2018 Ford C-Max Hybrid 2.0L gas, can't seem to resolve P035XX codes - please help!

[Savi]

Hey all, hoping one of y'all has some ideas about what I can do to get our 2018 Ford C-Max Hybrid w/2.0 gas engine running right. Although I have been working on cars for almost 40 years and have rebuilt engines and transmissions, engine swapped, rewired, and done most other procedures on many vehicle models, I just can't get this one acting right.

 

If any of y'all have specific experience dealing with this issue either on C-MAX 2.0 engines, or the Focus 2.0 which I understand is the same or very similar, I would really appreciate any insight you might have, links to specific replacement connectors that can be swapped with new pins, etc. etc. I know this set of behaviors is not unheard of with both C-MAX and Focus, and is often very hard to diagnose from the dozens of forum posts I've read, and most solutions I've read where folks got this working have been some variation of all the stuff I've already tried after Googling and forum surfing to the end of the internet and back and running through the Alldata test procedures for this issue. At this point I feel like I'm way past generic diagnostics with this thing and well on to the specific shitty quirks of this engine/platform.

 

Been several months now, but after we had a week or so of cold weather, our 2018 C-Max Hybrid (a little over 69,000 miles) started misfiring on the 2.0L gas engine. The codes it threw were primarily P0352 (and currently P0351 and P0354 as well - Ignition coil primary/secondary circuit) according to my torque app with an OBDII reader. Also checked with Forscan, and the results were pretty much the same.

 

Thus far I've thrown a ton of parts at it, covering all of the typical stuff that I have read contributes to both the codes and misfiring on these in general, and *nothing* moves the needle on the codes or misfire.

 

Parts that have been replaced:

 

Spark plugs, replaced with semi-generic iridium plugs, tested resistance, seem to be in spec (around 5K Ohms each)

 

Ignition coils, started with generics, swapped for Delphi when the first set failed to change the behavior

 

New set of Bosch fuel injectors - also added Lucas fuel treatment - obviously not implicated by the trouble codes, but a potential source of misfiring

 

Coil pack connector on the #2 cylinder replaced with a new OEM Ford connector

 

Replaced a suspicious looking knock sensor with a new one

 

Replaced rear engine mount with a new one

 

New 12V battery

 

PCV valve replaced with a new OEM Ford part

 

Intake manifold gasket set, FelPro

 

After all of the above failed to produce any change, I ordered a replacement PCM from Flagship One, programmed to the VIN number of the vehicle, no change running either PCM. Note that drive battery and 12 battery were disconnected before swapping PCMs.

 

After/during the PCM swap, I probed the wires running from the ignition coil connectors to the PCM and all had good continuity.

 

There was a janky solder point on the brown/white wire that all of the ignition coil packs have in common in the circuit, and I replaced that joint with a good quality butt connector with heat shrink tubing, no exposed copper that could potentially cause a short.

 

When all of the above failed, I went a little nuclear and completely bypassed the harness wiring to the two primary misbehaving ignition coils from the coil connectors to the last 2-ish inches of the harness before the relevant PCM plug (C175T), same resistance reading as the harness before the bypass (basically nothing - around .3 Ohms, what my meter typically shows when confirming resistance test function before use), and still the codes and misfire continue with no change in behavior.

 

The only two things that I noticed that seem to have any diagnostic value other than the codes and the misfire itself is that torque registers a low vacuum reading - typically 12 or fewer inches of mercury - not sure where I can get a manual vacuum gauge connected on this engine, as all of its vacuum lines seem to have specialty connectors. I know it should likely be closer to 18 inches or so, but if anyone knows the normal range for this specific engine, I'd love to know so I can get a legit baseline value to evaluate against. Presumably it just the misfiring causing the vacuum to be in the toilet, so I wouldn't be surprised if this reading stabilizes when the misfire is resolved.

 

Connecting an inline ignition tester that can show the spark when the coil pack fires demonstrated a far dimmer spark on the misfiring cylinder than a cylinder that was firing normally and not throwing codes. Swapping the coil packs and spark plugs did not move the problem around, so it's not the obvious faulty spark plug or coil.

 

I also did a compression check, which turned out fine, so not a compression issue, not that I'd expect one with miles this low and the regular maintenance that's been done, not to mention P035X trouble codes.

 

I also tried connecting my the ground lead of my ridiculously heavy duty old school jumper cables between the ground jumpstart bolt on the chassis and unpainted metal on the engine in case it was an engine ground issue. You guessed it: no change.

 

Seems like the problem is external to all of the systems that I have replaced parts on, but at this point the only thing that hasn't been swapped, bypassed, or replaced is that C175T plug to the PCM. The connector isn't broken or loose, but that doesn't mean the pins aren't loose or don't have some other kind of issue.

 

Cheapest used replacement harness I can find is pretty expensive, and I'm hesitant to go through that expense and the pain of swapping out an entire engine harness if it's likely to keep me in the same "no change" purgatory. Finding a replacement for the suspect PCM Connector might be a better solution, but I've only seen a single used connector on eBay for around $70, which is a good chunk of money and a lot of work sourcing and crimping pins, and I'd like a bit more certainty before going that route. I'd feel better about a PCM connector swap if I could find a new plug and pins. I have a crimper that should have the dies to crimp these - wouldn't be fun, but it is what it is.

 

Thanks in advance for any possible assistance and my apologies for the novel!

[twintornados]

This may sound simplistic but years ago when I had a Focus, it threw codes about misfiring.....I had done a tune up on it during an oil change and had put some fancy plugs in (don't remember which now). A buddy at the local Ford garage stated, "Put some Uncle Henry's (Motorcraft) plugs back in it...." I did and the problem went away.