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Run with EGR valve disconnected? 95 Park Ave Ultra

Is there anything wrong with temporarily disconnecting the EGR valve connector? 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 exhibits intermittent 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 driving with 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 analysis.

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 TPS voltage.

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?

TIA.

Ed

Reply to
Ed
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Reply to
Shep

Thanks, Shep.

I replaced the TPS several weeks ago, just because it was easy and not very expensive. No effect.

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 it's called.

Ed

Reply to
Ed

Reply to
Shep

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.

Chris

Reply to
halatos2000

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 thinking there may be a more pervasive electrical problem. The system voltage always shows up kind of ragged in the scans. Take a look at this:

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Here are my notes on the episode shown there:

+++++++++++++++ 4.18: 12.4 minutes into trip. CC set at 66 mph, maintaining 67, TCC on. Then 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. There were a few dives in inj. pulse width before and after the speed fall off.

suspicions: Since events seem to be preceded by drop in road speed, could it be a sudden increase in drive-train resistance? Or, ref voltage effects on speed sensor?

-----------------

Does anyone know if this kind of fluctuation is normal on one of these GM CS-130 alternators?

Ed

Reply to
Ed

Ed,

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.

Chris

Reply to
halatos2000

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