mendoza_ms

Hey everyone! I'm back and I can say with confidence that I've fixed my problem for good - the Z has been running fine for 3 weeks now (knock on wood). But before I share, I just want to note that my situation may be different from yours and as such my solution may not work for everyone, so definitely do your own research and get a second or third opinion.

TL : DR ; - It was the f**cking relays...

Since my last post I took my car to two different mechanics. The first shop didn't see anything wrong when I brought it in (I guess they ignored the P1606?), stated the car started up and drove fine and simply asked me to bring it back to them when the problem came back. The second shop stated that the only thing they could think of was to try and replace the entire EFI and engine room harnesses, then if that didn't work they would try replacing the ECM and hope for the best. However since parts & labor for those options weren't cost-effective solutions they said they didn't want to touch it and simply wished me the best of luck...

So I went to a local junk yard (Pick-U-Part in the San Fernando valley) and with the help of my brother who is an aspiring mechanic found a wrecked 2014 base model 370Z and salvaged the main two relays (VVEL and Window washer), an IPDM, a fuse box, a VVEL module and most of the Engine room harness. I spent days mapping out the harness by hand and studying the Factory Service Manual (specifically sections EC and PG).

In the end my process was to basically rip apart the car, revert the car back to stock in order to eliminate everything as a potential problem and meticulously put it back together. I basically removed the entire intake system (plenum, pipes, MAFs), reconstructed every electrical component near the battery compartment (fuse boxes, relay boxes, etc), replaced all the fuses (whether they were blown or not), cleaned up the wiring harnesses, checked for shorts to ground/power, brushed all the ground connections and then ran through all the major system calibrations (meaning initializing the VVEL, resetting the ECU, running the idle air volume learning process, etc). All this was probably overkill and I didn't find anything seriously wrong but I had to be absolutely sure.

Anyway that seemed to do the trick and I stress tested the s**t out of the Z wanting it to fail again. You name it I did it - I accelerated hard, sprayed water all over the engine bay and battery compartment, ran it cold, ran it hot, etc. The problem was fixed, but what was the root cause?

Well, my theory is that it was the relays all along. When I tried to swap them early in my troubleshooting I got a false positive and then ruled them out that thinking it had to be something else. The fact of the matter was that I didn't use the metal bracket that holds the relay box in place back when I first installed my Optima Yellow top battery because of wiring clearance issues. It is entirely possible that the relays were indeed faulty and that harsh driving conditions (such as a bumpy road) would shake up and trip the relays which would cut power to/from the VVEL module which explains the intermittent U1024 (CAN communication circuit). It wasn't the VVEL or the ECM like the manual says it is. I tried 3 different VVELs so I know it wasn't that and I wasn't getting codes for the ECM or anything else. It probably helped that the relays from the donor car were newer and made by a different manufacturer - My car is a 2009 and as a first-gen 370z it's understandable for parts to fail since the engineers probably haven't worked out all the bugs yet.

That's it! I hope you guys get some value out of this information and learn from my experience and mistakes. I also want to thank you guys for all your feedback and support - I was so close to giving up and selling my Z but right now am back to having good times!

Peace,

JMendoza
Mendoza Motorsports
Pacoima, CA