Running Lean

[kmborland]

Hey guyz,

 

As my name says, i have a 95 k2500 with the 350tbi in it. i have been having the same problem that i have been having since i have owned the truck. my problem is that it will throw a running lean code when driving on the highway, never driving around town for hours and everytime i turn the truck off then back on, the code goes away. this running lean problem is killing my already bad gas mileage. what are some things i should look for when trying to figure out whats wrong with my truck? this truck also has shortie headers and going to stock ypipe. could my o2 sensors be bad or FPR be bad? need help fast because i am running out of ideas.

[GMstrong]

check fuel pressure.

[Mike G]

Does it have a TBI spacer under it by any chance? You could be onto something with the O2, does that have one or two on it? Those are easy to change out. Start with the fuel pressure test though.

[txab]

check fuel pressure.

This is the place to start. Fuel pump pressure and pressure regulator.

[kmborland]

Ok, thanks guys. How do I check the pump pressure? Would an adjustable FPR be a good idea. Doesnt have a tb spacer but looking at getting one. It has 1 o2 sensor I believe after the cat. Should it have 1 before the it too? Like on the header or something like that?

[GMstrong]

It should only have one on the manifold.my 90 sierra isnt even running with a o2 sensor and it runs greeat smoother idle then when it did have a o2.Without an o2 the running will run richer since its using basic spark and fuel.My timiing is around 10* advanced.Adjustable FPR would only be good if you had a hell of alot of work in the motor cam,heads,etc,not needed.

[kmborland]

went out and checked. there is only one and the driver side header but its not connected to anything. i also cant find the connector for it anywhere. is this my problem or is there something else i am missing? it runs fine until the check engine comes on around 65-70miles on the highway (doesnt matter what speed) then it feels like it is drinking fuel. like the truck is dumping more fuel into the engine bc of the lean code.

[GMstrong]

Thats funny my service engine light comes on too for the o2.So i think the o2 is both or our problems.

[kmborland]

does it say running lean when the ses comes on? where does the o2 sensor connect to? i cant find the connector. is there a way i can tune it out? i hate seeing the ses light coming on.

[GMstrong]

You should have a o2 port its just closed up drill it out weld a bung in it and put the o2 in.The connector is a 1 wire connector should b lying around the dis somewhere.You can tune it out but that wont make it run any better.bottom line you cant do without the o2 sensor.

[kmborland]

were is the sensor suppose to be? driver or passenger side? like i said early, the truck has shortie on it with a driver side o2 port with an o2 sensor but it isnt connected to anything.

 

so i dont need the o2 sensor for anything? why is it even there then? so it isnt hurting anything when its like this? it seems like it is dumping more fuel in when the code comes on.

 

thanks for help

[GMstrong]

YOU NEED AN O2 SENSOR.its on the driver side header.you have to find the connector it has to be somewhere on the driver side firewall.

[kmborland]

what if its not?

[GMstrong]

go to a junk yard pull the wiring harness.I have to do the same but luckily i have a o2 connector so i just have to drill out the hole and weld in a bung then screw in the o2.

[kmborland]

i have 1 o2 sensor right in front of the cat. the headers on my truck were probably for multi year use so the previous owner plugged it with an o2 sensor. well, i just need to check and see if the 02 sensor is bad or not. how can i check to see if it is bad before i go buy a new one (60 bucks for a 3 wire o2 sensor)