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DIY Toyota V6 MZFE Fuel Injector Replacement

Hardlymoving writes about do-it-yourself automobile maintenance on various makes and models.



The 3.0 liter V6 MZFE engine is shared with the Toyota Camry, Avalon, RAV4, Solara and Lexus RX300 & ES300. The steps in this instruction can be used with the fore mentioned models with minor variations. The introduction of VVT (Variable Valve Timing) technology with late model MZFE engines resulted in the deletion of EGR (Exhaust Gas Recirculation) components attached to the intake runner. Since the V6 is transversely mounted with the intake runner (manifold) wrapped over the right bank of the engine, the intake runner must be removed to gain access to the three right bank injectors. This article will describe in detail the steps in replacing fuel injectors for a Lexus RX300 V6 MZFE engine with refurbished bench cleaned injectors. Toyota injectors rarely outright fail that a good off-engine injector cleaning job cannot correct. They can be professionally re-serviced with approximately a one week turn—around time or can be core exchanged at a price significantly less than a new injector. Adding fuel injector cleaner to your gas tank or obtaining fuel injection cleaning services may help restore some lost performance; however, it is no substitute for ultrasonic cleaning, filter screen replacement, solenoid OHM testing and multi-injector pattern testing—all things that cannot be performed with the injectors on the car. With refurbished injectors, expect lower emissions, smoother engine operation, improved performance and fuel economy.

Although Toyota fuel delivery systems (Fuel pump regulator, filter, fuel injectors) tend to be trouble free well over 100k miles, there will come a time when the pump, filter and the injectors will show signs of fatigue or lacking in peak performance. With extended use, the injectors will build up fuel varnish deposits on the injector’s valve or orifice that restricts consistent fuel flow resulting in poor fuel atomization. This disruption in the injector’s fuel vapor pattern will cause the engine to 1. run too rich or lean 2. idle poorly 3. increase fuel consumption 4. accelerate more slowly 5. create engine knock under load.

For the time and labor involved in replacing injectors, consider replacement of the spark plugs, coil packs or ignition wires for peace of mind. The absence of the intake runner allows easy access to these hard-to-get-to parts with the intake on. With a high mileage aged car, replacement of the fuel pump along with the fuel filter should also be considered. A less than optimal fuel pump combined with a partially clogged fuel filter may work fine at idle but can exhibit erratic pressure and fuel flow under load. Again, with old, high mileage cars, my preference is to spend time in replacement in lieu of testing—even though acceptable performance parameter test results may be indicated today, failure could happen weeks or months into the future (not years) and again, involve in more time repeating diagnostic testing.

Fuel Injector Technical Replacement Overview

The primary focus of this job is to remove the intake runner (manifold) to gain access to the right bank fuel injectors. Approximately 80% of this job will be focused on that task. To remove the intake runner, the air filter box and throttle body assembly must removed with all its electrical fittings, connections, vacuum tubes and coolant hoses. The remaining task details are commonly employed with most fuel injected gasoline cars. Expect to spend upwards of 6 hours to complete this job. The most difficult task item is removing the 14mm bolt securing the intake runner to the intake support bracket. This bracket is butted approximately 1 inch from the firewall and has a curved lip edge making it impossible to mount a box wrench. The tension on this bolt can be relieved using a flex head 3/8” foot long break bar attached to a 14mm socket. With these tools, the socket and bar can be squeezed between the firewall and bracket. The socket can then be fitted on to the bolt by non-sight finger feel. Once the bolt tension is relieved, a 14mm ratcheted box wrench may be fitted parallel with the bracket and attached to the bolt head. This allows 1 to 2 click turns on the wrench. The bolt will eventually pass the bracket lip allowing the box wrench to move beyond 2 clicks.

Tools Required

Metric sockets (10mm, 12mm, 14mm), box wrenches, 3/8” short breaker bar, ratchet extensions, needle nose pliers, needle nose hose pliers (rounded tips for grasping hoses), 3/8” metric hex bit sockets, long breaker bar to gain enough torque to remove the hex head bolts securing the intake runner.

Other Things: Silicone Spray and Penetrating Oil Spray cans. Use these to remove hoses that are fused to their fittings.

Remove the Air Filter Box Assembly

Detach the two electrical fittings and the Air Tube

Loosen the Air Hose Clamp, detach the Air Filter Box Spring Clips.

Detach the Air Intake Hose from the Air Filter Lid

Remove the Air Filter

Unbolt the three bolts securing the lower Air Filter box to the Car Frame

Remove the Air Filter lower Air Filter Box.

Remove the Air Intake Hose from the Throttle Body

Loosen the two Hose Clamps for the two air hoses attached to the throttle body

Remove the Air/Vacuum Hoses from the throttle body

Wiggle the Intake hoses off the Throttle Body

Remove the Throttle Body

Detach the throttle body cables (rotate throttle linkage clockwise and remove cable attachment point)—then unbolt the right side throttle cable bracket. For the Cruise Control Cable (left side), loosen the top most adjustment nut then remove the cable attachment)

Detach the two coolant hoses at the bottom of the Throttle Body.

Detach vacuum hose.

To the right of the throttle body inlet port, disconnect the electrical fitting.

Behind the Throttle body, remove the 12mm bolt that secures the Throttle body to a support bracket.

Remove the three 12mm nuts securing the throttle body to the intake manifold. (Use a 3/8” 12mm socket attached to a socket wrench and an 8” extension)

Remove the Throttle body from the Intake Runner. Remove the two remaining upper vacuum hoses. Tilt the Throttle body, bottom side up, and detach the last coolant hose.

Remove the Throttle body gasket.

Detach Intake Runner hoses, ground strap & support bracket bolt

Detach vacuum hoses.

By the left rear portion of the intake runner, remove the ground strap nut, detach the upper and lower vacuum hoses and remove the PCV value connection from the valve.

Unbolt the horn mount.

Behind the intake runner, reach round from the right side and remove the 10mm ground strap.

Using a 12" swivel head breaker bar attached to a 14mm socket, from the left side of the intake runner, squeeze the socket and breaker bar behind the intake runner support bracket. Use your right hand, coming in from the right side of the intake runner, to position the 14mm socket onto the support bracket bolt. Break the tension on the bracket bolt—then remove the breaker bar. From the right side of the intake runner, position the 14mm ratcheted socket wrench virtically with the support bracket, and begin loosening the support bracket bolt. (yes, this is a time consuming, arduous task)

Remove VSV and Other Vacuum Control Device Bracket

Disconnect the front bank Fuel Injector electrical connectors.

Remove the two 10mm nuts that secures the VSV (vacuum switch valve) and other vacuum control devices rail. The rail can then lifted and moved away from the front injectors.

Unbolt and Remove the Intake Runner

Two 12mm nuts and two hex bolts secures the intake runner to the engine. Use the hex bolt sockets attached to a long handle socket wrench or breaker bar to relieve the tension on the hex bolts. Ensure the hex bolt socket is mounted square inside in the bolt hex opening to prevent slippage. These bolts are on extremely tight. The outside nuts are not as tight and can be easily removed.

After the bolts and nuts have been removed, lift the intake runner clear of the outside mounting studs and lift out the intake.

Remove the Fuel Injectors

The left and right engine banks of the MZFE engine have two fuel injector rail mounts with each rail securing 3 injectors. Both rails share a fuel line that is in series. Two 10mm long bolts secures each injector rail to the cylinder head. A bango bolt (a perforated hollow bolt) links the fuel line feeding fuel from the rear rail to the front rail. A 12mm bolt secures the rear rail to the engine head.

Before removing the fuel injectors from the rails, apply compressed air to the base of each injector to clear away dust and debris. Afterwards, apply silcone or penetration oil at the based of each injector to ease injector removal.

Place a rag under the bango bolt to capture fuel leakage when loosening the bango bolt. Loosen, but do not remove, the bango bolt.

Remove the four 10mm rails bolts and the 12mm rear rail mount bolt.

Gently pull and wiggle the injector rail until the injectors pull out attached to the fuel rail.

Flip the rail with the injectors pointing up and lubricate where the injector meets the rail.

Gently twist and pull each injector out of the fuel rail.

Using a Q tip lightly lubricated with oil, clean up any debris in and around the injector port holes both in the rail and in the engine block.

Install the new injectors

Lightly lubricate the injector's base rubber seal and upper O rings with silicone spray lubricant.

Twist in the new injectors into the engine.

Apply a light coat of silcone spray on the injector rail's injector mounting ports.

Line up the rail's injector mounting ports with the top of each injector and press on the fuel rail. Applying pressure on the rail while twisting each injector will ease installation.

Re-install the 4 10mm injector rail bolts. The tightening of the bolts with further push the top of each injector into the rail's injector port holes.

Re-bolt the rear injector rail and re-torque the bango bolt to the front injector rail.

Post injector testing

Before putting everything back together, perform a fuel leakage test.

On the 99 RX300 and future toyota model cars, fuel is 'looped' back to the fuel tank/pump with any unused fuel. With this design, any air in the fuel line will be purged by getting pushed back to the fuel tank. By setting the ignition on (without starting the engine), the fuel pump will be activated. Check for any injector fuel leaks where the injector meets the fuel rail. If the injector O rings are not properly seated in the rails, the injector(s) will leak. Also check that the bango bolt for leakage. The copper or aluminum crush washers may require replacement.

Putting it all back together

All parts should be re-installed in the order they were removed. The most difficult task would be re-bolting the 14mm nut that secures the intake runner to the support bracket. The easiest way is to mount the intake runner on the mounting studs (with no nuts or bolts) and position the runner until the nut is square with the intake runner threads.

Since the rear engine bank access is no longer hindered by the intake runner, consider replacing the ignition wires (older V6 models with 1 coil pack per 2 cylinders), coil packs (one coil per cylinder) and the spark plugs. It will be significantly easier to replace them now rather than a few thousand miles in the future. The probability of failure may be high especially when combining high mileage with age.

Complete Fuel System Service

Between 150,000 to 200,000 miles, the fuel filter may be partially clogged and the fuel pump may not be putting out adequate pressure when the engine is under load. In any of these conditions, a fuel filter and pump replacement should be considered. With new injectors, there will be a noticeable improvement in idle, but a new filter with a pump will restore power.

Starting in 1999 with certain Lexus models and in 2000 with some Toyota models, the fuel filter was integrated into the fuel pump regulator situated inside the fuel tank. In the RX300, the fuel filter takes up almost half the interior space of the regulator assembly. Aside of this change, along with a fuel return line connected to the regulator, the fuel pump replacement is not that much different than the old regulator design.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: How many hours would you estimate for a rookie to complete replacing their fuel injector?

Answer: 8 hours