Let me apologize in advance for a long post, but any help would really be appreciated.

Got a 04 g35 coupe. I recently tore apart the front of the engine to fix a lifter tick, while simultaneously took off the cats to put some high flows on. Got everything back together except the exhaust for irrelevant reasons. Timing and idle sounds perfect, but I had a valve cover gasket leak so I took the valve cover off again to replace it. After getting everything together a second time, it would turn over but wouldn't start. After checking a bunch of fuses, and finding nothing wrong, just tried to start it up again and it started fine.

Then I took it for a short test drive with no exhaust, it stalled just moments out of the driveway, started back up immediately, hopped a couple times on the way back but stayed running let it idle for 30 minutes, everything ran perfect. Left it sit for a couple days waiting for the new exhaust to come in, hoping it was running rough due to lack of back pressure.

Few days later, tried to start it again to get it on ramps, would start but wouldnt stay running. Jacked it up, installed the exhaust and started right up no problem. Let it idle awhile, and once it just stopped running. Started right up again. Took it for a test drive, hopped once a couple moments before slowly dying and then stalling. Took like 4 tries to get it running again, got it to the nearest gas station and back to the driveway without any problems. Let it idle for about an hour, rpms would dip a tiny bit at points but by no means struggles to stay running, and then just dies as if I turned the key off, and won't restart.

I've heard these symptoms are sometimes because of cam sensors going bad but Its only throwing a pending code that said something like fuel trim-bank 1-mixture too lean, but there's no check engine light.

My buddy who knows more about cars than me whose been helping me with this thinks it needs to be tuned due to new high flow cats and new y pipe, and that just driving it will tune itself. Does this sound accurate?

Does anyone have any clue as to what the heck is going on?

 

It will probably need a tune to compensate it, but did you leave the battery unplugged at all or disconnect +/- from the battery and hold them together? It stores fuel trim data depending on driving condition. So, if it's still using your old settings with the new mods it could cause a problem.

The pending code means the ECU is saying there is too much air in the mixture. Could be because you need a tune, need to do the above, vacuum leak, weak fuel pump, engine timing, etc..

 

Yeah, battery was disconnected for almost two weeks while I took the engine apart. I'll look for vacuum leaks tomorrow and I would like to get it dyno'd and tuned since I've never done it anyway. But wouldn't the timing being off cause it to run and idle rough? I mean while idling it runs so smooth the only thing you can hear is the clicking from the spark plugs, and it seems to run nice when it's not trying to stall.

 

Can you read the freeze frame data for that pending code? It should tell you the conditions that caused the code to popup. Does it die while you are giving it gas or just idling pretty much?

You can do checks on the cam/crank sensors to see if they are within spec.

Try looking at the short term and long term fuel trims.

 

I'll have to see what I can find out.

It seems like it mostly dies during idle, but that's probly because it's mostly just been idling since I got it back together. The first test drive when it died I think I was off the gas and it started right back up, the second drive when it died I think I was coasting when it started dying and I tried to rev it right before it died, and it took a couple tries to get it running again.

 

The cam and crank position sensors can start to fail and cause lots of issues without throwing a code. A lot of the issues you talked about are symptoms of failing cam sensors: rough idle, hard start, sluggish acceleration etc. Don't know how many miles you have on the G but they are prone to failure over 100K miles. I'd recommend changing both at the same time, if you replace only 1 the question for the other one will be not "will it fail" but "when will it fail". Good news is they are very easy to replace and you can find them significantly cheaper on Amazon or other websites than you would pay at the dealer. Stick with OEM here, the off brands are attractive because they're usually dirt cheap but with sensors our motors don't usually play nice with aftermarket. HTH

 

But it idles and accelerates fine. When it shuts off it dies pretty quick, it's just real random. But now I can't even get the car to start. It will turn over but won't start so I can't get any kind of fuel trim data.

 

Try some brake, carb, or starting fluid sprayed into the plenum and see if starts. If it does you probably have a fuel delivery issue. If not then it's probably one of those sensors.

 

I think I figured it out. It was a combination of a dead enough battery due to the ground terminal making a bad connection, and A STUPID GROUND WIRE not making a good connection on the engine!

My buddy jump started it, started right up, and I let it run. I saw a small ground wire sitting on the post where the engine cover bolts on. I wiggled it and the engine started to bog and die, and if I took it off it died. So I put some washers on and screwed on a nut. Took it for a test drive, no problems at all and it runs perfect.

What the frick? I love my car and all, but this whole experience has taught me how stupid and over engineered these engines are. Why does there have to be a tiny ground wire connected to the engine to keep it running?