Hey guys.

I come seeking guidance. Long story short, my 2004 350z has been giving me some grief.

It all started when my CPS (crank pos sensor) died on me last year. I replaced the visually broken sensor with an aftermarket sensor and happily continued on. A month or 2 after then I experienced the same symptoms and assumed a dud CPS. Replaced it again, but that didn’t solve my problem.

I then suspected cam pos sensor. I took the car to a workshop to put in a new clutch and smf and asked them to fix the issues while they were there. They said that they ran some diagnostics and that my timing chain is stretched (I wouldn’t be surprised if that is the case as the car has 210k km on the clock). That job is too big for them and told me to seek help elsewhere (they gave recommendations). I can do that job myself, but don’t want to unless I have to.

AI then went and sought out a second opinion from a guy that specialises in Z’s but is on the other side of the country. He reckons its just non-OEM sensors causing all this nonsense. I replaced the CPS with an OEM sensor - car still sad. I’ve now ordered OEM cam sensors - they’re arriving next week.

In the meantime, I dug up my old 2-channel oscilloscope and ran some tests.

My symptoms are as follows: All sensors installed - car won’t start. Unplug CPS - car starts and will allow me to drive around a bit, but it will ultimately die on me.

When I ran the scopes, I got some interesting results. Some of the signals seem to be inverted, which is super weird - hopefully the new OEM sensors will fix that. (For info - the aftermarket sensors were Bremi’s). I also noticed that the timing was a bit out (I think).

My scopes were taking during crank as the car didn’t want to starts. Are there any experts here that can tell me if the chain is stretched or if I’ve jumped some teeth? I have also attached a scope that I found online of a healthy vq35de at idle.

Thanks,
Rob




Both cam sensors


Healthy VQ35DE

 

What codes did you get? Was it just the cps code?

 

P0335 - CPS and P0340 - camshaft sensor bank 1.

 

Maybe someone else can chime in to confirm, but I believe you would be seeing timing related codes if it were an issue with the chains. Potentially noises too from the chain slapping around.

Have you checked the ground, power and signal to the cps connector? Maybe an issue is present in the wires.

The crank sensor and cam sensor work in tandem. The crank sensor provides information to the cam sensors, to adjust timing accordingly via vvt. I think an issue with the crank sensor can cause hiccups on the cam side, potentially throwing a incorrect code for the cam sensor. Again, wait for someone else to confirm these suspicions as I am not entirely sure.

 

Maybe someone else can chime in to confirm, but I believe you would be seeing timing related codes if it were an issue with the chains. Potentially noises too from the chain slapping around.

Have you checked the ground, power and signal to the cps connector? Maybe an issue is present in the wires.

The crank sensor and cam sensor work in tandem. The crank sensor provides information to the cam sensors, to adjust timing accordingly via vvt. I think an issue with the crank sensor can cause hiccups on the cam side, potentially throwing a incorrect code for the cam sensor. Again, wait for someone else to confirm these suspicions as I am not entirely sure.

 

So, bank 1 sensor arrived. Installed it, no change. Still waiting on bank 2 sensor to arrive.

In the meantime, some more info:
1. a workshop installed a new clutch and flywheel for me a few weeks ago. After they installed it, the car would only run with the crankshaft sensor unplugged. I think that the installed the flywheel in the incorrect orientation. I did speak to the suppliers of the flywheel, and they said not possible, but I am, however, not entirely convinced. This is the flywheel: https://www.ebay.com/itm/12587525267...mis&media=COPY - Not sure if anyone has had any experience with this flywheel?

To me (i’m not an expert by any means), it looks like the timing between the crankshaft and camshaft is out by 1/3 of a flywheel rotation, which would coincidentally line up with one of the 3 possible flywheel installation orientations (if it is possible to install it in the incorrect orientation).

Here are some new scopes:


Camshaft signals. Engine idling. Crankshaft sensor unplugged.

Both camshaft signal during crank.

Crankshaft signal (yellow). Camshaft signal. Cranking engine.

 

Removed the cover for the main timing chain tensioner, and it seems ok to me - it at least ok enough to not cause problems

 

Almost guarantee you that the flywheel was not installed properly.

There is an alignment dowel pin, but folks unfamiliar with Z33s often overlook this and assume the alignment is strictly done via the hole spacing of the FW bolts! Long story short, yes you can install the flywheel incorrectly. The dowel pin would smash into it, causing it to sit cocked on the crank (not flush), but it would not be very noticeable at a glance. There is a relief cut drilled into the flywheel to accommodate the alignment pin/peg. It's hard to see in the photo of the part you linked, but it's there if you zoom in.

I think you need to have the shop re-do the job, hoping they stand by their work and take care of you. Btw, you can prove the flywheel isn't aligned correctly by removing the inspection cover, rotating the crank, and measuring the run-out on the flywheel. It should be pretty obvious.
-Icer



Here's what the crank looks like without the flywheel.

 

Thanks for all the info. I ran the car a bit. See below. Looks fine to me. What do you reckon? I also managed to grab a screenshot of a quick video that was sent to me after they installed the flywheel. Can you see anything that I’m not?

 

Watched the video taken through the inspection port, the flywheel runout looks normal. So it would appear my theory/assumption was incorrect, but I'm happy to be wrong in this case.

Most likely the aftermarket sensors are causing your problems. 210k km translates to roughly 130k mi. Your timing chain should last longer than that unless the engine had a severe lack of oil changes. You know the history of this engine/car better than I, but you should know that if the chain timing is off a lot (like it skipped time from a failed guide or tensioner), then the ECU will disable the spark or injectors and simply not start. You would need an oscilloscope to check the waveforms between crank and cam sensors and compare to a known good to confirm. Nissan gives you a known good example in the FSM. There's a good YT case study showing an example of this. It's a VQ35DE in a Nissan quest, but same waveforms apply.
LINK:


Fingers crossed the new OEM sensors solve your issues.
-Icer

 

After comparing the scope captures in the video from Royalty Auto (linked above) and your screencaps, specifically the crank + cam capture & both bank cam sensors, I came to the realization that your cam sensor data captures look totally different. There are are some weird long pulses that shouldn't be there. The only one that looks correct, is the two cam sensor capture (1st photo) with the crank unplugged, engine running.

I'm guessing the ECU defaults to expected timing values with the crank sensor unplugged, or it's able to accurately guess based on only the cam sensor readings. This isn't very uncommon on modern engines. In my opinion, your engine, mechanically speaking, appears to be in time. But the computer doesn't appear to be getting good signals from the cam sensors when the crank sensor is plugged in. The only way I can think to explain this behavior is the aftermarket sensors are the problem or you have a possible wiring fault involving the crank sensor.

So to recap...
Engine running with crank unplugged, your cam sensor captures look good.
Engine cranking (with or without crank sensor), the cam sensor captures look wrong.

Cheers!
-Icer