First timer

[ls260Z]

So, like many, many before me i was wondering if anyone would care to take a look at a log and tune and tell give me some advice on where to start or if things look messed up. this is a 5.3 out of a 2000 yukon 4l60e and put in a 81 cherokee chief. It seemed to run fine in the yukon but in the chief it's a bit lack luster. This is my first time looking at the tuning side of things and i have started to read but boy is it a lot to take in. So while i'm tryin to school myself have a look and tell me what you think.
Thanks
Jeff

[5FDP]

More details please.

Is the engine stock?

What fuel presure are you running?

Where are the o2 sensors installed?

Have you checked for vacuum leaks or exhaust leaks pre-o2 sensor yet?

I ask these because your fuel trims are off the charts, it's either a tiny bit rich or extremely lean under load. To me that says you are either running the wrong fuel pressure, this is fairly modded or you have vacuum/exhaust leaks causing a major issue.

[ls260Z]

More details please.

Is the engine stock?

What fuel presure are you running?

Where are the o2 sensors installed?

Have you checked for vacuum leaks or exhaust leaks pre-o2 sensor yet?

I ask these because your fuel trims are off the charts, it's either a tiny bit rich or extremely lean under load. To me that says you are either running the wrong fuel pressure, this is fairly modded or you have vacuum/exhaust leaks causing a major issue.

The engine is stock

I'm using the stock fuel rails and pressure regulator. But i may put in the corvette style filter/regulator just to make sure.

o2 sensors are installed but i have a feeling there is a leak at the manifold flange

Thanks for looking!

[5FDP]

What pressure though?

It needs to be 58 psi like factory.

[ls260Z]

What pressure though?

It needs to be 58 psi like factory.

I'm afraid i don't have a gauge on it. I'll have to get one. I just went out and double checked for intake leaks and didn't find any. I have a sneaking suspicion that it's an exhaust leak. I'll check that out tomorrow as well as the fuel pressure.

[ls260Z]

So checked fuel pressure and it's constant 58-60. Checked again for vacuum leaks and haven't found any. This is a short log i took.

[ls260Z]

Ok, i adjusted my maf table by x1.1 and i think that helped a little. this is my latest log if anyone would like to take a look and give feed back.

[5FDP]

It stays constant under load too right?

Did you verify no exhaust leaks too?

Just going by the logs and because this engine is not modded, something just seems off because the fuel trims should not peg out at +25 under load.

The 2nd log is just as bad as the first even when you added 10% fuel.

[ls260Z]

It stays constant under load too right?

Did you verify no exhaust leaks too?

Just going by the logs and because this engine is not modded, something just seems off because the fuel trims should not peg out at +25 under load.

The 2nd log is just as bad as the first even when you added 10% fuel.

I did verify the exhaust at least to the best of my ability, I'm wondering if the o2 sensors are wonky.
I agree with you on the fuel trims, The more posts i'm reading the more i'm starting to understand....slowly understand lol

[ls260Z]

I just check with a vacuum on reverse and i got leaks around the 02 sensors. I will fix and report back.
Sorry

[ls260Z]

Ok, I think i got all the leaks sorted out. Anyone care to look at this log and see how it looks? It definitely runs better but is still lacking something.

[5FDP]

Still very lean under load, like as is fuel pressure is dropping.

If the leaks are gone, the MAF sensor is working good, the o2 sensors are in good condition it really shouldn't go as lean as it does under throttle.

At idle the trims are good but it's once the rpms rise and you are driving that is becomes lean per the fuel trims. Can you drive around with a pressure gauge hooked up to watch the pressure??

[ls260Z]

I'll have to see if i can add a line to my tester. I also have another fuel pump and may just throw it on and see if there is a change.
Thanks
Jeff

[ls260Z]

Ok, new fuel pump and i built an intake leak tester. Found a big leak right behind the maf sensor. It seems to be running much better.

[5FDP]

I dunno, the log shows it's still bad on the trims and o2 sensors. Again I can only assume this stuff based on the logs. Trims still max out at +25% on the long terms under load. The o2 sensors take a nose dive when you get into the throttle enough. Surprised it's not throwing lean codes.

Are the sensor close to the manifolds are way down the exhaust?

If the vacuum leaks are gone, no o2 sensor problems or leaks, fuel pressure is steady around 58psi. Then all the basics are good I guess.

If it the truck was in front of me and still like that I'd be whacking the tune with 5-10% worth of fuel to the airflow model to see if it comes back down on the trims.

This is also where a wideband o2 sensor is a must because sometimes you just can't trust what the narrow band sensors are saying.

If you haven't reset the trims yet either, do that as well if you fixed some stuff.

[ls260Z]

Sensors are close to the manifolds. Stock position actually. I haven't reset the trims, I'll do that tomorrow and recheck everything for leaks. I finally have some oil for heat out in the shop so i can spend a little more time looking at stuff. It's been damn cold out there lately! Thanks for all your help 5FDP