The results (WAS: Differential Pressure Regulator Checking

[Bernard Littau]

Hi Tyson,

Some comments in-line...

> Yes, the car is a 4ksq.

It helps if you put the car type and year in every message.  Not everyone
follows every thread, but lots of people read every post.  Even those of us
that follow the thread tend to forget what kind of car, or year, after a few
days.  Your goal is to make it as easy as possible for someone to give you
good advice :-)

> Air Flow sensor?! The mechanical plate assembly that makes the
> plunger go up
> and down? That cant be right! The plunger stiffness is most definitely due
> to pressure lock. I have tested that again and again. Can someone jump in
> here and clear this up for me?

The airflow plate resists upward movement through the use of fuel pressure,
so the behavior you describe is normal.

>
> Full description of plunger stiffness:
> When plunger becomes stiff the air sensor plate will go freely up
> about 2mm
> after which it becomes VERY hard. When forced up, from below, there is
> constant pressure to push the plate down. If I raise the plate and let it
> go, it will go down to it's lowest position. When pressure is
> released from
> the system, the air plate moves very easily.

The 2mm sounds like slop in the mechanical connection.  I have no idea if
this is normal or not, but I seriously doubt it is a problem in your case.
The rest sounds normal, although the term VERY hard does raise a red flag.
But then, very hard is subjective, so it is hard to tell if that is too hard
via email.  The things that affect the air flow plate resistance are fuel
pressure and the piston diameter the air flow plate assembly must press
against.  Only the fuel pressure can change, so my guess is that the
resistance you are feeling is normal, subject to the fuel pressure to the
metering head being correct.

>
> Thanks for the suggestion, I just do not understand how this
> could be an air
> sensor plate problem... Can anyone elaborate?
>

It does not sound like you are having an air sensor plate problem.  It is
possible that your fuel metering is hosed, but I can't imagine a failure
situation that allows the metering head to deliver fuel as the air flow
plate is raised a small amount, and then cuts out completely as it is raised
further (this is from one of your previous posts).

Last I recollect, you had the car running for a short period of time.  Is
this still the case?

Have you removed the fuel pump relay and jumpered the fuel pump (using the
relay socket) with some wire?  Much of what you describe could be caused by
a bad fuel pump relay, or a bad signal to the fuel pump relay.

Most of the rest of the stuff you have been messing with will make the car
run poorly, but is unlikely to make the car stall at idle.  On my 4kq with a
bad thermo sensor, it idled fine, but would not take gas (way too rich in my
case).  The idle circuit is largely independent of the rest of CIS.  If it
does not idle correctly, or stalls after a short time of running at idle, I
would have to lean towards the problem being something other than CIS.

I think it would be helpful if you could post a recap of the basic problem,
and what you have done to test the car, and the results of those tests.
There have been a lot of suggestions, but I, and likely others, really don't
know which of those you have acted upon.  Case in point is the thermo sensor
that Ben mentioned.  Pull the connector, and stuff a 10k resistor across the
connector terminals, and see how the car behaves.

I, and I am sure others, really feel for you with the car disabled.  You
have been very patient and industrious at working through the problem.  At
this point, nothing would make me happier than to hear you have the car
running well.

Best,

Bernard Littau
Woodinville, WA
'86 4kq