One of my buddies from Arizona liked my Vette so much he picked up a used '05 a few weeks ago. I just got off the phone with him and he instantly upon getting the car to his house started a head and cam swap on the car. We didn't cover the details of what he put in, other than he was planning to bring the car up to me in couple of weeks to show it off and get the car tuned over here. I was telling him that without a tune on the car it won't be good for the car to drive that far with the recent work done? He said it would be fine and that he bought one of those Diablo Preditors?

As big headed my friend can be, I don't want him to mess up his new ride because of something that could have been avoided.

He has about a 4-5 hour drive up to my place. Would the car be ok with out a tune or am I correct that he will need a tune? Or will that Diablo Preditor cover his butt with a basic tune?

I wouldn't drive it with out the tune, I would call up a tuner just to verify.

Your friend should get a basic tune prior to driving that sort of distance.

If the injectors are stock...you can drive it to where it needs to be finally tuned. The PCM will be in closed loop and command a 14.7 AFR so you should be fine. Spark timing should be fine as well since the stock calibration will most likely get some timing "added" to it after the tuner gets done. Idle might be the biggest pain in the *** but once you get cruisin....you should be fine.

If the injectors are changed its a whole other story.

Just tell him to keep his boot out of it.

This same method apply's to boosted installs as long as you stay out of boost!!!! Got to love a closed loop system!

Howard

If the injectors are stock...you can drive it to where it needs to be finally tuned. The PCM will be in closed loop and command a 14.7 AFR so you should be fine. Spark timing should be fine as well since the stock calibration will most likely get some timing "added" to it after the tuner gets done. Idle might be the biggest pain in the *** but once you get cruisin....you should be fine.

If the injectors are changed its a whole other story.

Just tell him to keep his boot out of it.

This same method apply's to boosted installs as long as you stay out of boost!!!! Got to love a closed loop system!

Howard

So what happens if the injectors have been changed? Can't be done or just more pain in butt?

If the injectors are stock...you can drive it to where it needs to be finally tuned. The PCM will be in closed loop and command a 14.7 AFR so you should be fine. Spark timing should be fine as well since the stock calibration will most likely get some timing "added" to it after the tuner gets done. Idle might be the biggest pain in the *** but once you get cruisin....you should be fine.

If the injectors are changed its a whole other story.

Just tell him to keep his boot out of it.

This same method apply's to boosted installs as long as you stay out of boost!!!! Got to love a closed loop system!

Howard

Are all newer cars this way or is this just with Corvettes?

So what happens if the injectors have been changed? Can't be done or just more pain in butt?

I would like to know the answer to this question also?? :coffeetime:

Guys this is how it works it short form;

All fuel injection systems are what we call a "closed loop" system. Once the car warms up the oxygen sensors provide a signal to the PCM to tell if the AFR is above or below 14.7:1 AFR. This AFR is what is called the stoich ratio. This is where complete combustion and the least emissions are made. As long as the car is in "closed loop" the PCM will keep the AFR at this ratio. If it's richer the stoich it lowers the injector pulse width. If its leaner it increases the pulsewidth. This means that the AFR is always within range or at least good enough to cruise down the highway. Now this doesn't mean you leave it like this as the computer knows how much correction it needs to stay at 14.7. These are what we call fuel trims. The PCM will tolerate up to -/+ 25% before an engine light comes on. A properly tuned car should run at trims within 3-4 % of 0 correction. Many times the trim error can carry into other parts of the PCM's calculation.

Now power enrichment is a whole other story. When power enrichment is activated, the car goes back into open loop and fueling is now based off the MAF (typically) and also VE table values. These values are fixed values and could cause a rich or lean situation. Either way the car needs to be tuned. Again I'm skimming across this to give you an idea.

Since final fuel calculation considers injector flow rates and injector characteristics if those values are not corrected when injectors are changed, the computer has a hard time calculating anything. This will cause the PCM to way over correct to its threshold. One of the keys of tuning is to let the PCM know exactly what it is handling and what kind of air it is moving through the engine.

Injectors are easy enough to change that I just have customers bring them and we install them here when they show up.

Again this is a generic overview to make the point.

Hope it helps!

Howard

Guys this is how it works it short form;

All fuel injection systems are what we call a "closed loop" system. Once the car warms up the oxygen sensors provide a signal to the PCM to tell if the AFR is above or below 14.7:1 AFR. This AFR is what is called the stoich ratio. This is where complete combustion and the least emissions are made. As long as the car is in "closed loop" the PCM will keep the AFR at this ratio. If it's richer the stoich it lowers the injector pulse width. If its leaner it increases the pulsewidth. This means that the AFR is always within range or at least good enough to cruise down the highway. Now this doesn't mean you leave it like this as the computer knows how much correction it needs to stay at 14.7. These are what we call fuel trims. The PCM will tolerate up to -/+ 25% before an engine light comes on. A properly tuned car should run at trims within 3-4 % of 0 correction. Many times the trim error can carry into other parts of the PCM's calculation.

Now power enrichment is a whole other story. When power enrichment is activated, the car goes back into open loop and fueling is now based off the MAF (typically) and also VE table values. These values are fixed values and could cause a rich or lean situation. Either way the car needs to be tuned. Again I'm skimming across this to give you an idea.

Since final fuel calculation considers injector flow rates and injector characteristics if those values are not corrected when injectors are changed, the computer has a hard time calculating anything. This will cause the PCM to way over correct to its threshold. One of the keys of tuning is to let the PCM know exactly what it is handling and what kind of air it is moving through the engine.

Injectors are easy enough to change that I just have customers bring them and we install them here when they show up.

Again this is a generic overview to make the point.

Hope it helps!

Howard


Thank you so much, great answer! Round of beers for you!

Howard,

Couln't have said it better. :thumbsup3: