kmartin25

My 2003 350Z, 160,000 miles, A/T has finally started showing her age, I guess. SEL came on about a month ago and car began to idle rough causing the car to shutter. Code came back for a misfire on cylinder 6 and knock sensor. Changed out the knock sensor, checked the recently installed plugs (which showed no signs of wetness/oil) and cleaned all of the fuel injectors. I noticed one of the injectors had a cracked pintle cap so I replaced the cap with an aftermarket one (closest thing I could find to the original). Went and had my SEL cleared and car ran great for a solid week with AMAZING gas mileage, considerably different from before. Then, on Sunday, after driving home from my parents (2 miles down the road) the car started acting like it was flooding or running out of gas or something. The increase in rpm's and acceleration wasn't exactly timed with me pressing the gas pedal. It would start to stall and then sporadically rev up. A few minutes later, the engine stalled. I cranked the car again and revved the engine while in park but as soon as I let off the accelerator, it died again and wouldn't crank back up. Called a wrecker to come tow it the whole mile down the road (&#128580 and let it sit for the next day and a half while I tried to do some research on the symptoms. Couple days later, started the car up (with some effort) and she's running rough as he**. It's still doing the same thing when you try to push the accelerator; rpm's drop, almost bottoming out and stalling. Instinctually, you let off the pedal to not stall out the engine and then the rpm's shoot up as if you're pressing the accelerator. Idle is rough. If you very slowly press the accelerator, the rpm's won't plummet. Once you do this and get the rpm's up to about 4000 at a constant rate and just fluctuate the accelerator while keeping rpm's on the higher end, every time you let off the accelerator some, the cold air intake makes a vacuum/suction noise very quickly and strong sounding. Anyone have any idea what's going on with her? I was thinking maybe Cam sensors but they seem to be testing fine. I'm a bit baffled not having a CEL/SEL not present.

zakmartin

I'd start by checking your vacuum lines. One of them might have come loose over time after you worked on the engine. Also, I'd stick with OEM injectors if you can. 350Zs aren't super friendly with aftermarket parts.

kmartin25

Yeah, I've checked all the hoses. Unless I'm just mistakingly missing something. I was also curious if it could possibly be the fuel pump going out in it. I hear it prime when I turn the ignition to ON but what I'm wondering is if maybe it's not supplying enough pressure to supply a constant fuel feed. I don't know how to test for this other than checking the fuel pressure in the line feeding to the fuel rail but I don't have the kit to test that.

zakmartin

I know it sucks, but sometimes, buying diagnostic equipment is the only way to get things figured out. I've spread out $60-$70K in tool and diagnostic equipment purchases over the last 30 years, so it didn't hurt so much, and I rarely have to use my OTC fuel pressure kit, but when I need it, it's great to have.

To be honest, I'm guessing the misfire on cylinder 6 is what caused the knock sensor to register a code. If you're getting a huge amount of air into the engine after installing a non-OEM injector, it could be feeding your ECM a bad signal causing your stoichiometric ratio to be out of whack. The whole thing could be a domino effect starting with the misfire causing the knock sensor code causing a replacement with a bad part causing the ECM to go nuts.

A simple relative compression test with a scope can tell you if the misfire is still there. A vacuum test using a gauge should give you a pretty good idea if you have a vacuum leak somewhere that's causing the problem.

If that's over your head, take it to a reputable local shop and explain everything you've done in detail and see if they can get it figured out.