RESUME: 100Q engine problems

Wed Dec 22 16:36:09 EST 2004

1 atmosphere is 14.7 pounds (force)/square inch absolute, 760 millimeters of mercury (29.92 inches of mercury), 1 bar. note that 15,20 etc inches of mercury is less than full atmospheric of 29.92 inches. 15 inches of vacuum is then 29.92-15=14.92 inches of mercury absolute pressure.
Just thought I'd clear this up.
regards,
gabe

----- Original Message -----
From: SJ <syljay at optonline.net>
Date: Wednesday, December 22, 2004 12:20 pm
Subject: Re: RESUME: 100Q engine problems

> 
> > 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 
> pressureregulator 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 
> talkabout "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. 
> Thislimits 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 
> platefrom 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
> 
> 
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