help! 1/04/08

[flatpoint]

Smaller,longer tubes on a header will create more vilocity,(draw) at lower RPM. The same is true with an intake manifold.Where do you want to make your power????

[freewaydan]

i had a header put on my 99 2.5L and on the way home i started having a miss at 2000 rpm in fourth gear (its automatic) and at idle and i have changed the plug wires, plugs, cap, rotor, and 02 sensor and it still does it, and it doesnt read any codes on a scanner. any ideas?

Now that all that has been said,and im sure that all this wonderful and informative info is here, did you find out what the problem is/was?

Backpressure on a 4 cly in when the wind changes direction:smile::smile:

[Mr. Orange]

And, now, back to our scheduled debate.....

This is like a mini series drama.....

Seriously, did 99rangler ever figure any of this out??
Or is this gonna be a constant battle? :bart:

Either remove the header, or just keep the RPMs up all the time.... :haha:

Quick question, 99, did you remove all the other components of the exhaust? Cats, and/or muffler?
It could also be as simple as the header itself not seating right on the gasket to the head. If there is a little leak, sometimes that could cause an issue.

With all the :2: flyin around, I think we have a couple of bucks. :haha:

[99rangler]

i have taken it to many different mechanics to try and find out what it is i have just this past week replaced the o2 sensor and then i finally got the check engine light to come on and i had a scan tool put on it and it said injector 3 was open so i replaced the injector yesterday evening and drove it around for about thirty minutes and that fixed it but when i drove it to work this morning it started again and tonight the check engine light came on again now the scanner says injector 4 is open so now i guess i will replace the other three and see what happens then the only mod to the exhaust is the header the cat and muffler are there and factory

[Kodiak Spirit]

sounds like a computer issue to me, there is a place that rebuilds those computers for the 4 bangers, lemme see if I can git his contact info again...

[97sahara]

WAY OFF my friend.

I am a certified Aircraft mechanic. i work on 6 cyl, 9 cyl, turbine jet, radial and inline aircraft engines that put out hp ratings in the thousands of hp and I can agree that an engine DOES need some back pressure. the amounts that most of you guys are thinking about is more than what is actually needed. a piston engine is not a vacuum, it is a breathing machine just like you are. inhale and exhale.

when an intake valve opens, the exhaust valve is closing. when an exhaust valve is opening an intake valve is closing.(valve overlap). This design is to take avantage of the inertia of the outflowing exh gases to provide more complete scavengin and to allow the entering mixture to flow into the combustion chamber at the earliest possible moment, invproving volumetric efficiency. with that understood, you need a little back pressure in the exhaust to circulate and use fuel/air in the combustion chamber to the best efficiency possible. to much back pressure and you will get pre-ignition and pre-detination due to hot exh gases pushing there way thru the intake and starving the engine of O2 and cooler undetonated air. to little and you will get crappy performance on the other end of the scale due to unused gases on the exh end.
for the most part, the backpressure sales-pitch is a bit much but the theory and reality is that yes you need a little bit of back pressure.
Unless you are versed in piston engine theory, history, and tech, don't make such a bold statement.
cut off your cat, run a 70mm tb and run 4" exh tubing and see how well your engine runs.
For the poster who mentioned that backpressure was only needed during the carburator days, i understand your reasoning but regardless of how well vaporized and atomized the fuel is when it is ignited in the combustion chamber it is not completely used and properly circulated. you WANT some hot and cold air mixing together during the release of the exh during the good ol 4 stroke five event cycle principle "Otto cycle"'s exhaust stroke.

for the backfiring comment. a backfire occurs if an intake valve opens to early, pre-igniting incoming fuel-air with hot exh gases.

This debate can go on for ever, ive done over 2200 hrs of training and if you want an engine to run at full throttle and care little about the mpg or efficiency of the engine then back pressure is of little importance to you, hence the race car talk. if you want a long lasting, highly efficient motor then understand that they are indeed designed to burn the most gas and to keep the engine as cool as possible.

hate to burst your bubble their cowboy but the last part of this statement is FALSE, theres a power stroke between the two valves opening and closing, and with the vacuum, there vacuum happening in the intake when the pistion is on the intake stroke, its sucking in the air and fuel