P0171 code

I just tackled a 2000 Tundra 4.7 liter with P0171 (lean condition bank 1, which is driver's side on this gen 1 Tundra) with 193,000 miles. Here is what I recommend to do first:

1. Replace engine air filter
2. Change PCV Valve and Grommet and clear code and see if it comes back. If code returns.
3. Smoke Intake System at tube going from evap purge solenoid to intake. Removed hose at purge solenoid and input smoke into this hose. (you can buy a homemade smoke tester on Ebay for about $80). Note that some smoke will come past the throttle plate, but even if one or more intake valves are open, you will eventually fill the cylinders and entire intake assembly with smoke.

I found smoke coming out of the injector lower seals (at intake manifold) The seals were brittle and disintegrated.

Before I smoked it, I used carb cleaner to spray around the intake ports and vacuum hose fittings and it did not change engine sound.

After I smoked tested it, I used starting fluid and sprayed it around the the injector lower seals and the engine would hesitate for a bit. I have not have good luck with carb cleaner, and don't recommend using carb cleaner or starting fluid to find a leak (very dangerous).

What is unique about these injector seals, is that they are not the typical o-rings that are countersunk into the intake manifold that you seen on most engines and which seam to never fail. Tundra uses rubber seals that are smooshed between the injector tip shoulder and the intake. The rubber relaxes over time and is more exposed to the elements.

If you only have a lean code on one bank (one-half of the engine), then usually a mass air flow sensor is not the cause as it would impact both engine banks. It made sense in my case that we only had a lean condition on the driver's side where the injectors seal as only those cylinders would be ingesting unmetered air from these bad seals.

Make it a great day!