HELP LS Swap Runs Bad In Closed Loop

[WesFischer05]

I have just completed an LS Swap (2001 5.3) into my 1981 El Camino. When in Open Loop at first startup the car runs great and drives like a champ. As soon as it hits closed loop it absolutely falls on its face. Immediately in the Short Term Fuel Trims the passenger side (Bank 2) shoots up to +51% almost instantly. While the driver side (Bank 1) goes down to -31% in the same speed as Bank 2. I will separate my multiple concerns below in hopefully an easy way to read and answer to.

I put new 02 sensors in it on the upstream, they are AC Delco. The rears are not in the exhaust but still plugged in. They should not be able to effect the performance at all. When taking out the old ones the passenger side was dark black while the driver was just a little black which is because the car wants +51% more fuel on the passenger side for some reason.

Full exhaust system with hi flow cats and mufflers, problem occurs with and without exhaust on the car.

My theory right now is that it is something wrong with the tune in the computer. If there was a major vacuum leak or non firing sparkplug/fuel injector, to my understanding the car should run bad in open loop aswell but in open loop it runs completely fine. Please correct me if i am wrong on this and if I should be checkin all the plugs and injectors.

NO CODES AT ALL

The engine, transmission and PCM were taken from one donor truck that ran good in open and closed loop. The computer was sent out to get the wiring harness re-done and removed a lot of the unnecessary things that connecter to the car itself. Now it acts as a standalone computer. I did give the guy some info like tire size and rear end ratio so he could adjust the tune. Unfortunately he does not do the harnesses anymore and was hard to reach even when he did. I believe there is a chance something could have been messed up while he was in there and want other peoples opinions about it.

I know a few guys around that could possibly help me look at the tune but I wanted to share this here and get some other eyes on it.

Let me know if there is any info I am missing that is crucial to diagnose this.

 

[Rgpmalibu]

Are the downstream O2 sensors still turned on in the tune? It seems like it has to be something to do with the information that the computer is receiving from the O2s. In OL the car is running from pre-programmed tables. Access to scanning software?

 

[WesFischer05]

Are the downstream O2 sensors still turned on in the tune? It seems like it has to be something to do with the information that the computer is receiving from the O2s. In OL the car is running from pre-programmed tables. Access to scanning software?

One of my dad’s buddies might have access to a scanning software. That is what I’m gonna try next

 

[Supercharged111]

Make sure the sensors aren't swapped bank for bank. And post screenshots of the O2 activity once you have a chance to scan it.

 

[383_StealthRam]

If you plan on keeping this project for the long term, and running on factory ECU, harness, tune etc. I would highly recommend (if you don't have a friend that will lend it to you as needed) investing in the HP Tuners MPVI interface. It's not cheap at around $400, then maybe another $50-$100 for write licenses/credits should you want to make actually tuning changes, or have someone help with remote tuning, etc.

The HP Tuners software suite is free to download and use, and the VCM Scanner is hugely helpful for you to be able to not only read codes, but do data logging, and live readings to aid in any troubleshooting you may need to do. EFI Live is another, and has it's own OBD port interface as well you would. If you could borrow an MPVI, you can then just use VCM scanner with a laptop, then also use VCM Editor to "pull" the existing TUNE file from your ECU. It will be in HPT format, but at least if you know or find someone to look at it, you can simply send/email/dropbox it for them.

Having that type of access to read/write your ECU, and data log scan your setup really let's others help you, and you can learn a ton from the HPT forums, and other online resources and if you want to learn for yourself.

I know you've already invested in the ECU/Tune/Harness mods.....but you can also consider aftermarket ECU/Harness (like Holley EFI, or others) which allow easier access to a lot of functions, data logging and tuning that can be sometimes more difficult with the OEM ECU's. I have had and love Holley EFI, been in mine for 10+ yrs, and a few of my friends have used OEM ECU's with crate engine/trans setups (ie; LT4 w/6 spd) and while it came with "pre built" tune, there were some things we had to still go in and tweak for certain trouble codes, sensors, etc.

Some other guys have done the Holley Terminator X on LS swaps, and it's been very good and not brutal on the wallet. I'm not advocating one or another system...you'd have to weigh the options that work best for your finances, and goals...so I get that it's not a simple answer.

As has been said, getting access to data about what's going on will be the best thing you can do to get started toward resolving the issue, plus being able the diagnose other problems if/when they may pop up down the road.

Good luck!!

 

[doood]

You should be able to get a stock computer with vat deleted for like $150. Maybe that harness is no good. $500 on a new standalone harness was money well spent for me. Wired it up and fired it up. I don't have downstream O2 sensors.

 

[Rgpmalibu]

If you plan on keeping this project for the long term, and running on factory ECU, harness, tune etc. I would highly recommend (if you don't have a friend that will lend it to you as needed) investing in the HP Tuners MPVI interface. It's not cheap at around $400, then maybe another $50-$100 for write licenses/credits should you want to make actually tuning changes, or have someone help with remote tuning, etc.

The HP Tuners software suite is free to download and use, and the VCM Scanner is hugely helpful for you to be able to not only read codes, but do data logging, and live readings to aid in any troubleshooting you may need to do. EFI Live is another, and has it's own OBD port interface as well you would. If you could borrow an MPVI, you can then just use VCM scanner with a laptop, then also use VCM Editor to "pull" the existing TUNE file from your ECU. It will be in HPT format, but at least if you know or find someone to look at it, you can simply send/email/dropbox it for them.

Having that type of access to read/write your ECU, and data log scan your setup really let's others help you, and you can learn a ton from the HPT forums, and other online resources and if you want to learn for yourself.

I know you've already invested in the ECU/Tune/Harness mods.....but you can also consider aftermarket ECU/Harness (like Holley EFI, or others) which allow easier access to a lot of functions, data logging and tuning that can be sometimes more difficult with the OEM ECU's. I have had and love Holley EFI, been in mine for 10+ yrs, and a few of my friends have used OEM ECU's with crate engine/trans setups (ie; LT4 w/6 spd) and while it came with "pre built" tune, there were some things we had to still go in and tweak for certain trouble codes, sensors, etc.

Some other guys have done the Holley Terminator X on LS swaps, and it's been very good and not brutal on the wallet. I'm not advocating one or another system...you'd have to weigh the options that work best for your finances, and goals...so I get that it's not a simple answer.

As has been said, getting access to data about what's going on will be the best thing you can do to get started toward resolving the issue, plus being able the diagnose other problems if/when they may pop up down the road.

Good luck!!

X2

HP Tuners was one of the most important tools that I purchased to help me understand how my engine runs, to get it running right, to scan for any problems, to make tweaks and adjustments, and to get my engine to idle and run efficiently after a cam swap. I also used it to eliminate the MAF to create a speed density system. It's nice to be able to run diagnostics every once in a while just to see how the engine is performing. Even something as simple as dialing in the correct tire size so my speedo would read correctly. There are many systems available. I don't think I would've had the success with my swap without some way to read and tune the computer. Incidentally, I'm running the stock ECU, a $99 eBay harness, and HP Tuners.

 

[doood]

You should be able to get a stock computer with vat deleted for like $150. Maybe that harness is no good. $500 on a new standalone harness was money well spent for me. Wired it up and fired it up. I don't have downstream O2 sensors.

GEN III (24X) PCM/Programming

Looking for an Affordable, In Stock, Plug and Play wiring harness for your LS Swap? PSI sells Standalone Wiring Harnesses for GM Gen II, III, IV, & V

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$210 new PCM with technical support. Could get cheaper on ebay, but these guys are pros.