Long term fuel trim issue no codes

[Get Bent]

I have a 99 Tahoe and I am trying to figure out a loss of power and loss of mpg. Bank 1 LTFT about 0 and Bank 2 LTFT approx. -10 and the STFT Bank 1 & 2 were also approx. 0 after days of driving. I measured fuel pressure and my key on engine off was 54psi and idle was 48psi. Originally I thought it was the fuel pump, but I have since replaced it and I get the same readings. Don't know if the gauge is bad, because the readings look a little low. I then let it sit to see if it bled down and it did about 1 psi per minute. I figured it was the fuel pressure regulator. I changed it, cleared the ECU and now I have the above screenshots. I haven't been able to check fuel pressure, gauge is at work.

Apparently didn't fix it and I would appreciate any input.

Thanks in advance,
Jeff

 

[Mechanic421]

May have a small fuel leak in one of the fuel lines inside the intake manifold.

 

[Get Bent]

May have a small fuel leak in one of the fuel lines inside the intake manifold.

I hope it's not an injector, it's a brand new spider. I was reluctant to change the regulator as it was new and came with the spider. I'm going to recheck the fuel pressure.

 

[swathdiver]

There's something wrong on the passenger side of the motor. -10 means the engine is rich (on that side) and taking away fuel to compensate. So it is not a fuel pump but could be a specific injector or plug or wire or an exhaust leak on a certain cylinder or worse.

 

[Scottydoggs]

There's something wrong on the passenger side of the motor. -10 means the engine is lean (on that side) and adding more fuel to compensate. So it is not a fuel pump but could be a specific injector or plug or wire or an exhaust leak on a certain cylinder or worse.

neg trims are rich, pos is lean

that being said, it could be a stuck injector making the one bank so much richer then the other.

or the o2 is shot, truth is they only work well for about 50 to 60,000 miles.

 

[swathdiver]

Thanks Scott, confused myself again and fixed the post.

 

[Scottydoggs]

Thanks Scott, confused myself again and fixed the post.

its one ass backwards thing really. might make more sense the other way. being ive read till my eyes bled and i pulled some hair out learning to tune, it gets pounded home that neg is rich.

 

[Get Bent]

I appreciate all the input guys. Initially, I didn't have the fuel trim info. It just had a lack of power, loss of mpg and when starting in the am or after about 5-6 hours it would crank for second or two before actually starting. So I took a fuel pressure reading, turned ignition to the "on" position and only primed to 20-25 psi. I tried to start it and started fine, but was only running at 48 psi. I turned it off and it jumped to 56 psi and came down to 54 psi. With the obvious confusion over the 20 psi reading, I didn't bother checking for bleed off. I figured the pump was getting ready to go, so I changed it.

After a few days, I started noticing the same symptoms. Again I checked the fuel pressure with the same gauge and the measurements were identical. I checked for bleed off this time and it was losing about 1 psi per minute. Now I am suspecting a faulty fuel pressure gauge. I am going to get a different one tomorrow and recheck.

Since I had bleed off, that's when I started checking the fuel trims and educating myself. I saw that the right bank was rich and immediately suspected the regulator since they are known to fail. The spider (BWD 65886) was put on in November 2017. I'm going to see if I can get it warrantied, but before I do that, I wanted to get more info and/or possibilities of what the problem might be. Tired of replacing things that work. Again thanks for all the input, it is very much appreciated.

I'll post fuel pressure readings and Torque Pro screenshots tomorrow.

Jeff

 

[Get Bent]

Here is the new gauge information. It primed to 62 psi. 5 minutes-58 psi, 10 minutes-54 psi, 15 minutes-54 psi and 30 minutes-51 psi. Left is highway @2000 rpm and right is idle & op temp


I think it is the injector spider, but I'm going to replace the O2 sensors, too. Don't know when they were last changed.

Jeff

 

[Scottydoggs]

pull the dip stick, smell the oil on it, if its strong smelling of gas your flooding out for sure.