Do I need to document my findings when servicing a clunker? YES
The 1983 RWD Chrysler 318 with 2v carb would stall on decel. The carb was replaced and the vehicle continued to stall on decel. While checking idle solenoid operation, we decided to check computer strategy and timer circuits by also observing the EGR and AIR solenoids over a period of about 5 minutes.
The Chrysler troubleshooting manual for this vehicle says the idle solenoid should be energized for 20 seconds after a hot restart (which is the case here). The manual also says EGR should be disallowed for 90 seconds after a hot restart and the AIR solenoid should be energized to force air upstream for the same 90 seconds.
Above we find that the computer fed 12 volts to the idle solenoid for 22 seconds, this is about right. We also see that the computer grounded (energized) the EGR solenoid, thereby closing it's vacuum ports for the same 22 seconds. This is not in spec according to the manual, but it is logical. When the computer de-energizes the EGR vacuum solenoid, EGR vacuum can reach the EGR valve. The line at x-axis position #755 is measuring the voltage on the 3 solenoid control circuits just before the idle and EGR solenoids switched.
Each grid mark represents 1 minute. We can see the computer held the normally closed AIR solenoid energized for a period of almost 4 minutes. With vacuum applied to the air switch/relief valve, air is being forced upstream to heat the o2 sensor. This is not according to spec, but it could be normal especially because we have not touched the throttle.
QSCSC DAS allows us to check timer circuits and document changes in computer strategy.
According to the manual, the idle solenoid should only get power after starting, or with the AC ON, and/or for a second after decel. So why do we see the idle solenoid being briefly energized?
We work the throttle a few times and hook up to the idle switch and get the following results;
The idle switch (a 5 volt device) and base idle are improperly adjusted. The idle switch is chattering and false triggering the idle solenoid. We measure the false but 'real to the computer' decel 'ON' time and find it to be from 0.67 seconds to 0.98 seconds, this is realistic.
After adjusting idle, we placed the engine on fast idle to check the o2 sensor. We also watched 3 solenoids. The idle solenoid is energized, because the throttle is open.
The normally closed AIR solenoid is de-energized, no vacuum passes, and air goes downstream. The normally open EGR solenoid is de-energized, and vacuum can reach the EGR valve. So the solenoid control is all normal. But, look at the o2 sensor. It is so lazy it takes about 6.6 seconds per cycle.
Next we check the MC solenoid operation.
From the waveform we determine that it gets pulsed 10 times per just like a GM. Previous experience has taught us that the short duty cycle is a rich command, same as GM. The 27 volts is the spike from the MC solenoid being de-energized. The MC solenoid is OK.
What do we check next?
For more info, call: Quad Computer Systems Consultants, 973-472-0328, ASK FOR DAN
EMAIL to; qcscdas@aol.com
or; lody@delphi.com
or; danbuckley@worldnet.att.net
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QCSC DAS Copyright 1996 -- Developed by; Daniel A. Buckley (NIASE GAM-CMAT-L1)
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