You have been more then helpful, really. There are only a couple more things I think I can check on my own but those are things that I would also need spare parts of to test. Would really like to throw a new dme in, but that requires an immobilizer & key also.

If replacing the wiring weren't such a pain to do with the engine in the car I would just do that too, and still might.

Still going to get it to KC cause I want the cam actuator pads replaced and that is not something I want to do. I could do it, just dont want to.

RedTele58's post got me thinking (dangerous thing). I'm not too sure it is a connector issue, but it could still be a wiring issue, but this is where I need help understanding the wiring & coils.

When looking at the diagram the coil has 3 wires. 1 is +12v, 2 is ground. 3 goes to 42 welding point WL Motor, which I think goes to a relay if I am reading things right. The same ground is shared with coil 1-3, SAI pump motor & engine intake cooling fan motor. This ground is located right by the AOS & the outside corner of the intake manifold. Verified that it has 5 ground wires.

So, big question. If I disconnect that ground wire from the engine, should that wire still have ground connectivity? If I am reading the diagram right I dont think it should.

My question is if the gp 12 is disconnected from the motor, should there still be ground connectivity between those ground wires and ground?

I may be totally off-base on this as I have no real experience on P-cars' electornics. Having said that, most cars I've worked on, the DME or ECU, or whatever they call it, does not send voltage, it completes the ground. So, my theory is that post #1 is NOT +12v, but ground for the Primary circuit (low voltage) of the coil (when the DME grounds it), #2, GP12, is the ground for the Secondary (high voltage) circuit. The diagram shows a diode for the spark plug side, which would be the main ground, so maybe GP12 is to ground some transient voltage?? And #3, VS42, is acutally +12v. This would make sense why VS42 would hit all 3 coils and other parts.

You can test this if you have a circuit tester and connect one end to any ground and probe #3 on the harness and see if there's 12 volts. And if you have and OHM Meter, you can probe both ends of all three wires to check for continuity or excessive resistance. I'd at least check for a broken wire by testing continuity before worrying about replacing the entire harness.

Hopefully this helps get you on the right track towards troubleshooting.


EDIT: Actually, you don't need to check both ends of all the wires. If #3 is in fact +12v and you get +12v on the #3 post of each coil, then those are all good. If you have an OHM meter, you can check for continuity from #2 to any ground on the car. The only wires you need to check both ends for continuity are the #1 wires. You need to probe them at the both coil side and the DME side to check for continuity.

I think you are right. One of the pins is 12v, another is ground from the dme & the other is engine ground (gp12).

This is an area that is not my strongest. I do decent, but not great.

Here is the rub with all this though. the misfires are not constant, that are sporadic. sometimes get a lot of them, sometimes it's 30+ seconds in between misfires

I'm not great here either.

It could very well be a break in the wire with the broken ends close enough together. Somtimes it gets continuity, sometimes it doesn't. Temperature and engine vibrations would contribute to the problem. So would a short between two wires rubbing against each other in the harness. The latter is harder to diagnose because a continuity test would still show continuity. If you're lucky in that case you'd find voltage on a wire that's not supposed to have it, then that would indicate a short somewhere. Besides that, you'd have to cut the harness open and check each wire for a break in the jacket.

I've been following this thread and I empathize with you. Electrical gremlins are a PITA to solve. Hopefully at worst you just have a break in the wire and not a short.

What I found out about VS 42 is that VS=voltage supply.
It is a key on 12volt. So any VS with a number in these wiring diagrams is a key on constant Voltage Supply point.

I would think that any wire that has a break in it but still shows continuity would also show greater resistance on an ohms test.

Correct. Another way to check for breaks is by moving the wire harness while checking continuity.

Ok, well at least with all this I learned something.

So...Coil wiring is:
Pin 1 - DME
Pin 2 - Ground
Pin 3 - +12v

Oh good. I was correct and didn't give you bad info. :cheers:

Hopefully now you have the right info to determine the condition of the wiring and be one the right track to find your issue. 🤞

Well, That was more of a statement....AND....a question just to keep my own might right.

I'm already preparing myself (and potential parts list) of things I will most likely need and then things that should get done if the motor gets dropped.

Well, before I'd go dropping the engine I'd try some diagnostics on the wiring. Check for continuity, resistence. Check while you're physically moving the harness so if there is a break or issue in the wire you'll see varying values. Also check for +12V on the #3 with the igniton on. And even check for voltage on the wires that shouldn't have any.

If there's an issue with any of the wires you can run and splice it a new one without having to replace the whole harness.

So....checked things real quick. Don't know if this is right or not.

Ignition on
Coils all connected
Connector 5 at dme disconnected
There is 12v on the coil wires to the dme. For example green/blue (coil 1) and green/black (coil 4)

Since I'm getting the same on both banks I think it's normal

OK that's good. So that tells us there's a complete circuit from VS42 through each coil and to the DME. Did you try if there's consistent voltage while giggling the harness at various spots?

Another thing you may want to check is to diconnect the coils one by one and see if their respective wire still has 12V at the DME. To use your example, disconnect coil 1 and check green/blue for 12v. It shouldn't have any. If it does, it's shorting with another wire that carries voltage.

yup, wiggled the wires, pulled, pushed, etc. No difference.

On to the next test doing 1 at a time.

One other thought; Do you or anyone on here know if there's a cam sensor for each bank? If so, hopefully they are the same on both sides so you can just swap them and see if the problem follows. If it doesn't, then it rules out the sensor, but unfortunately it doesn't necessarily rule out that circuit.


EDIT: OK, so according to this Pelican article it does have 2 cam sensors:
https://www.pelicanparts.com/techarticles/Boxster_Tech/26-FUEL-Engine_Sensors/26-FUEL-Engine_Sensors.htm Check out figure 5.

Looking back at your OP there's no mention that you've changed it. If I understand it right, the cam sensor tells the DME when to ground the coils for a spark, based on the cam position. Maybe if the sensor sends a weak or irregular signal the DME doesn't complete the ground properly (garbage in, garbage out). The good news is that they are in fact the same on both sides, so you can swap them to see if the problem follows. Or maybe it's the crank sensor the signals when to send spark, I don't remember. But it's probably not a bad idea to swap the cam sensors anyway if they're not too hard to reach.

There is, but I'm not getting any cam codes only misfires.

Cam sensors are also brand new bosh ones.

So doing some onlie research, Cam sensors do a part to control spark. Crank sensor tells the DME what position the piston is in, while the cam sensor tells it whether it's in compression or exhaust stroke. Just because yours are new doesn't guarantee you didn't get a faulty one. If you can easily access them, it won't cost you anything to swap them and see if the problem goes to the other side. But then again like you said, if the sensor was sending an irregular signal, the DME would send a code for it. IDK. This is baffling.

Ok, here is a question for everyone.

What are the chances that all of this is being caused by gas? Specifically the wrong octane being in the car? Have a reason to ask cause I just had a Homer Simpson moment.

And I'll fess up. Went into the office this morning but needed to get gas first with the 03. Was distracted and put in 87 octane instead of my normal 91.

About 20 miles down the road started getting misfires on 1, 2 & 6. This car has never had an issue and it happening right after getting gas has me thinking.

Will be pumping out the tank in the 03 and putting that in the Jeep or the tractors tonight & tomorrow but it's really got me thinking the issue is fuel, fuel vapors/cannister...or fuel system related, just weird to get the same thing on a car that never had any issues. Given that its also not the car I usually drive it is very likely that 87 was put in the 00.

I tried 87 and 91 in mine and worked fine with both. Perhaps it`d matter with a combination with a knock sensor failure?