Anyone want to look over a 5.3 tune for my son's drag car?

[gtstorey]

Could the injector harness be swapped from side to side?

[kevin87turbot]

Could the injector harness be swapped from side to side?

I suppose that's possible.

[1991_z28_5.3]

I’m lost on where we are getting that the sensors or injectors are backward. This was the sequence of events:

1. Car fired, idled ok but REALLY rich. B1S1 O2 sensor reported way lean (8 mV), B2S1 O2 reported super rich (800+mV).

2. Unplugged O2 sensors (again the way the harness is laid in, there’s no way to reverse the plugs without pulling half the engine harness out), swapped the sensor side to side, plugged them back in with the wiring that was on that side of the car.

3. Same as 1. B1S1 went way lean, B2S2 went way rich.

Looked the car over and smoke tested, changed intake gaskets without removing injectors from the rails, or unplugging injector harnesses.

4. started car back up, NOW it’s B1S1 super rich, B2S2 super lean.

In all of the above situations, it idles well until fuel trims come in. It doesn’t seem to have the rich/lean imbalance until the computer starts taking the O2 sensors into account. That’s why I’m leaning towards a sensor issue. Am I smoking something, or is that logical?

[2xLS1]

Its such an easy thing to check by just unplugging one O2 and looking at the voltage of both. Doesn?t even have to be running. Just key on. You can check the injector harness by just ohming one injector plug to the correct pcm connector pins.

[1991_z28_5.3]

I just got a call from my son. He switched out the O2 sensors for some new Densos, with no change. It?s idling really well with STFTs disabled, but the O2 sensors still do the crazy split. That eliminates the sensors as the issue. What causes a bank to go lean? Vacuum leak, injector wiring/order - but it wouldn?t idle smooth if 4 injectors were out of sync, spark problems? I can?t think of any other causes for a lean bank. Am I on the right track here?

[1991_z28_5.3]

It’s not easy on that car, it is low and the exhaust is in the way. That said, I just asked my son to do it. He unplugged the driver’s side sensor and got a voltage drop on B1S1. Looks like they are wired correctly.

[2xLS1]

Reading is fundamental. You get a reading if 450 mv with an O2 open circuit.

[jsf55]

I reckon it's the injector wiring that's wrong, when warming up there's no O2 sensors being used, as soon as you hit the right temperature, the right hand O2 is controlling the left hand bank and telling it the exact opposite of what it needs, vice a versa on the left O2 sensor I'm not the first suggesting it !

[1991_z28_5.3]

I’m relying on a 14 year old with mechanical aptitude and a lot to learn. I travel frequently for work and am heading out of town today. I just had an entire flight to think about what you guys are saying, and it makes total sense. So much that I told my son to just swap plugs side to side and and see what happens. I suspect he was reading the wrong value in the scanner. I’ll report back later today with the result, but I’m guessing that it will be much improved. Luckily I’m smart enough to stay away from changing the things that I don’t understand yet, so we aren’t far off of a stock config, aside from the injector sizing, VATS and torque management. Hopefully the thing decides to cooperate with this change. Thanks for all of the input, and apologies if I came across as ignorant earlier. I was trying to wrap my head around the issue, and working with information related from home. Good times.

[1991_z28_5.3]

I was trying to figure out a mechanical cause of the rich bank/lean bank issue, and wasn?t considering that the sensors were sending the right data for the exhaust stream they are sensing, but that the PCM can be (likely is) the cause of the condition by making decisions based on bad data. I finally realized that if the PCM tells bank 1 to make a small adjustment richer, and doesn?t see that reflected in the signal from the O2 sender that *should* be reading bank 1, then it will go richer and richer. At the same time, that enrichment shows up on bank 2, so the PCM is commanding leaner and leaner. The results of those trims appear on the opposite bank of the engine, and snowball to the extreme.

Does that sound about right for swapped O2 sensors?

You guys were saying it, but it wasn?t immediately clicking. Sorry about that. I?m usually swifter on the uptake. Thanks again for the input, and for not banning me because I was being a moron!

Chris

[2xLS1]

it's a very common mistake made on swaps and has been seen here numerous times and has that exact telltale signature. More times than the injector sides swapped. I would still verify both.

[1991_z28_5.3]

2xLS1 - I really appreciate the help, and will report back with the results. My wife said they are going back to the shop after dinner to swap the wires. I’m as certain as I can be that the injectors are right. I toned them out with my multimeter when I was building the harness, and kept them bundled during my looming process. I would be really surprised if that was the case. Apparently I needed better labeling on the O2 leads.

[jsf55]

When i had an issue with my altered loom i went on lt1 swap . com and worked out which colour wire should be on No1 injector and pulled the sleeve back a bit to confirm, luckily i checked for earth at the same time and had snipped that wire out by mistake (slaps head smiley)

[2xLS1]

Earth? I thought you spoke English over there.

[1991_z28_5.3]

Funny. I’m working from a plane somewhere over Texas, but my son has swapped the O2 sensor plugs. I told him to unplug one and look for 450 mV, and he verified that he pulled the driver side plug, and B1S1 was reading 450mV. . It’s still doing the sensor split, so I’ll have him double check injector wiring. This is going to drive me insane, and my work schedule does not currently support a ton of time in the shop.

[jsf55]

Earth? I thought you spoke English over there.

Ground = Earth !

[1991_z28_5.3]

I've attached 2 logs from yesterday evening. My son unplugged the Driver's side O2 sensor after swapping the plugs around, and the log verifies that they are now correct. The second log shows that the sensors are still doing the crazy split. The car idles well, right up to the point that either fuel trims or closed loop kick in. Since the sensor plugs are verified correct, am I now looking for a mechanical/electrical cause? My Google-fu indicates that the causes are most likely vacuum leak, exhaust leak, O2 sensor wiring issue, or misfire on a cylinder caused by an injector/injector wiring issue, or a spark issue. Does that cover most of the mechanical causes?

I'm logging misfires as part of the VCM Scanner config. Is that an accurate value? I'm only asking because I've never seen a single misfire logged there. That leads me to believe that either the engine is running fine, or the PCM doesn't accurately log them.

[jsf55]

Without using your channel file and looking at spark advance it seems to be going the wrong way ? less at higher rpm than i would have thought ?

[1991_z28_5.3]

I haven’t spent much time looking at the spark, but it should be stock 5.3 tables, as read initially from the PCM. I haven’t touched them. I did notice that the line for spark advance seems to follow the rich cylinder. Anywhere there was a dip in O2 reading on the rich cylinder, the spark advance fell off just behind it. I’m thinking that the computer is trying to compensate for it.

I’m still perplexed by the rich/lean readings. I noticed one spot where the engine was around 3k RPM, and the O2 sensor readings became more normal for a split second I’ve read that a tiny exhaust leak will introduce extra oxygen at lower RPM, but the gas pressure will overcome that at higher RPM. Is that what I’m seeing here, or am I just hoping that it will be an easy fix?

[Alvin]

I've attached 2 logs from yesterday evening. My son unplugged the Driver's side O2 sensor after swapping the plugs around, and the log verifies that they are now correct. The second log shows that the sensors are still doing the crazy split. The car idles well, right up to the point that either fuel trims or closed loop kick in. Since the sensor plugs are verified correct, am I now looking for a mechanical/electrical cause? My Google-fu indicates that the causes are most likely vacuum leak, exhaust leak, O2 sensor wiring issue, or misfire on a cylinder caused by an injector/injector wiring issue, or a spark issue. Does that cover most of the mechanical causes?

I'm logging misfires as part of the VCM Scanner config. Is that an accurate value? I'm only asking because I've never seen a single misfire logged there. That leads me to believe that either the engine is running fine, or the PCM doesn't accurately log them.

I made this diagram a while ago because customers make this mistake more times than not. You can tell left/right bank by color codes, specifically if it has a tracer or not... See this link to know for sure that stuff is correct or maybe it will help the next person.

https://www.pcmofnc.com/2020/04/08/c...r-information/