1995 Cirrus 2.5L stall condition

  • Thread starter Thread starter Mopar_Elvis
  • Start date Start date
M

Mopar_Elvis

1995 JA 2.5L intermittent stall condition.
At stall all sensor data on DRB is normal.
If key is not cycled, vehicle will restart and show incorrect data (low
ps) on MAP.
Baro is normal and voltage is normal. The PCM will show no change in
map from start to run. If you cycle the key off for 1 or 2 min before
restart, the code is cleared as if never there, the PCM resets to 0 and
the DRB reads all normal again. This complaint has been ongoing since
June of 05. At one service visit the vehicle stalled and would not
restart, replacement of the distributor/coil resolved the no start
condition and it did set codes for this repair. It did not resolve the
stall condition. PCM, Crank and map sensor, Idle motor replaced,
overlays ran with no effect. ADS is up, will still stall with VSS pin
removed from PCM, Trans controller disconnected, ABS controller
disconnected. Overlay on 8 volt distributor ground to engine block
splice (it does not ground in PCM) with no effect. The only way to
duplicate the loss of ground or transient voltage spike that would
cause this, is to interrupt the main PCM supply or ground, we can do
this and it will mimic the same condition, including the key cycle/
clear the code. Overlays on every ground or reference voltage we can
think of have no effect, eliminating ignition feed, no effect. Any
thoughts or similar strange grounding problems that could spike the 8
volt reference and trick the PCM into thinking it is being programmed?
Another direction maybe? A Mopar claim on a second PCM?

Thanks,
Steve
 
--
Glenn Beasley
Chrysler Tech
Mopar_Elvis said:
1995 JA 2.5L intermittent stall condition.
At stall all sensor data on DRB is normal.
If key is not cycled, vehicle will restart and show incorrect data (low
ps) on MAP.
Baro is normal and voltage is normal. The PCM will show no change in
map from start to run. If you cycle the key off for 1 or 2 min before
restart, the code is cleared as if never there, the PCM resets to 0 and
the DRB reads all normal again. This complaint has been ongoing since
June of 05. At one service visit the vehicle stalled and would not
restart, replacement of the distributor/coil resolved the no start
condition and it did set codes for this repair. It did not resolve the
stall condition. PCM, Crank and map sensor, Idle motor replaced,
overlays ran with no effect. ADS is up, will still stall with VSS pin
removed from PCM, Trans controller disconnected, ABS controller
disconnected. Overlay on 8 volt distributor ground to engine block
splice (it does not ground in PCM) with no effect. The only way to
duplicate the loss of ground or transient voltage spike that would
cause this, is to interrupt the main PCM supply or ground, we can do
this and it will mimic the same condition, including the key cycle/
clear the code. Overlays on every ground or reference voltage we can
think of have no effect, eliminating ignition feed, no effect. Any
thoughts or similar strange grounding problems that could spike the 8
volt reference and trick the PCM into thinking it is being programmed?
Another direction maybe? A Mopar claim on a second PCM?

Thanks,
Steve
Click to expand...

Well if you work at a dealer you may want to get a data recording from the
co-pilot and see if you can pick something up from that.

Since it is a reman PCM and Chrysler does not remanufacture them, (they are
subleted out and you would be surprised of how many they put back out on the
market with problems) you could have a faulty one.
If the key counter is resetting to zero each key cycle I would think the PCM
is at fault. Was the other PCM doing the same thing or was that replaced
because of the no start (distributor repair?)
 
Glen,
I am a fixed ops manager at a DCX dealership, first posts here, thanks
for responding. We do have very good diagnostic techs, but this one is
kicking our butt.
The co-pilot shows nothing, and the DRB is too slow in scope to show
much of a spike, at times we can see it at stall, so there is something
there. You know the problems we have had on the grounds of these
2.5L's, problems in the harness bends and splices. We assume it is a
similar condition, but cannot get an out right failure or wrong voltage
reference to point to anything. I will add one more strange glitch, and
it might not even be related as the vehicle still stalls with the VSS
pin out, the DRB will at times show speed sensor flashs upwards of 200
mph, only for a second or so. I have not seen this, the tech reports
this to me. I'm not a diagnostic tech, but do have a vested interest in
helping our techs solve difficult problems. Sometimes I ask some really
stupid questions of them to review the problem, but it just might be
enough to shift the thought train to a resolution.
The PCM is a reman, all numbers have a supersedence to R5012458-AA and
the original PCM had exactly the same responce. When the distributor
died in the stall, I belive everyone thought, "ok, another one, problem
solved"...I would have too, not the case, came back still stalling, so
with the counter resetting and showing garbage in MAP with correct
voltage and barometric we replaced the PCM. Drove 100 miles no stall,
back in a week, same condition. Correct me if I'm wrong but a spike on
the 8v sensors, the main PCM supply/ground or something on the
programing bus wire is about the only thing that could cause a reset?
Can you think of any really strange, off the wall conditions with the
grounds or supplys you have seen?

Steve Wells
 
Mopar_Elvis said:
Glen,
I am a fixed ops manager at a DCX dealership, first posts here, thanks
for responding. We do have very good diagnostic techs, but this one is
kicking our butt.
The co-pilot shows nothing, and the DRB is too slow in scope to show
much of a spike, at times we can see it at stall, so there is something
there. You know the problems we have had on the grounds of these
2.5L's, problems in the harness bends and splices. We assume it is a
similar condition, but cannot get an out right failure or wrong voltage
reference to point to anything. I will add one more strange glitch, and
it might not even be related as the vehicle still stalls with the VSS
pin out, the DRB will at times show speed sensor flashs upwards of 200
mph, only for a second or so. I have not seen this, the tech reports
this to me. I'm not a diagnostic tech, but do have a vested interest in
helping our techs solve difficult problems. Sometimes I ask some really
stupid questions of them to review the problem, but it just might be
enough to shift the thought train to a resolution.
The PCM is a reman, all numbers have a supersedence to R5012458-AA and
the original PCM had exactly the same responce. When the distributor
died in the stall, I belive everyone thought, "ok, another one, problem
solved"...I would have too, not the case, came back still stalling, so
with the counter resetting and showing garbage in MAP with correct
voltage and barometric we replaced the PCM. Drove 100 miles no stall,
back in a week, same condition. Correct me if I'm wrong but a spike on
the 8v sensors, the main PCM supply/ground or something on the
programing bus wire is about the only thing that could cause a reset?
Can you think of any really strange, off the wall conditions with the
grounds or supplys you have seen?

Steve Wells
Click to expand...

Keep in mind that the speed sensor cut off speed is I believe 114 mph, if
for some reason the PCM is seeing this speed is it possible that this is
causing the problem? Can you see this on the data recording and compare the
stall to the MPH glitch? But then again, you say you disconnected the VSS.
(possible pcm problem?) what about secondary indicators has the tech
monitored those when the problem occurs?
I have never seen a spike on the 8 volt, I have seen alot of sensors pulling
the 8volt supply down and causing all kinds of problems. What about the a/c
transducer, if im not mistaken isnt that 8 volt on the same circuit, is it
possible that is is pulling the voltage down?
Normally when I came across ground problems in the sensor circuit A fault
was set for sensor voltage high, and if the fault wasnt set most times I
could monitor that in the sensor voltage screen.
And last thing and I hate to ask this because normally its a waste of
time......Have you contacted STAR?
My opinion only

Glenn Beasley
Chrysler Tech
 
--
Glenn Beasley
Chrysler Tech
Mopar_Elvis said:
Glen,
I am a fixed ops manager at a DCX dealership, first posts here, thanks
for responding. We do have very good diagnostic techs, but this one is
kicking our butt.
The co-pilot shows nothing, and the DRB is too slow in scope to show
much of a spike, at times we can see it at stall, so there is something
there. You know the problems we have had on the grounds of these
2.5L's, problems in the harness bends and splices. We assume it is a
similar condition, but cannot get an out right failure or wrong voltage
reference to point to anything. I will add one more strange glitch, and
it might not even be related as the vehicle still stalls with the VSS
pin out, the DRB will at times show speed sensor flashs upwards of 200
mph, only for a second or so. I have not seen this, the tech reports
this to me. I'm not a diagnostic tech, but do have a vested interest in
helping our techs solve difficult problems. Sometimes I ask some really
stupid questions of them to review the problem, but it just might be
enough to shift the thought train to a resolution.
The PCM is a reman, all numbers have a supersedence to R5012458-AA and
the original PCM had exactly the same responce. When the distributor
died in the stall, I belive everyone thought, "ok, another one, problem
solved"...I would have too, not the case, came back still stalling, so
with the counter resetting and showing garbage in MAP with correct
voltage and barometric we replaced the PCM. Drove 100 miles no stall,
back in a week, same condition. Correct me if I'm wrong but a spike on
the 8v sensors, the main PCM supply/ground or something on the
programing bus wire is about the only thing that could cause a reset?
Can you think of any really strange, off the wall conditions with the
grounds or supplys you have seen?

Steve Wells
Click to expand...
REPOST
Keep in mind that the speed sensor cut off speed is I believe 114 mph, if
for some reason the PCM is seeing this speed is it possible that this is
causing the problem? Can you see this on the data recording and compare the
stall to the MPH glitch? But then again, you say you disconnected the VSS.
(possible pcm problem?) what about secondary indicators has the tech
monitored those when the problem occurs?
I have never seen a spike on the 8 volt, I have seen alot of sensors pulling
the 8volt supply down and causing all kinds of problems. What about the a/c
transducer, if im not mistaken isn't that 8 volt on the same circuit, is it
possible that it is pulling the voltage down?
Normally when I came across ground problems in the sensor circuit A fault
was set for sensor voltage high, and if the fault wasn't set most times I
could monitor that in the sensor voltage screen.
And last thing and I hate to ask this because normally its a waste of
time......Have you contacted STAR?
My opinion only

Glenn Beasley
Chrysler Tech
 
Mopar_Elvis said:
Glen,
I am a fixed ops manager at a DCX dealership, first posts here, thanks
for responding. We do have very good diagnostic techs, but this one is
kicking our butt.
The co-pilot shows nothing, and the DRB is too slow in scope to show
much of a spike, at times we can see it at stall, so there is something
there. You know the problems we have had on the grounds of these
2.5L's, problems in the harness bends and splices. We assume it is a
similar condition, but cannot get an out right failure or wrong voltage
reference to point to anything.
Click to expand...

Steve,

I've not troubleshot one of these so what I will suggest may have no
value, but if you think it is a possible ground problem why don't you
simply run heavy guage stranded wire from the negative battery post to
as many convenient bolts and such on the engine that you can find as
well as to the PCM and other sensor grounds not right on the engine.

It may look a little corn pone but who cares, if the problem goes away
you know it was an intermittent ground connection and if you don't
want to leave the octopus of wire in there, just start pulling the
grounds one at a time until the problem comes back, then troubleshoot
that ground.

One other issue with spikes in a vehicle electrical system - most vehicle
electrical systems I've seen take the cheesy way out and depend on
the low internal resistance of a good battery to act as a giant surge
supressor. But, batteries age and over time their internal resistance
rises, it is not uncommon with a big fat high CCA battery and a small
engine easy to start to have a battery that will have plenty of
amps to spin over the engine and start it, but still have high internal
resistance. It is paramout as you know to have solid connections
from the vehicle electrical system to the battery, but you should also
change out the battery for a new one if you are suspecting spikes.
There is some really exotic new battery test gear on the market to check for
this, a simple load tester won't do it, most shops I've seen don't have the
expensive battery test gear.

Ted
 
Glenn,
Yes, VSS limit is 126 mph on this reman and if we pull pin 66 that
should cancel any intermittent transient to the PCM and again point to
internal failure. I was not clear in saying "spike", yes, you are
correct in assuming it is a voltage drop that is recorded on both the
8v and 5v...again this points to PCM failure in the fact that it causes
a reset/clear DTC's on key cycle condition. If you ground either of
the 8v or 5v , you will kill the engine, but not cause the wrong psi on
the map reading or neither will it clear dtc's on key cycle. The only
way to duplicate this condition is a momentary (I mean very fast)
interruption of B+ or B-. The a/c transducer is a 5v supply and the
stall still occurs with a/c circuits disconnected. Star center was no
help. If we try to induce a condition on any sensor or supply it will
show the hiccup on the drb and set a fault as normal, but not duplicate
the PMC shutdown/glitch condition. At this point I have found another
reman PCM in parts and we are going to swap them out again...just to
see if it repeats.
Ted,
We are only assuming it is grounding because of the results of the only
indicator we can observe, which is a voltage drop (down spike recorded)
at stall. The action of the PCM after the stall (reporting garbage psi
in the map on restart without key cycle) is another matter, the PCM has
been pulled down below 8v somehow, (I assume) to cause a counter reset
after key cycle. The extra wires (overlays) you speak of have been ran
on every ground and supply there is(sensors also). We test between the
battery B+ and B- to view down or up spikes and record Min/Max voltage
all the way to the PCM, this checks battery & cables and any
connections in-between, we overlay the ignition to eliminate that side
of car.
There are no drop outs in the Main B+ or B-....now if there is no drops
going in and a drop coming out of both 5v & 8v at stall and after stall
the PCM has a glitch and must be key cycled you would think it's got
to be the PCM....I'll let you know what the second replacement
does...but please keep thinking of a resolution because I don't think
it's going to work either.
 
--

Mopar_Elvis said:
Glenn,
Yes, VSS limit is 126 mph on this reman and if we pull pin 66 that
should cancel any intermittent transient to the PCM and again point to
internal failure. I was not clear in saying "spike", yes, you are
correct in assuming it is a voltage drop that is recorded on both the
8v and 5v...again this points to PCM failure in the fact that it causes
a reset/clear DTC's on key cycle condition. If you ground either of
the 8v or 5v , you will kill the engine, but not cause the wrong psi on
the map reading or neither will it clear dtc's on key cycle. The only
way to duplicate this condition is a momentary (I mean very fast)
interruption of B+ or B-. The a/c transducer is a 5v supply and the
stall still occurs with a/c circuits disconnected. Star center was no
help. If we try to induce a condition on any sensor or supply it will
show the hiccup on the drb and set a fault as normal, but not duplicate
the PMC shutdown/glitch condition. At this point I have found another
reman PCM in parts and we are going to swap them out again...just to
see if it repeats.
Ted,
We are only assuming it is grounding because of the results of the only
indicator we can observe, which is a voltage drop (down spike recorded)
at stall. The action of the PCM after the stall (reporting garbage psi
in the map on restart without key cycle) is another matter, the PCM has
been pulled down below 8v somehow, (I assume) to cause a counter reset
after key cycle. The extra wires (overlays) you speak of have been ran
on every ground and supply there is(sensors also). We test between the
battery B+ and B- to view down or up spikes and record Min/Max voltage
all the way to the PCM, this checks battery & cables and any
connections in-between, we overlay the ignition to eliminate that side
of car.
There are no drop outs in the Main B+ or B-....now if there is no drops
going in and a drop coming out of both 5v & 8v at stall and after stall
the PCM has a glitch and must be key cycled you would think it's got
to be the PCM....I'll let you know what the second replacement
does...but please keep thinking of a resolution because I don't think
it's going to work either.
Click to expand...
Grounding either one of those 8 volts or 5 volts supply will cause a shut
down and I believe a reset on the PCM. I would bet that the other PCM will
do the same thing and the fix is going to be find the shorted
supply.....unless both 5 volts and 8 volts supply are being pulled down the
PCM may fix it.
I have run into many problems such as that on the 2.5 and normally it was a
shorted crank sensor. I have had a few Convertibles 2.7 litre do the same
thing and the first was an ass kicking because it showed up nothing, I got
the job after the one of our technical advisors told the tech to install a
wire harness, he did, it didn't fix it... it came down to a faulty MAP
sensor shorting out and shutting down the supply to all sensors on the
circuit.
This is going to be one of those problems that a guess is going to fix it. I
just hope this vehicle belongs to an owner that understands!!!

Glenn Beasley
Chrysler Tech
 
Philthy,
From memory I would say an EGR open would cause a stumble condition
Click to expand...
before stall and the stall would almost always transpire while coming
to a stop. In a condition where a mil lamp is not illuminated in this
95 SBEC3 controller for EGR you probably could key cycle a code 32, we
would be able to see a p0401 or a p0403 at some point if the PCM is
completing it's tests. I personally have seen a JA model EGR
transducer solenoid intermittently failing and it did not set a code
strangely, but it stumbled and did the rpm's down stall.

Steve Wells
 
--

Mopar_Elvis said:
Philthy,
before stall and the stall would almost always transpire while coming
to a stop. In a condition where a mil lamp is not illuminated in this
95 SBEC3 controller for EGR you probably could key cycle a code 32, we
would be able to see a p0401 or a p0403 at some point if the PCM is
completing it's tests. I personally have seen a JA model EGR
transducer solenoid intermittently failing and it did not set a code
strangely, but it stumbled and did the rpm's down stall.

Steve Wells
Click to expand...
EGR is not going to cause any of those PCM problems. An EGR valve that was
stuck open on that vehicle would cause other problems and the Air intake
temperature sensor would show a high reading

Glenn Beasley
Chrsler Tech
 
nope no joke
there is a term for that and i can't frinking remember it, it has to do with
the start up software writing and pids
 
i have replaced 3 egr valves for the same issue and the engine vac pulls
open the egr and it dies, never a stumble felt
the valve works and so does the transducer so a code is never
watch the long term adapitives it will go 30% + if that is the case
 
Mopar_Elvis said:
Glenn,
Yes, VSS limit is 126 mph on this reman and if we pull pin 66 that
should cancel any intermittent transient to the PCM and again point to
internal failure. I was not clear in saying "spike", yes, you are
correct in assuming it is a voltage drop that is recorded on both the
8v and 5v...again this points to PCM failure in the fact that it causes
a reset/clear DTC's on key cycle condition. If you ground either of
the 8v or 5v , you will kill the engine, but not cause the wrong psi on
the map reading or neither will it clear dtc's on key cycle. The only
way to duplicate this condition is a momentary (I mean very fast)
interruption of B+ or B-. The a/c transducer is a 5v supply and the
stall still occurs with a/c circuits disconnected. Star center was no
help. If we try to induce a condition on any sensor or supply it will
show the hiccup on the drb and set a fault as normal, but not duplicate
the PMC shutdown/glitch condition. At this point I have found another
reman PCM in parts and we are going to swap them out again...just to
see if it repeats.
Ted,
We are only assuming it is grounding because of the results of the only
indicator we can observe, which is a voltage drop (down spike recorded)
at stall. The action of the PCM after the stall (reporting garbage psi
in the map on restart without key cycle) is another matter, the PCM has
been pulled down below 8v somehow, (I assume) to cause a counter reset
after key cycle. The extra wires (overlays) you speak of have been ran
on every ground and supply there is(sensors also).
Click to expand...

Ah, that's what you meant by overlays, sorry I didn't recognize
the terminology.

We test between the
battery B+ and B- to view down or up spikes and record Min/Max voltage
all the way to the PCM, this checks battery & cables and any
connections in-between, we overlay the ignition to eliminate that side
of car.
Click to expand...
There are no drop outs in the Main B+ or B-....now if there is no drops
going in and a drop coming out of both 5v & 8v at stall and after stall
the PCM has a glitch and must be key cycled you would think it's got
to be the PCM....I'll let you know what the second replacement
does...but please keep thinking of a resolution because I don't think
it's going to work either.
Click to expand...

Well, here's another suggestion for you, along the lines of what
maxpower recommended, if your specifically looking for a short
or intermittent somewhere in the wiring harness or sensors. This won't help
for a bad sensor that has just changed value or is not reacting, but only
specifically for a short or open on sensor or wiring.

You need a breakout box
to the PCM. These are used a lot in datacom work, I haven't heard
of anything like this for a car computer but the idea is the same.

What you do is go find a busted PCM and a scrap wire harness
and construct a cable that one side plugs into the PCM and the
other side plugs into the cable going to the PCM. The cable is
brought out to a panel. In datacom work the panel is normally
filled by jumpers, what you want to do here at the panel is
basically insert 1K ohm resistors in all the sensor lines to the PCM
and measure the voltage drop across the resistor. What this will
do is find out if you have any shorted sensors - because voltage
drop on a good sensor should be negligible (only a few mA of
current is probably flowing through a good sensor) On a shorted
sensor you will have much larger voltage drop. On an open
sensor you will have 0 voltage measured across the sense
resistor when the sensor opens. You will have to experiement
with resistor values to see what will work without interfereing
with the sensor input. If it's a power supply lead, use only a
few ohms of resistance, and a high wattage resistor.

Most likely on an intermittent sensor to see the problem your
going to need a scope sitting on the sense resistor, as the
activity will happen for such a small duration.

This also will work if the problem is something like a pinched
wire that's being shorted to ground, or a bad connection like
a break in the wire that is inside the insulating sheath.

If you have a specific circuit you suspect, you can cut the
wire to that and wire in a resistor, without using a breakout
box.

One last suggestion, this is probably not going to help but
just a thought. - take a hammer and punch and go through
the sensors on the car, give each of them a firm tap while
the engine is running. We can guess the intermittent stall is
being caused by vibration - if the vehicle sits in the lot idling for
2 hours it doesen't stall out, right?

Ted
 
actually d.c does have a breakout box for this gen car but it's not a required
tool for the dealer so i would bet the dealer does not have one
 
The EGR is not the problem with this vehicle; the most common causes
have been stated above and tested for. We just have not been able to
"catch the gremlin" in the act. It may be that once the
intermittent failing sensor causes an over current condition and blips
the PCM, we then have two conditions that may mimic, even if we replace
the correct sensor, except that the PCM will give false data that we
know from the internal data tables should be correct. Take for example
the a/c transducer that Glenn mentioned, a known problem on these
vehicles, I was wrong about the 8v supply, it does have it and the 5v
pull up sense.
This sensor as any of the others on the 8v (or 5v) can take down the
PCM and now after seeing it myself, will state that it can also over
current the PCM and cause a very similar stall condition. Another
vehicle has an a/c problem and stalls (a different 1995 JA 2.5L with
same controller) The PCM also sets a code for IAT voltage high, this
sensor checks good, but when plugged in, reads voltage low...bad data
in the PCM...and it does a key cycle reset to 0 with no codes. The a/c
transducer is the old brown one, it also meets the fault criteria of
the TBS for this a/c problem and needs to be replaced and a new harness
plug. We plug a reman PCM in and the IAT readings go back to normal, no
codes. The a/c transducer most likely knocked out the PCM.
In reviewing the first 1995 vehicle we see that the crank sensor was
not replaced until after the first reman PCM was installed, and it
drove approximately 100 miles before repeating the stall condition. Now
the second PCM is installed and has reached 100 miles with no
stall...we will get another 50 miles on this afternoon and see. I
believe the crank sensor knocked out the first reman PMC ...but that is
a guess...just as Glenn stated...
These PCM's are just not that well over current protected. The pull
up resistors in the PMC function something like your testing scenario,
Ted and that is how it sets faults and runs its tests, measures etc,
and the later controllers do a much better job of protection of over
current and supply. I do appreciate the discussion from everyone and
thankful there is a forum like this to facilitate it.

Thanks
Steve Wells
 
The EGR is not the problem with this vehicle; the most common causes
have been stated above and tested for. We just have not been able to
"catch the gremlin" in the act. It may be that once the
intermittent failing sensor causes an over current condition and blips
the PCM, we then have two conditions that may mimic, even if we replace
the correct sensor, except that the PCM will give false data that we
know from the internal data tables should be correct. Take for example
the a/c transducer that Glenn mentioned, a known problem on these
vehicles, I was wrong about the 8v supply, it does have it and the 5v
pull up sense.
This sensor as any of the others on the 8v (or 5v) can take down the
PCM and now after seeing it myself, will state that it can also over
current the PCM and cause a very similar stall condition. Another
vehicle has an a/c problem and stalls (a different 1995 JA 2.5L with
same controller) The PCM also sets a code for IAT voltage high, this
sensor checks good, but when plugged in, reads voltage low...bad data
in the PCM...and it does a key cycle reset to 0 with no codes. The a/c
transducer is the old brown one, it also meets the fault criteria of
the TBS for this a/c problem and needs to be replaced and a new harness
plug. We plug a reman PCM in and the IAT readings go back to normal, no
codes. The a/c transducer most likely knocked out the PCM.
In reviewing the first 1995 vehicle we see that the crank sensor was
not replaced until after the first reman PCM was installed, and it
drove approximately 100 miles before repeating the stall condition. Now
the second PCM is installed and has reached 100 miles with no
stall...we will get another 50 miles on this afternoon and see. I
believe the crank sensor knocked out the first reman PMC ...but that is
a guess...just as Glenn stated...
These PCM's are just not that well over current protected. The pull
up resistors in the PMC function something like your testing scenario,
Ted and that is how it sets faults and runs its tests, measures etc,
and the later controllers do a much better job of protection of over
current and supply. I do appreciate the discussion from everyone and
thankful there is a forum like this to facilitate it.

Thanks
Steve Wells
 
Mopar_Elvis said:
The EGR is not the problem with this vehicle; the most common causes
have been stated above and tested for. We just have not been able to
"catch the gremlin" in the act. It may be that once the
intermittent failing sensor causes an over current condition and blips
the PCM, we then have two conditions that may mimic, even if we replace
the correct sensor, except that the PCM will give false data that we
know from the internal data tables should be correct. Take for example
the a/c transducer that Glenn mentioned, a known problem on these
vehicles, I was wrong about the 8v supply, it does have it and the 5v
pull up sense.
This sensor as any of the others on the 8v (or 5v) can take down the
PCM and now after seeing it myself, will state that it can also over
current the PCM and cause a very similar stall condition. Another
vehicle has an a/c problem and stalls (a different 1995 JA 2.5L with
same controller) The PCM also sets a code for IAT voltage high, this
sensor checks good, but when plugged in, reads voltage low...bad data
in the PCM...and it does a key cycle reset to 0 with no codes. The a/c
transducer is the old brown one, it also meets the fault criteria of
the TBS for this a/c problem and needs to be replaced and a new harness
plug. We plug a reman PCM in and the IAT readings go back to normal, no
codes. The a/c transducer most likely knocked out the PCM.
In reviewing the first 1995 vehicle we see that the crank sensor was
not replaced until after the first reman PCM was installed, and it
drove approximately 100 miles before repeating the stall condition. Now
the second PCM is installed and has reached 100 miles with no
stall...we will get another 50 miles on this afternoon and see. I
believe the crank sensor knocked out the first reman PMC ...but that is
a guess...just as Glenn stated...
Click to expand...
These PCM's are just not that well over current protected. The pull
up resistors in the PMC function something like your testing scenario,
Ted and that is how it sets faults and runs its tests, measures etc,
and the later controllers do a much better job of protection of over
current and supply. I do appreciate the discussion from everyone and
thankful there is a forum like this to facilitate it.
Click to expand...

Your welcome, Steve. Just a FYI, a pull-up resistor, at least all
the ones I've seen, are connected from B+ to the sense line, not
in series with the sensor. Their purpose is not to protect anything,
what they are there for is to prevent the inputs from floating into
the "undefined" voltage region of neither logic 0 or logic 1.

It isn't really considered good design to have a computer logic
input that exits the case of the computer to be unprotected, without
a current limiting resistor in series to the logic input. That has been
good electronic design practice ever since they started using transistors
in digital circuits, as any of the EEs on this group could probably attest.

Ted
 
Ted,
Thanks for correcting me on "between" (didn't mean series) B+ and B- ,
poor wording on my part. I do understand your explanation of a pull up
or pull down "circuit" and know their primary function is to create a
default value, and hold the state stable. If allowed to float in a weak
condition, any electrical transient might change the input state. The
resistor's function in the "circuit" is to limit the amount of current
that can flow. If we are talking about just a simple gate as an
example, it could be a pull up to Vcc or Vcc pull down to ground. No
doubt now that something did trash the PCM and when it stalled maybe
the KAM has bad voltage data for the map that has to be key cycled to
reset. The second controller has passed the 150 mile mark and we
released the vehicle to the customer. The crank sensor seems to be the
only thing that could have solved this problem. Hey, thanks again, I
like this interaction.
Now can someone suggest a handheld dvom/scope that is faster than the
star scan or star mobile...hmmm

Steve Wells
 
You must log in or register to reply here.

Latest threads

Back
Top