1995 Cirrus 2.5L stall condition

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

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

>

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.

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

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

maxpower wrote:

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

We test between the

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

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

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