2003 Nissan Pathfinder Power / MPG Problem

[analog154]

Hey I have a 2003 Nissan Pathfinder LE 4x4 3.5L. I have a k&n cold air intake and a custom flowmaster 50 series muffler exhaust and also a jet chip ecu recalibration. Ever since I got the exhaust put on my truck seem "limp" when giving it gas and also my gas mileage has been really poor. Before the exhaust my truck had a ton of torque from like 1K-3K RPM. Now it just sorta feels wimpy and like its going no where. Also when starting it shoots up to like 2K RPM then falls all the way down to like 100 RPM and just barely starts? I am going crazy trying to find out the problem since I don't have any check engine lights going on? What is wrong it seems like the exhaust did me in?

[Buzzman]

I'm no expert, but 2 things jump to mind.First, there may be a vacuum leak somewhere. You may have disturbed some other bits when installing the exhaust.The second thing that comes to mind is lack of back pressure in your exhaust system. A free flowing exhaust is well and good, but you still need some back pressure to balance the flow. Actually, one more thing comes to mind. Maybe your re calibrated ECU doesn't like your new set-up. Not sure how you would check that out, except maybe to go back to the stock setup.Anyway, keep us up to date on how you make out. Good luck.

[analog154]

Well I did the things in order of k&n->exhaust->chip. I put the chip in thinking that it would help to fix the problem. How do I check for the vacum leak? The guy told me that backpressure is caused by your catalytic converter and not the muffler? Is there a way to create some back pressure in the custom system?

[fueler]

Ahhh the classic K&N filter question... ***** Nissan MAF sensors hate K&N air filters ****** those performance air filters are heavily oiled up and the oil will gunk up your MAF sensor, causing very poor acceleration, bad MPG, and eventually a check engine light when it gets bad enough. Switch to a paper or non-oiled filter, and clean your MAF with electrical contact cleaner very carefully, dont break it cause its about $400+ for a new one

[Buzzman]

Fueler may be right. We've had many discussions on the K&N filter issue. However, if I read the original post correctly, the truck ran fine until he did the exhaust system. The only way to alter the back pressure is by installing a different system.Now, I would still suggest checking out the MAF sensor like Fueler said.Did you recently clean and re-oil the filter element by the way?I've run my truck with a K&N filter for over two years, and have not had a problem. When I clean and oil it, I leave it out in the open for 24 hours before installing it back in the truck.As for finding vacuum leaks, I have a rather strange way of finding them, but it has worked for me in the past. It's probably a little dangerous, so be careful. Do this in a WELL ventilated location (outdoors):With the engine running, take a plumbers propane torch (like one for soldering water pipes), and open it up a bit, but DON'T light it. move the nozzle around the engine compartment, near hose connections and such. If there is a vacuum leak, it will suck in the propane and change your engine speed. Trust me, when you find one, you'll know it right away. Good luck.

[SnowSurfLax]

Haha! Nice way of finding vacuum leaks! Very shadetree mechanic of you.

I'm going to clean my K&N this Saturday. I'm thinking that if I oil it and then leave it under my BFG fan in my house for an hour or two it'll dry out enough to work.

Or what if I don't oil it? Technically I should be able to damage my engine. And it's likely to be rehoned in the next 5 years....

Let me know what you think. Going to this Saturday and want honest input.

[SnowSurfLax]

Forgot to mention I'm cleaning my MAF this weekend too. Performance has seemed a little less than perky last couple of months.

[analog154]

I have recently cleaned my K&N but I have't really had any problems with that. It all seems to be from the exhaust. What happened was I went to Midas and a guy did a really bad job. I then had to have it redone by another midas store and they did it the proper way. What I am thinking is that the first guy some how did something to the 02 sensors or something else to really mess my truck up. Do you think a loss of backpressure could cause a torqueless feeling when accelerating?

[Buzzman]

Another question pops to mind: With the truck running this poorly, does it not throw a trouble code at you? Is the check engine light on?I would think if the Midas guys messed up the O2 sensor, then you would/should get a trouble code.Also, does the exhaust show any signs of leaks, like hissing sounds, etc.?Loss of back pressure will affect how it runs, but not as much as what you are experiencing. The more I think of it, the more I'm leaning towards some kind of sensor issues.

[analog154]

That is the really wierd thing. I am not getting any check engine lights. And to only add to that as soon as the guy put the first exhaust on it has never been right since that. I also passed the emissions inspection so its not like its burning to much fuel or something? Could there be a error code but it not come up on a check engine light? During running the system sounds fine, the only thing is when I give it gas in N or P and then let go, it makes like a turbo Blow Off Valve sound like all the exhaust gas is hissing out. But that is only when it is idiling in park or netural and during normal driving I have never had one problem with wierd sounds. What I am thinking after researching is either the sensors are wrong? Or that the pipe size that he used is incorrect and not providing enough velocity to flow. What do you guys think?

[SnowSurfLax]

I think buzzman is right on the ECU. I think it might not be set correctly for your setup. It's possible that it's starving the engine for fuel until it feels enough back pressure and then starts feeding it like a mexican mother.

That would also explain why there's no SES light. The sensors are working perfectly, the brain isn't.

[analog154]

Heres the thing though I just got my ECU reprogrammed by JET Chips and I told them I had an exhaust? So they could compensate for it.

[analog154]

Would pipe size be causing me this power loss? To big exhaust diameter?

[fueler]

Too big of a pipe = no backpressure = lost torque = slower acceleration Whats your exhaust piping diameter?? http://www.proficientperforman...e.php Note the 3.3L is equiv to 205ci and the 3.5L is equiv to 215ci The recommended exhaust diameter for our trucks is 2.25" according to this article

[analog154]

Here is the thing though. A first guy did a really ****ty job on the exhaust and that is what messed it up. However, a second guy redid it and it was 100% better. So what I think happened was that while the first guy was doing the exhaust he somehow messed something up or unplugged something that is non related to the exhaust. Because the 2nd one should be alot better but it isn't.

[bullrid]

have you found the problem yet??