07 LS7...car runs very lean during startup in open loop

[ssbowtie1]

Hi all,

I'm attempting to tune my 07 LS7 MAF in open loop. On startup, the car runs very lean for about 10-15 minutes, then the EQ error falls back in line. Looking for suggestions on what might cause this?

I've attached a log and tune that shows the issue. You'll notice the lean eq ratio reported by the wideband for the first 10-15 minutes of the log, then near the end of the log, the eq error is almost zero.

This issue happens on cold and warm starts.

[kevin87turbot]

Try this and see what happens. I just populated your Open Loop Inj Gain tables back to stock.
This may cause it to go rich upon startup. If so, you can zero your Offset vs Inj Temp table and fix that issue.

2007 z06_Ihab starter file OL MAF MS9 KW Mod.hpt

[jpierro79]

first of all your running a maf based tune we need to step back. Lets start with the car can NOT trim fuel in open loop. Youre VVE tables are not adujusted properly can we see your OEM tune to do a comparison and have your mod list and year of vehicle?It might be a 2007 ls7 is it the original car and motor or a swap? Just pertinent info i need to help? I can help you and help A ton more over the phone to explain and help you understand issue. I going to assume youve made at least 2 mods that being headers and an air intake. Based on the lean and tuning maf only is really not the best as the car resorts to VVE open loop idle and will stay that way until it reaches a temp that allows closed loop. There is a lot of info to log. some missing like open vs closed loop commanded ect. Id be more than happy to help. But we kind of need to get a full understanding of what your knowledge base is and where your car is at so to speak and what you expect from it. PM me if your interested I do not charge cause I just have this passion. If you bring the car to me on the other hand and say fix it yes i charge. Please keep in mind as you are making the adjustments. Unless you wish me to then we go on other terms.

[ssbowtie1]

Try this and see what happens. I just populated your Open Loop Inj Gain tables back to stock.
This may cause it to go rich upon startup. If so, you can zero your Offset vs Inj Temp table and fix that issue.

2007 z06_Ihab starter file OL MAF MS9 KW Mod.hpt

Thank you for the reply. Per your suggestion I set the open loop gains back to stock and got the same results. The attached log shows pretty clearly large lean error on startup, then after a ride around the neighborhood, things settle back down.

[ssbowtie1]

first of all your running a maf based tune we need to step back. Lets start with the car can NOT trim fuel in open loop. Youre VVE tables are not adujusted properly can we see your OEM tune to do a comparison and have your mod list and year of vehicle?It might be a 2007 ls7 is it the original car and motor or a swap? Just pertinent info i need to help? I can help you and help A ton more over the phone to explain and help you understand issue. I going to assume youve made at least 2 mods that being headers and an air intake. Based on the lean and tuning maf only is really not the best as the car resorts to VVE open loop idle and will stay that way until it reaches a temp that allows closed loop. There is a lot of info to log. some missing like open vs closed loop commanded ect. Id be more than happy to help. But we kind of need to get a full understanding of what your knowledge base is and where your car is at so to speak and what you expect from it. PM me if your interested I do not charge cause I just have this passion. If you bring the car to me on the other hand and say fix it yes i charge. Please keep in mind as you are making the adjustments. Unless you wish me to then we go on other terms.

Thank you for the reply. I have not tuned the VVE yet. So far I'm just working on the MAF tune in open loop. I am ready to start open loop VVE tuning, but I was hoping to resolve the lean issue I'm seeing before I move on. I do plan on running a blended MAF/VVE tune as well as turning closed loop and fuel trims back on. Everything is off to allow me to tune using my wideband. My mod list and stock tune file is below:

2007 Corvette z06 (6spd)
Halltech MF103 CAI
Mamo ported throttle body
Mamo ported MSD intake
Stock unported heads with PSI 1511 springs
220/244 115.5 cam on Comp Cams XE-R lobes
Kooks 1 7/8 headers and catted X-Pipe
AMT motor mounts
AFR 500 wideband
91 octane E10 California Fuel

[jpierro79]

there are a lot of adjustmenst required per each cam design. Here's where you need to start. 1 Your idle must come up depending on stage of cam. You need a certain amount of vaccuum. 2 91 e10 is hurting you bad.3 your volume of the intake must be changed as youve changed that. The ported thottle body is not too big of issue.
Heres what im going to suggest you raise your idle to 700-800. A lot youve done
Now youve done a fair amount of timing adjustments most of which are safe please one thing. ANY spark multiplier can apply to multiple charts causing many erratic timing and knock retard issues. IAT timing only adding a degree or 2 is ok but beyond that do rember its all multiplied. I would suggest against the ect multi hot = detonation. One thing forgotten is intake valve temperature afr and timing multipliers. Redcuding the ect multiplier is a good idea for more consistent timing giving you the play room so to speak on high temp timing. Less variation. So Id say you have a fair amount of knowledge. Looking at changes i think we might need a phone convo to figure this out. including you dont need to change stoich to get afr to change just turn on virtual sensor
your o2 readiness is set at an ect of 490 i think this is your problem truthfully2007 z06_Ihab starter file OL MAF MS9 (2) ltft reenable.hpt
try this you put your ltft enablement at over 400 degrees ect
dont feel dumb either please you probably didnt know the knew vcm scanner can turn off ltft and closed loop and forgot to reenable your fuel trims you basically disable your o2 sensors to trim your fuel by accident
if you wish to dial it in further i can be of assistance if your truly interested pm me your phone and ill contact you via text. You might know something i dont. LOL we learn everyday even if weve beeen doing it for 20 years

[ssbowtie1]

there are a lot of adjustmenst required per each cam design. Here's where you need to start. 1 Your idle must come up depending on stage of cam. You need a certain amount of vaccuum. 2 91 e10 is hurting you bad.3 your volume of the intake must be changed as youve changed that. The ported thottle body is not too big of issue.
Heres what im going to suggest you raise your idle to 700-800. A lot youve done
Now youve done a fair amount of timing adjustments most of which are safe please one thing. ANY spark multiplier can apply to multiple charts causing many erratic timing and knock retard issues. IAT timing only adding a degree or 2 is ok but beyond that do rember its all multiplied. I would suggest against the ect multi hot = detonation. One thing forgotten is intake valve temperature afr and timing multipliers. Redcuding the ect multiplier is a good idea for more consistent timing giving you the play room so to speak on high temp timing. Less variation. So Id say you have a fair amount of knowledge. Looking at changes i think we might need a phone convo to figure this out. including you dont need to change stoich to get afr to change just turn on virtual sensor
your o2 readiness is set at an ect of 490 i think this is your problem truthfully2007 z06_Ihab starter file OL MAF MS9 (2) ltft reenable.hpt
try this you put your ltft enablement at over 400 degrees ect
dont feel dumb either please you probably didnt know the knew vcm scanner can turn off ltft and closed loop and forgot to reenable your fuel trims you basically disable your o2 sensors to trim your fuel by accident
if you wish to dial it in further i can be of assistance if your truly interested pm me your phone and ill contact you via text. You might know something i dont. LOL we learn everyday even if weve beeen doing it for 20 years

Thank you for the feedback and all the good points you've listed which I will take into account as I move further into the tune. I'll shoot you a PM with some more questions.

Right now my main concern is trying to figure out why the car is so lean when I turn the car on in open loop, but after a short drive everything settles back to normal. Perhaps this issue will resolve itself once I finish tuning the VVE and go back into closed loop, but I haven't seen anyone else have this issue, so I'm concerned and feel like it would be better to resolve it before moving further with the tune.

I'm sure CL and turning my o2's back on will trim the lean condition at startup, but there must be an issue with the tune, or mechanical causing the lean condition. Ideally I'd like to fix that so when I turn the o2's back on, they won't have to trim to correct this.

[240sxpooter]

Have you done a smoke test to make sure there are no intake leaks?
Maybe there is a mechanical air leak that is reducing as the engine comes up to operating temp.
What about a fuel pressure check?

[jpierro79]

of course vacuum leak but let me explain if its not surging its not leaking. GM will surge. Doubt its a leak headers and intake as I stated before alter characteristics as long as vacuum maintains at idle its no vacuum leak. Im seeing for a cammed car consistently good vacuum. Its in the vve maf blend tune . I suggest tunning the VVE on NA up to about 70-75 kpa and then enable pe and as long as your pe isnt overshooting meaning going past your intended afr then dont move the maf lower. If at 2700 your pe shoot to 11.1 and you intend 12 then move youre maf down till you get the desired effect of your afr under airlfow dynamic and rpm disable.
I tune maf second cause gen 4 has intake valve temp calculator that modifies fuel and you can have same airflow at 3200 1/4 throttle and 1/3 throttle at 2500 and 2 different intake valve temp multipliers so I tune VVE first.
of course though you must use a wideband.