Re: Fuel Injection Q's

[Phil@sievers.com (Phil Payne)]

In message <335B5F78.15EA@prodigy.net> scottmo writes:

> If your MAC12 ECU is based on the MAC11 ECU then only
> having one knock sensor makes sense. To give you an
> idea of what the The MAC11 ECU looks like ...

Forgotten.  And I only had the damn thing out at the weekend.

> Orin and I would be interested
> in seeing the code out of that one.

I would be interested in you seeing it as well.  Even when an MB is
working perfectly, there's a genuine "unintended acceleration"
effect at medium to heavy load when the coolant temperature is one
segment below the "N" in the centre of the gauge.  Several MB owners
have reported this effect.  You get kicked up the backside by the
seat, and the fuel pump cuts.

> So your car has the pressure regulator rubber hose
> connected to your intake manifold? That would seem a
> bit odd, ...

No, not the manifold - the air mass sensor plenum.  Vacuum only.

> >>But what is the vacuum tap-off on the intake plenum
>  for, otherwise?
>
> Don't know for sure, but I have one vacuum port on
> my intake that is plugged off and not used for
> anything. The unused port is near the back of the intake.

I checked both the parts and service fiche.  Both clearly show this
hose in place between the air mass sensor and the valve.

> Sounds like your regulator is also setup as mine for some
> altitude correction. I don't remember from
> your previous post, but I assume that if you apply
> vacuum to this port the control pressure goes up
> which would lean out the mixture as stated before.

Haven't tried it, but it might be worth a go, just to see.

> As I mentioned before, I have never
> run across a CIS fuel system that changes the system
> pressure at different engine intake manifold conditions,
> i.e. vacuum/pressure.

See the Micro Dynamics devices discussed in the last section of
Probst's book.

> Yes, Orin located the information in the MAC11 ECU code
> where the computer uses two different boost maps (low boost
> and high boost)to set the frequency valve duty cycle
> to be somewhere around 60-75%. As you know this
> helps to richen up the mixture under 2/3 -full throttle
> boost conditions. Normally on a non-O2 sensor
> equipped car I believe the duty cycle is set by the
> ECU to be 50% at idle. Is that what your car does?

Don't know - haven't measured the duty cycle.  How do I go about doing
this?

> What was your original problem that you have been
> trying to resolve? I never bothered to ask before..
> Silly me.....

Poor full load performance - perhaps missing or poor enrichment.

> Are you still planning on making it out for the Pikes
> Peak aniversary? I should be going assuming my car
> makes it there from Oregon......

No.  Our organiser didn't.

--
 Phil Payne
 Phone: +44 385302803  Fax: +44 1536723021  CIS: 100012,1660