There is a lot of reading which, thanks to you folks, have appeared since I have been away doing tests. Here are some new numbers which might shed some light:
Per Nevada_545’s recommendation, I conducted two new compression checks one with the engine at operating temperature, one with the engine warm. In both cases, the throttle was open. The original compression test was done with the engine warm and no throttle.
Engine at operating temperature with throttle open:
2 152 psi
4 148 psi
6 149 psi
Engine warm with throttle open:
2 152 psi
4 146 psi
6 152 psi
Per db4690’s recommendation which I stated to someone earlier: GeorgeSanJose, thanks for the suggestion but two shops have told me the same thing, you have a misfire at 1 & 4 but we have no idea why - could be the computer or it could be something else. Perhaps they didn’t want to trace the problem down or whatever, but no help to me. I had a garage replace the plugs and wires -$226 - replace the coil and cam sensor $295 - and still no solution.
With all present company the exception, I don’t know if a good shop exists. Maybe they just do not want to spend the time, even though I pay them, to track whatever problem there is. Having two shops, who I thought were good, just say you have a problem and we don’t know what it is does affect my impression of shops.
I did do primary and secondary resistance checks on the coil which I will post shortly.
I am going to do the light test which Nevada_545 recommended and then I will post the results to that.
GWilliamT, the sequence of events. MPG dropped about 2 mpg. The van had 373,000 and plugs had never been changed. Had shop change plugs and wires. Drove for about 2 weeks with no improvement in mpg. Van seemed to be running fine, just drop in mpg. Went on 230 mile trip, van running great. All of a sudden cut off. Would run but very rough at low idle, CEL had come on and was flashing instead of steady. Had the van towed to a Firestone Store, only one available. They informed me that the #1 plug was not installed properly and was actually flopping around. They also said that in order to get to the #1 plug, the alternator had been taken off and that I was lucky it had not fallen off. They fastened down the alternator and installed the plug correctly, still running rough. They had no one available to scan the vehicle. Drove 100 miles to final destination, rough at low speeds, ran ok except for going up grades. Took to shop and advised them that I had had problems in the past finding shops that could scan the vehicle - needed older type scanner (or whatever you call them). No reply, but they scanned the vehicle and said the coil was bad. Replaced the coil and same result, rough idle, scan showing coil. Out of desperation I asked them to put in a new cam sensor, which they did. Van ran smoother but not right. They said if I left the vehicle 3 or 4 days they would try to find out what was wrong.
Took the van to another shop and they had the older type scanner. It showed # 1 & # 4 misfires. I had the old coil, it was put back on the van and the same codes were thrown.
Since returning home I replaced the ASD and fuel pump relay, which did help the idle, but it is still not right.
Nevada_545, I did as you recommended regarding the light with the exact results you stated:
The number 1 gray wire is a solid light
The number 2 and 3 wires are pulsing - not a distinct off/on flash (guess that is because of the rapid firing.
So, as you recommended, I need to back track on the gray wire.
As I stated earlier, I am not a mechanic in any sense. In back tracking, do I go to a coupling/connection or something and check for a flashing light at some point?
Repeat the same test at the PCM connector. This should indicate if the wire is broke or the PCM has failed.
There are 2 connectors at the PCM, one has wire cavity # 1 to 40, the other connector # 41 to 80. The cavity numbers are stamped in the corners of the connectors to help identify the rows. The grey ignition wire is in cavity #11. You will have to remove the protective cap from the back of the connector to access the wire.
You could also test the wire with your ohm meter for an open circuit.
Nevada_545, I checked the wire with an ohm meter. There is continuity from the PCM connector to the coil connector. That would mean a bad PCM? There is no repairing the PCM, only replacement?
@Nevada_545 looks to be spot-on the diagnosis. It looks like pin 11 is grounded by the PCM when it wants to fire either cylinder 1 or 4. The primary of the coils on one side is always connected to 12 volts. When pin 11 is grounded, the primary of the coil on the other side gets a current path to ground, so the magnetic energy field charges up. Then when pin 11 is ungrounded, the magnetic field collapses and the spark occurs, the high voltage pulse going to both cylinders 1 and 4, with only one of the sparks igniting the fuel and gas, the other has a spark but not igniting anything b/c that one is at the wrong point of the cycle presumably.
If pin 11 has a steady-on test light, that means it is always at the battery voltage. So either
the PCM is broken, likely a transistor is burned out, and not grounding that pin; or
there’s a break in that conductive path between the circuit on the PCM that ground pin 11, and the point you are back-probing. Could be anything from a bad solder joint or a broken trace on the pcm to an oxidized or corroded connector.
If you discover the PCM is broken, there’s a company called “Module Master” which might be able to help you. If not, they can probably suggest somebody who can.
Mechanics will sometimes fix PCM’s themselves in-house, as in many cases the problem is a broken solder joint due to heat flex on the pcb, and all that is needed is to re-solder all the solder joints.
“the other has a spark but not igniting anything b/c that one is at the wrong point of the cycle presumably.”
This is called a “wasted spark” system.
On one cylinder the spark occurs near the end of the compression stroke, the other is near the end of the exhaust stroke.
If I were designing one of these systems I’d put the driving power transistors in a separate case from the PCM since they are more prone to failure.
Of course that would cost more to produce, but make repair cheaper and simpler than replacing the whole PCM.
One final question/verification: Is there any possibility that the circuits running through the instrument cluster in the dash have this type of affect on the PCM?
I guess anything is possible. You’d need an expert on this make/model’s configuration to answer your question with any certainty, but that seems unlikely to me. My bet is either a power transistor on the PCM has failed or there’s a break in the electrical path somewhere between that transistor’s output and the coil.
The van has 274K miles and the front three cylinders has approx. 150psi with the throttle open, 125 psi with the throttle closed.
Using both the original coil and a new coil, at the connector I have gotten a solid light at pin 1, flashing light at pins 2 & 3, solid light at pin 4. I have found two conflicting schematics, one showing 3 as common and the other showing 4 as common. Since 3 flashes and 4 does not, I made the assumption that 4 is actually the common.
Cylinder break down appears to be pin 1 cylinders 1 & 4, pin 2 2 & 5, and pin 3 3&6.
Since the code thrown was misfires on 1 & 4, and pin 1 being a solid light, I took it that pin 1/wire was the problem. I traced the wire back to the PCM and the light was still solid.
I know of nothing else to test and now think the PCM is the problem. I did replace the ASD and fuel pump relays.
If anyone has additional tests or thoughts, your feed back would be appreciated.
For those offering observations and suggestions, and especially Nevada_545, I thank you.
One idea, remove the PCM, and if it is the type where the pcb traces are visible, look at it carefully under a bright light & magnifying glass. Try to trace out where the pcb trace goes, the one which goes to “1”. Follow it wherever it goes, and look for cracks in the trace, or broken solder joints.
I will close this out and, in the event some other soul runs into the same problem, it appears that back tracking to the PCM indicates that the PCM is bad. However, on my particular van - which does not have an alarm system - the PCM is easy to remove but when you take the back cover off it is evident that you cannot fix the PCM. The entire PCM from the board - located in the front of the unit - to the back cover is covered with a gel which makes it impossible to get to the board and check for any faults. The gel is supposedly to protect the electronics from vibrating, etc. Any way, end of the story. I either have to buy a PCM or trash the van. For those of you who might want to buy a PCM, it is essential that you buy a PCM with or without alarm because if you put in PCM which looks for an alarm system on a van which does not have an alarm system - it will not work and will shut the van down, entirely (at least that is what I have been told).
Thanks for the follow up OP. Make sure to give your auto recycler a call. Most of these businesses are on a nationwide car-parts network, and they might have the exact PCM you need. Best of luck.
Please let us know if you replace the PCM and if it works. My local Chrysler dealer offered to try a PCM he had in stock for a car I had been told had a bad PCM and only charge me 1/2 to 1 hour labor if it didn’t work because he could put it back in stock if that wasn’t the problem. That was about 15 years ago.
I didn’t take him up on the offer because I found out my two Plymouths, although different models and engines used the same pcm.
George and oldtimer, I will let you know what the final solution (hopefully) is. One thing I have found out, since my van is 1996, there are a lot of computer scanner out there that cannot read the PCM. I just went to a local garage which can read the PCM and the code was for basically the things I have already addressed. However, the guy that runs the garage said that if it was him doing the repair he would strip the harness apart and verify that wires have not melted together, etc., prior to buying a new PCM. He also said, since I have pretty much zeroed in on the pin 1 wire, that I could just eliminate the current wire and more or less jump a new wire between the PCM and the coil connector to verify absolutely that it is the PCM. I will post my findings.
Also check eBay and such for used auto parts. Lots of junk yards sell things on eBay these days. That is a good idea to bypass the wire in question and see what happens. No point in buying a new PCM only to find it didn’t fix the problem.