit does, 
although I suspect others (Hi Elvis) have done this too. I don't 
thing just saying "all that other circuitry" does the analysis 
justice without truly decoding and understanding the cicuit. 

My suspicion is that there are two versions of the device floating 
around because I have seen them both ways, and I have seen many 
actual "new" ones, from several sources, that don't do the "priming". 
It's likely that Bosch did a design change over time for different 
applications, and this has made its way into the supply chain.  If so 
I'd be curious to know which came first! 

In normal operation of the car, the driver turns the key from off to 
start in one motion so the priming benefit would be minimal since the 
circuit activates as soon as the engine cranks anyway(in the 
apparent "no-prime" version). I don't know too many people who turn 
the key to run, wait a second, and then start the car (in normal 
driving, not testing!). 

I don't think it has anything do do with the 555 itself, rather the 
circuitry around it.

It's an interesting study in any case. 


--- In dmcnews@xxxxxxxxxxxxxxx, "John Hervey" <john@...> wrote:
> Dave S. 
> I would think you have it back wards and David T has it correct.  
Priming of
> the fuel system is part of the function of the 555 chip on the pc 
board in
> the RPM relay. If you didn't prime first then what would be the 
point of all
> the circuit components on the PC board? All you would need is a 
pick up from
> the pulse coil. I have not seen or heard of a car under normal 
> that doesn't prime first before starting. I'm not saying it won't, 
> it should if the system is still under pressure and the relay on 
the board
> is still good. The timer chip could be bad.  
> John Hervey
> www.specialtauto.com
> -----Original Message-----
> From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On 
Behalf Of
> David Teitelbaum
> Sent: Monday, April 30, 2007 10:13 AM
> To: dmcnews@xxxxxxxxxxxxxxx
> Subject: [DML] Re: RPM relay (was I think my fuel pump...)
> There are black ones and green ones. The black ones are considered 
> earlier version and are more prone to failure. I am not sure which 
> "primes". I think it is more an indivdual part than green ones or
> black ones. IMHO I would consider the priming function "correct" and
> the ones that do not prime "defective". Some Deloreans start up a 
> faster than others, probably due to the "priming". I consider 
that "a
> good thing" as it reduces the strain on the batttery and the 
> Since this is "undocumented" anyone's opinion is valid. Anyway, I 
> not think of any way such a device could fail in manner where it 
> "prime". It had to be built that way to do it with the timer put in.
> David Teitelbaum
> vin 10757
> --- In dmcnews@xxxxxxxxxxxxxxx, "Dave Swingle" <swingle_dmc@> wrote:
> >
> > A couple of updates from this weekend on this topic - according 
> > some discussion I had with the other DeLorean Motor Company 
> > that were here, the RPM relays that "prime" (i.e. turn on with 
> > key for a few seconds) are considered "defective" and the other 
> > that don't turn on until the engine cranks are 
considered "correct".
> > 
> > I've seen black ones and green ones, in fact I have a green one 
in my 
> > car but I have no idea where it came from. 
> >  
> > Dave S.
> > 
> > www.dmcmidwest.com
> > 
> > 
> > --- In dmcnews@xxxxxxxxxxxxxxx, "John Hervey" <john@> wrote:
> > >
> > > Andy, Can you tell us more on the replacement or different RPM 
> > relay. I have
> > > seen a different fuel pump relay but I have never seen a 
> > RPM relay
> > > in the DeLorean. What color is the case.
> > > John Hervey
> > > www.specialtauto.com
> > >
> >

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