88 5kq - Intermittant Hard Starting

[SJ]

From: "Huw Powell" <audi at humanspeakers.com>
Subject: Re: 88 5kq - Intermittant Hard Starting


> > I was thinking of adjusting the idle mixture by watching the DVM. When
the
> > O2 sensor starts working (swinging), the mixture is on the low (lean)
side
> > of the DPR's control range. Maybe adjusting another 1/4 turn or so to
richen
> > the mixture will get the mixture centered in the DPR's control range.
>
> To make this adjustment without a CO meter, you hook up a milliammeter
> in series with the DPR and adjust the static fuel mixture at idle until
> the DPR current swings back and forth (with OXS voltage) around 0 mA.
> (it will go back and forth a few mA - you need a fine scale on your
> meter).  It helps to make a harness from male to female for the DPR
> plug, but you can get by without.
**** OK, this is the same as watching the O2 sensor voltage start to swing
around 0.5 volts >  0.2v  <-->  0.9v
The DPR current wont swing if the O2 dont swing >>.  "Wont you be my partner
. .and dance with me?".

I think the DPR current is 10 ma at Stoich(14:7). Lean stop is at 0 ma, and
rich stop is at 20 ma. In normal operation, the current should fluctuate
around the center value of 10 ma. No?

> And as you say, it might need to be richer to enable the ECU to get it
> to swing at all.
**** I was looking for some easy way to set the basic fuel mixture without
having to use a CO meter, or a swinging milliampmeter.
I was thinking of checking the O2 voltage on my 100Q with the O2 sensor
disconnected. Then adjusting the idle mixture on the 5000q to get the same
reading on the O2 sensor as the 100Q reading. But, an O2 sensor is not very
accurate above and below its operating range. So, forget that idea.

On the other hand, how about setting the basic(mechanical) idle mixture this
way.
1. Disconnect O2 sensor from its harness to CPU
2. Apply 0.5 volts to the CPU, this will fool the cpu into setting DPR
current at 10 ma
3. Monitor the disconnected O2 sensor with DVM
4. Adjust idle mixture until O2 sensor reads 0.5 volts(Stoich)
Cool, eh?
Oh wait, the CPU aint dumb . . if it dont see any O2 crossovers, it goes
into open loop mode. Hmmmm, we could fool the CPU by using a sine or square
wave generator . .. no . . no good, cause the DPR current is fluctuating and
hard to read.
Drats! Foiled again!!

Whats the difference between open loop mode and limp home mode? What is the
DPR current for each mode?

Open loop is when CPU does not use O2 sensor input, but uses the internal
0.5 volt reference and it uses the temp sensor to regulate DPR current for
temperature only? With engine fully warmed up, the Open loop DPR current
will be around 10 ma?

Limp home mode is when the CPU electrical system is dead? The DPR current is
0 ma? An unplugged DPR would simulate Limp home mode, right?

If Open loop mode works as described above, then I can use this mode of
operation to set the idle mixture. Adjust the mixture until the DVM on
disconnected O2 sensor reads 0.5 volts. Now, the Open loop 10 ma DPR current
will coincide with a Stoich O2 reading of 0.5 volts. Will this work?

I got another idea for setting the idle mixture.
1. disconnect the DPR
2. Disconnect the ISV
3. Adjust mixture for highest RPM's
Will this work? Engine is most efficient at Stoich, the RPM's should max out
at Stoich.
Oh, wait . .DPR disconnected is Limp home mode . .its supposed to be lean.
Foiled again!
On the other hand, with DPR connected and O2 AND ISV disconnected, the ECU
is in Open loop mode. Can you now use RPM's as an indication of Stoich
mixture?

I went shopping for a 3mm allen T handle adjusting tool. Nobody has one.
Sears only sells sets, and the tools are short.
How long does the tool need to be in order to clear the top of the fuel
distributor? Can a normal Allen wrench be modified to work?

SJ



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