I replaced the 4.8 in a SBSC 99 chevy with a 6.0 form a 02 chevy.

I installed a built 4L60E from TansDepot in prep for future upgrades but for now the engine is stock.

The SES light would flash on the interstate when above around 68 mph, i resolved this with a CASE re-learn procedure but still get random misfires at idle, not as bad but still there.

We used HPTuner to re-program the computer with a stock 6.0 tune. Once the tune was installed the truck would not crank, if we left the 4.8 tune it would crank. We ended up installing the 6.0 tune but replacing the MAF table with the 4.8 to get the truck to crank and run.

We replaced the intake with the 4.8 intake due to the 6.0 intake was broke at the MAP sensor tabs. We also replaced the 4.8 injectors with the 6.0 injectors, everything I read said the injectors were the same but i gave it a try anyway.

This is where we are at as of now but are still trying to figure this our. I have a scanner and am able to use HPTuner from a buddy.

The truck is a little slow to start in the mornings when its been sitting over night. I've checked the fuel pressure and regulator to make sure everything is good there and all checks out good.

We are also having issues with the firing order, in the 6.0 tune the order starts with #1 but with the 4.8 tune the firing order starts with #3. The truck will not run when we place the 6.0 firing order (I did not personally do this change a friend did so I may have this wrong but will find out for sure on what he did).

Thanks for any help and ideas

Neal

 

With ths low starting thing check the fuel pressure before cranking it after its sat or for that matter put fuel pressure guage on it and see how much it bleeds off, you may have a leakdown issue with fuel pump.... What is your fp anyway?? Running and koeo??

 

running with regulator plugged in its 52 psi, pull the vacuum line and it jumps to 58 psi.

I've let it sit after killing it with the pressure gauge connected and it holds pressure well over 30 minutes. It dropped a couple psi in that time frame.

what is koeo?

I've shut the truck off, bled off the fuel pressure and then turned the key to on but did not start it, the pressure will jump to 52 psi.

Neal

 

Koeo is key on engine off, sorry..... Are you using same vin or different vin when you program the computer??? Know it sounds like a dumb question but if youre trying to put a different vin in it could cause a mismatch error which wont allow it to start... Fuel pressure looks good id be curious to see what it is after it sits overnight... Ive seen numerous fuel pumps that after the initial prime in the morning are fine all day until they sit for 6 or more hours.... The the process starts all over again... Tryin to think, when i did my 04 6.0 swap in my 99 it ran as soon as i fired it up... On the stock 5.3 tune.... Are you using all the sensors from the 99 or the 02??? If i remember right, the maf and map sensors where actually different between the two...

 

Not sure on the VIN, I'll have to check,

how long should it hold fuel pressure after shutting down?

Using the sensors that came with the 02 engine,

I looked up the part #'s for the MAF for both the 99 and the 02 they were the same, i didn't check the MAP.

 

The Injector tables are also different between the 2 tunes even though the injectors may flow the same volume.

 

injector tables are the factory 6.0 tune

the LTFT's are around -3.5 and -2.5 so things look good there. I still need to take a drive with the scanner plugged in so I can watch everything while driving.

Neal

 

If you have really low fuel pressure on the initial start up it will basically take cranking the engine, turning the key off, waiting for the power down beep on an aftermarket radio(that was my telltale in my 99) and then cranking again and it will have enough fuel to start as i said before its a slow process but i have seen them drop to 0psi after sitting for 6 hours, but initial bleed off of no more than like 5psi over 10 minutes as good... But im thinking this is more a tune issue than fuel supply problem.... I am not as knowledgable with tuning processes as some of the others on here are.... But in all reality its probably something fairly simple youve missed or crossed...been there, done that!!

 

yeah its more than likely something I'm overlooking

I'll keep at it until I figure it out,

appreciate the help,

Neal

 

A little more info on my issue,

I am getting the P0300 random misfires code and have been trying to locate the cause.

All the PID's on the scanner looked good until now, last night I noticed the MAF flow was low compared to my Denali (6.0).

I disconnected the MAF sensor and the misfires stopped, when I plug it back in the misfires come back. Also when I unplug the MAF the fuel trims get closer to 0 so now I just have to figure out what is going on with the MAF.

I've verified the calibration of the MAP along with the calculation of the engine vacuum (BARO - MAP) and all looks good.

I'm going to pull the MAF from my Denali and try it on the 99 6.0 to see if that corrects my issues. I cross referenced the part numbers and the MAF sensors are the same from the 99 silverado and the 03 Denali so all should be good to swap and see what happens.

I did verify we did use the VIN form the truck so all is good there.

Neal