Help! Car randomly won't start when its cold.
 

I'll try to make this quick: When the weather turns cold my 2006 Base Z (6 spd) sometimes won't start. The starter is cranking with fury. Voltage is great in the car. The car has gas. If I'm fortunate enough to be parked on a hill the car will always start when popping second gear.

Last winter I suspected there to be some sort of problem with my UTEC ECU piggyback so I removed it and plugged the stock ecu in directly. The problem went away...until now.

After a rough day at work I took my frustration out on the car (but nothing it shouldn't be able to handle). After starting the car I hammered the gas in 1st gear and kept the rpm high for about 10 seconds...the car started to sputter as I drove away normally.

It almost stalled. So I pulled into the closest gas station to inspect the engine bay and put some more gas in the car. The car would not start back up untill the 8-9th try.

My mods:
JWT pop charger
AAM Angled plenum spacer
Motordyne MREV2 with aramid gasket
Strup headers
AAM High flow cats
Stock y Pipe (I know :/ )
Nismo y-pipe back

Anyone have any ideas what could be causing this based on my long description?

Update:
I found an old thread of mine that was posted for this exact issue (unresolved)

https://my350z.com/forum/maintenance...lar-issue.html

My car now has 44k miles

I also noticed that this problem happened to me this exact same time of year last year.

Is your ECU flashed? Has your idle been adjusted?

:icon9: Maybe fuel pump???? I had the same problem with a 240sx I had years ago. Changed the fuel pump and all fixed :icon21:

Stock ecu is not flashed. I had a UTEC and removed it and put the stock ecu back into place.
It was doing the exact same thing with the UTEC last year.

Do fuel pumps go bad after 40k miles?

If it always starts when popping 2nd gear, but won't start using the key and starter, I would have an auto parts store check your battery. Even if it is holding the voltage, it may not have enough cold cranking amps to turn over the engine in the cold weather. (IMO the most likely culprit if your battery isn't new.)

If that isn't the problem, I'd do the throttle body relearn, check your starter, plugs, MAF, and fuel pump next.

Update:
Saturday I disconnected the battery for 1 hour while I took the MAF sensor out and soaked it in alcohol and gently cleaned the sensors with a q-tip. I also cleaned the JWT Popcharger filter and lightly re-oiled it. The car started up fine for the rest of that day. I parked it in the garage sat. night.

This morning the car started and then idled more rough then usual. When this problem of not starting occurs this time of the year the exhaust also has a bubbly sound. This morning this was the case as well except much worse. The car stalled out as I hit the gas to go up my street.

Now the car is sitting on the side of my road and won't turn over.

The exhaust reeks of fuel (too much) the battery is a Bosch that is 1.5 years old.

I sold my BMW because I wanted a reliable car and I thought Japanese was the way to go and I come from a Nissan family.

So far I'm disappointed with my Nissan.

Have you ever tried to pull codes for it? Even if the check engine light isn't on, it could still be throwing a code.

As Sparkle has said I would check the battery condition. The fact that it won't turn over indicates some problem with the battery or the battery cables. Could just be a loose/corroded cable.

Another commonly overlooked issue is moisture getting into the ECM. The issue is most apparent, usually after driving or parked in the rain. The main harness boot is right above the ECM and if any extra wires have been ran thru/around it chances are it leaks, and eventually corrodes the main connection on the ECM. Seen it at least a dozen times over the years on the forums, both G's and Z's having very similar symptoms as you do.

Ive been having a similar issue. I have also noticed my z doing this when it is cold but doesnt do it all the time. The wierd thing about it is that it will not make any noise at all. I'm familiar with bad battery noises, or starters giving out. But nothing this. Does it sound familiar OP? Any ideas?

Sounds like the dreaded bad throttle body issue.

No choice but replacing it and then the problem goes away.