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Ford Explorer Community - Maintenance - Modifications - Performance Upgrades - Problem Solving - Off-Road - Street
Explorer Forum Covers the Explorer ST, Explorer Sport, Explorer Sport Trac, Lincoln Aviator, Mercury Mountaineer, Mazda Navajo, Ford Ranger, Mazda Pickups, and the Ford Aerostar
My 1996 Explorer just rolled over 200.000 miles, replaced plugs, wires and coil pack with DENSO parts. Before the new parts there was no check engine light, truck ran OK, quick start, not a lot of power, now it is showing PO 351 and PO 353. Bought Motorcraft wires, coil and plugs and replaced the Denso I had installed. Still shows same codes.. Swapped PCM, same codes. Kicked bumper, same codes. Checked wiring sequence to coil left-123, right 465.
Any clues to what may be wrong. I like my Explorer, should I take it to a dealer for a $1.000,00 checkup?
only other thing i can think about would be both are bad? highly unlikely though... still got the original pack? maybe try clearing CEL (disconnect battery for 10(?) mins or clear w scanner) and drive for a bit to see if it come back... if it comes back, then reclear codes and try putting the old pack in... thats the only other thing i can think of, as that one was 100% proven to have worked prior to swap
I'm not seeing any ground on the ignition coils (on the wiring diagram) except when the PCM does it through the "IGN Coil" wires. See attached PDF.
Pictured below is an item of potential interest. At the risk of being annoying by asking about mixing up wires again, did you notice that on the ignition coil module, that the 4/6/5 side is out of order?
Also notice the pins, IGN Start/Run should always have 12V (with ignition in run position), then PCM grounds each in sequence with the engine running. Using a multimeter, you should get the same resistance (on the unplugged coil pack itself) reading between the 12V power lead pin and CD1, as you get between 12V pin and CD2, and 12V pin and CD3. If any of those read open circuit instead of *similar* resistance, the coil is bad. I know it seems unlikely since you replaced the coils.
Probing the plug to the coil pack (while plugged in, engine running) it should read near 12V on each respective CD1, CD2, and CD3 pin, until the PCM momentarily grounds it to complete the circuit for each cylinder spark. If it never gets momentarily pulled down below 12V to fire the spark plug, would seem like PCM is bad yet you replaced that too, so I begin to wonder about bad wiring or one of the two bulk connectors as mentioned here:
Sometimes a gremlin can be caused by the smallest thing. There are 2 large wire bundle connectors on the firewall. Both are held tight with a 10mm bolt. Any bad connection in either plug can cause just about any issue. from bad transmission shifting, bad o2 sensor readings, no start, no...
www.explorerforum.com
On the attached wiring diagram, the coil wire that's tan/Lt-Green, also goes to the PCM but they routed it the long way, goes to PCM pin # 78. All else fails, use a multimeter to check resistance between each respective CD1, CD2, and CD2 connector contact, and the respective pin on the PCM connector... but they go through one of the bulk connectors in the topic linked above so that is another place to look for a bad connection as already mentioned.
There are more wiring diagrams linked in my sig below, but the only one I thought relevant (besides mentioning PCM pin #78 is where the tan/lt-green wire from the coil pack goes) is attached.
^ It would not surprise me if that is a chassis ground, but only to a sort of faraday cage assembly (internal metal plate) to decrease EMI, not to make the coils themselves function. I suppose in theory, it might be possible that the magnetic field in one coil, could induce a charge in an adjacent coil if the structure isn't grounded, but that doesn't seem like it would prevent the coil from functioning, would manifest itself more at higher RPM (? Just guessing on that).
It can't be a ground for the coils themselves because it's an always live 12V going to them, has to have the PCM make and break ground to fire the plugs.
To clarify, the coil pack does not need bolted on or grounded through the bolts at all for the bare minimum function of running. That will serve as a % of heatsinking, which is good, but that is long term lifespan related, and as far as EMI shunting to ground, better AM radio reception related, not make or break functionality to run the engine.
Ignore the numbers on the actual coil pack if they do not match this diagram
Many people forget that the front cyl on pass side is 4 not 6
I know you said it’s covered because you numbered the wires etc but it is good practice to check firing order one wire at time against the correct chart
