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I recently installed long tube headers and hi flow cats, the manufacturer stated there might be an issue with the air/fuel ratio. If my car isn't showing the dreaded check engine light, is everything cool?

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Welcome to the forum. I just installed headers as well but I installed extra O2 bungs for a wideband as I am running a supercharger, which will come in handy when I get the tune modified. You are not going to see the full gains of LT headers with the factory PCM tune and you run the risk of running lean at WOT. A custom tune will also ensure you will not get the CEL due to the high flow cats.
 

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Welcome to the forum. I just installed headers as well but I installed extra O2 bungs for a wideband as I am running a supercharger, which will come in handy when I get the tune modified. You are not going to see the full gains of LT headers with the factory PCM tune and you run the risk of running lean at WOT. A custom tune will also ensure you will not get the CEL due to the high flow cats.
I am running a custom tune, but the headers etc weren't installed yet. Do you think I should get an update?

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Back in the day, cars were rich from the factory and headers were just bolt on and go. In the 70's they leaned out the A/F and when I put headers on my '75 I bought a carter street/strip kit and rejetted and changed the metering rods to get it right. Now days, you need to change the tune to affect how long the injectors spray, I guess. Too bad they don't just sell bigger injectors.
 

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I recently installed long tube headers and hi flow cats, the manufacturer stated there might be an issue with the air/fuel ratio. If my car isn't showing the dreaded check engine light, is everything cool?

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If the exhaust changes result in better flow through the engine -- which may be questionable without a corresponding change to the intake system -- the engine controller should "adapt" to the higher air flow and add more fuel. This is done by simply leaving the injector on longer.

But this can bring with it other problems. Essentially the fuel system is having to flow more fuel, maybe most of the time. If the fuel system has plenty of margin this extra fuel flow may not over tax the fuel system. But the system may not have extra margin, at least not in all areas. I'm not worried about the fuel pump but the fuel lines that feed the injectors. When the fuel injector is opened and left on longer this can result in a pressure drop that might have the injector output tapering off towards the end of the injector pulse. This might lead to erratic fueling and the engine running sub-optimally.

Worst case is under WOT. A high output engine running at WOT uses a ferocious amount of fuel. Instantaneous fuel consumption can drop to the low single digits. At WOT some cars can drain their fuel tank in just minutes. Even with a stock engine/exhaust the fuel system may be hard pressed to keep up. Make changes that increase the amount of air the engine can flow and thus the amount of fuel the engine requires at any given RPM/load and you may have an engine that doesn't get under all conditions the proper supply of fuel.

This may or may not result in a CEL. If the engine is too starved for fuel to the point it misfires, well, that's a check engine light. If the engine controller's attempt to adapt by adding more fuel goes too far this can trigger a CEL. But less than optimum fueling that may not be bad enough to trigger a CEL is still less than optimum fueling and can have consequences beyond just leaving some HP on the table, so to speak.

To really know the fueling is ok the engine should be dyno'd and the exhaust gas fed to a 4 gas exhaust gas analyzer to verify the engine is receiving the correct AFR throughout it full RPM range. A custom "tune" can be created to supplement the factory "tune" but at the same time the rest of the fueling system's performance can be validated to ensure that it can meet the demands the custom tune puts upon it.
 

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Yes, you’ll need a tune. To make more horsepower you’ll need more fuel.

Increased air in the cylinders from improved exhaust scavenging will lean your a/f ratio.

Don’t add more fuel, don’t get more horsepower. Kinda like Monopoly.

The factory tune won’t magically figure it out at WOT and may be trimming fuel at part throttle. It may set a code if long term fuel trim strays too far from the desired target.
 

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The size of the stock injectors can provide plenty of fuel, it's the waveform that dictates how much fuel is delivered...hence the need for a tune.
The amount of fuel added is based on the amount of air the engine flows. This is measured by the MAF. Additional fueling precision is obtained using the O2 sensors.

Within reason the engine controller can adapt/adjust to a change in air flow by increasing the width of the injector pulse. While there is a considerable range of adjustment if the adjustment range gets close to +/- 10% off the the base line the engine controller may throw an error code.

Under WOT throttle -- and even close to it -- the engine controller can go open loop mode and rely on fuel maps to fuel the engine. However, these fuel maps may not be optimum for a modified engine, one that has an exhaust that can flow better. In this case the engine can run lean.

Thus a tune may be needed -- a tune based on info gleaned from dyno testing with exhaust gas analysis -- to provide for a more optimum fueling based on the engine mod's. The base line may need to be adjusted so the engine controller can add more fuel without exceeding its limits and for WOT (or at least open loop) operation the fuel maps can be made richer to ensure the engine receives the proper amount of fuel.
 

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The amount of fuel added is based on the amount of air the engine flows. This is measured by the MAF. Additional fueling precision is obtained using the O2 sensors.

Within reason the engine controller can adapt/adjust to a change in air flow by increasing the width of the injector pulse. While there is a considerable range of adjustment if the adjustment range gets close to +/- 10% off the the base line the engine controller may throw an error code.

Under WOT throttle -- and even close to it -- the engine controller can go open loop mode and rely on fuel maps to fuel the engine. However, these fuel maps may not be optimum for a modified engine, one that has an exhaust that can flow better. In this case the engine can run lean.

Thus a tune may be needed -- a tune based on info gleaned from dyno testing with exhaust gas analysis -- to provide for a more optimum fueling based on the engine mod's. The base line may need to be adjusted so the engine controller can add more fuel without exceeding its limits and for WOT (or at least open loop) operation the fuel maps can be made richer to ensure the engine receives the proper amount of fuel.
Umm, the 5.7 and 6.4 use a MAP sensor...no MAF. Not sure why this is turning into a big discussion, if you add headers a tune is needed.
 

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if no CEL, you don't NEED a tune. To take advantage of the investment you just made, you WANT a tune. A Guy
 

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Back in the day, cars were rich from the factory and headers were just bolt on and go. In the 70's they leaned out the A/F and when I put headers on my '75 I bought a carter street/strip kit and rejetted and changed the metering rods to get it right. Now days, you need to change the tune to affect how long the injectors spray, I guess. Too bad they don't just sell bigger injectors.

Performance Injectors - Page -1


they do.......:armed:
 

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I was told long tube headers it WILL run lean and before you can get a custom tune just add 5% fuel.
Even without a CEL it could still run lean in some spots?
 

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Oxygen sensors read Lambda. So as long as your are out of cold idle the o2 sensors handle the rest of the fuel trim until Wide open throttle WOT. WOT the PCM ignores the o2 sensors and goes to fixed fuel maps. Very over simple explanation.

Its possible it could run lean at WOT you wont know unless you have a wideband o2 sensor hooked up. A lean running car at WOT will feel like it is "holding back" and if you reduce the throttle slowly out of WOT it will start to pick up again since it is going back to closed loop mode and using the o2 sensors.

Only other problem is headers sometimes give false knock and if the cars "hears" knock it reduces timing and that means less power.

You will be miles ahead if you get your car with mods custom tuned. Look for kennandjen post on this on this forum.
 

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Correct they do, but you can't just swap those, at least I don't think you can just swap those when you put headers on instead of tuning...

Sure you can swap them....but it will most likely run rich. Bottom line...putting on headers...get a tune. There was a post about this a while back and one of our vendors (I think it was Modern Muscle) even stated a tune is required with headers. Maybe not absolutely necessary (on SC application I would say required) but a very, very.....very good idea. :deadhorse:
 

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I can't say anything about Mopar tuning, but when I first put my headers on my old C5 Vette (LS1 motor), I didn't tune it and it threw no codes, knock or anything strange.

After getting my tuning software, WB02 and stuff and before I put the blower on her, I did some logging and actually found that the header made it fat (rich). I thought this was strange, but the facts don't lie.

As far injectors, tuning a GM required me to change the IFR (Injector Flow Rate) to the specific sized injectors that I installed after installing a blower. There was other data that needed changing too (scaling and such), but this isn't a GM so I won't bore you with that.

Just changing the injectors would allow it to supply more fuel, but it would be like going from a garden hose to a fire hose. The flow is higher but it's not metered. I'd think that this would throw your AFR all over the place and make your computer crazy.

My suggestion would be if you already had paid for a tune and updates were included (or relatively cheap), then you'd be smart to get it updated. If not, then I believe that it would be safe to wait until you modded your Challenger more and get it done then.

Just my thoughts. :cheers:
 

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Discussion Starter #19
I can't say anything about Mopar tuning, but when I first put my headers on my old C5 Vette (LS1 motor), I didn't tune it and it threw no codes, knock or anything strange.

After getting my tuning software, WB02 and stuff and before I put the blower on her, I did some logging and actually found that the header made it fat (rich). I thought this was strange, but the facts don't lie.

As far injectors, tuning a GM required me to change the IFR (Injector Flow Rate) to the specific sized injectors that I installed after installing a blower. There was other data that needed changing too (scaling and such), but this isn't a GM so I won't bore you with that.

Just changing the injectors would allow it to supply more fuel, but it would be like going from a garden hose to a fire hose. The flow is higher but it's not metered. I'd think that this would throw your AFR all over the place and make your computer crazy.

My suggestion would be if you already had paid for a tune and updates were included (or relatively cheap), then you'd be smart to get it updated. If not, then I believe that it would be safe to wait until you modded your Challenger more and get it done then.

Just my thoughts. :cheers:
I talked to the company, (Hemifever)that did my original tune and they gave me an updated version.

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