Re: [DML] Re: Setting Fuelling - Why does the DMC PRV Hunt? [long]

[Martin Gutkowski <webmaster@xxxx>]

Hi David - replies inserted.

David Teitelbaum wrote:

> All of the
> cylinders of the engine must fire equally with very nearly the same
> compression, spark plug gap, and injector settings. If any cylinder is
> different from the other it causes the idle motor to try to compensate
> resulting in "overshoot". By the time the correction kicks in the
> engine is on another cylinder and now it is too fast so the idle motor
> tries to slow it down, hence the hunting.

If this were the case, the idle "hunt" would occur near enough once every rev of the
engine - more like a diesel does (the "galloping horse" syndrome). I am not convinced of
this given the *extremely* low mileage DeLoreans that ALL do it. I'm no expert, but
Darren IS and categorically told me that Renault 25's, complete with the same idlespeed
system and the 2458cc (from memory) PRV, do not hunt. It can't just be down to tiny
adjustments that can go out of wack causing the hunt, or you'd get more Renaults and
Volvos doing it, surely?

> You also have the lambda
> cycling up and down so when these 2 functions overlap the hunting is
> even more noticeable.

Actually I said that mine stops hunting when the lambda system kicks in, and on asking
other club members, this is the case with them too.

> The first thing I
> would suggest is a compression test, if the cylinders are not within
> 10% (5% is better) then you will never get it smooth. Clean and regap
> the plugs to .028, replace the ignition wires, clean the fuel
> injectors, fix all of the vacuum leaks, and now you can begin to get
> it smooth.

My query was in relation to building my new engine, and establishing the theory before
Darren (a very knowledgable PRV guy) builds one to DMC spec. He turned up evidence that
the DMC workshop manual is WRONG, and the hunting charachteristics of just about all
DeLoreans (even those still factory-fresh cars) being the main symptom. I am drawing my
own conclusions about this - thanks for your input, but I'm not entirely convinced.

Martin
#1458
#4426