I have researched this a little bit and have seen a few similar threads, but nothing really exact or I show less signs/errors than others so I figured it'd be best to start from scratch.

2006 G35X with about 134,000 miles. I will go over the issues/symptoms first and then follow up with my troubleshooting thus far. I try to be detailed so it is clear, please be patient if this gets long.

A month or so back I started to experience the engine having a hard time starting ONLY after it previously ran a fair amount and warmed up. So like drive 30 minutes, go to a store and come back out after 10 minutes, and then try to start the car again. Usually the first and maybe 2nd crank will have the RPMs bounce off really low and struggle to not choke & die. Sometimes it will catch and start, others it dies after a few seconds and the next crank it basically turns on fine. Again, no issues from a cold start, only warm.

I have also started to see a trend of gas mileage dropping over the past few months, but didn't think a ton about it. If i recall correctly, I think I used to get 20ish MPG combined maybe 21. Then it would drop to 19s, 18.5, maybe a bit lower, and now the last 2 times filling up it is at 16 mpg! This is always doing it based on the odometer since I have the fuel sensor problem and don't ever trust the gauge.

The 16 MPG really snuck up on me since I usually let it reach near 300 miles and then fill up thinking there is 3+ gallons left (18mpg avg) but that time it took like 18.5 or 19 gallons so now i fill up by 250 miles.

SES codes so far have been P0462 which is semi-common and related to the gas gauge and comes up basically every time I fill up, one time I had a C1109 for abnormal battery voltage, and maybe one or two other codes, but I don't recall them being related and they'd again be a one time deal.

Now on to my troubleshooting...

The obvious first things to try were cleaning the MAF sensor, cleaning the throttle body, and cleaning my air filter. This apparently wasn't enough to solve my problem since I still have trouble starting at times after it is warm. I also removed the MAF sensor a 2nd time to spray it again after maybe 500 miles since I re-oiled my filter after cleaning it. I did have to do the ECU reset and other relearn procedures since idle was a touch high (1050?) and I got a code for high idle during that time, but I think that is all under control now (800?). Oh, and I cracked the rubber hose at the nipple of my Z-tube since it wouldn't budge so i left it connected and worked around it. I wrapped some electrical tape around the hose and think it is sealed up. If there is any form of an air leak, it is BEFORE the throttle body. I also didn't change out my gasket between the TB and my copper plate thing from my motordyne kit since it looked OK and I didn't physically touch it.

I read somewhere that maybe the camshaft sensors are bad, but those people usually got either a code for them or additional warning lights like the SLIP light staying on I believe and I haven't experienced either. Could they still have a high chance of being the problem? Is another sensor like an O2 sensor or something a high possibility? Maybe the MAF or TB is bad, but wouldn't they throw some code? I don't want to blindly change things out and spend money on just guess work, but if it's fairly inexpensive and a decent probability to be the problem, I'll try one or two. What else could be a possibility and how can I test it as opposed to just replacing it blindly?

Also, and this is important for me to know, is my low gas mileage related to the rough/choking warm starts (e.g. same faulty sensor) or 2 separate issues?

I assume the ECU is just sending more fuel than necessary, but I don't know how to diagnose that nor know what symptoms to look for.

Thanks for your help!

 

You're idle should be 650 +or- 50 rpms. Could be a failing fuel pump. If it starts fine on every cold start I believe you can try pulling the temperature sensor on a warm start and see if it makes a difference. It should trick the ecu into thinking it's a cold start

 

Get a fuel pressure test. That could eliminate a couple things. The fuel pump assembly can be bought for under $100 which should fix your fuel gauge problem also. That would drive me crazy not knowing how much gas is in my tank. I also wouldn't trust the electrical tape around the z tube hose tear.

 

I think you have a vacuum leak, pay particular attention to the z-tube hose where it attaches down at the driver side manifold, also REMOVE your pcv valve, shake it to make sure it still rattles and doesn't sound gummed up. Also check that connector hose between the two valve covers.

Retorque the upper plenum since it sounds like you're running a spacer.

Perform ALL the resets especially the idle air reset (motor needs to be at operating temp when you do it).

http://www.nicoclub.com/archives/g35...procedure.html

I would also thoroughly clean ALL the chassis ground points starting at the battery, the little jumper connects to the chassis in the battery well, remove the single 12mm bolt holding the coolant reservoir and lift it straight up (leave the tube attached there's enough slack) the next bonding jumper is below it and held down with 2x bolts and it connects to the timing cover. Use a wire brush and clean the contact points and reassemble using electrical anti-oxidation grease. Clean the positive side as well which has 3 connection points, battery to lug, lug to fusible link, fusible link to wire which goes to the starter, take them all apart and clean/de-ox.

Next take the vehicle down to get the battery load-bank tested at a parts house, this is done with the BATTERY DISCONNECTED FROM THE CAR, if they're leaving it connected they're not actually using a load bank tester which is usually mounted on a cart they roll around, using a digital multimeter to measure voltage is not what I'm talking about.

With the electrical system eliminated, vacuum leaks eliminated, if you still have problems then focus on the fuel dampers at the back side of each fuel rail.

Just to verify, the engine CRANKS with the proper power and doesn't feel sluggish to crank when hot yes? It cranks normally but when it catches (or stutters and then catches) it just runs rough and shitty yes?

I wouldn't trust the electrical tape around the z-tube either, tape gets hot and gummy and no longer seals, I'm an electrician and use tape almost literally EVERY DAY and I'd be surprised if it lasted a month in that kind of application. If the z-tube itself is damaged you can probably repair it with some JB Weld or maybe some Sikaflex or something. If the HOSE is what's damaged just order another one from Z1 or somebody.

 

Speedy replies, I appreciate that!

FreshLikeAG - I am in the process of verifying what my idle RPM is set to, I recall it being bumped up a bit with my UpRev tune (*Edit: it looks like it is stock 700*). I can also double check my idle RPMs since I was doing a quick guess and I likely need to have the radio and AC turned off to show it at reduced load. (*Edit: Radio and AC off after driving it about 20 minutes to reach operating temp and in park shows it drop to probably 750 RPMs, that 600 to 800 gap is so much wider than the 2,4,600 before it. AC and radio on bring it back up to 800/820*). I'll have to look into the temperature sensor idea as that sounds fairly easy depending where it is located and make some sense as a possible cause for error when warm.

The fuel gauge could be a sensor on or near the fuel pump, but it seems a few other people have confirmed that theirs was indeed the instrument cluster that needed repair. One just got his done the other day and mentioned it in another thread. Does the fuel pump assembly include a new fuel pump or just the stuff around it? I know there is one sensor with the fuel pump and a second one in the other hole or whatever to the gas tank under the back seat. Unfortunately this is a semi-common problem with our cars (P0462) kind of like the airbag light blinking is also semi-common.

Cleric670 - I do have a spacer and just to be clear when I mentioned the copper plate at the throttle body it is the piece in this image:


Also to clarify, the hose tear didn't occur until after I took things off to clean the MAF and TB, this warm start problem was already going on. I can still work on replacing the hose though, the Z-tube is unharmed and the plastic tube itself has no tape on it, just the rubber hose NEAR the Z-tube nipple. I may be able to just cut off the last 2 inches and reuse the existing hose. I think the struggle with replacing the hose was the back side isn't easy to get to in order to remove and replace. I also didn't think the hose itself would get all that hot and the tape claimed to be rated for like 180 degrees.

The engine is never running rough/shitty it's just those first few seconds to get it to actually start and not grumble or struggle to get air, fuel, or something like that. The RPMs might bounce from near zero to only like 400 a few times and then either fully start or die. Once it truly starts up (RPMs shoot to like 2000 and then settle down) I feel like it is running like normal. If it helps, I can record a short video of this.

I did always do my resets after a fair amount of driving so it would have reached operating temp. The only thing I may have cut short would be after you start your car for the idle relearn, wait the 20 seconds, and rev a few times. I may need to let it idle longer and rev a few more times as well since I turn it off after I see it seeming to be settled below 1000 RPMs.

I assume the battery stuff is because of the one time code on voltage? This was a few months back with no return, but I can certainly still look into it. Also the battery disconnected from the car for the load-bank test just means to undo the negative (or both terminals), but the battery can still be in its housing and not pulled out of the car, correct?

To help me understand, did you guys things these are related or unrelated issues? Like is the vacuum leak a gas mileage issue only and we are troubleshooting these things at the same time or is it probable that fixing one will solve the other?

 

Oh I forgot to add:

As of now the other sensors don't really stand out to either of you as being a problem? Most should be built to last the lifetime of the car?

Not sure if it should be on my radar, but my spark plugs were changed at like.... 67,000 miles at an Infiniti dealership and haven't been touched since (another 67k on the new ones).

 

You can manually read the fuel sender from the main harness with a digital multimeter, pull up the back seat, unplug the harness and read for resistance across pins 2 and 5 (read left to right). The resistance scales from 3 to 80 ohms depending on whether you are full or empty. If your gauge doesn't read below 1/4 tank for example then run it to that point, run it a little more and read resistance, if it's reading less than 20 ohms then the problem is likely the instrument cluster (combination meter). This is all covered in section DI of the factory service manual on like page 19-20 or so?

http://www.nicoclub.com/archives/inf...e-manuals.html

The z-tube hose on the driver side manifold is really easy to access once the z-tube is removed, it's right below the throttle body.

Yeah the battery and lug cleaning is just to verify you don't actually have an electrical problem, these cars are SUPER sensitive to resistance, especially since it's such a long path back to ground, my vehicle was running normally and after cleaning the grounds thoroughly it's actually running significantly better. Load bank testing can be done with the battery still in the car but the lugs need to be removed from the battery terminals.

I do think you have multiple unrelated issues happening but there's still a chance it's the fuel dampers which could affect both, I think they usually start getting really noisy when they do go out so you might throw a stethoscope on each one (end of the fuel rail near the firewall) and make sure one isn't significantly louder than the other.

That's a lot of miles on those spark plugs and you're probably due for a replacement, I wouldn't go too crazy on any further troubleshooting until they were replaced with more OEM plugs. Inspect the coil packs thoroughly as well for any scorching/blistering/bubbling of the epoxy resin encapsulation (black shiny part on top) or scorching of the spark plug well socket, or corrosion of the spring inside the spark plug well socket, possibly also oil inside one of the spark plug well tubes. Spark plugs will probably tell you what the problem is on startup, I expect they're highly worn.

 

 

So has anyone confirmed whats going on with that i bought an 07 g35s sedan thats having the same problem just warm starts is when it has problems

 

This should be a pretty simple problem to locate.
Make an appointment for an oil change at your local Infiniti dealer
Usually there are two drive up service lanes. When you pull in park in the middle of the two of them so both lanes are blocked.and turn off your vehicle

I'm sure the problem will be quickly diagnosed

 

wait why do i have to block both service lanes ill just look like a dick

 

Check your cam sensors.

 

Because then they will want to get it fixed quickly to get it out of there.