The necessity for a transmission in an automobile is a result of the characteristics for the internal-combustion motor. Motors usually run over a selection of 600 to about 7000 rpm (though this changes, and is typically less for diesel engines), whilst automobile's tires rotate between 0 rpm and around 1800 rpm.
In addition, the system provides their finest torque and energy outputs unevenly throughout the rev number resulting in a torque band and an electric band. Usually the best torque is needed as soon as the car is going from rest or traveling slowly, while greatest energy becomes necessary at high speed. Therefore, something is needed that transforms the engine's output so that it can supply large torque at reduced rates, but in addition operate at highway rates because of the engine still operating within its limitations. Transmissions do this transformation.
a drawing contrasting the ability and torque groups of a "torquey" engine versus a "peaky" one
The dynamics of an automobile differ with speed: at low rates, acceleration is bound because of the inertia of vehicular gross mass; while at cruising or maximum speeds breeze opposition could be the dominant barrier.
Most transmissions and gears used in automotive and truck applications are found in a cast-iron instance, though more often aluminum can be used for lower weight especially in cars. You will find usually three shafts: a mainshaft, a countershaft, and an idler shaft.
The mainshaft stretches outside of the case in both guidelines: the input shaft towards system, in addition to production shaft towards the rear axle (on backside wheel drive vehicles. Front-wheel drives generally speaking possess engine and transmission mounted transversely, the differential being part of the transmission installation.) The shaft was suspended by the main bearings, and it is separate towards feedback end. During the aim of the separate, a pilot bearing keeps the shafts together. The gears and clutches ride on mainshaft, the gears being able to switch relative to the mainshaft except when engaged by the clutches.
Handbook transmissions often showcase a driver-operated clutch and a movable equipment stick. Many automobile guide transmissions let the motorist to pick any forward gear ratio ("gear") at any time, however some, like those commonly attached to motorbikes and some kinds of rushing vehicles, only allow the motorist to choose the next-higher or next-lower equipment. This sort of transmission is sometimes labeled as a sequential handbook transmission.
In a manual transmission, the flywheel are connected to the engine's crankshaft and spins along side it. The clutch disk is within between the stress dish therefore the flywheel, and is presented contrary to the flywheel under some pressure from stress dish. Whenever motor are operating together with clutch was involved (i.e., clutch pedal up), the flywheel spins the clutch plate and therefore the transmission. As the clutch pedal try depressed, the throw out bearing are activated, which in turn causes the pressure plate to end applying pressure towards clutch disk. This will make the clutch plate avoid getting power from the system, so your gear may be shifted without harming the transmission. If the clutch pedal try released, the throw out bearing is deactivated, together with clutch disk is once again held up against the flywheel, allowing it to start getting energy from system.
Handbook transmissions are described as equipment ratios that are selectable by locking chosen gear sets to the result shaft inside transmission. Alternatively, most automated transmissions function epicyclic (planetary) gearing influenced by brake groups and/or clutch bundle to select gear ratio. Automated transmissions that allow the driver to manually choose the present equipment are known as manumatics. A manual-style transmission managed by computer is actually labeled as an automated transmission instead of an automatic, even though no difference between your two terminology need-be made.
Modern automobile manual transmissions typically incorporate 4-6 forward equipment ratios and another reverse equipment, although customer vehicle manual transmissions are built with merely two and as numerous as seven gears. Transmissions for hefty vehicles and other hefty products often have 8 to 25 gears so that the transmission could offer both an array of gears and close gear ratios to help keep the motor operating into the power musical organization. Operating aforementioned transmissions usually use the exact same pattern of shifter action with one or several switches to engage the following series of equipment selection.
Unsynchronized transmission
Principal article: Non-synchronous transmission
Cherrier two-speed gear, circa 1900
The initial kind of a manual transmission is believed having been invented by Joe Clulow and mile Levassor in belated nineteenth century. This sort of transmission offered numerous gear ratios and, more often than not, reverse. The gears are typically engaged by sliding them to their shafts (thus the term shifting gears), which required mindful time and throttle manipulation whenever moving, therefore the gears could be rotating at about the same speeds when involved; usually, tooth would will not mesh. These transmissions are known as sliding mesh transmissions or sometimes crash boxes, due to the difficulty in altering gears therefore the noisy grinding sound that often followed. Newer guide transmissions on vehicles have all gears mesh always and generally are described as constant-mesh transmissions, with "synchro-mesh" being an additional refinement of continual mesh concept.
In both types, a particular equipment combination is only able to be engaged if the two section to activate (either gears or clutches) are at exactly the same speed. To move to a higher equipment, the transmission are invest basic and also the motor permitted to decelerate before transmission areas for the following equipment are in a proper speeds to activate. The vehicle furthermore slows while in basic and therefore slows more transmission areas, and so the time in natural is dependent on the class, wind, also these types of factors. To move to a diminished equipment, the transmission is place in neutral plus the throttle is employed to increase the engine and therefore the relevant transmission parts, to complement speeds for engaging next lower equipment. Both for upshifts and downshifts, the clutch is revealed (engaged) while in basic. Some drivers utilize the clutch limited to starting from an end, and changes were finished without clutch. More motorists will depress (disengage) the clutch, shift to basic, after that engage the clutch momentarily to make transmission areas to fit the engine speed, then depress the clutch again to move to another equipment, an activity called dual clutching. Dual clutching is a lot easier to have smooth, as rates which are close although not very matched should speed up or delay only transmission components, whereas using the clutch involved towards motor, mismatched speeds are combat the rotational inertia and energy of this engine.
Despite the fact that vehicle and lighter truck transmissions are now actually almost universally synchronized, transmissions for hefty trucks and equipment, motorcycles, as well as devoted racing are often not. Non-synchronized transmission design are used for several reasons. The friction product, such brass, in synchronizers is much more prone to don and breakage than gears, that are forged metal, and ease of use of the procedure gets better dependability and reduces price. Besides, the entire process of moving a synchromesh transmission is slow than compared to moving a non-synchromesh transmission. For race of production-based transmissions, occasionally half one's teeth on dog clutches were eliminated to speed the shifting techniques, at the expense of greater wear.
High quality trucks often use unsynchronized transmissions, though army vehicles normally have synchronized transmissions, enabling untrained workers to use them in emergencies. In america, traffic safety principles refer to non-synchronous transmissions in classes of bigger commercial motor vehicles. In European countries, heavy-duty vehicles incorporate synchronized gearboxes as standard.
Similarly, most modern motorcycles use unsynchronized transmissions: their particular lower gear inertias and higher strengths mean that pushing the gears to alter rate is certainly not damaging, plus the pedal run selector on modern-day motorcycles, without natural position between gears (except, commonly, 1st and 2nd), isn't conducive to using the lengthy shift period of a synchronized gearbox. On bicycles with a 1-N-2(-3-4...) transmission, it's important either to quit, delay, or synchronize gear rates by blipping the throttle whenever shifting from 2nd into 1st.
Synchronized transmission
Top and side view of the manual transmission, in this instance a Ford Toploader, utilized in automobiles with exterior flooring shifters.
Modern manual-transmission cars were fitted with a synchronized equipment field. Transmission gears are often in mesh and rotating, but gears on one shaft can freely turn or perhaps locked to your shaft. The fastener for an equipment contains a collar (or dog collar) regarding shaft which will be able to slip laterally to make certain that teeth (or dogs) on its internal area bridge two circular bands with teeth to their outer circumference: one attached to the equipment, anyone to the shaft hub. If the bands is bridged because of the collar, that equipment is rotationally closed towards shaft and find the result speed of the transmission. The gearshift lever manipulates the collars utilizing a set of linkages, so organized so one collar might be allowed to lock only one equipment at anyone time; whenever "moving gears", the locking collar from 1 gear try disengaged before compared to another try engaged. One collar frequently serves for two gears; sliding in a single movement chooses one transmission speeds, when you look at the other direction selects another.
In a synchromesh gearbox, to precisely match the speed associated with gear to that particular associated with shaft once the equipment is engaged the collar at first applies a force to a cone-shaped brass clutch connected to the equipment, which brings the speeds to match before the collar locking into put. The collar are avoided from bridging the securing bands as soon as the rates are mismatched by synchro rings (also referred to as blocker bands or baulk rings, the latter becoming spelled balk into the U.S.). The synchro ring rotates somewhat as a result of the frictional torque from the cone clutch. Within place, your dog clutch is avoided from engaging. The brass clutch band gradually causes parts to twist at the exact same speeds. If they do twist similar speeds, there is no more torque through the cone clutch as well as the puppy clutch try permitted to fall under engagement. In today's gearbox, the action of all of the of the elements is so smooth and quick its barely noticed.
The modern cone system originated by Porsche and launched when you look at the 1952 Porsche 356; cone synchronisers had been called Porsche-type for many years next. During the early 1950s, only the second-third move was synchromesh generally in most automobiles, calling for only a single synchro and a simple linkage; motorists' guides in automobiles suggested that when the motorist had a need to shift from 2nd to very first, it had been best to come to a whole stop then shift into first and start up once again. With continuing elegance of mechanical development, totally synchromesh transmissions with three speeds, after that four, after which five, became universal because of the 1980s. Many modern-day handbook transmission automobiles, specially activities automobiles, today offering six speeds. The 2012 Porsche 911 provides a seven-speed manual transmission, with the seventh equipment meant for cruising- top speed becoming accomplished on sixth.
Reverse equipment is normally not synchromesh, as discover only one reverse gear inside regular automotive transmission and changing gears into reverse while going just isn't required---and frequently highly unwelcome, especially at highest forward speeds. Furthermore, the typical way of supplying reverse, with an idler equipment sliding into location to bridge exactly what would otherwise become two mismatched forward gears, was fundamentally much like the process of a collision box. On the list of cars which have synchromesh in reverse will be the 1995--2000 Ford Contour and Mercury Mystique, '00--'05 Chevrolet Cavalier, Mercedes 190 2.3-16, the V6 prepared Alfa Romeo GTV/Spider (916), certain Chrysler, Jeep, and GM products which use the brand new endeavor NV3500 and NV3550 models, the European Ford Sierra and Granada/Scorpio designed with the MT75 gearbox, the Volvo 850, and pretty much all Lamborghinis, Hondas and BMWs.
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Toyota H41 H42 H50 H55F Transmission Repair Manual | eBay
Find best value and selection for your Toyota H41 H42 H50 H55F Transmission Repair Manual search on eBay. World's leading marketplace.
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H42-H55F TRANSMISSION SWAP - Part II: Trucks & 4x4 : Remove Transmission Output Shaft Cover and Nut Just take off the 6 bolts holding the cover on and
- **Safety Gear**
- **Gloves**: Protects your hands from sharp edges and contaminants.
- **Safety Glasses**: Shields your eyes from debris and fluids.
- **Basic Tools Required**
- **Socket Wrench Set**: For removing and tightening bolts. Use the correct size socket to avoid stripping bolts.
- **Torque Wrench**: Ensures bolts are tightened to the manufacturer's specifications, preventing over-tightening or under-tightening.
- **Screwdrivers (Flathead & Phillips)**: Useful for removing any covers or panels that may obstruct access to the gearbox.
- **Pliers**: For gripping and manipulating small parts or clips.
- **Hammer**: May be needed to gently tap components into place if they are stuck.
- **Extra Tools Required**
- **Gear Puller**: If the rocker arms are stuck, this tool helps to pull them off without damaging them.
- **Cleaning Brush**: To clean any debris or old grease from the components.
- **Magnet Tool**: To retrieve dropped screws or small parts in hard-to-reach areas.
- **Steps to Access Rocker Arms**
- **Disconnect Battery**: Always disconnect the negative terminal to prevent electrical shorts.
- **Drain Transmission Fluid**: Use a pan to catch the fluid when removing the drain plug. This helps to avoid spills.
- **Remove Transmission Cover**: Use a socket wrench to unbolt the cover. This may require removing other components like the starter or exhaust.
- **Inspect Rocker Arms**
- **Visual Check**: Look for signs of wear or damage like cracks or excessive wear on the rocker arms.
- **Replacement Parts**
- **New Rocker Arms**: If they are worn or damaged, they should be replaced to ensure proper engine performance.
- **Gaskets and Seals**: Often, old gaskets will leak when reassembled. Replace them to prevent leaks.
- **Installation of New Rocker Arms**
- **Position New Rocker Arms**: Align them according to the manufacturer's specifications. Ensure they are seated properly.
- **Tighten Bolts**: Use a torque wrench to tighten bolts to the recommended torque settings found in the service manual. This prevents future issues.
- **Reassemble Gearbox**
- **Reattach Transmission Cover**: Ensure all bolts are tightened evenly.
- **Refill Transmission Fluid**: Use the correct type of fluid as specified in the manual.
- **Final Checks**
- **Reconnect Battery**: Ensure everything is secure before reconnecting.
- **Test Drive**: Check for any unusual noises or issues after reassembly.
- **Maintenance Tips**
- **Regular Inspections**: Check rocker arms periodically to catch any issues early.
- **Fluid Changes**: Regularly change transmission fluid to extend the life of components.
rteeqp73
Below is a focused, step‑by‑step procedure for inspecting and repairing worn cylindrical bores (case bushings / “cylinder walls”) in Toyota H41 / H42 / H50 / H55F manual gearbox cases. This covers diagnosis, removal of old bushings, installation and finishing of new bushings/sleeves, tools used, safety, and common pitfalls. Refer to the Toyota service manual for exact torque and dimensional specs for your exact model/year — do not guess final clearances.
Summary of scope
- “Cylinder walls” in this context = the cylindrical bearing/bushing bores in the transmission case (bushings for input/output/lay shafts, reverse idler, etc.), not engine cylinders. These are bronze/white-metal bushings or pressed‑in sleeves that support shafts. The job: remove gearbox, assess bores, replace/renew bushings or ream to proper ID, check clearances, reassemble.
Tools & supplies
- Full metric mechanic hand tool set (sockets, ratchets, extensions, hex/torx as required)
- Engine/transmission jack or hoist, transmission stand
- Drain pan, fluid pump, rags, cleaning solvent, degreaser
- Bench vise with soft jaws or dedicated gearbox stand
- Hydraulic / arbor press (2–10 ton) or shop press
- Bushing removal drivers / drift set and punch set
- Bushing install drivers (flat/stepped drivers sized to bushing OD) or bronze bushing driver kit
- Drill press (optional, for pilot holes) and/or smallest drill for alignment pins
- Precision reamers (hand/straight-fluted or machine reamer) sized to bushing ID and shaft journal, or line/boring reamer if machining case bores
- Reamer pilot if required, cutting oil/lubricant
- Dial bore gauge or inside micrometer, telescoping gauges, micrometer for shaft journal measurement
- Torque wrench, feeler gauges, Plastigage (for trial check), anti-seize, Loctite if required
- Replacement parts: OEM bronze bushings / sleeves (specific to H41/H42/H50/H55F), new oil seals, bearings, gaskets, snap rings as needed
- Cleaning brushes, compressed air (caution), lint-free cloths
- PPE: safety glasses, gloves, hearing protection
Safety & setup
- Work on a flat stable surface with good lighting.
- Use proper lifting equipment for gearbox removal; never rely on jacks alone without stands.
- Disconnect battery before starting vehicle work.
- Drain gearbox fluid into a proper container and dispose/recycle per local regulations.
- Wear eye protection and gloves; avoid loose clothing around presses/rotating tools.
- Keep gearbox internals and bushings clean — contamination kills bearings.
Step‑by‑step procedure
1) Preparation and diagnosis (on vehicle or after removal)
- Drain gear oil and remove gearbox from vehicle following manufacturer procedure (shift linkage disconnected, driveshafts, crossmember, etc.).
- Clean external surface so you can inspect mating flanges and mark positions of shift levers/links for reassembly.
- On the bench, remove cover plates, shift forks, shift rails, shafts and gears per manual so you can access case bores. Keep parts organized in order.
- Visually inspect bores for scoring, ovality, discoloration (overheating), fretting and check for play by measuring shaft endplay and radial runout by moving shafts in and out of the bore. Excessive radial clearance or knocking indicates worn bushings.
2) Measure & decide
- Measure shaft journal diameters with a micrometer and measure bore ID with a dial bore gauge or inside micrometer to determine clearance.
- Compare to Toyota service manual tolerances. Typical worn clearance that requires replacement varies; if clearance exceeds spec or if surface is scored/grooved beyond repair, proceed to replace bushings or sleeve the bore.
- If the case bore itself (aluminum) is worn, you may fit oversize bushings, press-in sleeves, or in extreme cases send the case for machine work or replace the case.
3) Remove old bushings / sleeves
- Identify each bushing type and orientation (many have oil holes that must align).
- Use a drift and arbor press or bushing removal driver sized to the ID/OD and press out the old bushing from inside the case toward the outside. Support the case evenly — don't press on thin walls or flange faces.
- If bushing is seized, heat the case locally with an induction heater or oven (careful — don’t exceed safe temps) to expand the case, or use a bushing puller that grips the OD. Avoid hammering the case directly.
- Clean the bore and remove burrs with a deburring tool. Inspect the bore ID and surrounding material for cracks or thin walls.
4) Prepare for installation
- Obtain the correct OEM replacement bushings (or quality aftermarket equivalents) sized for the gearbox model. Confirm outer diameter and required interference press fit spec in manual.
- If the new bushings are interference fit, you can heat the case mildly or heat the bushing slightly (oil-heat method recommended 80–100°C — follow bushing supplier guidance) to ease installation; do not use direct flame.
- Clean the bushing OD and bore; apply light assembly lube or engine oil to help alignment.
5) Install new bushings
- Use a proper driver sized to the bushing OD and a hydraulic press. Press the bushing straight in until it seats flush with the machined shoulder or to the specified depth. If bushing must be installed to a register, confirm orientation so any oil holes align with oil passages.
- Use gentle, even pressure. Avoid cocking the bushing; if resistance changes, back off and realign the driver.
- For very small bores, you may use a manual arbor press and a drift; for large bores use shop press.
6) Ream to final size / hone the ID
- Most replacement bushings require final reaming/honing to the exact shaft clearance. Use the correct reamer size recommended (ream to a target ID that gives proper clearance with the shaft).
- Install a pilot or use a reamer designed for bronze bushings. Use cutting oil; run the reamer smoothly with light feed. If hand reaming, ensure reamer is square and rotate only forward with steady pressure — don’t reverse or rock.
- Typical target radial clearance might be on the order of 0.02–0.08 mm depending on the bearing; DO NOT rely on these numbers for final — use factory spec. The goal is a smooth mirror finish without excessive clearance.
- After reaming, deburr edges with a fine file, clean thoroughly and blow out chips (use low-pressure air, after wiping with solvent).
- If using line reaming for mating case halves, make sure the halves are aligned on dowels and ream in assembled condition per manual.
7) Check fit and clearance
- Insert shaft and spin by hand. Check for smooth rotation, no tight spots and correct endplay.
- Use plastigage or measure with micrometer to confirm radial clearance where applicable.
- Verify oil hole alignment and that oil galleries are unobstructed.
8) Reassembly
- Clean both case halves, apply new gaskets/seals or use the specified RTV, and assemble per manual. Torque all bolts to spec in the correct sequence.
- Replace all seals, bearings and snap rings where recommended. Replace any worn gears, synchros, or shift parts found during disassembly.
- Refill with the proper grade and amount of gear oil as specified.
9) Test
- Bench test shifting through gears to ensure smoothness.
- Reinstall in vehicle, connect linkage, driveshafts, and crossmember. Torque to spec.
- On road test: check for leaks, unusual noise, proper engagement. Recheck fluid after initial run-in per manual.
How the tools are used — practical notes
- Arbor/Hydraulic press: used to push out old bushings and press new ones in. Support case on blocks so force transfers to bushing OD and not thin walls. Press slowly and evenly.
- Reamer: used to finish the bushing ID to precise size. Use pilot to keep it concentric. Rotate at recommended RPM, apply cutting oil, and advance steadily. Back out carefully only when clear of the cut. For machine reaming (drill press), clamp case so it won’t move & ensure concentricity.
- Dial bore gauge / inside micrometer: measure bore in several positions (top/bottom, 90° increments) to detect ovality and confirm dimension.
- Micrometer: measure shaft journals to compute required final bore and clearance.
Replacement parts typically required
- OEM bronze bushings/sleeves for input/output/lay shafts (model-specific)
- Oil seals at output/input shafts and tail housing
- Bearings and snap rings if out of spec
- Gaskets, sealant, and possibly new shims/spacers
- Gear oil
Common pitfalls and how to avoid them
- Reaming misalignment: always use pilot and ensure press/reamer is concentric with the bore; misaligned reaming ruins the case.
- Wrong reamer size: leads to too tight/tight clearance or too loose — always check the shaft journal and use manual specs before cutting.
- Pressing bushing in crooked: support case correctly and use a proper driver; stop and realign if it binds.
- Overheating or cracking the case: avoid direct open flame; heat slowly and evenly if thermal expansion is required.
- Not replacing seals/bearings: old seals compromise the job; replace all related wear items while apart.
- Skipping cleanliness: metal chips or grit left in the gearbox will cause rapid wear; clean thoroughly.
- Ignoring oil hole alignment: a bushing installed rotated incorrectly will starve oil passages.
- Exceeding case wall tolerance: if case material is too thin/worn or cracked, don’t attempt patch repairs — replace the case or have it professionally sleeved/line-bored by a machine shop.
When to send the case to a machine shop / replace it
- Excessive bore ovality or worn beyond the ability to fit a standard oversized bushing.
- Cracks in the case or material too thin around bores.
- If precision line reaming between halves is required and you lack the tooling — a machine shop can ream/line bore to perfect alignment.
Final notes
- Always follow the Toyota service manual for torque values, sequence, and any special procedures for your specific H41/H42/H50/H55F variant.
- If you are not experienced with bench reaming and press work, consider having the bushings installed and reamed by a machine shop — incorrect machining is expensive to fix.
No extra commentary.
rteeqp73
1) What the “cold start injector” is, and why it matters (theory)
- The cold start injector (cold‑start valve / cold‑enrichment injector) is a small solenoid‑operated fuel valve that adds extra fuel during cranking and the first seconds of warm‑up when the engine coolant/air temperature is below a threshold.
- It is an engine fueling device, not part of the H41/H42/H50/H55F gearbox. But engine cold‑enrichment directly affects engine torque, idle speed and combustion quality during warm‑up; those engine conditions change torque converter load and throttle‑linked hydraulic pressures, so a faulty cold start injector can produce poor cold shift quality, slipping, hunting or harsh shifts in an automatic H‑series transmission.
- Operation principle: a temperature switch (thermo‑time switch) or ECU closes when cold and during cranking, energizing the cold start injector. The solenoid lifts a needle/valve and meters a steady extra fuel flow into the intake for a fixed time, enriching the mixture until the engine warms. When open/stuck/blocked, the engine is either flooded (stuck open) or starved for cold enrichment (stuck closed), causing the observed driveability and consequent transmission symptoms.
2) Typical failure modes and how each affects gearbox behavior (theory)
- Stuck open (mechanical/solenoid fault or shorted control): continuous extra fuel → hard starting when warm, black smoke, high cold idle, flooded cylinder(s). Resulting excessive torque fluctuations or rich misfire can make the transmission shift harshly or slip until engine stabilizes.
- Stuck closed/blocked: no enrichment → long cranks, multiple start attempts, weak low‑temperature torque; low engine torque can delay or soften gear changes and may upset throttle‑pressure balance that controls shift timing.
- Intermittent electrical fault or wiring: unpredictable enrichment → intermittent cold misbehavior and inconsistent shift feel.
- Leaking nozzle/O‑ring: vacuum leak or dribble → rough idle and mixture error until warm, affecting shift behaviour similarly.
3) Ordered diagnostic procedure (theory + test order)
1. Visual inspection: check mounting, vacuum/fuel lines nearby, look for obvious leaks, cracked connector, corrosion. This helps separate mechanical/fuel leak vs electrical fault.
2. Symptom confirmation: verify cold‑only problem (cold start hard or flood) vs persistent problem. If fault only when cold, prioritize cold‑enrichment system.
3. Electrical check at connector: with meter, measure for continuity of injector coil (resistance spec typically a low ohm value — consult OEM spec for exact number). Check for voltage at the injector connector during cranking (requires assist/second person or starter engagement): the cold‑start control should energize during cranking if temp sensor indicates cold. If no voltage, suspect thermo‑time switch/wiring/ECU.
4. Functional fuel flow test (bench or on‑vehicle): remove the injector and crank to observe whether it sprays when energized. A stuck‑open injector will flow continuously; a stuck/blocked one will not spray. On‑vehicle, you can observe fuel dribble or odor.
5. Thermo‑time switch/temperature sensor test: measure its operation (open/closed) relative to coolant temp to verify it energizes injector only when cold.
6. Cylinder balance/spark checks if suspicious of flooding causing misfires.
7. If tests show injector bad (stuck, leaky, no flow but has drive voltage, coil OK) proceed to replacement.
4) Ordered removal and replacement (concise, practical theory + key actions in order)
1. Safety: relieve fuel system pressure and disconnect battery negative. Work in ventilated area, no sparks.
2. Access: locate cold start injector on intake manifold (near throttle or idle air control on older Toyotas). It’s mounted with one screw/clip and has a single electrical connector and a fuel feed line. Note orientation and O‑ring location.
3. Disconnect electrical connector and fuel feed line (have shop rag/plug to catch/plug fuel).
4. Remove mounting screw/clip and withdraw injector. Inspect O‑ring and mounting bore for varnish/deposits. Clean bore lightly; don’t damage injector seat.
5. Fit new injector (replace O‑ring), lubricate O‑ring with clean engine oil, seat injector, torque fastener to spec, reconnect fuel feed and electrical connector.
6. Reconnect battery, prime fuel system (turn ignition ON several times) and check for leaks.
7. Perform functional check: start cold and verify normal cold cranking and that the injector energizes only when cold (observe behavior/voltage during cranking). Verify improved idle and normal warm‑up behaviour.
8. Road test to confirm cold shift quality restored.
5) How the repair fixes the fault (mechanical/causal chain)
- If the injector was stuck open: replacing it removes the continuous extra fuel flow. That stops flooding, reduces rough idling and eliminates the excess torque spikes and combustion irregularities that upset torque converter loading and the hydraulic pressures the transmission uses for shift timing. Result: smoother, correct cold shifts and quicker normal shift behaviour as engine warms.
- If the injector was stuck closed or blocked: replacement restores intended cold enrichment so the engine cranks easily and produces expected torque during warm‑up. Proper torque and steady idle produce correct throttle/kickdown pressures and governor/TV balance in the H‑series gearbox, restoring correct shift points and preventing lazy or soft shifts when cold.
- If the issue was electrical/wiring: fixing wiring or the thermo‑time switch guarantees the injector is only energized for the correct duration. That returns fuel metering to specification during warm‑up and removes the variable load the transmission was compensating for.
6) Brief notes on transmission interaction (key theory points)
- H41/H42/H50/H55F automatics use hydraulic pressures modulated by throttle valve/kick‑down and governor speeds; engine torque/load influences hydraulic pressure and converter slip. Erratic torque or incorrect idle caused by cold‑enrichment faults changes those pressures and shift timing/quality. Correcting fueling re‑establishes predictable engine torque and thus predictable hydraulic behaviour in the gearbox.
7) Safety and verification checklist (short)
- No fuel leaks, correct connector seating, correct O‑ring used, electrical voltage present only during appropriate cold/crank window, cold start symptoms resolved, transmission shifts normal during warm‑up and after.
That is the ordered theory and practical repair logic.
rteeqp73