Hi all, I am about to tear my hair out shortly. Let me tell you my story. I am working on getting a 2004 5.3 DBW motor set up to run on a run stand. I Built my harness off of LT1 Swap.com and currently using HP Tuners to delete Vats and such. I have very little knowledge of HP Tuners but very little has been changed. Here is the problem. I first fired up the motor and it fired up and ran great. Once the motor goes into open loop it starts to have a rough idle and gets a P0300 code as well as some other trans codes I figured I would see, since there is no trans hooked to it. The motor idles up great and seems to smooth out when you get on the gas, however when it idles down in wants to hang and then bounces idle between 450-650. You can deff hear it has a miss when at idle. So hear is what I have tried.

New plugs and wires
New Maf, MAP, and TPS sensors.
I have checked everywhere for vacuum leaks and replaced intake gaskets.
I have tried 2 sets of 02 sensors and my exhaust is fully welded with new manifold gaskets.
Compression is 120k on all cylinders
I have built 2 harnesses to make sure i did not have a break in a wire somewhere
I have 56PSI of fuel and the rails and checked injectors with noid light

I am at a loss here other than the rough idle the thing runs great. It does seem like i get high LTFT at around 8ish on both banks and 02s look to be functioning 0-850.

is there something that needs to be done in the tune so the computer knows there is no trans behind it. I have left the VSS sensor plugged wired into the computer, it is set up for a 4l60E. Could this be giving me a problem. Sorry for the long post i am just at a loss. My TPS bounces from 2-7 at idle but smooths out and stays steady when you hold the pedal at a certain spot.

Thanks for any help you could give

 

Anyone?

 

Aren't the oxygen sensors swapped side to side?
You may want to try open loop for now, unplug both O2 from harness and try again.
There are several things that can cause the rough idle, you need to check one by one. Lean mixture is the most frequent and it can be caused by a bad MAF, O2 sensors, untuned MAF tables etc.

 

U have HPT, post a data log, and the tune file...

 

Nothing related to the missing trans is causing the engine problems.
Follow Geezer's suggestion.

 

I will run a scan tommorrow and post the tube file. The tune is basically untouched and the 5.3 is bone stock right out of the truck. Thanks for the replies

 

The compression should be a little higher.

I would try a leak down test to verify sealing integrity.

 

OK I have got a scan update. I ran the motor with the MAF plugged in and unplugged. The miss seemed to be better with the MAF unplugged but was not nearly as responsive. I have checked for Vac leaks everywhere and also has tried new MAF and 02s. Let me know if you see something. I have also copied my tune. I am extremely new to HP Tuners, and am not real sure how to read the graphs yet. I have changed nothing in the tune other than deleting vats and 02s. Please let me know if you see anything missing. I have also linked a couple pics of the motor set up.

 

I also unplugged the 02s and it definitely runs worse. I swapped them side to side and fuel trims went crazy so they are plugged into the right sensor

 

Have you disabled the downstream O2 sensors, disabled EGR, the normal swap related stuff?

 

Ya, its non EGR but Down streams and vats are disabled

 

FYI the fuel pressure is now at 56PSI and the rail

 

Anyone get a chance to look at this

 

Make sure all the proper trans codes are disabled. Check for vacuum leaks and coil spark problems.

 

For the Idle-In-Drive Spark table, insert 20 or 22 for the entire 0, 400 and 800 RPM rows.
For the Idle-In-Park Spark table, insert 18 or 20 (2 less) for the entire 0, 400 and 800 RPM rows.
For the High Octane Spark table, insert the same 20 or 22 for the top half of the 0, 400, 600 and 800 RPM rows. By top half I mean from 0.08 to .44 Cylinder Airmass.
Then insert about 10 in 1.20 column for those rows and blend the .44 to .120 columns.

Look at the Jake's tune in post #51 of this thread to get some idea of what I am suggesting:
https://ls1tech.com/forums/pcm-diagn...ng-stop-3.html

This should improve your idle. If it does, you should blend your 800 column into your 1000 and 1200+ columns; but that can wait.

Perhaps someone else has the time to look at your logs and make other/different suggestions. Sorry I've been busy lately.