Backpressure issue.
12-03-2003, 03:39 PM
#1
Thread Starter
Backpressure issue.
My check engine light came on the other day, so I took my car to Honda. They said that cylinder number four was miss-firing due to increased back pressure from my Spoon header and Spoon exhaust. Makes sense, but do you think that this is a common problem? Will tuning and leaning the air-fuel mixture prevent this problem? It cost me 195 bucks for them to fix it. Not under warrenty due to modifications. What a waste of money.
Any input would be appreciated.
Thanks,
Matt
Any input would be appreciated.
Thanks,
Matt
12-04-2003, 09:46 AM
#3
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Join Date: Oct 2000
Location: HouStook TX
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Ditto, Uncle Fester. That's the kind of bad service which is sending the Honda name to the bottom of manufacturers list. I can't believe how quick they are to shift the blame to you aftermarket parts. It's just sad that we have to fight so hard to get the bare minimum amount of service and respect. Remember, Honda thinks that we're all a bunch of racers who abuse the car constantly.
I had all 4 cylinders misfiring on my MY00. It took Honda 1 month to figure out that all of the fuel injectors were bad. There had recently been a big flood in Houston and the drying agents in the gas was deemed to be the cause.
Have them look at that fuel injector, because it might save you some time.
Good luck.
joe
I had all 4 cylinders misfiring on my MY00. It took Honda 1 month to figure out that all of the fuel injectors were bad. There had recently been a big flood in Houston and the drying agents in the gas was deemed to be the cause.
Have them look at that fuel injector, because it might save you some time.
Good luck.
joe
12-05-2003, 02:07 PM
#4
Thread Starter
Thanks for the input. Guess what happens today. Check engine light is back on. I want to kill those guys from Honda. Most people that buy a $30,000+ car and modify it with expensive aftermarket parts right away, take better care of their car than some idiot driving over curbs and changing thier oil ever 10,000 miles. They give a soccer mom a new motor when she redlines it 9 times and blows it up, but doen't support the car enthusiast.
I'll have them check the injectors. That's sounds like a good idea. All I have is an I/H/E. Pretty basic stuff. I don't see how any of these products, which help the car not hurt the car, can cause a problem. By the way all parts are Spoon if anyone thinks that would make a difference.
Matt
P.S. I guess I'll have to buy a BMW next time. Maybe they'll help me out when my new car doesn't work.
I'll have them check the injectors. That's sounds like a good idea. All I have is an I/H/E. Pretty basic stuff. I don't see how any of these products, which help the car not hurt the car, can cause a problem. By the way all parts are Spoon if anyone thinks that would make a difference.
Matt
P.S. I guess I'll have to buy a BMW next time. Maybe they'll help me out when my new car doesn't work.
12-06-2003, 05:58 AM
#5
Community Organizer
Have them pull the COIL PACKS on top of the spark plugs.
It is not UNCOMMON for them to go bad on the #1 & 2 as mine were but it's probably that.
Have them pull them out and if they are overly hot or charred or discolored then you got an issue!!!! Have them refund your $$$ if I am right. That is a Honda defect/warr. issue there.
If it is the coils have them do a valve adjustment too..........if you can get them to do that under warr. as well.
It is not UNCOMMON for them to go bad on the #1 & 2 as mine were but it's probably that.
Have them pull them out and if they are overly hot or charred or discolored then you got an issue!!!! Have them refund your $$$ if I am right. That is a Honda defect/warr. issue there.
If it is the coils have them do a valve adjustment too..........if you can get them to do that under warr. as well.
12-06-2003, 07:14 AM
#6
Registered User
Good info on BP:
"Before we begin this discussion, take note that 1 atmosphere is the pressure that air is at naturally (uncontained) at sea level.
During the combustion process, when the exhaust valve is open, all of the compressed (and depeleted) air-fuel mixture spills out from the cylinders as fast as it can, through your exhaust manifold, into your catalytic converter(s), the muffler, and finally out the tail pipe. The problem with this is, just before your exhaust valve is about to close again, your intake valve opens up, allowing the fresh air-fuel mixture to rush into the cylinders. This is called overlap, and one of the things you take into consideration when choosing a cam, because it can be used to your advantage.
If there was no valve overlap, it would be 100% impossible to completely irradicate all of the spent gases from the cylinder. This has a two-fold effect on power output, depending on what RPM the motor is running at. At low RPM, this effect actually increases torque, because the least amount of compression is lost during the intake stroke, and the ratio of intake to exhaust gases is high. Unfortunately, as the RPMs increase, there is increasingly less time to evacuate the exhaust gases during the exhaust stroke, and more and more depleted air-fuel remains in the cylinders when the exhaust valve closes. The motor becomes incredibly inefficient near its readline. A motor designed for high-torque applications, such as towing, tends to exhibit less valve overlap then normal. The type of cam used in this application is often called an "RV" cam, because a recreational vehicle doesn't need horsepower as much as it needs low-end torque to get it moving.
Your car would also run terribly if there was too much valve overlap as well. When exhaust gases rush out of the cylinder, they create a low pressure area in the cylinder and the exhaust system, sucking the intake charge right into the cylinder, and right back out into the exhaust system. This is called scavenging. When that air spills out, so does the fuel it was carrying, so the O2 sensor reports a rich condition to the computer, often causing further decreases in the amount of fuel the computer injects. At low RPMs, this effect is most pronounced as there is sufficient time to suck out a significant portion of the intake charge, reducing torque. As the RPMs increase, however, the extra velocity imparted to the intake charge increases the amount that squeezes into the cylinder after the exhaust valve closes, as the valve closes so quickly at high RPMs that barely any intake charge escapes through the exhaust system.
No doubt you see the dilemna posed to designers when they choose a cam for the motor - the right combination of power must be achieved at the intended RPM range of the vehicle - if this is a tiny four cylinder, which must spin high RPM to make any power at all, you have to design in a higher amount of overlap. If the vehicle is mostly intended for low speed towing, you design in a smaller amount of overlap for more low-end grunt. Overlap is one of the reasons why the four-cylinder Acura Integra GS-R makes 170hp at almost 7000 RPM, and your 3.0L makes 171lb-ft of torque at 2000 RPM.
You can't control your overlap without changing the cams, but the effects caused by changing the back pressure are the same. When you reduce back pressure, it is equivalent to increasing valve overlap, and when you increase back pressure, it is the same as decreasing the amount of valve overlap. That's why some people will say, "you need a muffler for torque", or, "you'll have more high-end, but less torque, if you run straight exhaust". They are right, but a muffler's purpose is to reduce sound output, not horsepower! By reducing back pressure in an exhaust system, you increase high-end horsepower at the cost of low-end torque.
You can compensate for this by increasing the velocity of the intake charge. Increasing the intake velocity has the added side effect of increasing back pressure, because there is more air to be evacuated during the exhaust stroke. Note that if you increase intake velocity past the limits of the exhaust system, the gains you achieve are diminished to the point of being non-existent. That power will be there when you do upgrade the exhaust system, which is why something as simple as upgrading the exhaust system can result in huge horsepower gains.
You can decrease back pressure by increasing the size of your exhaust manifolds, or using separate tubes for each cylinder (called headers). Increasing the size of the exhaust pipe and decreasing its length also helps, as well as installing high-flow catalytic converters and mufflers. Of course, you could just cut them off. Although it is illegal in the United States to remove the catalytic converter in a registered vehicle, the muffler is a different story..."
"Before we begin this discussion, take note that 1 atmosphere is the pressure that air is at naturally (uncontained) at sea level.
During the combustion process, when the exhaust valve is open, all of the compressed (and depeleted) air-fuel mixture spills out from the cylinders as fast as it can, through your exhaust manifold, into your catalytic converter(s), the muffler, and finally out the tail pipe. The problem with this is, just before your exhaust valve is about to close again, your intake valve opens up, allowing the fresh air-fuel mixture to rush into the cylinders. This is called overlap, and one of the things you take into consideration when choosing a cam, because it can be used to your advantage.
If there was no valve overlap, it would be 100% impossible to completely irradicate all of the spent gases from the cylinder. This has a two-fold effect on power output, depending on what RPM the motor is running at. At low RPM, this effect actually increases torque, because the least amount of compression is lost during the intake stroke, and the ratio of intake to exhaust gases is high. Unfortunately, as the RPMs increase, there is increasingly less time to evacuate the exhaust gases during the exhaust stroke, and more and more depleted air-fuel remains in the cylinders when the exhaust valve closes. The motor becomes incredibly inefficient near its readline. A motor designed for high-torque applications, such as towing, tends to exhibit less valve overlap then normal. The type of cam used in this application is often called an "RV" cam, because a recreational vehicle doesn't need horsepower as much as it needs low-end torque to get it moving.
Your car would also run terribly if there was too much valve overlap as well. When exhaust gases rush out of the cylinder, they create a low pressure area in the cylinder and the exhaust system, sucking the intake charge right into the cylinder, and right back out into the exhaust system. This is called scavenging. When that air spills out, so does the fuel it was carrying, so the O2 sensor reports a rich condition to the computer, often causing further decreases in the amount of fuel the computer injects. At low RPMs, this effect is most pronounced as there is sufficient time to suck out a significant portion of the intake charge, reducing torque. As the RPMs increase, however, the extra velocity imparted to the intake charge increases the amount that squeezes into the cylinder after the exhaust valve closes, as the valve closes so quickly at high RPMs that barely any intake charge escapes through the exhaust system.
No doubt you see the dilemna posed to designers when they choose a cam for the motor - the right combination of power must be achieved at the intended RPM range of the vehicle - if this is a tiny four cylinder, which must spin high RPM to make any power at all, you have to design in a higher amount of overlap. If the vehicle is mostly intended for low speed towing, you design in a smaller amount of overlap for more low-end grunt. Overlap is one of the reasons why the four-cylinder Acura Integra GS-R makes 170hp at almost 7000 RPM, and your 3.0L makes 171lb-ft of torque at 2000 RPM.
You can't control your overlap without changing the cams, but the effects caused by changing the back pressure are the same. When you reduce back pressure, it is equivalent to increasing valve overlap, and when you increase back pressure, it is the same as decreasing the amount of valve overlap. That's why some people will say, "you need a muffler for torque", or, "you'll have more high-end, but less torque, if you run straight exhaust". They are right, but a muffler's purpose is to reduce sound output, not horsepower! By reducing back pressure in an exhaust system, you increase high-end horsepower at the cost of low-end torque.
You can compensate for this by increasing the velocity of the intake charge. Increasing the intake velocity has the added side effect of increasing back pressure, because there is more air to be evacuated during the exhaust stroke. Note that if you increase intake velocity past the limits of the exhaust system, the gains you achieve are diminished to the point of being non-existent. That power will be there when you do upgrade the exhaust system, which is why something as simple as upgrading the exhaust system can result in huge horsepower gains.
You can decrease back pressure by increasing the size of your exhaust manifolds, or using separate tubes for each cylinder (called headers). Increasing the size of the exhaust pipe and decreasing its length also helps, as well as installing high-flow catalytic converters and mufflers. Of course, you could just cut them off. Although it is illegal in the United States to remove the catalytic converter in a registered vehicle, the muffler is a different story..."
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