My 2004 G35 MT with 225k miles developed a problem today. When I shut off the engine for more than 5 minutes, it is very hard to restart. If I shut off the engine and attempt to restart within 5 minutes it will restart just fine. After the engine is restarted it runs fine, idles smooth, gets good gas mileage (22-24mpg) and over all is great. No Check Engine Lights. Nevertheless, it has been a while since the last tune up. Does it sound like a spark plug issue? Any other thoughts?

 

could be a number of things. spark plugs. fuel pump, injectors, coil packs, starter. on my old truck when the fuel pump started to go bad it would take a while to start.

 

Yikes. Any way to diagnose or do I just start throwing money at it?

 

How's your battery?

 

2 month old Interstate battery

 

So when was the last time you changed your plugs? I'd at least pull a few plugs and take a peek at them. With over 200K miles, theres a lot that could be going on there. You are pretty much going to just have to go and check things and see if everything is as it should be.

Things like check clean the MAF. Check plugs, makes sure no oil leaking on the coil packs, etc etc.

 

Maybe a fuel delivery related issue? Try priming the fuel pump a fuel times before starting it after it has been sitting. Maybe it's losing pressure overtime and takes longer to get it up to the correct PSI. Since, you restart it after it's been running and fuel has been delivered that could possibly explain it.

 

How do you prime the pump? Turn the key on and off a few times before starting the engine?

 

Yep.

 

I tried priming the pump multiple times and it doesn't seem to have an effect. The fuel pump is original and I recently ran out of gas (inoperable fuel level gauge) so I'm willing to be it's burnt out. I purchased a new one (aftermarket spectra premium from amazon) so we'll see if that's the problem. I also bought new NGK laser-platinum spark plugs since I have no idea how old the existing plugs are.

 

Replaced spark plugs but that didn't fix the problem. Replaced the fuel pump and now it's all fixed!!!

 

Nice! Good call

 

Even though you fixed your problem, I know from my VQ35 Maxima days a dirty throttle body can also cause difficult hot restarts. First place to look since it is relatively easy to rectify.

 

I have a few leaky spark plug gaskets in the valve cover so when I remove the IM and valve covers I'll tackle the throttle body. I did clean the MAF as was recommended above. That plus new spark plugs plus a properly operating fuel pump has transformed the engine. It runs so smooth now. I thought it was running smooth before but it was nothing like this.