Date: Wed, 3 Dec 2003 16:13:56 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: 85' 1.9 still running rich help :-(
In-Reply-To: <20031203045154.88015.qmail@web80202.mail.yahoo.com>
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At 11:51 PM 12/2/2003, Tracy Bonin wrote:
>Hey guys, any ideas on this one.......runs rich ....at about 8% CO will
>fluctuate, from 5% to 8% , but starts off lean and gets worse on warm up,
>at times it will fluctuate an idle and at that point is when it drops
>dramatically, but will catch itself on 5% and rise back up as if it thinks
>that 5% is 1% or somehting.......
>
>have changed:& checked
>o2,
As I see it...
If the sensor-ECU loop is working correctly it's basically impossible for
the beast to run rich, so that loop isn't functioning -- either the sensor
is driving the mix rich by lying to the ECU, or the ECU isn't listening to
the sensor, or the ECU is being overpowered by some external condition.
Sanity check --> 1) The CAT shouldn't affect your measurements at the test
port, that's what it's for. If you're measuring at the tailpipe, compare
it with the test port readings and see what's going on with the CAT. If
you don't have a test port, the CAT has to go away and be replaced with a
straight pipe until you've verified that everything works right without it.
2) What's the behavior of the O2 sensor line, referenced to ECU
ground? Oscilloscope is ideal, or Ken Lewis's little bar-graph voltmeter
(or a similar one you build yourself using the same National Semiconductor
driver chip and calibrated for 0-1 volt); ordinary digital multimeter will
do but gives less information because it's not fast enough to keep up with
the transitions. Normal behavior is quite distinctive: At cold start,
voltage should be near 500 mv and stable -- this is the bias voltage coming
from the ECU. As the engine warms the sensor voltage will start to rise,
indicating the sensor is getting hot enough to work and the mixture is
rich. Fairly soon after that the ECU should go into closed-loop
operation. When it does, sensor voltage will alternate between roughly .2
and .7 volts at roughly equal intervals (given constant speed and
load). The period may be ?a couple seconds? at idle, several times a
second at high rpm. The digital meter won't show the alternations as such,
but will show some readings above a half volt and some below -- the exact
value of any single reading is meaningless, and there are severe artifacts
because of phase interaction between the transition periods and the meter
averaging period. The other instruments will show whether the transitions
are crisp and levels where they should be, or the sensor is struggling, so
they're valuable on this account. WOT should show steady rich (~.7 v);
deceleration with closed throttle steady lean (~.2v) until the engine slows
enough for the ECU to turn the fuel back on somewhere around 1000 rpm.
Semi-digression: If the initial bias voltage is low some of the voltage is
probably being lost in the ground side of the circuit. [How much is too
much I don't know -- I *think* that a tenth of a volt won't bother things
particularly. But it would be useful in general to quantify the voltage
difference between various things that are nominally ground -- alternator
case, engine case, engine heads, exhaust system at the O2 sensor, sensor
ground leads measured at the sensor, body sheet metal, ECU ground inside
the ECU (on my Bosch ECU ground pin 7 is directly connected to pin 6 which
supplies the AFM ground and the O2 sensor shield; and also connected by an
internal wire and ring terminal to the aluminum mounting tab of the ECU
which ought to ground to the body through the mounting bracket. Ground pin
25 appears to be involved primarily with the fuel injector drive circuit
while pin 7 is the internal ground reference for the senders and the rest
of the circuit). The drop from alternator case to engine case isn't
related to this issue, but it *is* coming directly from your charging
voltage and you may be surprised at the amount when the alternator is
charging hard. ECU-related grounds in general should show minimum
deviation from each other]
If all that other stuff *is* happening, the sensor is detecting the
presence and absence of oxygen in the exhaust and the ECU is effectively
controlling the mixture to its own satisfaction. If it's not, then either
the sensor's lying and causing the fault (poor connections/grounding, maybe
poisoned sensor -- suspect it would go lean instead of rich if so, leakage
from some 12v source into the sender circuit) or it's correctly detecting
oxygen in the pipe that shouldn't be there (exhaust leak, faulty
combustion) and contributing to the fault, or the ECU is either out to
lunch or incapable of overcoming the fault. Regardless, unhook the sensor
and leave it out of the system until the engine's running right without
it. Use it to watch what's going on...it will tell you if there's oxygen
in the exhaust or not and this will help show what's going on. Likewise,
get the CAT out of the measurement loop until measurements are what they're
supposed to be ahead of it -- and try to look at hydrocarbons as well as CO
for clues. Someone who understands combustion better than I do could help
there...
> AFM, distributer, coil, coolant temp II sensor,
Make sure AFM / TI / TII are correct by voltage when operating, not just by
resistance measurements. If the TII line is open/poor connection/poor
ground for example, the ECU will see its own bias voltage and never go out
of open-loop cold-engine mode. Should be very close to the TI voltage
when the engine is dead cold and equal to air temp, and get down close to
zero volts (few tenths or less) when engine is at operating temp. I don't
know what the threshold is for the ECU to go into closed-loop mode.
david
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
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