2004 Toyota 4Runner 4.0 Running Lean

This thing is running way lean. At idle long term trims on both banks are running at 29.64 and short term around 5 on bank 1 and around 8 on bank 2. At 2000 rpm the short term trims go to around 0 with the long term just beginning to come down. At 3000 rpm the short term trims go slightly negative to around -2 or so and the long term trims come down to around 22. At 4000 rpm the short term trims stay around -2, -3 and the long term trims come down to around 11. Under full power brake the short term trims go to 0 and long term to 2 or 3. Both banks stay pretty well balanced. Mass air sensor is new and seems to be functioning properly. Everything I have read suggests a vacuum leak but I cannot find one. I have smoked this thing and have found nothing. I hosed it down with brake cleaner with absolutely no change in the short term trims. It runs fine and does not seem to lack power, It responds well to a throttle snap and the trims all usually go to 0. I don't pick up any misfires on any cylinders at all. The fuel pressure holds at 42 and does not drop. I'd appreciate any thoughts on this as I am not very good at diagnosing this sort of thing yet. It's also only the second Toyota I've worked on.

On the day you got those readings, what was the outside temperature?

About 40 F. It was in a shop at about 60 F.

fixn_junk wrote:

Everything I have read suggests a vacuum leak but I cannot find one. I have smoked this thing and have found nothing. I hosed it down with brake cleaner with absolutely no change in the short term

The brake booster is a vacuum leak source. You would have to look under the dash where the brake rod comes through the firewall. Pinch or block off the brake booster vacuum line and check trims again.

Will do. Thanks.

It appears to have some type of hydra boost.

Did you fix this? A leaking purge valve is also a possibility.

I have not. Been working on some other stuff. I plan on bringing it back in early next week. I needed to take a break from it because I was out of ideas. I did plug the line to the purge valve with no change. I know I'm missing something, just can't figure out what it is.

You said the MAF is new? Is it an OE Toyota part? If not, it's VERY suspect. So many aftermarket components like that are pure junk and don't work properly even when new. Connect your scan tool and take it out and do a wide open throttle run in first gear while looking at your O2 data. The upstream O2's should go full rich during your wide open throttle run. If you're unfamiliar with how wideband O2's (air fuel ratio sensors) work then use the downstreams as they should go full rich, as well. If they do, that means fuel delivery is fine. If you don't have a vacuum leak that really only leaves the MAF. What does it show in grams per second at idle on the scan tool?

The other thing I've seen cause issues are the O2 sensors. The downstream sensors are often providing some means of fuel control when the upstreams are wideband O2's (air/fuel ratio sensors.) I've seen faulty downstream sensors cause high fuel trims. You want to make sure you're using only NTK or Denso O2 sensors, and preferably Denso as that's what Toyota used from the factory.

Thank you! The MAF is Napa Eichlin. I have seen issues with non oem sensors on some other makes but I'm new to Toyota. I will say, I saw no difference between the original sensor and the new. I will check what you have suggested and report back.

John Clark wrote:

You said the MAF is new? Is it an OE Toyota part? If not, it's VERY suspect. So many aftermarket components like that are pure junk and don't work properly even when new. Connect your scan tool and take it out and do a wide open throttle run in first gear while looking at your O2 data. The upstream O2's should go full rich during your wide open throttle run. If you're unfamiliar with how wideband O2's (air fuel ratio sensors) work then use the downstreams as they should go full rich, as well. If they do, that means fuel delivery is fine. If you don't have a vacuum leak that really only leaves the MAF. What does it show in grams per second at idle on the scan tool?

The other thing I've seen cause issues are the O2 sensors. The downstream sensors are often providing some means of fuel control when the upstreams are wideband O2's (air/fuel ratio sensors.) I've seen faulty downstream sensors cause high fuel trims. You want to make sure you're using only NTK or Denso O2 sensors, and preferably Denso as that's what Toyota used from the factory.

I am going to run this thing shortly. I will try to graph all of the data you suggested and will post it when completed. I am unfamiliar with wideband O2's and need to do some learning on those.

John Clark wrote:

You said the MAF is new? Is it an OE Toyota part? If not, it's VERY suspect. So many aftermarket components like that are pure junk and don't work properly even when new. Connect your scan tool and take it out and do a wide open throttle run in first gear while looking at your O2 data. The upstream O2's should go full rich during your wide open throttle run. If you're unfamiliar with how wideband O2's (air fuel ratio sensors) work then use the downstreams as they should go full rich, as well. If they do, that means fuel delivery is fine. If you don't have a vacuum leak that really only leaves the MAF. What does it show in grams per second at idle on the scan tool?

The other thing I've seen cause issues are the O2 sensors. The downstream sensors are often providing some means of fuel control when the upstreams are wideband O2's (air/fuel ratio sensors.) I've seen faulty downstream sensors cause high fuel trims. You want to make sure you're using only NTK or Denso O2 sensors, and preferably Denso as that's what Toyota used from the factory.

I am unable to attach documents for some reason. Here is some of the data I pulled:

Key On Engine Off

Calculated Load: 0%
MAF: 0.65 g/sec
STFT B1: 0
LTFT B: 29.64
STFT B2: 0
LTFT B2: 29.64
B1S1: 3.303V
B1S1 Equivalence Ratio: 1.001 Lam
B2S1: 3.305V
B2S1 Equivalence Ratio: 1.002 Lam
B1S2: 0.035V
B1S2 Fuel Trim: 99.06
B2S2: 0.015V
B2S2 Fuel Trim: 99.06

Low Idle

Calculated Load: 12%
MAF: 3.00 g/sec
STFT B1: 3.9
LTFT B1: 29.64
STFT B2: 7.02
LTFT B2: 29.64
B1S1: 3.319V
B1S1 Equivalence Ratio: 1.008 Lam
B2S1: 3.344V
B2S1 Equivalence Ratio: 1.008 Lam
B1S2: 0.115V
B1S2 Fuel Trim: 99.06
B2S2: 0.075V
B2S2 Fuel Trim: 99.06

Wide Open Throttle 1st Gear

Calculated Load: 78%
MAF: 164.35 g/sec
STFT B1: 0
LTFT B1: 2.34
STFT B2: 0
LTFT B2: 3.90
B1S1: 4.997V
B1S1: Equivalence Ratio: 1.117 Lam
B2S1: 4.997
B2S1: Equivalence Ratio: 1.234 Lam
B1S2: 0.015V
B1S2: Fuel Trim: 99.06
B2S2: 0.00V
B2S2 Fuel Trim: 99.06

60 MPH

RPM: 1853
Calculated Load: 22%
MAF: 17.46 g/sec
STFT B1: -2.34
LTFT B1: 22.62
STFT B2: -1.56
LTFT B2: 23.40
B1S1: 3.308V
B1S1 Equivalence Ratio: 0.994 Lam
B2S1: 3.270V
B2S1 Equivalence Ratio: 0.998 Lam
B1S2: 0.585V
B1S2 Fuel Trim: 99.06
B2S2: 0.465V
B2S2 Fuel Trim: 99.06

I realize this isn't the ideal way to show data but as I said, it won't let me upload attachments right now and I haven't figured out how to get recorded data to a graph in Auto Enginuity.

Can you get us engine rpm at wot we need iat engine rpm maf g/s it looks way lean with the front O2 sensors going over 4 volts in first gear w.o.t.

I don't remember exactly, but it was right around 5550.

Can you deadhead the fuel pump?? Pinch off a return line if it has one?

It's all hard lines. It does have return. I do have an adapter I rigged up for another one with a ball valve I could put inline. What are you thinking? I'm not sure where you are going with this. Excessive return?

Dead head to see what your fuel pump can put out max pressure. Toyota is known for injector problems becoming restricted

That first gear pull you did caught my attention. All 4 O2 sensors are lean. Rears are near 0 mv fronts over 4 volts.

I will try to do that tomorrow and let you know max pressure.

What’s fuel pressure spec?