QuestionQUESTION: I have a 96 Plymouth voyager and there is no drive signal to coil 3&6. There is continuity in the wire from computer to coil but test diode does not flash when engine cranking. Is there any substitute pcm that will work for my r4727219 pcm. A wrecking yard told me to try a pcm from a 97 (4727204AG) but I don't know if it can produce any harmful results.
ANSWER: Hi Konrad,
I don't know for sure about the implications of that exchange, except that '96 and '97 were the dividing lines between OBD-I and OBD-II code systems. You would lost the ability to do a OBD-I readout if you went to a '97. Did you check for codes using you ignition key? "On-off-on-off-on and leave on" doing that in 5 seconds or less? Then watch the check engine light to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to assure accurate count. Group the counts in pairs in the order of appearance to form the two digit fault codes. Then go to www.allpar.com/fix/codes.html for a code list.
I would suggest that you measure for pulsing from the cam sensor as you turn the engine over by hand with a ratchet on the crank pulley bolt. It may be that your sensor is not catching the 3 and 6 slot pattern due to it being slightly too far from the surface. Measure the voltage between the tan/yellow and the black/light blue to see if it pulses at uniform rotational points from 5 to 0.3V in a consistent pattern as opposed to missing a set consistently. That could also explain the lack of driver signals.
Roland
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QUESTION: Hi Thank you for your quick response. I got a 43 twice from the ignition code and a code p0353 from the OBD. When I measured the cam sensor there was a spot where it remaind on 5 volts twice as long as the other pulses. The cam sensor is down as far as it can go. Is it possible that the sensor can go bad for (only for that portion of the coil signal) If so I will replace it. Any other suggestions? Thanks
ANSWER: Hi Konrad,
Are you speaking of the cam sensor? because that one is inside the distributor and is not adjustable, or are you speaking of the crank sensor whose position is adjustable. In other words which color wires were you checking the pulses on when you lost signal? If it was the crank, then I would try a new crank sensor; it it was the cam then unfortunately you may have a distributor with a warn shaft bearing that will require a new/rebuilt distributor (which is said to be near $1k new, or $ several hundred rebuilt). If it was the crank, then your new sensor will have paper spacer and you can position the engine rotation at the area where you lost the signal when you put it in and press the tip/paper spacer till it touches the flex plate surface, then firm it up there. That will assure your best shot at picking up the signal again, in case it is out of round or has a little play in the crank bearing that is causing the signal loss. Please let me know what is happening.
Roland
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QUESTION: Hi again Roland. I forgot to tell you that I have a 3.3 ltr no distrib. on this eng. It was the cam sensor I tested. Can it or the crank sensor give only a partial signal to the PCM or does the fact that they're sending signals to the PCM for the other coils mean they're OK. I haven't tested the crank sensor yet.
AnswerHi Konrad,
Sorry, I somehow thought you had a sedan (with the 2.5L V-6 which does have the distributor). OK, now I see the picture. It turns out that the cam shaft sprocket has 5 pulsed segments, and one segment with no notches (I won't go into the details of the pulse numbers) so what you saw is correct for the cam sensor. You should see a twice as long pulse dead period every two rotations of the crankshaft as that is indication that the # 1 cylinder is coming to TDC. That is for ID'ing which plug to spark. The actual timing of the spark is done by the crank sensor which has 12 slots total, three sets of 4 slots each at 120 degrees separatation from one another.
Because 3 and 6 use the same 4 set pulse on the crank sensor (i.e. they fire at 360 degree rotation difference of the crankshaft) my thought is that for some reason the crank sensor is not seeing that particular 4 pulse segment, thus no 3 or 6 driver signal. I would test that out by indeed reading the crank wires to see if you are missing 4 out of the 12 pulses in one complete crank rotation. If so, then either the flex plate is bent, or the crank sensor-to-flex plate position is slightly larger for that part of the flex plate because it isn't round or there is sufficient free play in crank bearing so as to cause it to not "see" those 4 slots, or the sensor is getting "weak" or too far from the surface in general. Because every theory except a weak/badly positioned sensor costs big dollars to repair, my suggestion, if you indeed verify it isn't seeing all 12 pulses (only seeing 8), would be to replace the crank sensor, again as described earlier, setting it up with the crank positioned near the region of the 'missing' pulses.
Roland
PS Please let me know what you learn.
PPS The wires on the crank sensor that you want to look are the black/light blue and the gray/black. It may in fact see some number of pulses betweek 8 and 11; all it has to do to fail is see the 12th and it won't cause a spark via the #3 and #6 drivers not getting sufficient info. The crank sensor is accessed by lifting either front wheel so you can get to it. It is mounted on the rear side of the engine-transaxle seam, on the tran side of the that seam, just above the surface of the transaxle bell housing and has a 3 wire connector, just like the cam sensor has. Once you attach your voltmeter you can go back from the top side to turn the crank pulley bolt if that is more convenient.
Hi Roland I measured the crank sensor and there seemed to be a cycle of 3 pulses and then the 4th had an extra long 5v reading before dropping down to .1v I only have a very short space to move the ratchet to turn the crank pulley. This pattern went on for about 4 times while I was turning the crank. So it was 3 rather quick pulses and the 4th had an extra long 5v pulse before dropping to .1v then the pattern would repeat. If this doesn't make any sense then I probably lost count or I didn't continue long enough.
Hi Konrad,
The pattern makes sense. When the sensor is opposite metal it reads 5v, when it is opposite a slot it reads 0.3V, so that is why you saw 3 followed by one long one rather than 4 close together (you were looking at the inverse pattern). My thoughts are still that because you aren't getting spark driver pusles on 3 and 6 cylinders the problem has to be this crank sensor but you can't see it when the engine is turned by hand. It manifests itself only when the engine is spinning dynamically at higher rpm. That is the only basis that I can imagine for it to miss 3 and 6, unless it is indeed the pcm but it just happens by chance that the circuit for those exact two drivers failed simultaneously. My suggestion would be to try replacing the crank sensor first, with the engine near TDC for 3/6 (take the spark plug out of 6 and turn the engine until the piston is near the top of its stroke) and install sensor with the paper pressed against the flex plate metal. That would be much less expensive than buying the used/new pcm which may not be necessary. If that doesn't solve it, then you buy the pcm.
Roland
