What did I do? Got a miss...PTU harness, fixed!

[DCaff300ZX]

Well, as some of you may know I've been making a maintenance run through my TT's engine bay, replacing any and all perishable bits and pieces in preparation for many more years of fun.
Each step has produced positive results, my latest work was replacing the fuel lines and clamps and FPR and Dampener, cleaning the POP charger, etc...with the only work left to do to get the last pieces of hose I needed (auto supply didn't have as much as I needed) to use the hard protective covers on the supply and return leg of fuel lines at the filter.

Today I replaced/installed those hoses and protector pieces, and also threw on what I felt was a newer fuel filter from the NA that had already supplied the newer Dampener and FPR. In the process I had to remove and replace the two large vacuum hoses from the brake booster, I added new clamps and streamlined it all for looks.
I also did some wire wrapping up front to finish off my PTU relocate and after that, replaced the long extra-small vacuum hose running at the back of the engine bay from the balance tube to the boost sensor, then played around with cleaning up the wiring at the fuse box since I am looking at potentially relocating the fuse box.
I loosened the fuse box and removed all of the brackets and such holding the harness, other wiring and fuse box in place, worked the wiring and connectors off the brackets to the other side of the fuse box, wrapped them all together in protective wrap and re-installed the fuse box and cleaned up. I was fairly gentle with this but of course some effort and brute force moving things around is necessary, but it didn't seem like anything got broken or abused.

Trouble began when I started her up to go home after finishing up, she had a pronounced miss and although not loud, has a strange almost tapping-like sound coming from the back of the motor as if something is working extra-hard or out of sync...obvious to me because she is SO smooth and quiet otherwise. I checked all connections I'd worked around finding nothing, checked everything I could check such as checking/wiggling coil packs and any other connectors/whatever I could see or were near the noise area and where I'd worked- nothing helped. I drove her home and she's Subaru-city off the line, and shakes a bit at idle but also sometimes smooths out a little until you give it gas and she wants to boost a little all the time, and it's definitely a miss. She also had a strange "hot smell" for a little while after I shut down at home but no overheating or anything amiss from the dash lights/sensors, it is about 8 miles from where I was working to home.

So I checked to make sure TT and NA fuel filters are the same- check.
I replaced the wiring as it was and that didn't help, and wiggling it around while the engine was running made no changes.
All vacuum hoses passed testing of wiggling/pinching/twisting/connectors tight. I checked the TPS connection which near my work and is a little loose behind the connector, it made no obvious difference at idle.

Any ideas?
I'm stumped beyond the filter may not be so new an is clogged, and is the only thing I replaced today that could have changed anything IMO. I will replace it ASAP with new.
When I wrapped the PTU wiring, I really didn't move it much and it was fine for weeks previously, could a loosened connection there be behind my sudden mystery miss?
Has anyone moved or relocated the fuse box, and had any issues from that?
I'm racking my brain for more but it's late, hopefully you guys have some ideas...toss out anything and everything!

[DCaff300ZX]

OK, more-
After racking my brain I realized that after swapping the fuel stuff, I of course started the car to check for leaks and such and all was well...ran it for 30-40 seconds anyway, and with a few revs thrown in...she was quiet as always and ran perfectly.
So now I am thinking about the PTU. During my mind racking and thread/site searching I remembered a thread about the new PTU going slightly bad, and also how actually when I first moved the PTU by the fuse box for 1 day I got a small miss, which after moving it around and then moved up front it went away. I will be checking that whole area ASAP, maybe I loosened a connection.
I cannot think of anything that could have been done around the fuse box to affect the engine in any way other than a loose vacuum hose on a boost hose, but I checked those and they were intact.

Anyone who has more ideas toss 'em out, no matter how simple/stupid it may seem...

[Oh Em Zee]

Power drop test
If this is a misfire on one cylinder, it will be obvious with a power drop test. Unplug 1 coilpack at a time with the car idling. If there is no change in RPM and sound, that cylinder is not firing.

If there is a systematic misfire (one cylinder is the culprit), you can then check everything for the one cylinder.
- Coilpack, w/ car off, switch with a properly working neighbor coilpack, see if problem moves to the donor cylinder
- Fuel injector, w/ car off, Pull the injector clip and OHM test the injector. 10Ω~14Ω is within spec. Check for green corrosion, and also signs of the wiring being previously tampered and cut. (Usually within 4 inches of the clip)
- PTU, if you have a second PTU, swap it in at this point.
- Test for spark. I typically use a long screwdriver and put it against the metal body of the coilpack. I put the handle to my ear and listen for a ticking of the coilpack firing. This is just a quick diagnostics. To verify spark 100%, put a screw driver down the bad cylinder's coilpack, with the screwdriver ~1/4" from the plenum to visably see the spark. This is risky. Keep the screwdriver close to the plenum, otherwise the charge will find another way to dissipate if it can't reach ground (through you)

Most of the time, if it's systematic, you'll catch it by then.

Non systematic - Check timing and TPS settings first, then work from there.

[DCaff300ZX]

Good stuff that I will do if/when no inspection/check of my work solution is found, thanks for the all in one place checklist!

I should have mentioned that part of my maintenance run was replacing all of the injector connectors and cleaning them, along with the coil connectors, and inspecting/wrapping/re-routing in some cases the injector harness. This was done about a month ago now, all has been well there but of course if necessary I will go through it all again. All vacuum hoses and boost hoses and a few other odds and ends have been replaced as well, only major components that have not been worked on such are rad hoses and anything with the turbos.

I want to concentrate first on the fact that the car ran perfectly before the work I did Sunday that should have had no real effect on the motor missing or not, since most likely it was something I did Sunday after the fuel line/filter replacement that caused the sudden issue.
Heading out there in a few minutes, I am very hopeful that I just loosened some of the PTU harness in it's new home when wrapping it up (the next thing I did)...that now seems the best bet for easy to find trouble although my loose connector mount on the TPS also gives me concern because it always gets bumped when working on the car and did when doing the fuse box/wiring movement, and therefore could possibly be in the mix IMO...

[DCaff300ZX]

-UPDATE-
OK, I started her up and she barely did...I had pulled the nose panel and so I moved the PTU harness and viola- it ran better, worse, etc. every time I moved it so that's the issue.
I will now be pulling that all apart and troubleshooting it, anyone with ideas there chime in and I will update as I hopefully finish up.
Thanks Oh Em Zee!

[DCaff300ZX]

-FINAL UPDATE-
And here's the culprit, seems someone (me) didn't check BOTH PTU connections!


I cleaned this mess up, di-greased the now-clean connection and re-assembled after CHECKING THE OTHER CONNECTION JUST TO BE SURE, and she purrs again!

Hopefully this gives everyone who views this another option when she begins to miss, do everything Oh Em Zee mentioned and add checking your PTU harness connections for corrosion before moving into more detailed tests and replacement.

[Z-owned]

Mmmm gotta love that green corrosion lol.

[300ZXttZMAN]

Very nice, glad to see you found some green trolls and it wasn't something serious.

[Oh Em Zee]

90% of the time, it will be a bad electrical connection.
Glad you caught your misfire very easily! That amount of corrosion will definitely be the cause.

[DCaff300ZX]

90% of the time, it will be a bad electrical connection.
Glad you caught your misfire very easily! That amount of corrosion will definitely be the cause.

Yes indeed, once I saw that green flower in each receptacle I knew what was up for sure...and wondered how she ever ran smoothly previously!
De-green-gunking all of the electrical connections is a must to be sure, no matter how you car seems to run, as I have found it nearly everywhere I've checked since owning her.

Made for an interesting day getting her fixed before a doctor's appt. this AM, and then off to work on time.
Lessons learned here are to be SURE to check each thing you do both by looking AND running the car, and try harder to be more consistent doing work so as not to miss something like this that causes a problem further down the road in an area you may overlook because of having done work there recently, and being over-confident in your work because of having had few problems in this area before.

Hopefully this helps others if they encounter a similar situation where a previously good-running car suddenly starts missing.

[DCaff300ZX]

Very nice, glad to see you found some green trolls and it wasn't something serious.

Mmmm gotta love that green corrosion lol.

I loves my greens in salads and bank accounts, but NOT in my electrical connectors!!