07 Z06 long term fuel trim issues

[jtrakel]

Hello,

Hoping to find some ideas for an issue I am having with my Z06. I've included a data log, current tune, and modification list.

If outside temps are higher (70+) and I'm really getting into the car it's a matter of time before it starts to act up like it has a massive air leak, the car has been smoked multiple times for leaks. It's hard to replicate given unknown parameters besides it just being hot. The long-term fuel trim goes crazy when this happens as the car appears to be going lean. It happens almost like the flick of a switch, cars working fine and then suddenly it's not.

The issue seems to present itself after a few hours of driving. It's happened twice now:

First time during road tuning at highway speed going up a 2-4% grade under acceleration. Was able to do this around 7-10 times before the car acted up, bucking under acceleration acting as if fuel starvation was present. Had to sit at a gas station to cool down and limp home.

The second time this has happened, the logs attached was this past week during an Autocross event. Temps around 65-75 I did multiple runs and let the car cool when needed. Again, it just decided to enter a lean scenario and add tons of fuel. I had to end my autocross day, let the car cool for around 2 hours, and then drive it home. During the drive home, it appeared to act normally again but out of caution, I did not really "get on" the car.

- Compression test August 23: 140psi on all cylinders
- Leak down test August 23: Resulted in no leak down on any cylinder.
- OEM AC Delco spark plugs installed August 23: Gapped to .40
- OEM AC Delco spark wires were installed on August 23 as well
- Brand new OEM coil packs were installed in August, we also tested each coil/wire to ensure pulse and voltage were all even and working correctly with injectors, wires, and coils. I don't recall the computer setup used but it was alot of wires hooked up to the car!

[gtstorey]

Have you confirmed fuel pressure, especially when it's acting up?

[jtrakel]

Have you confirmed fuel pressure, especially when it's acting up?

We have via the HP program, I will be installing a manual gauge as well to verify rail pressure but from what the program can see it was steady

[gtstorey]

I can't see the logs at work. You say the long term trims go crazy, but what do the short terms do?

[blindsquirrel]

In the steady-state/idle parts of the log both O2s are switching normally, in the normal range. Looks an awful lot like it really is legit super lean and it's taking 25-30% added fuel to get it back to stoich.

The middle part of the log when you're on throttle O2s nosedive and flatline at less than 20mV. It doesn't have enough fuel to keep up. Check fuel pressure with mechanical gauge.

[blindsquirrel]

but from what the program can see it was steady

Whatever PID you're looking at does not mean what you think it means. There is no real-time fuel pressure data. The Flow Rate is simply a calculation, looked up from MAP vs the injector flow rate table.

[edcmat-l1]

100% fuel pressure problem. This is why I preach to the shops I tune for EVERY VEHICLE gets a mechanical gauge put on it, mounted where you can see it from the driver's seat, taped to the windshield, etc. the entire time we're tuning. No exceptions. You can't possibly PROPERLY tune an EFI vehicle without knowing what the fuel pressure is at all times. You can't make assumptions.

[edcmat-l1]

We have via the HP program, I will be installing a manual gauge as well to verify rail pressure but from what the program can see it was steady

That's interesting. That car doesn't have a pressure sensor.

[jtrakel]

That's interesting. That car doesn't have a pressure sensor.

The exact term of fuel pressure within the software could be wrong. I will be hooking up a mechanical pressure sensor in the very near future.

[blindsquirrel]

The PID for 'Injector Flow Rate' is not a measurement, it is a calculation derived from a lookup in the ECM table. Put a different number in that table and the scanner PID will show the new value. Hence the 'it does not mean what you think it means' comment.

[edcmat-l1]

The exact term of fuel pressure within the software could be wrong. I will be hooking up a mechanical pressure sensor in the very near future.

I'm saying there's no way for you to monitor fuel pressure through the scanner. Doesn't matter the exact term. You can't do it.

[blindsquirrel]

Oh. Just looked at the tune file.

Your injectors are bigger than the hard limit of 63.5lb-hr, they will need to be scaled. It's easy to do. Put in half the actual flow rate, half the IVT Term table, and double the Stoich table.

With a fixed rail pressure of 58 PSI and a naturally aspirated engine, the plausible range in the flow rate vs. delta table is from the 400kPa column (at WOT) to the 480kPa column (at max vacuum, like closed throttle coastdown). With the IFR table flatlined like that the ECM thinks the flow rate is the same whether there is lots of vacuum helping to suck fuel out the injector tips, as it is at WOT with normal atmo pressure resisting the injector flow. Obviously, the flow rate is not the same under those two extremes. There's a greater pressure differential ('Delta') across the injector at high vacuum so flow will be higher.

This is not the cause of your running problem, but injector data is the foundation every-damn-thing else in the tune is built on top of so might as well fix it sooner rather than later.

[edcmat-l1]

Totally off topic but not of fan of any of the spark table mods. Some of them just don't make sense. I can tell by looking at them whoever is doing the "tuning" doesn't quite have a full picture of how the E38 tables interact.

PS would love to know the cam specs. Idle set at 950? Solid roller .700 lift?

[edcmat-l1]

VVE can't be right. Not just the shape but comparing how the MAF has been dialed in the VVE can't be right. Especially if it has a cam that needs to idle at 950. My bet is it would not run on that VVE if you just failed the MAF.

[blindsquirrel]

I am so sorry. I am a bad person.

screenshot.25-09-2023 16.49.32.png

To make up for it, here's your file with the FIClinic 540cc injector data properly scaled by 50%.
2023-09-18 DEFCO Disabled MAF Trendline Smoothed - FIC540 injdata scaled.hpt

[edcmat-l1]

I am so sorry. I am a bad person.

screenshot.25-09-2023 16.49.32.png

To make up for it, here's your file with the FIClinic 540cc injector data properly scaled by 50%.
2023-09-18 DEFCO Disabled MAF Trendline Smoothed - FIC540 injdata scaled.hpt

Shame on you LOL

[jtrakel]

I am so sorry. I am a bad person.

screenshot.25-09-2023 16.49.32.png

To make up for it, here's your file with the FIClinic 540cc injector data properly scaled by 50%.
2023-09-18 DEFCO Disabled MAF Trendline Smoothed - FIC540 injdata scaled.hpt

Shame on you LOL

Thank you for responding so quickly, it shows this forum has humor and a desire to help out, very appreciated. The person working on my car with me is a good friend and this is a work in progress, not a final product so any feedback has been helpful thus far.

Let me enter an imaginary world for a moment. If my fuel pressure is good with a mechanical gauge, should there still be a concern with something mechanical given my original post and knowing the fuel pressure is accurate/good? I'm trying to rule out anything else that I can affect physically with parts etc.?

Back to the real world, I'll report back with idle fuel pressures once the gauge is installed. Are there other areas I should focus on or look into? The weather has turned so getting a good run outside right now is not the easiest!

Again, I appreciate all the feedback. Thick skin makes the world a better place!

[blindsquirrel]

For the fuel pressure test, it may be fine at idle. Usually snapping the throttle open will show a drop in pressure if there is a problem bad enough to cause what's in that log - though there was not much on-throttle data to go on. Enough to require a pressure test, though.

A vacuum leak will be worse at idle and run pretty much normal at heavy throttle and your log doesn't show that. The data and the way you've described the problem all sound like a fuel pressure issue. They'll do that, go from being fine to being not fine with no warning, then sometimes come back and act normal again. If you do find a low-pressure issue it would be good to be able to look at fuel pump current draw on both power & ground - connector overheating is pretty common, GM is not known for using robust FP connectors. Could be wiring, could be the pump, could be the regulator.

[Guy With A Chevy]

I'm saying there's no way for you to monitor fuel pressure through the scanner. Doesn't matter the exact term. You can't do it.

All the fuel pressure PID's are just readings from tables and approximates? Your saying the ecu does not even know the actual PSI? At the most someone could log pressure via a rail mounted sensor right?

So no more 40 degree timing at wot on a stage 2 cam NA setup?!

I see where they made the Idle Spark Advance-Base and Coastdown tables into dancefloors is that appropriate?! I know it helps with idle tuning to set it to a single value such as 24 degrees, any other reason?

These guys are amazing nice to see those IVT changes first hand, does that apply to upgrading injectors?

[kingtal0n]

I'm saying there's no way for you to monitor fuel pressure through the scanner. Doesn't matter the exact term. You can't do it.

People can use this
eBay item number:364492084876

0-100psi 0.5-4.5v Pressure sensor

Bring into EGR just like a wideband, 0-5v signal , analog offset in maths to calibrate

They can also do this with 0-300psi sensor for the transmission pressure to log wideband, fuel press, and trans pressure

Never say something can't be done because there is always a way