diagnostics: FICM healthy (>48V), ether-start signature narrows to ICP path

- FICM measured >48V on M during cranking AND key-ON. Healthy. Removed
  as a suspect.
- Truck starts cleanly on starting fluid (ether) every time, then idles
  and runs normally until shut off -- then needs ether again, even when
  warm. This is a textbook signature for high-pressure oil (ICP) bleed
  during cranking that the HPOP can outrun at running RPM.
- Updated working hypothesis to focus on STC fitting / oil rail O-rings /
  HPOP / IPR. Compression, FICM, CMP/CKP, fuel supply all confirmed good
  by virtue of the engine running cleanly once started.
- Reordered open items to put visual inspection of valve covers + STC
  fitting first.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

diagnostics/2026-06-29-no-start/README.md

@@ -27,19 +27,69 @@ No engine P-codes, no FICM codes, no injector codes, no CMP/CKP codes.
   (see `watch-cranking.log`). Bus sagged to 10.8–11.2V during ~11s crank,
   borderline-low but not catastrophic. Healthy starter spin means batteries
   have current to give.
-- **Fuel supply** — HFCM lift pump audibly primes and shuts off correctly
-  on key-RUN.
+- **Fuel supply (low-pressure)** — HFCM lift pump audibly primes and shuts
+  off correctly on key-RUN. And the truck runs fine once started, so the
+  whole fuel-supply chain delivers under load.
 - **Compression / mechanical** — fast even cranking, would feel different
-  with a low-compression cylinder.
+  with a low-compression cylinder. Ether ignition (see below) confirms
+  good compression and valve timing.
+- **FICM** — meter showed **>48V on cranking AND key-ON**. FICM is healthy.
+- **Injector electrical / CMP / CKP** — truck runs fine once started, so
+  injector drive, cam/crank sync, and the FICM-to-injector path are all
+  good when the engine is turning at running RPM.
+
+## ⭐ Key diagnostic finding: ether starts it every time
+
+Spraying starting fluid (ether) into the intake **gets the truck to fire,
+catch, and run normally** — and it then **idles and runs fine until shut
+off**. Then it needs ether *again* to restart, even when warm.
+
+This is a near-textbook signature on a 6.0:
+
+- Ether ignites at much lower temperature and pressure than diesel. If
+  the engine fires and runs on ether, **compression, timing, and valves
+  are fine**.
+- If it runs cleanly once started, **injectors are firing correctly at
+  running ICP** and the high-pressure oil system is making enough
+  pressure *at running RPM* to drive the injectors.
+- Needing ether **every** time — even after warm-up — means the failure
+  is in the **starting-pressure window**, not a cold-soak / temperature
+  issue.
+
+Mechanism: at cranking RPM the HPOP can only generate ICP so fast.
+Anything that bleeds high-pressure oil at cranking speeds will starve
+ICP below the ~500 psi firing threshold. Once the engine catches (on
+ether) and gets to idle RPM, the HPOP can outpace the leak and ICP
+holds normal — so it runs fine. Shut it off, oil pressure drops to
+zero, the leak path is still there next crank.
 
 ## Working hypothesis (in order of suspicion)
 
-1. **ICP / high-pressure oil leak** — STC fitting is the classic 6.0 culprit
-   for "cranks great, won't fire, no codes". Need ≥500 psi ICP to fire even
-   one injector.
-2. **FICM weakness** — should boost to ~48V. Sometimes doesn't throw a code
-   even when failing. **Not yet measured** — see open items.
-3. **CMP sensor** — would usually throw P0340/P0341 but not always.
+The new symptom set narrows the field hard. **It is almost certainly
+in the high-pressure oil (ICP) path that feeds the injectors:**
+
+1. **STC fitting** — the high-pressure oil branch tube where it joins
+   the oil rails. Classic 6.0 wear item. Cracks at the fitting let oil
+   bleed off during cranking when the HPOP can't keep up; pressure
+   recovers at running RPM. Ford TSB exists. **#1 suspect.**
+2. **High-pressure oil rail O-rings** (under the valve covers) — same
+   failure mode: leak at cranking pressure, mask at running pressure.
+3. **HPOP discharge tube / O-rings** — same family.
+4. **IPR valve** seat/seal worn or stuck — bleeds oil back to sump
+   during cranking.
+5. **HPOP itself worn** — gears can't pressurize fast enough at
+   cranking RPM. Less common than STC/rails.
+6. **Sticky injector spool valves** — some 6.0 injectors won't open at
+   marginal ICP but work fine once pressure is up. Less likely if it
+   needs ether *every* time, more likely if it's "some cold starts."
+
+What this is **NOT** (given runs-fine-once-started + needs-ether-even-warm):
+- ❌ FICM (measured >48V; also injectors fire fine when running)
+- ❌ CMP/CKP (sync is good when running)
+- ❌ Glow plugs / glow plug control (needing ether when *warm* rules
+  this out — warm engine doesn't need glow assist)
+- ❌ Fuel filters / HFCM / lift pump (runs fine = fuel delivery works)
+- ❌ Compression / valve seal (ether fires and engine runs cleanly)
 
 ## What we did with the tool this session
 
@@ -88,21 +138,30 @@ To know what each one *is*, compare against a known measurement:
 
 ## Open items / what's next
 
-1. **FICM meter test was started but no readings reported back yet.**
-   Measure M / S / L on the FICM body, key-ON and during a (short) crank:
-   - M (Main) target ~48V cranking, <45V suspect, <40V dead
-   - S (Sync) target ~48V cranking
-   - L (Logic) target ~12V (mirrors battery)
-2. **Visual under-engine check** for STC-fitting oil leak (wet/oily mess
-   at the rear of the engine, around the turbo / bell housing).
-3. **Verify scan-hit PIDs.** Re-probe the clean ones above with
-   `--pid XXXX` to get uncontaminated readings, log them against known
-   conditions.
-4. **Try addressing other modules with `ATSH`** — particularly the FICM
-   on its CAN address if it has one (uncertain on 6.0 — likely on SCP).
-5. Try **FORScan** when forscan.org / CyanLabs mirror is back, on the
-   same CH340 adapter, to capture FORScan's actual PID requests for
-   ICP/FICM/IPR.  That gives us the ground truth.
+Order is now: confirm the ICP-side leak source, then fix.
+
+1. **Visual inspection under valve covers / around STC fitting.**
+   Pull both valve covers and look for oil flooding, weeping at the
+   STC fitting (high-pressure oil branch tube), and the condition of
+   the high-pressure oil rail O-rings on each head.
+2. **Crank and watch ICP build** (once we have a verified ICP PID, or
+   with FORScan / IDS). A healthy 6.0 builds ~500+ psi in 1–2 seconds
+   of cranking. If ours stalls below 500 psi or builds very slowly,
+   that confirms the high-pressure leak.
+3. **Verify scan-hit PIDs.** Re-probe the cleanest hits with
+   `--pid XXXX` (`1310`, `1440-1451`, `11Bx` cluster) for uncontaminated
+   readings. The cluster around `1440-1451` looks like a related sensor
+   group — could include ICP_V / IPR / ICP_DES if we're lucky.
+4. **FORScan** via CyanLabs mirror when it's back, on the same CH340.
+   With ICP and IPR live data in front of us, the leak source is much
+   easier to nail down (e.g., IPR commanded high but ICP stays low =
+   leak; IPR low and ICP low = control side).
+5. **Optional cheap check**: pull the IPR valve and inspect the seat
+   for wear / debris / a stuck pintle. ~$0, takes 15 minutes.
+6. **Address other modules with `ATSH`** — particularly trying the FICM
+   on its CAN address if it has one (uncertain on 6.0 — FICM likely on
+   SCP, not directly reachable from OBD-CAN). Lower priority now that
+   FICM is confirmed healthy by meter.
 
 ## Tool state at end of session