put a 5.3L in my C10 a while back... it ran like crap and i kept getting lean bank one codes. searched for weeks for vacuum leaks, put in new injectors, checked for exhaust leaks, verified o2 sensors wired correct and on the right sides... i even replaced the wiring harness with one from PSI.

Someone told me to have the tune checked, ut thst is very hard to do where i currently live. so here is the question... what kind of symptoms will i see if the ecu was tuned for a returnless system but i am running a return system? been searching all day and havent found a straight answer yet. dont want to try to solve this by throwing more money at it.... piggy bank is damn near empty.

 

post the tune and any logs you have.

 

i would if i could, but I had it tune by Brendan on LT1swap. i cant remember if i specified return or returnless. so im am thinking i may have just said it was an 04 engine, but it turns out it is an 03... blue green connectors but return system...

might just have to have it retuned...

 

where u live? yea having return or returnless could change up the injector data? but it should still run decent I would think. Maybe a dead cylinder? bad coil?

Do a compression test on it. Bad plugs will make one act crazy and have a dead cylinder as well.

 

what does the setup consist of?

 

are you only getting lean bank 1 codes, or both banks? If the fuel system return\returnless is the problem I would expect both banks to show lean.

Do you have a hand held code reader? Check to see if both front 02's are getting a reading and switching.

What are your long term and short term fuel trims at?

Are all sensors connected? Coolant temp\maf\iat\...ect

With this information we can determine if the 02's are working properly and if the issue is related to just one side of the motor or both.

 

IF u can gain access to tuning software u can force it into openloop and see how it acts. openloop doesn't use o2s. When u first start a vehicle its in openloop until around 140* and thin converts to closedloop and used o2 feedback for fuel trims.

 

Its a 5.3 that I was told was an 04 out of a silverado. Turns out it was probably an 03 as it is a return style but has the blue and green connectors. running a 1998 S10 Blazer transmission (that seems to be holding up just fine). All sensors were connected, and all sensors including MAF are stock.

using oem truck manifolds and had an exhaust shop connect them to my existing dual exhaust (no x or h pipe). they did a crappy job, no leaks but one pipe goes under my transmission crossmember and one above. truck is lowered so it bugs me.

i use torque as my gauges and to monitor trims. it has been sitting for a year now, so i am going off memory. (busy life, in the navy, and frustration caused the delay).

for a while i was getting constant high readings on my bank one o2, it wasnt switching at all. tried swapping them side 2 side, still same readings. couldnt find vacuum leak or exhaust leak. did find one injector that wouldnt cycle when 12 volts were applied. replaced that and thouroughly cleaned injectors and fuel rail. stsrted her up and went for a drive and she seemed to be working perfectly....

that lasted about a day before the bank one fuel trims started rising. o2 was switching, but bank ine seemed to be higher voltage most of the time. long term kept going up and was at 40% when i parked her and left her at my moms while i changed duty stations.

about 9 months later i bought a new harness, slapped it in and tried to drive it to my new house.got about 20 miles... now the bank one was still lean, but bank 2 was reading rich. then she died and i thought i blew my engine.... got it towed the rest of the way and eventualky found the hot wired from the battrry to the starter had melted to my exhaudt manifold on the passenger side. i fixed that, and now she will start. thats where i am now.

 

Returnless vs return shouldn't make a difference to the tune if they are both configured correctly. Either way you should have the correct pressure at the injector. You may want to put a pressure gauge on your rail to verify fuel pressure?

I think it is most likely you have a mechanical or electrical problem. I'd pull each of the plugs and take a read on them. Do they look consistent? Check the coils, plug wires, and the connectors and wires to each injector. If you put new injectors into it they should be fine. It is also possible it is a mechanical problem in the engine, like a bent pushrod, or a valve sticking. I once chased a problem I thought was tuning, and a push rod had a crack in it that was allowing it to flex, was hard to determine without tearing the engine apart.

In the normally modified tables in the tune, there is no where to bias one bank vs the other. There is a way to do this, but that table in not normally touched by a tuner. The only people I've heard of modifying this is people looking for MPG at a cost of performance, not the normal guys doing swaps. They try to get each bank running as lean as possible. If you needed to modify that table there is something wrong with the engine, as both banks should be balanced in the factory tune.