Is there anything wrong with temporarily disconnecting the EGR valve
I'm trying still trying to diagnose my "Herky Jerky" problem, and
wanted to see if the
EGR valve is playing a role.
Here's some background, covered in many earlier posts. The car
loss of forward momentum... just a brief moment of loss of power to
the wheels. The last
few days I've been using a really good scanner, the SPX NemiSys. When
it connected I push the record button when the problem occurs, causing
the previous 20
seconds and the next 20 seconds to be recorded in the scanner. All the
OBD II values are
saved for later review on the scanner or uploaded to my PC for
One thing I've noticed is unexpected change in the throttle position
sensor voltage corresponding
with the symptom. The possible tie-in to the EGR is that it shares the
same reference voltage
as the TPS. Add to this reports from several people in this forum that
the EGR can cause
symptoms like mine. Moreover, a friend who has worked in GM
dealerships quite a bit
told me of a case where an intermittent short or something in the EGR
was pulling down the
So, there you have it. Before popping $120 for a new EGR valve I'd
like to confirm the
diagnosis. Can I just pull the connector and drive for a few days?
I replaced the TPS several weeks ago, just because it was easy and not
Not sure about what you mean by reference signal and feed back signal.
I know what the terms
mean in control parlance, but don't know what they are called in the
OBD II list of
available parameters. There are 2 that seem to be related to throttle
position. One is called
Throttle Angle (%), and the other is TP SensorV. The plots of these
two are exactly the same,
as close as I can tell. In other words, it looks like Throttle Angle
is simply calculated from
TP sensorV rather than being a separate, measured signal. I would be
inclined to call either
one of these "feed back signal." If there is anything that is a
"reference signal" I don't know what
If you pull the EGR sensor you may find that you have a problem with
detonation, since the EGR is designed to cool the burn to prevent the
formation of NOX emissions and prevent detonation. But if the
herky-jerky goes away, then it would probably be safe to say that you
found your problem. Just be prepared for some pinging in the meantime
thanks to low quality gasoline and high ambient temps.
Thanks, Chris. I've been driving a couple days with it disconnected,
no signs of
detonation. Unfortunately, the herky jerky is still there. I'm now
may be a more pervasive electrical problem. The system voltage always
up kind of ragged in the scans. Take a look at this:
Here are my notes on the episode shown there:
4.18: 12.4 minutes into trip. CC set at 66 mph, maintaining 67, TCC
speed (or at least the speed sensor?) suddenly drops to 61. Throttle
opens (as it should
this time!) but seems happy to hold 61 mph for 8-9 seconds, why? TCC
stays on. Battery voltage looks rough throughout, between 13.4-13.6.
were a few dives in inj. pulse width before and after the speed fall
suspicions: Since events seem to be preceded by drop in road speed,
it be a sudden increase in drive-train resistance? Or, ref voltage
on speed sensor?
Does anyone know if this kind of fluctuation is normal on one of
A swing of 2/10ths of a volt is probably not the source of your
trouble. You'll see at least that much change(if not more) if your AC
compressor cycles, you hit the turn signals, hit the brakes, etc.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.