Before you close this out, I am curious about one thing. Assuming that Firestone was correct when they told you that plug 1 was flopping around, doesn’t that sound like too much of a coincidence? Isn’t the known issue on cylinders 1 & 4 which share a coil pack? How about checking resistance on plug wire on #1 to make sure it’s good? Then follow up by switching that coil pack with a different one to see if the misfire follows the coil pack from cylinders 1 & 4. The theory I am considering is the improper installation of plug 1 damaged that coil pack, causing the misfire for cylinders 1 & 4
wmm2, I changed out the coil pack. The original coil and the new coil both code as misfires at #1 and #4 cylinders. Earlier in this post, Nevada_545 advised me of a way to test the #1 wire (there is a picture he posted illustrating). I placed a safety pin in each wire, one at a time, on the connector of the coil and used an alligator clip to capture the wire and then touched the other end of the test light to the negative battery terminal. pin #1 wire, cylinders 1 & 4 was a solid light, pin #2, cylinders 2 & 5 was a flashing light, pin #3 wire, cylinders 3 & 6 was a flashing light, pin # 4 is common.
This would indicate something is wrong with wire #1, since wires 1, 2 and 3 handle the cylinders - two are flashing and one is not.
I then did the pin test on #1 at the PCM and the light was still solid.
I also did an ohms test on wire #1 from the PCM to the coil connector. No resistance which would indicate there is no break in the wire.
I took the wiring harness off yesterday and the wires were all stuck together from age and heat. I separated each wire from the others and there was an abrasion on a couple of the wires, probably from me pulling them apart. I taped the two spots and will be putting the harness back in today. I doubt I have solved the problem, but just maybe.
Incidentally, when Firestone told me that the #1 plug was loose, they also told me that the alternator had not been bolted down correctly and that a nut was missing off one of the bolts. In order to remove the plenum and get to the harness, it was necessary to remove the alternator. Much to my surprise, the bolts to the alternator were in but neither bold had a nut on them. Foolish me, I assumed Firestone had put nuts on the bolt(s) when they found them missing. I will be checking the #1 plug now, for all I know right now, they may have not tightened the plug - but surely they did?
cwatkin, I thought about totally bypassing wire #1 which is in the harness with a wire between the PCM and the coil connector, but I do not want to splice the wire and I do not want to pull the old wire out of the PCM or the coil connector. You know of any other way of testing between the PCM and the coil connector without splicing or removing the old wire from the PCM and coil connector?
I will post a final on this hopefully someone will benefit from my situation.
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.
That is called a conformal coating and it primary purpose is to protect against moisture and corrosion. It’s actually easy to get through it to check the circuit, you just need needle point probes on your meter. It’s done all the time in industry.
Many, many years ago now I designed a control system for Rexnord for train track gauging and spiking equipment. The conformal coating was 3/8" thick by design due to the environmental conditions the equipment worked under. We had to heat up exacto blades to carve through it when repairs were necessary.
When replacing components, the coating will rapidly degrade under soldering iron temperatures so repairs are possible, just not fun 
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.
Except that it might actually not end up saving any money and be just the opposite. The drivers/heatsinks are probably where the lion’s share of the cost is in the assembly. The rest of the PCM (controller, discretes) are not that expensive. If you separate them out, you have two enclosures, another harness, increased labor etc. When the driver(s) fail, the rest is just along for the ride
Since my last post and prior to buying a PCM, which seems to be the consensus on my problem, I did the following:
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Removed the plenum in order to have better access to the wiring harness which runs from the coil, under the plenum, and plugs into a connection with wires after the connection joining up with other wires and ends at the PCM.
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The wiring harness is nearly 20 years old. It was very hard and the wires within the harness were stuck together - from age and heat.
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I carefully separated all the wires and then checked each for any tears or abrasions. I found two wires, which coincidentally were also two of the wires which run to the coil connector which had visible wires showing through the insulation. I taped both with tape.
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I then checked the four wires which run to the coil connector for resistance and there was not indication of a break.
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I put everything back together and tried to crank the van. It will not start.
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Prior to taking the above steps, checking the wires at the coil connector with a test light by turning the engine over, the four wires did the following:
Pin 1 was a solid light - this is the pin which controls cylinders 1 & 4 which are the coded misfires.
Pin 2 was a flashing light - controls cylinders 2 & 5.
Pin 3 was a flashing light - controls cylinders 3 & 6. -
After taking the above steps, checking the wires at the coil connector with a test light by turning the engine over, the four wires did the following:
All four pins - nothing, like there is no power
However, if the four wires are jumped as above, except the ignition is just turned to on and the engine is not cranked - all four lights initially light but then go out.
I’m not sure what this means, but it would appear the PCM (perhaps) is sending some type signal but then does nothing further.
I did put a spark plug on a coil post and cranked the engine - no spark.
Any observation would be appreciated.
I wonder if you are battling a degraded wiring harness, and every time you handle it, it gets worse. I realize from your perspective it appears you are moving away from the solution, but what you’ve done may be providing important clues. And I think the clue is that the particular wiring harness you are working with is kaput and needs to be replaced.
If I understand this correctly, when the ignition switch is turned to the run position there is power to the coil B+ terminal for 2 seconds (ASD relay on to prime the fuel system) then no power to the coil when cranking the engine. I think you disturbed the wiring to the crankshaft position sensor and have no crank signal. Without a crank signal the PCM won’t turn on the ASD relay.
A new engine wiring harness will be expensive. Removing a harness from a 20 year old junk yard engine then installing on your engine will be a challenge, the harness insulation will be brittle and cracking.
You might consider searching your local pick-a-part yard for a PCM with the same part # and from a vehicle with no factory alarm, after you solve this wiring problem. This vehicle does not have an immobilizer system so a used PCM should work. The only problem is that you can’t rewrite the VIN in the PCM so there will be a mismatch if checked during an emissions test.
Nevada_545, you are good! I didn’t even remember disconnecting the crankshaft sensor, but that is exactly what it was. Plugged it in and the van started right up. But, same problem.
Do you think, from what I have described, that there is a very high probability of “frying” a new PCM if I were to buy one? I think I have seen them for around $199 on line.
If I bought one new is there programming involved or are they just plug-in play?
BTW, I took the van to a garage and they had the old time scanners and it gave a code of PO351 which points at pin #1 with bottom diagnosis of PCM. Do you know if this vehicle has a ECM and a PCM?
Thanks a million.
It is not unusual for the wire insulation to stick together and expose bare copper when pulled apart. The question is was there wire to wire contact? If the cylinder #1&4 control wire is shorted to battery voltage it could damage the PCM but at the same time if that wire was shorted to the 12 volt supply to the coil and injectors I would expect the engine to die and possibly blow a fuse.
You might check for continuity between each wire to the coil to see if the wires are shorted together. This won’t assure against intermittent shorts.
The VIN and EMR mileage should be entered into the new PCM with a scan tool but that wouldn’t stop you from driving the vehicle.
Nevada_545, the initial problem was that the van did die, but then it did crank and run rough at low idle with a scan showing the #1 and #4 misfire, but it has not died since the one time.
Just to ensure I understand what you mean by the “continuity between each wire”. While the harness was off the van I checked the continuity of each of the four coil connector wires and none of them indicated a break, the ohms were .3 when the meter was set at 200. Is that what you meant to do or is there some other way you meant to check the wires?
At the coil pack connector test the resistance between any two wires (with the PCM connector disconnected), it should read infinite or open circuit if the wires are not shorted together.
Nevada_545, I checked all the wires as you described. I set the meter at both 200 and 2000 and the meter stayed at 1. That should be the infinite resistance you referred?
Should the wiring have been connected or disconnected to the PCM to do this test, or does that matter?
I assume that would mean all indications are that the PCM is bad?
NOTE:
P.S. Sorry I misread your instructions about disconnecting the PCM. In the below post I have done that.
Stayed at 1? The meter should read “O.L” or “Open” for infinite resistance. If you touch the leads together it will show a short. A short between wire points is what you want. If the wire from end to end shows Open, then that means there is a break in the wire. You can not read resistance with power on the car. Meters use voltage to determine resistance. The battery has to be disconnected. This is true when every you plug or unplug modules.
knfenimore, it would appear my meter does not display O.L or Open. What the paperwork says is, "Over range indicator: Displays “1” on LCD. I assume that relates to what you are saying.
When I set my meter to any ohms, from 200 to 20M, and touch the leads together, the reading goes from 1 to 0.00, which I thought indicated no resistance and therefore no breaks in the wire.
I took two pieces of wire which I know have no breaks. I set the meter to 200 ohms. I touched the leads to the two ends to each of the wires. The reading goes from 1 to 00.4 on each of the wires.
If I touch the leads to one end of each of the wires, thereby creating a break, the reading stays at 1 .
I disconnected both terminals on the battery and disconnected the PCM. In theory I should have then four wires running from the coil connector to the plug-in connector on the PCM, but not making contact with the PCM.
I checked each of the coil connector wires with each of the other wires in the connector and the reading stayed at 1 .
Would making the assumption that no wires are stuck together be correct?
My DVM does what yours does OP. If the resistance is higher than the scale it is set to, it displays a “1”. How DVM’s handle the out of range condition, it varies by make and model of the DVM.
OP, I expect you already understand this, but when checking for continuity you should use the lowest ohm range available; i.ee don’t check for simple continutity on the 1M-ohm scale, use the 200 ohm scale instead. On the 200 ohm scale good continuity might well be displayed as 0.2 ohms, not zero. That’s b/c of a combination of inaccuracies in the DVM and imperfect contact between the probes and the wires being measured.
Don’t forget to turn on the beep, when checking continuity
Thanks to everyone. I am going to order a PCM and see if that is the problem - I’ve apparently eliminated everything else - but it will probably end up being some useless tail light wire or something. Will post to hopefully help someone down the road.
Thanks for keeping us up to date OP. It sounds like you’ve decided against having an auto-electric mechanic do the job.