For the benefit of future readers of the forum, my question today is very specific regarding the ECM fuel injector circuitry.

I am writing with regards to a 1992 ES300 which I have owned since new.

Specifically, my problem is the car is currently delivering extremely poor fuel consumption - in the vicinity of 15mpg (US gallons) around town, and/or 17.5mpg (British gallons).

My 20 year old daughter mostly drives the car nowadays to and from university, like most 20 years tend to do.

My daughter has quite an emotional attachment to this ES300, given she came home from hospital in it the day after she was born, and as you might imagine, she's grown up in the car etc etc.

As you can see in my first photo, the car has been kept in immaculate condition. I am very fastidious regarding all my cars and motorbikes.


This is the engine bay - sans beauty plate - after recently refurbishing the upper and lower manifolds, along with new OEM injectors and connector wiring etc


I'm hoping this thread will help future readers also track down hard to diagnose fuel metering issues for the 3VZ-FE engine.

Before I continue, here's the list of brand new parts which have been applied to this engine since July 2022 - some 4 months ago at the time of writing.

1 x OEM Denso distributor, cap, and rotor

1 x OEM set of spark plug leads

2 x OEM Denso oxygen sensors

1 x OEM Denso set of "twin tip" iridium spark plugs

1 x OEM iginition coil

1 x OEM ignition module

1 x OEM set of brand new Denso fuel injectors (all six measure at exactly 62cc per 15 seconds of fuel under testing)

1 x OEM set of new injector wiring connectors

Further, in 2019 I fitted a new OEM Power Steering pump, along with a new water pump, timing gear, and a new oil pump etc.

Also, recent compression testing showed 5 of the 6 cylinders delivered 170psi, and Number One cyclinder deliver 163psi - so the engine is fundamentally very good inside.

And yet, despite all this... having tested voltage between the E1 to OX1 and OX2 connectors in the ODB1 data link connector... at idle both O2 sensors are consistently reading 0.7v and my local mechanic's exhaust analyser consistently reads an air fuel ratio hovering around 10:1 at idle, sometimes as low as 8:1.

Yes, while performing the ODB1 connection tests, if I blip the throttle I can see the voltages move - briefly dipping under 0.5v (which for those who don't know represents ideal fuel/air ratio) but it's only briefly.

All the indications indicate the engine (or ECM) has lost it's ability to adjust a rich fuel/air ratio back to optimal.

I have also temporarily shut off the fuel supply to the cold start injector - so there's no chance fuel is being sprayed into the upper plenum due to a leaking cold start injector.

Hence, we're now at the moment in this thread where I'm requiring some VERY knowledgeable members to offer their advice on what to test next?

Please note: In the attached photos, you'll see various vacuum connectors still open. The photos were taken while the installation of new parts was still in progress.


Keen eyes will note the new Denso injectors under the fuel rails. Also, the injector electrical connectors were rewired and repinned too. The engine is running great, the compression on all 6 cylinders is well within spec.

 

Wow that engine bay is even cleaner than my '93 was (Camry, same engine). Are you sure there is no external issue like dragging brakes? My car got around 18-20 mpg in city driving which is typical for this car. Technically the correct plug for the car is PQ20R aka Denso 3117, which ones did you use exactly?

This engine is known to run rich. You can fix this by opening up the AFM and clocking the spring to trick computer into a leaner mixture. You will also gain 10-15hp, this is legit not some made up thing. 3VZ-FE in markets not North America have 200hp (you have 185) due to different ECU tuning, meaning the engine runs leaner.

Wouldn't hurt to try a different ECU see if anything changes.

 

Why thank you sir! Yes, for some of us a clean engine bay is a source of pride.

And may I thank you for your suggestions. A fresh set of eyes is all we need sometimes to solve a problem.

So let's consider your dragging suggestion? I have (waiting to be fitted) a brand new "bolt in" catalytic converter made by Magnaflow. It's quite reasonable to suggest the OEM catalytic converter (which is still part of the exhaust system) could well be clogged.

As for your other suggestion regarding the ratchet spring within the Air Flow Meter? Yes! An excellent suggestion. It could very well be the door in the Air Flow Meter simply has a tired spring. Hence, tightening it up by a notch or two will almost certainly have a positive effect.

Thanks so much for the fresh eyes!

 

I just looked up my records and the official MPN for the Denso plugs that I purchased is "IQ20TTCamryV1."

If I recall correctly it's now the "recommended plug" by Denso for the 3VZ-FE.

 

I think the opposite, quite likely the cat on your car is perfectly fine. You'll know right away when you look at it.
Don't know if the spring gets weak, maybe.

If you mess with the AFM spring MARK THE POSITION clearly before loosening the set screw. You'll know what I mean if you open it up. My car, notice the AFM cap was removed.

 

Yes, the Denso Fuel Injection system used by Toyota on the 3VZ-FE was 100% licensed from Bosch in the late 1980's.

For all intents and purposes, the Denso system on the 3VZ-FE is identical in operation to the Bosch L-Jetronic system - including the Air Flow "swinging door" Meter.

And the tired spring door is a known thing on the L-Jetronic system. Which is why they incorporated the ratchet system in the Fuel Air Meter.

Yep, very good advice. Shall do.

So once again, my I thank you for the fresh set of eyes.