LTFT/STFT Split - One bank adding way more fuel - LS3 Heads/Cam

[Gabbiani]

Heads/Cam/Headers LS3 Vette.

Take a look at the log. At just about all lower air flow ranges the drivers side adds significantly more fuel than the pass side. Wideband was not connected on this run.

Installed new factory 02 sensors.

Disabling fuel trims makes the car run rough at low rpms. It seems to want the fuel which makes me think air leak.

Stock ls3 intake manifold. Replaced intake gaskets and issue continues.

Installed new plugs. Old ones looked fine.

New MSD wires.

I checked manifolds and collectors for leaks with stethoscope. None found. Still changed gaskets at request of vendor. I am almost positive there are no leaks before or around the 02 sensors.

Motor seems healthy. Runs very well wide open throttle and fuel seems spot on to what I command at WOT according to wideband.

I'm running out of ideas. Could the installer have cracked the intake manifold with too much torque on bolts? Cracked around one of the driver side ports so only affecting that side?

Using extensions that came with ARH headers. About to swap extensions to opposite sides just to check.

Have another set of stock injectors I may try.

Drive 5 is with fuel trims enabled still. Other is with them disabled. After WOT run on disabled log it felt like it was missing and wideband would fall off the scale lean at times.

Thanks - Sorry such a long post

Drive 6.hpl

Drive5.hpl
17.hpt
LS Gen 4 Auto.cfg

[HartRod]

Can't help, but am along for the ride.

[neoh2ning]

vacuum leak or bad injector

[Gabbiani]

Tried another set of low mile stock ls3 injectors. Same split. All injector orings looked good on both sets.

So I really think that leaves vacuum leak. The npp port is still sealed on the intake. Brake booster is connected and can't feel/hear any leaks in its tube. LS3 intake doesn't have any other vacuum ports. EVAP?

I think that pretty much leaves either cracked intake or not sealing on the head surface. They are the new PRC heads. Vendor said they weren't milled enough to cause issues.

Thanks all.

[Gabbiani]

I turned dynamic airflow back on. (Still stock haven't tuned speed density side yet) It kept the same differential between sides just pushed both richer. To be expected because the cammed VE should be lower and low rpm/map.

[Gabbiani]

Swapped to a known good intake. Same split.
Swapped sided on the 02 extensions. Same split.

Turned off all fuel trims and started tuning with the wideband in the xpipe. Car runs and drives ok. Seems to make power. Will have it on the dyno soon.

I'm just about at a loss. Either something mechanical is going on with head/valves sealing or there is an electrical issue. I did see one code for bcm but it never came back after clearing. A audio shop did tie into stuff below the dash at the pass kick panel. Going to have to find out what each of those are. I'm hoping they grabbed an 02 sensor for amp turn on or something.

Still get regular codes for pass 02 sensor (performance, heater, ground pretty much all of them). Again new sensor and swapped the extensions.

[HartRod]

Have you logged the misfires?

[Gabbiani]

Global or per cyl? I have looked at the total count. On a cam/exhaust car I find the misfires get pretty unreliable. Usually desensitize until it stops incrementing. (Assuming a car that runs right)

[HartRod]

Global or per cyl? I have looked at the total count. On a cam/exhaust car I find the misfires get pretty unreliable. Usually desensitize until it stops incrementing. (Assuming a car that runs right)

Per cylinder. I have a similar problem going on with mine. The misfire count on the passenger side (2/4/6/8) goes crazy when I rev the engine up. The drivers side has virtually none. So I know I have something going on on just the right side, just not sure if it is electrical or mechanical. Just thought this may help you narrow it down.

[Gabbiani]

Will log them all next time I see the car.

[ingsteve]

Do you have cats? If yes check them, are u sure you didn't damage one cat only?

[Gabbiani]

No cats. Thanks.

[silverbullet08]

Having the exact same issue on a cammed ls3 twin turbo vett we just finished. Cometic gaskets ARP studs and big cam. Driver side 02 reads leaner adding +3-5% while passenger side is pulling 3-4%. I put a wideband in each bank to see what the deal was. Commanding 14.7 stoich and idles 13.8-14.2 on my LM2 programmed for 14.7. Tried the wideband in another car and read 14.7 fine. Even pulled both cars side by side hooking both cars to the WB at the same time. Still showed a split of about 7%. Checked for vacuum leaks and found none. Tried pulling injector plugs and all responded well "DW 65lb with 2k miles". All the plugs match up good with even color.... Car runs good and pulls hard up top with consistent fueling...

Question for "Gabbiani" what type of cam did you go with? Dual valve springs?

[realcanuk]

Having the exact same issue on a cammed ls3 twin turbo vett we just finished. Cometic gaskets ARP studs and big cam. Driver side 02 reads leaner adding +3-5% while passenger side is pulling 3-4%. I put a wideband in each bank to see what the deal was. Commanding 14.7 stoich and idles 13.8-14.2 on my LM2 programmed for 14.7. Tried the wideband in another car and read 14.7 fine. Even pulled both cars side by side hooking both cars to the WB at the same time. Still showed a split of about 7%. Checked for vacuum leaks and found none. Tried pulling injector plugs and all responded well "DW 65lb with 2k miles". All the plugs match up good with even color.... Car runs good and pulls hard up top with consistent fueling...



Question for "Gabbiani" what type of cam did you go with? Dual valve springs?

I have a similar split in trims. I don't think its an issue.. I chased this issue for a long time and decided to ignore it. You can get it a bit better by playing with cylinder gain in the fuel injectors.. but I think its a waste of time. I would assume its due to slight differences in something like cam lobes... runner... valves... don't really know.

[Gabbiani]

I'm trying to remember now. Its something like a 228/234 on a 112. Dual valve springs on the PRC as cast heads with cometic gaskets..

Pretty much similar situation as the two above. My split is more like 15% though. Right now fuel trims are off and it runs fine. As soon as we get another nice weather day I'm going to try the wideband in each collector to see if it is really different. If not then just leaving them off and tuning to the wideband.

[Gabbiani]

Dug through all the wiring the audio shop did. There was one pink wire they stripped that was not an O2 wire. I did solder and heat shrink it though.

I ohm'd out the connectors on the O2 sensors back to the computer and the banks were identical for each pin.

Still waiting for a chance to get under the car with a wideband.

[Gabbiani]

And finally the answer:

Doesn't matter what part it is or who you buy it from - measure and verify everything that goes in the motor. One of the pushrods was a couple tenths shorter than the others. Not enough to notice when you hold all in your hand but two side by side you sure do. They were labled the same. Manufacturer screw up?

Car now idles and sounds much better. Split is gone. I'm really surprised it had that big a swing one O2 readings.

[HartRod]

That suxs, but glad you found the problem. I had a similar issue. It was due to me not having the exhaust hooked up...:-(. Oh well, live and learn!