Tune memory loss
 

I have a 2003 Z06 running a 6.0 iron block using Zo6 heads and intake with a 601 competition cam. Took the car on trade so know nothing about the internals, tune etc but it had a bottle on it and had been used as a toy ... we've had the bottle removed.

On initial start up it will load up and burn rich to the point of almost flooding itself out. If I hold the pedal steady it will surge 500 rpm or so. Almost like the computer is not recognizing any of the sensors but the check engine light is not coming on.

When driving it is very erratic and you must constantly burp it to burn the excess fuel - As long as you're accelerating it goes like a demon but at low rpm "in town " driving it will spit and sputter then catch and take off. Open road immediate fuel is 8-9 mpg. After driving about 9 miles it will clear up and like you flipped a light switch it runs perfect - immediate mpg jumps to 18-19 at the same gear and rpm. Until you turn off the key. Once it clears up you can park and it idles perfectly as long as you do not turn off the key. Once killed it but kept the key in the on position and when I restarted it it continued to run fine.

I don't feel that it could be temperature related because it will start flooding again when you restart it even though it's still hot. If it were a mechanical problem I doubt that it would fix itself every time at around 9 miles or XX minutes. It's pretty consistent.

I've tried disconnecting the battery and pulling the fuses but neither makes a difference. Someone told me that the computer has the ability to reset itself (?) - Can the computer "forget" it's tune? Is there a power wire or fuse I can look for?

There is no way for it to "forget" the tune, it is what it is. That's not to say things like LTFT's aren't reset when you pull power, etc.

Need to pull the tune and get a log of it behaving this way, especially around the time when it switches over to being normal'ish. Sounds like it may be running (poorly/rich) in open loop for a while or something then finally going into closed loop and behaving normally. But I'd have to see the tune and a log to say any more than that.

A different size block, different cam and running on a "bottle". Lots of room for the tune to be off, not to mention faulty parts. Find a way to send Schpenxel the tune and a log. He can fix it if it is the tune.

open loop
 

When it was on the scanner I do remember seeing open and closed loop on the read out, and the fuel pressure is the only thing that was reading in the red - but we didn't record it. If it is tuned too rich would the system automatically reset it to run properly after a period of driving or would it just continue to run as tuned? (Please pardon my ignorance about this ).

Thank You

Fuel pressure won't read correctly on these cars (no fuel pressure sensor), so it'll always say 58psi no matter what (except on ZR1's)

It depends on whether it's in closed loop or open loop. Once it's in closed loop it's going to target lambda=1 (14.7:1 for gasoline) regardless. It could be running richer or leaner when in open loop though, as the computer doesn't do any corrections to fueling then.

That's why I was thinking it's in open loop when it's running like crap/rich/etc. then is OK once it switches to closed loop where the computer will adjust fueling back to 14.7:1 on it's own regardless of the tune. If that's the case then there's two things I would look at--1. why is it so rich when in open loop? MAF or VE tables are the obvious place to start and 2. why is it taking so long to go into closed loop

Thanks for the insight, I really appreciate it. What you've described reflects the problem I'm having. I don't know if it was ever properly re-tuned after the bottle was taken off or if they may have "turned it up" trying to get more power. If the tune is way out of spec could that cause it to stay in open loop longer while the computer self corrected?

Am going to re-scan it and see if any new codes have shown up - check engine light has not come on since we cleared it. How long of a run time should I record (2-3 minutes or just a snapshot) - Before and after is easy, should I also try and capture it as it transitions from bad to good while driving?

Again, Thank You.

G

What are you using as a scanner?

There are some settings that can be changed in the tune for how long it has to wait before it goes into closed loop. I think it can be set based on time and/or engine coolant temp but would have to look to be sure

If you are still using your MAF sensor and the stock open/closed loop system there can be numerous reasons why you are having issues with starting/idle and P/T fueling
1st The stock tune your engine is started in OPEN LOOP this is where the ECM is NOT making any adjustments to fueling and the fueling is dictated strictly based on your OPEN loop tables--NO 02 input is used this is all correctable with tuning
Once your coolant temp reaches approx 140* it switches to CLOSED LOOP where now the fueling is adjusted based on your front 02 data-----( after the engine is warm past 140* to switch to CL is on a timer rather than temperature The timer is like 20 seconds
In closed loop the fueling is constantly being adjusted based on your front 02 data and is adjusted at P/T via your fuel trims---
If you have LT headers this is a common issue for a rich stumbling idle as the front 02's get moved as much as 3' back and never read right again-They never heat up properly and always read RICH This is why LT's are illegal in most states as it skews your P/T AFR's to run way rich
You can make adjustments with tuning but it will never ever be as stock--to try and make it leaner at P/T---Often times with highly modded engines tuners will simply disable all the long term fuel corrections OR by lowering the front 02 switching points Only by using a wideband 02 set up can you get the P/T fueling close back to the stoich AFR of 14.68-1
WOT fueling is a whole other thing and requires again the use of a wideband to correct--However WOT fueling is much easier to get to what you want it to be ( on a N/A engine for a DD car I would shoot for a safe 12.7 AFR --On a boosted engine you need a WOT AFR in the 11's
With NOS it depends whether you have a dry or wet system--But ideally just as an N/A engine it should be safe at 12.7 as the NOS system either wet or dry should self correct the WOT fueling
More info on your mods may help like knowing if you installed larger injectors ( never install larger injectors than you need--There is NO HP advantage with too big injectors !!!)Plus larger than needed injectors seem to be what;s going on in your car as they create all your mentioned issues at P/T

Thanks for all the info - Working under the assumption that no codes means that everything should be working properly, I know where to start looking now - wish I knew more about what may have been done to the car and what injectors I'm working with. Going to make sure the loop wasn't left open for tuning and then see how it's set to close ( time or temp), then check the temps on the front o2's and the AFR while rough and when it's running properly.

Will let y'all know what the scan says. Thanks Again.

You are being misled. Deal with Schpenxel.

Seems to be the same basic info. Staying in open loop appears to be the culprit - does have long tube headers so it's possible the o2 isn't heating up quickly enough, and the previous owner may have just screwed up the tune. Getting it scanned and having the results reviewed by someone who knows what they are looking at is my next step.

Thanks for the info

Not really unfortunately. Any engine/transmission code can be disabled in the tune so it will never be reported, no matter what. So you could literally be missing a spark plug and still not have misfire codes, for example.

tblu92 is great at typing long posts with enough basic tidbits that are correct enough that people think he knows more about tuning than he does--but the details are almost always wrong (and some of them are in this case as well). But, to your point, I agree that it does sound like the issue is coming/going when it's going to closed loop, so I'll try to refrain from this turning into me picking apart his posts.

Just a guess at this point, but the open loop running like crap / closed loop running better idea seems like a likely candidate to me

On a stock tune it goes into closed loop almost immediately though (like, within seconds). Short term fuel trims are active initially, then long term fuel trims turn on at a higher coolant temp (more like the 140* temp tblu said earlier) but yeah, all that can be changed.. so there's no way to know how it's setup without reading the tune

The good news is anyone with HPTuners can log and pull the tune that is in there FOR FREE. No credits required until you're trying to write changes, so if you can find someone local that has HPTuners they can pull the tune for you easy enough

[QUOTE=schpenxel;1598023926]Not really unfortunately. Any engine/transmission code can be disabled in the tune so it will never be reported, no matter what. So you could literally be missing a spark plug and still not have misfire codes, for example.

tblu92 is great at typing long posts with enough basic tidbits that are correct enough that people think he knows more about tuning than he does--but the details are almost always wrong (and some of them are in this case as well). But, to your point, I agree that it does sound like the issue is coming/going when it's going to closed loop, so I'll try to refrain from this turning into me picking apart his posts.

Just a guess at this point, but the open loop running like crap / closed loop running better idea seems like a likely candidate to me

On a stock tune it goes into closed loop almost immediately though (like, within seconds). Short term fuel trims are active initially, then long term fuel trims turn on at a higher coolant temp (more like the 140* temp tblu said earlier) but yeah, all that can be changed.. so there's no way to know how it's setup without reading the tune

The good news is anyone with HPTuners can log and pull the tune that is in there FOR FREE. No credits required until you're trying to write changes, so if you can find someone local that has HPTuners th

ALL the information and data I quote comes directly from the tune files using EFILIVE software--I do not make this stuff up--If someone challenges the data I quote I ask If the are a tuner at all or if they have any true facts from readiing a tune file with real software--- All the OL/CL facts i quote aew taken directly from most all LS tube files

[QUOTE=tblu92;1598064863]Honestly, the fine details are a little over my head anyway but I now have a better understanding of where to start looking. Have found some local guys who will scan it for me, just need the time to run it by their shop.

Thank You again for the help, I'll let you know what I find out - is there a preferred amount of time that I should record the data download or is it more like a snapshot?

[QUOTE=tblu92;1598064863]Reason for long posts is this tuning stuff is "complicated " When having issues that won't go away there are usually no simple answers----