RESUME: 100Q engine problems

[SJ]

> From: "Denis" <sparkplugvw at hotmail.com>
> Subject: Re: RESUME: 100Q engine problems

Car: Audi 100Q 1989
> Engine: 2.3 NA CSI-3
> symptoms:
> - Hard starting hot and cold, starting as a big lazy
> cow.

>
> The problem is the fuel regulator, i m quite sure. I m stuck here cause i
> cant get parts around here for that old car.So the only way to get home is
> towing or tricks the fuel pressure with a queezed hose on the return line
to
> up the system pressure.
**** I suspect the fuel pressure regulator is the culprit.
The "squeezed hose" on the return line is essentially what the pressure
regulator does.


> > **** Whats this? What vacuum? Vacuum when engine is running(YES WHEN I
> COULD MAKE IT RUN)?
> > Is this what you mean by a vacuum leak? Extra air coming into the engine
> > thru a broken hose?(YES)
> > How are you testing for this? Vacuum readings are in inches nor PSI.(MY
> METER HAS MORE UNITS BUT I LL VERIFY)
**** Your car has a manifold vacuum guage in its instruments? I dont have a
turbo, so I dont know what guages come with a turbo model. Listers talk
about "boost" , but thats not vacuum, thats pressurized air from the turbo.
The boost guage is in "bars", I think 1 bar = 17 psi  = atmospheric pressure
at sea level.

It just so happens that "All motors regardless of number of cylinders all
have about the same vacuum. 15 to 20 inches of mercury (in-Hg) " "15-20
in-Hg at idle. 19-21 in-Hg at steady 2500 rpm. About 0 at WOT"

So its confusing when you mention vacuum in PSI units. Engine at idle is
about 18 inches, while a turbo car at full boost is 1.4 Bar or 24 PSI.
Partial boost is at 18 PSI. So we can have 18 inches in a NA engine vs 18
PSI in a turbo engine. Same numbers but they mean different things.

Ok, I checked your "patient" info(good idea, wasnt it?), and you have the NA
engine. So we are talking about vacuum.
I'm curious, what did you tap into to read the vacuum? The only place I see
on my NA engine is around the ISV plumbing. Modifying the plumbing a bit
would get you a tap into the intake manifold. How did you do it?


> > > -Checked the ISV with 12v charger:ok. But when i plug the wires to the
> ISV
> > the 12 V drop to 0volts
> > ***** Huh?
> > You test the ISV with a 9 volt battery.
> > Explain about the 12 volts dropping to zero. What 12 volts? What are you
> > doing?(I PLUGGED A VOLTMETER ON THE ISV PLUG, THE I PLUGGED IT TO THE
ISV,
> THE VOLTAGE DROPPED TO 0V)I USED AN HARNESS TO DO IT.
**** I may be wrong here, but the voltage going to the ISV is square wave
DC. The computer varies the duty cycle to control the valve opening. The
square wave looks like an AC signal to a DC voltmeter. . Thats why you may
be getting funky readings with a DC voltmeter.
Like I said before, you test the ISV using a 9 volt radio battery. This
limits the current so you dont cook the ISV. The 9 volts is enough to show
you that the ISV valve is opening and closing.


> > > Note: The engine seems to start when someone start while i push the
> distr
> > plate with my hand !!!!
> > **** I mentioned before about a sticking sensor plate. Make sure its
clean
> > and free to move.
> > Push or pull? PUSH FROM THE AIR FILTER.
***** Ahhhh!  You remove the air cleaner and push up on the sensor plate
from the bottom.
Essentially, what you are doing is fooling the fuel system. You are
increasing the fuel flow thru the injectors, thus making a richer fuel
mixture.
This confirms my theory that you have low system pressure. What you are
doing is compensating for low system pressure by increasing fuel flow.  Fuel
volume = High pressure and small hole = low pressure and big hole.


> > Are you trying to start the car with the air bonnet off?YES ALWAYS WHEN
IT
> DID NOT WANT TO START.
***** I may be wrong, but the "Air Bonnet" is that rubber thingy that
connects the fuel distributor to the throttle body at the intake manifold.
Taking that off would give you a BIG vacuum leak!
What you take off is the air filter cover and the air filter. Right?

In conclusion, the problem seems to be narrowed down to the pressure
regulator or a problem in fuel system pressure.
You still have not checked the fuel pump for proper delivery volume.

You also mentioned that you "Checked the vacuum: 9psi. suppose to be around
20. The only leak i
found" . I'll read that as 9 inches Hg of vacuum with the engine running at
idle.
I dont know what to make of this. Either big vacuum leak someplace, or valve
timing problem(slipped timing belt)?
I think Huw suggested checking engine cylinder compression. If you have low
compression, then that points to valve problem or rings.
Here is a link for interpreting vacuum readings.
http://www.ifsja.org/tech/motors/vacuum.shtml


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q