1999 F150 4.6L, ~120K miles, one owner.

Monday (Labor Day) evening, about 2 blocks from the house, it suddenly started running rough and threw code #P0352 (Ignition Coil B Primary/Secondary Circuit Malfunction). I parked the truck.

This morning I pulled the indicated coil pack; the primary and secondary windings on both coils ohm out as good (same as the other coil pack). I then checked the primary signals from the PCM at the coil pack connector (using LED test light). One side got a good signal, the other side - no signal at all.

I should probably note that about 3 months ago, it threw the code for the other coil pack (I think it was P0353). That problem turned out to be a bad #5 plug wire, so I replaced the entire wire set at that time. The plugs are Motorcraft replaced less than a year ago.

Any ideas? Bad PCM? Bad primary wire that suddenly went bad with no warning at all? Some other problem I haven't thought of?

Thanks,
Ron

 

Well, first, since you have primary - secondary issues - What plugs are you running? Sounds like your running the wrong heat range.

 

Thanks for the fast reply. I don't want to get side-tracked on plugs cause they're not the problem. However, since you asked; these are Motorcraft plugs, I don't have my log book in front of me and can't say for sure the part number, but I looked them up myself at the time on motorcraft.com and verified that the parts house came up with the same number.

Also, please be sure to note that these are coil packs, not COP. The primary/secondary label was simply the description from the OBD-II code reader, but it is not the actual problem. The primary and secondary windings of both coils in each coil pack are fine (I even swapped the 2 packs at one point). Thus the problem is also not the coil packs.

The problem is, however, that one of the coils in one of the coil packs is not getting the trigger signal from the PCM. I verified this using an LED test light. Thus 2 of 8 cylinders are not firing. I also verified that all 3 other coils are getting proper signals. Both coil packs do have power (+12v).

So the questions remain:
- If only 1 of the 4 trigger (low) signals from the PCM is not getting to the coil pack, is the PCM bad?
- Given that this problem appeared without warning, are there other possibilities, such as a bad trigger wire (the wire that runs between the PCM and the coil pack)? Or a bad connector somewhere in that trigger circuit?
- Could something like the crankshaft position sensor (or even camshaft) be causing this phenomenon (that is, of losing only 1 of the 4 trigger signals)?

Thanks again for your fast reply, and I hope you'll take another look at my problem.

Ron

 

Yea, I know what you have - Coil Packs = two transformers, -changes low voltage pulses from the powertrain control module to high voltage pulses.
Sends high voltage pulses to spark plugs through spark plug wires.

IMO - I don't think so, -on the crank and cam sensors. I've never seen or heard of those sensors causing such a problem.

I would lean towards the (low) volt signal wire from the PCM. First note location of this harness itself, -in relation to the AC accumulator. There has been numerous problems in the past with the accumulators Mag field creating havoc on the ignition systems when to close. At times the harness would be resting on and has bared wires. It doesn't have to bare wires to cause disturbance or disruption. So check that (if it's fairly close to the accumulator, tie it back further / also check the pin out as well (signal wire)/ lastly, yes the PCM could be at fault. It's not very common, but has happened in the past.

 

You can check it this way since your greater than 10 volts on the Ign start/run voltage @ the coil pack itself and if you have a test lamp.

Coil Driver (CD) -

1. Connect incandescent test lamp between IGN START/RUN and suspect CD circuit at the coil pack harness connector.

2. Disable fuel pump by disconnecting inertia fuel shutoff switch

3. Observe incandescent test lamp while cranking engine.

Lamp should blink constantly.
_________________________

You can also check for suspect CD circuit for open in harness this way to determine fault-

1. Disconnect PCM.

2. Measure resistance of suspect CD circuit between PCM harness connector pin and coil pack harness connector.

Resistance should be less than 5 ohms. If not - Repair open circuit.

 

How about the ignition voltage at the power pack?.
I have seen problems at the Jack/Plug connector that should be remediated. One strange addition with an older unit. There is a small capacitor attached to the Jack/Plug connector that is used for "RF Interference" filtering.
I have seen them short or suffer an internal problem causing and intermittent shortage at times. If you can check out that "RED" wire at the terminals on the left power coil pack.
Hope it works

 

Sorry I haven't replied sooner - I've been offline since yesterday afternoon. Nor did I have a chance to work on the truck last evening. But I really appreciate the responses - thanks, as I'll be working on it this evening for sure.

jbrew - Your test was pretty much exactly what I did, except that I used an LED test light rather than an incandescent (I've read that an incandescent can blow the output from the PCM, but that an LED is safe. Unfortunately, it may be that this particular output is already blown).

Your second suggestion about ohming out the control line is exactly what I'm planning to do tonight. However, I did not know the allowable tolerance (5 ohms) - thanks!

98Expedition10 - My truck does indeed have the attached capacitor. Since these are prone to problems, I will certainly check it out a little more carefully again. However, my problem really seems to be with the lack of pulse from the PCM (2 of the cylinders on that same coil pack seem to be firing just fine).

Thanks again guys!
Ron

 

BTW - Has anyone ever installed a remanufactured PCM (Powertrain Control Module) computer? I've checked with 3 parts stores (Auto Zoo, Advance, and O'Reillys), they all carry the same brand, A1/Cardone, and all say it will take about a week to get one flashed and shipped here to Austin, TX. The cost is pretty reasonable at all 3 ($150-$200).

I was just wondering if anyone had ever installed one of these rebuilt PCMs and how it worked out for them?

Thanks,
Ron

Edit - I also posted this question in its own thread, sorry about the duplication:
https://www.f150online.com/forums/v8...tured-pcm.html

 

Just so you know; The coil pack ignition uses wasted spark. It sends secondary current to both plugs. The PCM grounds the coils and breaks the ground to fire the plug. Unplug the capacitor on the B coil and test the power circuit again. You should have 12v on the Red with light green striped wire at both coils. If you still have no current there is most likely a break in the wire after the splice. Both coils receive 12v off of the same fuse.

.

 

JMC - Thanks so much for the info! Recapping a couple of things I had mentioned earlier in this thread:
- I've checked power at both coil packs - both are good.
- Two of the cylinders on this same coil pack are firing just fine.
- One side of the coil is not receiving the low signal from the PCM, the other side is (I tested this with an LED test light).

This indicates a couple of possibilities to me:
1. That that wire between the PCM and the coil pack has opened up.
2. The output from the PCM has blown for this side of the coil pack, which would mean the PCM needs to be replaced.

Do you know of other ways the PCM signal might not make it to the coil?

I'll be nailing this down this weekend; I plan to ohm out the wire from the PCM, and then attempt to check the signal right at the PCM. If the wire checks out okay and I can't get a signal close to the PCM, I'm planning to order a new PCM. If the wire is indeed open, I guess I'll be running a new wire to the coil.

All suggestions/comments are much appreciated!

Thanks,
Ron

 

Did you check the harness in relation to the AC accumulator? - Need to get that done and out of the way, -specially that model year.

 

Not yet, but yep, that will be at the top of the list of stuff to check! I plan to work on it this evening.

 

Ron: You know it's pretty hard to diagnose problems remotely. At this point you are going to need a through physical inspection from plugs back to the ECM.

I checked my notes for the Coil Pack of these units, and this is what I had noted from previous diagnoses.
Presumably you have a precision Volt/Ohm/Milli-Amp Meter available.( These figures presume that's what you'll be using)

Each coil pack is equipped with two secondary (HV) coils.
Measuring across the total coil you should measure:
10-15K ohms (the actual measurement should be above 10K ohms, but more important that they be within 10% of each other). This is measured tower to tower.
If you don't have the circuit diagram note this info on your note pad.
a. Cyls 1-6 Ohm Reading 10K Ohm (optimum 13K Ohm)
b. Cyls 5-3 Same as
c. Cyls 4-7 Same as
d. Cyls 2-8 Same as

If necessary to test out each of your Spark Leads don't trust any lead that has a reading over 7.5 K Ohm. (max.)
A credible reading over 8.0 K Ohm will cause misfires or intermittent firing.

Each coil pack is equipped with two primary (LV) coils.
They are paired according to spark plug positions:
I don't recommend testing but checking the J/P Connector is best. Check for tarnish & corrosion of the contacts and clean where possible.
These coils are internally cross connected(they are not center tapped as shown on most diagrams), but may be measured at the J/P Connector. If properly connected your VOM should read .35 to 1 Ohm. There are three contacts at the J/P connector. The center contact is the common terminal. Measure Center to Outer contacts to measure these readings.
Most lost cost VOM's have a problem reading resistance below 1 ohm with precision, so be careful of the reading. In any circumstance the optimum reading would be about .5 ohms +/-5%.
Watch out with trouble lights connected into ignition circuits just because there is +12VDC at the common terminal there {could/should} be a 65 Volt pulse voltage pulse available at the alternate terminal . You would really need an oscilloscope to really see what is going on if you intend to use your diagnosis.
I would stick with physically checking the wiring circuits and plugs and connectors.
Seriously I hate these type of problems they can be a real P.I.T.A to fix.
Hope this helps
:o

 

There are 3 wires at the coil pack connector. One is a hot in run and start fused 12volt source from the battery. The other two are grounds. The PCM opens the ground to fire the coils. Unplug the suspect coil then run a test light from the 12v lead to one of the grounds at the harness connector. Crank the engine. The light should flash. Check the other ground. If it flashes the PCM is doing its job and the coil is defective. If any of the lights do not flash then either the wires are open, shorted to ground or the PCM is not grounding.


Regards

Jean Marc Chartier

 

REPAIRED and RESOLVED! Here is the final outcome and procedure:

I disconnected the PCM connector (after removing the battery and the battery box in order to get full access to the connector), located the coil lines on the connector, and then checked them for continuity to the coils. All 4 of them checked out perfectly (effectively 0 ohms). So I'm starting to think, "Hmm, I may have a bad PCM."

At this point, I also checked the A/C accumulator as had been suggested. It turns out on my truck, the accumulator is mounted fairly low and only a battery cable (running down to the starter) runs anywhere close to it. So that was not the problem.

Nonetheless, I carefully put it all back together and re-check the signals with my LED test light. Voila', all 4 signals are now there (as mentioned early on, the ground pulse signal to coil B signal had been missing previously).

I start it up - it's better but still missing a bit (not nearly as badly though). I swap the 2 coil packs, better still, but after a good bit of running time it eventually gives code P0354, coil D (it had been P0352, coil B). Obviously, the miss followed the coil pack. Again, I check the resistance of all 4 coils, paying special attention to the 2nd coil of that particular coil pack; and again the primaries check (~0.5 ohms on each coil), and the secondaries check (~14K on each coil). All 4 primary and secondary coils measure with perfect resistance!

I finally decide to replace the coil pack anyway, which I did this afternoon. And the engine is now purring beautifully once again.

Conclusion: I had not been getting a pulse on coil B from the PCM earlier, which was solved after I messed with the connector. I wonder if disconnecting the PCM, cleaning the contacts (which I did with electronics cleaner, even though the contacts looked perfectly good), and reconnecting acted to re-establish the connection of that coil pulse. It also just so happens that the pins for all 4 coil signals are on the last column of pins of the connector, which puts them at the extreme bottom of the connector once it's plugged in (the connector plugs in vertically). Then I also noticed that the very hefty wiring harness on the connector tends to torque against the connector, putting a force on it that tends to pull the connector upward (thereby tending to unplug the connector starting at the bottom, where the coil pins are). And yes, there's a hefty bolt holding the PCM connector in, but the connector is so large that the ends can clearly still move a bit when under pressure. So the question would be, if the coil had been getting a weak (and eventually no) ground signal from the PCM, could that end up weakening the coil itself until it eventually failed? And weirder still, cause the coil to fail in such a way that it ohmed out right on spec?

I don't know, it's all conjecture at this point. But clearly - it took both of working with the PCM connector and then replacing the coil pack to completely solve the problem. And I did not end up having to replace the PCM! But it sure took some time, effort, and thinking to track this one down.