UPDATED 6/16 - Darned near new magnaflow CARB legal getting progressively more raunchy loud

r3dn3ck · May 23, 2023

I'm not sure if this is a normal thing with Magnaflow's CARB legal (and otherwise) catted X pipes. When I put it on it seemed almost a little more tame than I was looking for. Very street friendly level of sound. Over the last 2 weeks it's gotten progressively louder to where it now sounds like it's on bare headers. Yes, I crawled under to see if someone stole my cats and they're still there. I don't see any sign of exhaust leakage, no codes or visible outgassing or ripply air where there should not be so I'm doubtful that one of the cats has pooped the bed. None of the welds appears fragged, all the bolt-together joints are looking good.

Anyone ever have this kind of thing with Magnaflow cats? I leave for work in the mornings when it's still dark and I don't come back until it's dark again so I know I'm pissing the neighbors right the hell off at the moment. Would really like to figure out if I need to just take it to the shop so they can eat $1000 from me or if I need to call MFlow and if I did call them, if they'd give two squirts of cold hippie piss or not.

There's only about 5k miles on the thing since I had it installed back in October/November time frame.

r3dn3ck · May 25, 2023

Figured it out. I had to go for a smog check and while we were attending to that the tech offered to assist and put his little mirror on a stick down by the manifold flanges. Nothing but a gap between the passenger side manifold and the mid-pipe. Must have been gradually burning the gasket out for the last few weeks. Heading to the shop hopefully today to get it replaced. I don't know if they failed to put the donut in or if it fell out or if I burned it out. I don't pull mid-pipes off enough to even remember if there is supposed to be one in there on an 01 snake. Grumble...

r3dn3ck · Jun 14, 2023

Update: I've been fighting a P1000 code that just won't go away and it's stopping me passing smog which stops me renewing my registration. The smog shop found that the P1000 is because a rear O2 sensor isn't showing as ready.

Realizing that I had a way to see the raw voltage signal, I grabbed my SCT handheld and watched the O2 sensor data live. 3 of 4 were showing >100mv and <990mv with plenty of jitter. The driver side rear O2 (Bank 2, Sensor 2) only shows >100mv when I'm at relatively high throttle angles and then wobbles around from 10-40mv and it spends a lot of time at 0mv. This indicated either a lazy O2 sensor or an intermittent short or a bad connection. I replaced the sensor and right out of the gate I was seeing >100mv for a minute during idle and driving but it quickly reverted to the prior behavior so I figure it's probably an intermittent short. The harness wrapping right at the end of the trans is in visibly good shape but the wrapping and the number of forks in the road make tracing the wire a bit of a yuk job... I don't want to unwrap anything I don't have to.

I'm hoping someone can help me out with the path of where the relevant wires run or places where it/they is/are more vulnerable to damage than others.

In a separate effort I've ordered some MIL eliminators which basically throw a small capacitor and a resistor inline to simulate the needed <1v signal as well as sufficient jitter in the signal for it to appear legit to the ECU. I don't know if this is guaranteed to get flagged by Kommiefornia's OBD2 scan (I already passed the visual) and I'm curious to know if any of you have concrete knowledge on the topic.

r3dn3ck · Jun 16, 2023

The MIL elims came in but only one of them fits the connector. The other has 2 spuds off the side in inverse postitions to where they need to be. I guess I needed to order 2 different units, not 2 of the same unit. Uggh. I did a quick start up and idle and the other 3 are showing north of 500mv but still not getting good voltage from the 4th. It's definitely got to be an intermittent short. Anytime I give the car a stomp on the pedal and the g's pick up a little it starts reading properly so it's got to be somewhere that the wires are either running transverse to the long axis of the car or where they are running parallel to the long axis of the car and come in contact with a sharp surface that does or where engine torquing over to one side moves the harness sufficiently. This is seriously frustrating. I'm taking the thing down to SoCal this weekend and installing the suspension. While I have it up in the air I'll make another fist of finding the short.

@white95 and @ttocs I'm wondering if either of you might have chased such gremlins in the past?

white95 · Jun 16, 2023

No sir, I haven’t had to worry about emissions equipment for years.

ttocs · Jun 17, 2023

harnesses and connections are where you want to look first, but it will more than likely come down to you tracing the wires as far as you can to ensure that it isn't broken or have a bad connection somewhere. Tracing wires sucks...

weendoggy · Jun 17, 2023

My '02 manual shows the LR O2 connector going to the 8-pin round harness plug, which is near the 42-pin connector. It also has the RR O2. Color for the LR is VT/LG (to pin 61 PCM), YN/YL (to pin 96 PCM), GY/RD...sig. ret. (to pin 91 PCM), RD/YL (CJB fuse key-on). I doubt its the RD/YL due to the others working. I'd trace the wires to the 8-pin connector.

Also, the eliminators most likely won't pass either. Corrected positions of O2's.