Engine running rich, poor fuel mileage and loss of power at low RPMs

SMOKE MEAT

MEMBER
1998 TOYOTA TACOMA
3.4L
V6
4WD
MANUAL
280,000 MILES

Truck is burning a lot of fuel. Changed the air filter, spark plugs, injectors, and did an oil change. Checking engine light is on and sometimes it will blink then sometimes it won’t be on. Truck runs a little rough sometimes and I did notice a reduction in power. Low RPMs it feels like it is missing give it the gas to about 2,000 RPMs and it sounds and feels fine when not moving. So, my question is, what else do I need to look at for running rich?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

If you feel it is running rich, the first thing to check is fuel pressure. There could be an issue with the fuel pressure regulator.

Now, the idea that the check engine light flashes at times indicates a misfire. By chance, have you ever noticed a dark gray or black smoke from the exhaust?

Here is what I suggest. Let's confirm what the fuel pressure is. Here is a link that explains in general how to test fuel pressure. You will need a fuel pressure gauge, but oftentimes, a parts store will lend one to you.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If you look at the pics below, I included the manufacturer's pressure specifications. Pic 2 shows the fuel pressure regulator. When you disconnect the vacuum hose to it, make sure there is no evidence of fuel in it. Also, with the engine running, confirm there is vacuum to the regulator.

Let me know what you find or if you have other questions.

Take care,

Joe

See pics below. Note: Let me know if you have a live data scan tool. If you do, let me know what the short-term fuel trims are.

Images (Click to make bigger)