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LQ9 Swap, Programming Issues?? Lean, Rich, etc!

robster495

robster495

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Hey guys, I have an lq9/4l65e out of an Escalade in my '91 burb. It starts up every time, and runs great in the beginning. Once it warms up and gets to operating temperature it acts crazy. Most of the issue is when idling in gear, not in neutral or park.

I have long term fuel trims way off :

Bank 1 is at -16%
Bank 2 is at +25%

Also when at a stop in gear, the MAF is pulling about 3lbs/min and my fuel rate jumps over 2gal/hr. All of this is happening at around 550rpm...as opposed to around 1lb/min and 1gal/hr normally in park or neutral.

This is also mind boggling because when stopped facing up an incline, giving gas does nothing and I have no power to move at all. Thing just lugs at around 550rpm and stays still.

Engine codes present are Bank 1 Rich, Bank 2 Lean, Knock sensor circuit low.
I'm running a return style intake with the typical multec injectors.

Thoughts???
 
Id log command fuel pressure vs actual. A week fuel pump can cause the issue you are having. Did you do any VE tuning, Maf tuning, different cam or is it all stock? Do you have a wideband to confirm it is actually rich? Using stfm ltfm as a base isn't the best method. It can work but a wideband will help you tremendously. I'd also log Knock retard to see if it is pulling timing as well as adding fuel. The knock sensor code maybe your clue as well. Gotta log to find out.
 
Everything in the programming should be stock. As for the fuel pump its brand new and it's an aeromotive with a max of 90psi, so I'm definitely getting the pressure I need (I used a fuel pressure gauge at the rail during the entirety of the test drives, always within 55-60)

The programming is also something I cant do, I have a tuner who knows how to get the ecm for standalone and some other tuning, but I dont have access to wideband. The only means of reading anything live is from the OBD app I'm using.

I did notice last night that one of my O2 sensors wasnt getting any voltage (Bank 2), but the system was way too hot to deal with at the moment. Today I'm going to swap them around and see if one is just a dud for verification.

To keep with the suburban details, my fuel lines are entirely AN hosing from the tank to the rail with an aeromotive fuel filter inline. My throttle body is electronic.
 
Without a log its really a shot in the dark. Burst knock, and IAT advance and knock retard all could be pulling timing down low to prevent knock. Have you tried failing the MAF and see how it performs in speed density?
 
It's nice to see somebody working on an EFI issue know what their fuel pressure is. Here are a few things that come to mind:

  • Plugged cat on one side imbalances the airflow. But you might not have cats and if it has decent power at times, this is not likely.
  • A wiring or harness routing error has swapped the O2 sensors for bank 1 and bank 2
  • General ignition misfire issue
  • You have 1 or more bad injectors on the lean side. Some people say that LS engines always pile crud in the rear of the fuel rails (although I've never seen it)
  • There is a problem reading engine position, like a crank or cam sensor issue, or likewise the actual timing is off (could be as simple as damage to the harness)
  • LS engines like to form vacuum leaks on the intake, at lest through the mid-2000's. Not sure when they changed the intake gaskets. Probably a good idea to go all over and check for vacuum leaks anyway.
  • Has DoD been tuned out?
Can you scan the actual O2 signals when the problem is happening? If they are properly oscillating you know it has actually reached stoich. If the signal is just high or low the ECM may have overtuned due to misfires and you can't trust the fuel trims or O2 readings at that point.
 
Hey guys, major update:

I got new O2s in and the fuel trims are in MUCH better shape! However, one issue still remains.

At operating temperature: when I'm in drive or reverse and stopped, the motor will start pulling a lot of air and doubling the fuel. My MAF will read around 3.5lbs/min and the fuel rate will more than double to around 2.5gal/hr.

BUT

Once I let off the brake and start coasting, it immediately drops back down to normal, like 1.5lbs/min and 1gal/hr. It only does this when at a stop in gear.

Thoughts?
 
The increased fuel is just following the increased airflow reading. There is no reason for the engine to flow more air while stopped than it does idling forward. It's possible your MAF install flows air differently through the sensor than it was calibrated for, which throws off the calculation. Did you remove a screen or anything like that? The MAF calculates the power required to maintain temp on a heated wire and provides a frequency telling the ECU how much air that is.
 
The MAF is stock and brand new. It only has this problem in gear. If I'm in park or neutral with the brakes on, it idles completely fine.
 
I think there is still a vacuum leak. Pretty common thing to deal with. If your fuel trims aren't equal side to side, go to the lean side and fog it down with carb cleaner. Spray topside at the runners and then under the intake. If there is a leak you'll hear the rpm increase.
 
Having replaced the O2 sensors, the fuel trims have balanced out on both sides. I can check the manifold to see if there are any leaks, but I'm pretty sure I made sure before slapping it on.

I also read somewhere that it might be a faulty Throttle Body? I'm using Drive By Wire. I have one other electronic throttle body to slap in that I'll use to test that out!

Last thing, right before having to leave the garage today, I noticed I havent wired up the TCC control lead out of my PCM. So I'm guessing it doesnt know that I'm stopped on gear, could that be it?
 
If the tcc was applied coming to a stop the engine would stall.

Since you said the fuel trims are not running a big difference side to side but still going lean in gear it still can be a vacuum leak. But since it's not specific to one side it would be common to both banks. Spray carb cleaner around the throttle body and snorkel up to the maf.
 
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