SEA-DOO GTX DI

PART 01Diagnostic — Power Loss After 25-Hour Rebuild

Context

The reframe from generic pre-launch to active diagnostic happened mid-conversation. End-of-last-season symptoms: 10–20% loss in both max RPM and top speed compared to baseline 2 years prior at purchase, plus maintenance light ON. The ski has been rebuilt — only ~25 hours on the rebuild, ~120 hull total. Storage is incidental to the diagnosis; the problem was already developing pre-storage.

The combined RPM-and-speed deficit is diagnostic. Pump slip would show RPM rising while speed falls — worn impeller, blown wear ring, cavitation all manifest as the pump losing load on the engine. Both falling together points upstream of the impeller, into the engine itself. This rules out the pump bearing / impeller / wear ring family of causes and focuses attention on the engine, fuel, air, and exhaust systems.

Hypothesis ranking — see DHL-002 for full structure

Diagnostic Hypothesis Log DHL-001 documents the engine-family identification (resolved: 2001 GTX DI, not 4-TEC supercharged). DHL-002 (to be opened at next active diagnostic session) will track the power-loss hypotheses with evidence as findings come in. Current ranking, derived from symptom pattern + 25-hour rebuild context:

1. MPEM in protect/limp mode from stored fault. Single hypothesis cleanly explains both symptoms + maintenance light. Resolves with scan. Highest priority because it's also the cheapest to verify.
2. Crank seal leak (PTO or magneto side). Classic two-stroke power-loss mode. Common rebuild shortcut if seals were reused. Indicator: plug color asymmetry between cylinders.
3. Air compressor wear (DI-specific). If reed valves not refreshed in rebuild, air rail pressure drops → mixture goes rich → power falls progressively. Plausible at 25 hours if rebuild scope was incomplete.
4. Cylinder glazing / rings not seated. Improper break-in by previous owner. Bluish smoke under load is the tell. Recoverable if caught early.
5. RAVE valves carboned/sticking. Lower probability at 25 hours but possible if running rich.
6. Exhaust restriction. Water-logged tuned pipe or collapsed muffler. Caps top end specifically.

Diagnostic procedure (in order)

1. DTC scan. See Tier 1 of shopping list. Note codes before clearing — clearing without fixing is masking.
2. Plug pull and color comparison. NGK ZFR4F-11. Cold engine. Pull both, photograph side by side under same lighting. Tan/light brown = healthy. Wet black = injector dribble or rich. Oily wet = compression/seal issue. White/blistered = lean / overheated. Asymmetric color across the two cylinders is the crank seal indicator.
3. Compression test, both cylinders. Cold engine, plugs out, DESS key disconnected (no fuel/spark), throttle WOT. Crank ~5 revolutions per cylinder, record peak. Record both numbers.
4. Air compressor audible. Plugs out, DESS off. Crank briefly. Listen for tick-tick-tick rhythm from the air compressor on top of the engine. Place finger over air rail Schrader (top of engine) during cranking — should feel pressure pulses.
5. Oil pump bleed verification. If oil tank ran dry over winter or after rebuild, the pump line MUST be bled before any start. Loosen bleed screw on oil pump, let oil flow until no air bubbles, retighten.

Acceptance for launch

Compression both cylinders within 10% of each other and ≥110 psi. // UNVERIFIED — service manual minimum needs OEM cross-check. No active DTCs after Phase 1 service. Air compressor audibly functional. Plugs visually symmetric in color after a brief run.

PART 02Pre-Launch Service

Standard de-winterization items, ordered to surface diagnostic information rather than just "service the unit." Items overlap with the diagnostic procedure above; this section is the destination if Part 01 came back clean.

Battery

1. Pull, bench charge to 100%. Resting voltage spec ≥12.6V after 12 hours off charger.
2. Load test should hold ≥9.6V under 50% CCA load for 15 sec.
3. Clean terminals, dielectric grease, snug terminals (do not gorilla-tighten lead posts).

Spark plugs (replace as part of pre-launch)

Spec: NGK ZFR4F-11, gap 0.043" / 1.1 mm. Source: EPA emission label affixed to ski (verified physical evidence).

Anti-seize light on threads. Torque to manufacturer spec — // UNVERIFIED — service manual reference needed. Plug-size class for this thread is typically in the 11–18 ft-lb range; do not torque from this guide alone, cross-check before final.

Fuel system

1. If fuel is >6 months old or stored on ethanol fuel, drain and replace.
2. Fresh fill: 91 octane non-ethanol preferred. Otherwise 87+ with marine stabilizer (Sta-Bil 360 Marine, PRI-G).
3. Inspect external fuel filter under airbox/electrical box. Replace if >2 years or unknown service history.
4. Check fuel lines at clamp points for cracking and swelling.

Oil injection (2-stroke specific)

1. Top off injection tank with XPS Synthetic 2-stroke or quality TC-W3 marine 2-stroke oil.
2. If tank ran dry over winter, bleed pump line before any start (see Diagnostic procedure).
3. Verify oil pump cable adjustment intact — throttle linkage pulls the oil pump arm; out-of-sync = high-RPM oil starvation.

RAVE valves (highly recommended on a stored DI)

RAVE = variable exhaust valves on each cylinder. They carbon up, especially over storage. Cleaning is the highest-impact pre-launch task on a 951 DI.

1. Remove the two RAVE valve covers (one per cylinder, exhaust side of each head).
2. Note orientation, withdraw the valve assembly.
3. Inspect bellows (rubber diaphragm) — replace if torn or stiff.
4. Clean valve face and exhaust port with carb cleaner and a soft brass brush. Do not score the cylinder wall.
5. Reinstall, torque cover bolts to spec. // UNVERIFIED — service manual torque needed.

Drive train

• Pump shaft: spin by hand (lanyard removed). Smooth rotation, slight resistance from carbon ring is normal. Roughness or grinding = pump bearing failure, do not launch.
• Impeller: inspect through intake grate. Chips/dings = lost top end.
• Carbon ring / drive shaft seal: axial play up to ~1mm OK, more = service the seal.

First start on trailer

1. Connect garden hose to flush adapter, hose OFF.
2. Start engine. Within 15 seconds, water ON to medium flow.
3. Idle 60–90 seconds. Listen for: smooth idle ~1450 RPM, even pulse from pisser, no metallic knock, no fuel smell at airbox.
4. Some 2-stroke smoke at startup is normal (oil-injection priming). Persistent heavy smoke = oil pump over-pumping or injector stuck open.
5. Water OFF first. Engine OFF within 10 seconds. Brief 3500 RPM blip on shutdown.

On-water shakedown

1. First 5 min: idle out of no-wake, cruise at ~3500 RPM, check bilge for water intrusion at the dock.
2. Next 5 min: half-throttle pulls (5500–6000 RPM), listen for misfire under load.
3. Then: brief WOT pull, watch for fuel cut, knock, or top RPM short of spec.
4. After ride: flush 2 min on hose, drain plugs out for storage.

Top speed sanity check: ~60 mph factory // UNVERIFIED — should source from period reviews or BRP spec sheet. 5+ mph short = injector, RAVE, or compression issue.

PART 03Seat Cover Replacement

Cover only — foam to be reused pending press-test verification once cover is stripped. The 1997–2002 GTX seat shape is shared across the entire pre-2003 GTX generation (RFI / DI / non-RFI all use the same body), which widens sourcing options. Avoid any kit listed for "2003+ GTX" or "GTX 4-TEC" — completely different seat, will not fit.

Brand options

Recommended path

Foam press-test (do this before ordering)

1. Pull seat from hull (rear latch, lift forward — should be 30 seconds).
2. Strip old cover, photographing staple pattern and edge wrap before destroying it.
3. Press foam firmly with thumb in main riding zone — should spring back fully within a second or two.
4. Look for dark staining or moisture on the foam underside (water enters through staple holes).
5. Check edges and corners for crumbling or tears.

If foam passes: cover-only path proceeds, ~$200 budget.

If foam fails: add 3/4" closed-cell marine foam (~$60) and 3M Super 77 spray adhesive (~$10) to order. Total ~$270.

Install

1. Pre-warm new cover in sun for ~30 min — pliable vinyl stretches and conforms cleanly.
2. Lay cover centered on seat, anchor center seam first with 4–6 staples.
3. Work outward symmetrically. Pull tension front-to-back and side-to-side, watch for wrinkles in the riding zone.
4. Use 1/4" stainless monel staples in pneumatic stapler. Do not use galvanized — they rust through and stain the cover from beneath in a couple seasons.
5. Hog rings on the inside lip where the cover wraps under the seat pan — staples don't bite well on that radius.
6. Trim excess with sharp utility knife after final stretch.

Time: 1 hr cover-only, 2–3 hr with foam replacement. Solo job.

PART 04Shopping List

Tier 1 — Mandatory for confident launch

Tier 2 — Strongly recommended (while inspecting)

Tier 3 — As needed

Minimum (Tier 1 only): ~$50–100. Tier 1+2 with seat cover: ~$300. Full session including scan tool: ~$500.

PART 05References & Sources

Verified physical evidence (primary sources)

• EPA emission label — affixed to ski; engine family 1BCXM.9514CD, displacement 951.2 cc, emission control DFI, idle spec 1450 ± 50 RPM, plug NGK ZFR4F-11 / 0.043" gap, power 93 kW
• Seat tag — "GTX DI" model identification at point of manufacture
• Michigan boat registration (verified 2026-04-28) — HIN ZZN39747A101, Watercraft Decal 6052920, expiration 31-Mar-2028

Items requiring OEM cross-check

• // UNVERIFIED — Spark plug torque (cross-check against Sea-Doo 951 DI service manual)
• // UNVERIFIED — Compression spec OEM minimum (field range 115–135 psi recalled; service manual minimum needed)
• // UNVERIFIED — RAVE valve cover bolt torque
• // UNVERIFIED — Air rail pressure spec
• // UNVERIFIED — Top speed factory spec (~60 mph recalled, period review citation needed)
• // UNVERIFIED — External fuel filter, RAVE bellows, air compressor kit, crank seal kit part numbers

System reference documents (from substrate)

• METHODOLOGY.md — guide rendered against v1.2 (Principle 8 reflected in process). Note: canonical fetch from this session returned v1.1; v1.2 reconstructed via SESSION-PRELUDE.md companion reference. Surface as Class 2 substrate failure for Sam's resolution.
• SESSION-PRELUDE.md v1.0 — fetched cleanly, served as v1.2 methodology reconstruction source

Diagnostic Hypothesis Logs for this equipment

• DHL-001 — Engine family identification (status: converged). Retroactive log of 4-TEC supercharged hypothesis abandonment in favor of 951 DI two-stroke. Includes lessons-captured section on the failure pattern that motivated the DHL artifact format.

Document history

• v0.1 (current, draft) — Initial render against METHODOLOGY.md v1.2 (companion-reconstructed) and template v1.0. HIN verified from MI registration as ZZN39747A101, replacing chat-conversation transcription path of A181 → A1?1 → A101. Includes retroactive DHL-001 documenting the 4-TEC supercharger wrong turn that occurred earlier in the session. Many specs marked // UNVERIFIED pending OEM service manual cross-check; this is intentional — the v0.1 milestone was substrate format validation, not OEM verification completion. v0.2 should resolve all UNVERIFIED items via service manual access.