My 1990 300zx Twin Turbo build by megaDan

21 minute(s) of a 731 minute read

So....its been a bit of a rollercoster. Please stick around because I need some input at the end....Before adding any fluids, pressurized the cooling system before filling to verify there were no major issues. Then I did a boost leak test and discovered leaks at both my VTC solenoids at the back of the intake valve covers. This added a decent delay as I had to remove the intake manifold and both valve covers, apply RTV to the top half of the solenoid (I haven't done this in the past), wait 24h for cure, and reassemble.

After a little more adjusting I managed to get the intake system airtight. I added a 50/50 mix of coolant and distilled water, oil, and after a few stumbles got her going.....and found a fuel leak at the return side of the rail. Since installation 9 years ago I've never dealt with any fuel leak issues, but I must have bumped it once or the way I had it resting for a few months didn't agree with the braided line > AN connection. I disassembled the fittings, installed the rail to a spare intake manifold, pressurized the system, let it sit for an hour or so, and reinstalled it for real after confirming I corrected the leak.

Thank god for spare parts. Rudimentary test bench.

Fired her up again, and discovered a slight miss. I re-used the plugs I had in before as they were all in great condition; so I swapped out the plug in cylinder 5 only (the location of the blown HG) and everything was butter smooth. Yay! I let it run for 3 minutes or so while continuing to add coolant.

I shut it off, drained the oil...or what should have been oil, and was met with more opaque tan fluid. My heart sank pretty much immediately and my brain went to worst case scenario. Headgasket didn't seal. Something major is wrong. Need to pull the engine and start over or find a junkyard. Bad times.

I filled it up with more oil, let it run a little longer while I kept checking the oil fill port on the valve cover for what I was hoping would be oil. While running it still seemed to be more opaque tan than clear oil.

Since then:
-Dipstick looks super clean. Clear, not frothy. Wiping it on a white towel shows exactly what brand new oil would look like.
-Valve cover shows mostly clear residual oil in the valve cover, but when running it takes on an opaque quality.
-Leakdown test on all 6 cylinders was between 18% and 22%; however I'm not sure I trust my US GENERAL tester as the regulator pressure to zero the unit out is only 14PSI. I ended up setting my compressor regulator to 60psi and bypassed the gage and fed air straight to the cylinder. Very similar results, but with much less resolution on the data as I had to take readings from the compressor itself. Regulator pressure was close to 60, and it looked like it might have dropped to 53PSI, which is ~13%. No sound or bubbles from the radiator/exhaust/intake, everything was through the crankcase as it should be.

I have NOT done a compression test yet. My plan is to buy another 10qts of oil on the way home, do another flush and see if the color of the oil has improved. If it has, I guess I'll stop panicing. If it has not, I'll do a compression test. I'll probably do a compression test either way because I'd like to establish a baseline for future reference.

My question is....am I worked up for nothing? I didn't remove the pan during my rebuild...now I wish I had. Should it take a few flushes to get all the residual milkshake out? Water is denser than oil, is it possible there's still a layer at the bottom of the oilpan? I have hope after encouraging leakdown results, but the condition of the oil is still incredibly concerning. Do I get it up to temperature and add seafoam? Take a few gentle drives to heatcycle the engine and boil off any residual oil? That's my last resort as I'd prefer to run the engine as little as possible until I can confirm the oil is mostly water-free.

Ugh.

5-8-2021

It turns out my power steering intermittency was related to my intermittent speedometer. I knew these clusters were known to fail; but so are the speed sensors at the transmission. I've realized that I need to start behaving differently if I want to keep this car 'forever'. I need to be proactive with spares, and I need to have specialized work done now, before the opportunity disappears and I have to do it myself. I finally bit the bullet and pulled the cluster and sent it out for a rebuild. At $150 for the service, I'd consider it a steal; and hopefully it gives me another 25 years of trouble-free service. Next on the list of 'just get it done' is seat repair. I've had my eye on a set of seat skins for 5 years now; but its always been de-prioritized. I think its time to change that.

While waiting for the cluster repair; I got my spring detail done over a few evenings. I gave the wheels and body a good claybar and wax. I think the results were fantastic.

The cluster came back on Tuesday; I installed it that evening, and I've driven it to work the last two days to put some gentle miles on it before I start commuting 100 miles with it every weekend. Everything feels great; but my tank of E85 is about 7 months old so I'm trying to burn through it before I really give it any boost.

No major revelations this update. That's probably a good thing.

6-12-2021

Big update. I've been busy. Mostly with family/summer activities, but what tiny free time I've had has gone to the Z.

Custom gage design: I designed, built, and programmed an arduino nano based gage. My initial concept was a multi-function gage capable of providing an estimated horsepower or % power display based on known power, vehicle weight, gear ratios, and acceleration; but that got scaled WAY back as I realized how challenging this was. Initial gage function is accelerometer and ethanol content only and will evolve this winter as I play and troubleshoot. Proof of concept works, and I had a buddy 3D print a structure to hold all the components in a spare 52mm gage housing I have.

Cooling:
It got hot early this year. Temps in the mid-high 80's since beginning of June. I've been particularly sensitive to cooling issues since my headgasket and radiator issues last year; so on my first few drives I kept my laptop open to get an accurate picture of coolant temps. Mid 80's with the AC on saw temps sit at about 205 which had me concerned.

(The Z is mostly shroudless, aside from the SMIC's. I broke my OEM fan shroud a few years back after installing the 2.5" IC piping and a replacement is ~$200 and there are no aftermarket options. The cost alone had me brainstorming an EFAN solution all of last year, but while I appreciated the 'simplification' and added cooling control it turned out the biggest upside (engine bay space) was nonexistent. The ideal EFAN setup (Taurus SHO) actually takes up more space than the existing mechanical fan. Ugh.)

After weighing my options and trying to get the biggest bang for my buck on a very small budget this year; I opted to go with an aluminum front bumper undershroud, to ensure that the air going into the bumper also went through the radiator.

Pics are terrible this post, I apologize. Its always hot and late when I get garage time now. Undershroud installed!

With the undershroud installed, temps peaked at 195F on a hotter day. I'm really happy with those results, however during the undershroud install I saw how poor my front end airflow really is. My current intake forces the filter splash shield straight down, reducing air through the radiator by ~40%.

Ugh. Ignore the bug goo. I took this picture mid-install so the filters are resting on the underbody tray. 

The 'X' identifies the bumper opening that is completely blocked by the splash shield (it even intrudes on the lower opening a small amount). I thought about removing the splash shield but it leaves the filters exposed to road debris, rain, etc which I'm not comfortable with. The only way to correct this is change intakes. The replacement was delivered today. More on this later.

Interior:
I finally ordered seat skins. It's my birthday, fathers day, and christmas present from my wife this year. I'm very fortunate that there isn't much I need or want; and this was the top item on that short list. I don't recall why, but I've had a spare set of seats (which now seems to be spare 'seat') for years across multiple moves. Not getting rid of it finally paid off as I have a test bed to do disassembly on. In about an hour this morning I got 60 some hog rings and staples pulled and the leather off the front passenger seat. We've got a few household projects that have been placed on hold thanks to the summer, so workspace is at a premium. I set up shop in the sunroom on a folding table; I've got a laptop with some helpful videos and instructions, a set of post-it notes to identify large components as they come off, and a organizing bin for the small components. I've never done anything like this before, so I'm photographing EVERYTHING.

Relatively efficient workspace.

These are the photos from just this morning



With 1-2 hours a day devoted to this I hope to be done in 2 weeks tops. Mostly because we've got a busy July and my fear is that I walk away from this project I'll never figure out how to install the new skins in a way that I'm happy with.

New intake shows up tonight and it's supposed to cool off. Here's hoping I can find time.

Oh great, thanks; what has seen cannot be unseen. I guess this is one of those things that you just grow blind to. I've never really 'noticed' that second intake, much less how ugly it is, probably because mine is black. ?

New intake installed. Test drive has been great, but haven't had weather warm enough to compare to previous temperatures yet.

Old intake on the bottom. 

Not as 'out of the way' as I had hoped, but still an improvement. I guess stubby 370Z cone filters will be eventual upgrades.


I'm continuing to make fantastic progress despite very little free time. In what seems like a never ending battle, I'm battling a misfire under boost again, only above 12psi. I encountered this earlier this year, swapped all 6 coils and thought that solved my problem but apparently not. I did some logging to ensure I had adequate fuel pressure, sensor readings, etc and everything looked fine to my partially trained eye. I'm pretty much convinced its a spark related issue, be it blowout. weak spark, etc so I've developed a plan of attack.
1. Gap plugs down to .028" from .032". I have a new set of plugs but I want to be very methodical in how I troubleshoot this to ensure I really address the root cause. If gapping the plugs down works, then it likely indicates a weak coil.
2. Replace all plugs
3. Compression test (god I hope not)
4. PTU subharness delete

I got as far as removing the coilpacks to start step 1 when for whatever reason I decided to look up into the coil boot on the first one I pulled and saw this:

Why yes, that IS a spider egg. 

I was immediately frustrated and elated. "A smoking gun!" I thought, surely this increased resistance between the coil conductor and the plug would result in a less than optimal spark in harsh conditions. I removed the boot to carefully dislodge the egg with a 10 foot screwdriver (safety first) and discovered that the graphite conductor at the end of the conductor wire was also broken.

I'm not 100% sure I didn't break it when removing the boot, but I'm pretty sure. I grabbed another spare coil, threw it in and went for another test drive ready for 18psi of bliss.

Nope. Now its not just missing like a stumble (raspberries, or BBBBB), but it's giving me the occasional pop too. Super frustrated. I brought it back home and went inside to work on my seats. The engine is way too hot to work on after a summer drive. Plus I needed to clear my head. In short order (with a few hew helping hands from the wife) I nearly completed the recovering of the lower section of my first seat. I still need to cut some holes for hardware and pull some sections of fabric tight, but I think it looks spectacular.

Not bad

All of the above took place on Tuesday. Wow. Wednesday I had no time whatsoever. This morning was a slow start, but I still managed to pull all the plugs, (to complete item 1 above) found #5 insulator badly cracked, replace with new plug, and button everything back up. Another smoking gun but I'm really trying not to get my hopes up. Again, I'm not 100% sure it didn't break upon removal; but cracked plugs seem to be a theme with this motor for some reason.

Leftmost plug. Kinda hard to miss. Another crack like that on the opposite side

I used what free-time I had left before work and the rest of the family woke up to completely disassemble the upper portion of the seat I've been working on. Tonight is calling for storms, so I likely won't get to drive the Z; but I'll probably finish recovering the upper portion of the seat. I'm honestly thrilled at the progress I'm able to make with what little time I have between 5:30-7AM and 8-10pm. The upholstery work is tedious and kinda gross (I hate foam); but at the same time it's somewhat calming. I'm very much a 'make progress' to stay motivated kind of person; so breaking up each project into discrete tasks is essential to keep a project moving for me. I've become an expert at this because of my new schedule.

Moving forward: anytime I have a misfire; check the plugs first. Ran some errands Saturday evening and the Z drove great. Spent a few days chasing ghosts all because I refused to believe spark plugs were bad when I checked them earlier this season. Dumb.

I finished the passenger seat Sunday night. I had hemmed and hawed about completely finishing it because I wasn't sure how to cut/punch/poke holes for the seat hardware....I eventually settled on a pen-knife. It took a little while to build up the courage to make an incision on my brand new seat cover; but everything turned out great. I used chalk to provide some contract to the area I needed to cut and went to work.

Absolutely terrifying.

There are some wrinkles, but the camera flash and overhead lighting in the dark definitely make them stand out. They don't quite look OEM, but they're darn close and they match the interior and existing leather/red stitching accents quite well.

Unflattering lighting, finished up around 9pm Sunday

More of the same

One down, one to go!

Of course, as soon as I got the seat installed I had to take it for a test sit. I knew the OEM seats were weathered, but I didn't realize how bad they really were. The leather was badly dried, mostly to the point of becoming plastic and affording no movement or flexibility. It was like sitting in a rubbermaid tub. The new seat skins are soft (duh), pliable, and wrap around the user. Sure it sounds weird, but it's absolutely night and day between before and after comfort. I'm thrilled I finally stepped up and got this done.

I removed the driver's seat this morning and began disassembly. I'm hoping to finish by this weekend, as I have another automotive 'surprise' lined up that might get in the way and keep me distracted. If I can get this seat done, the Z should be in 'pleasure mode' for the rest of the summer, freeing me up for other projects.

It only took 10 years of dreaming, hemming, hawing, and reprioritizing; but I've finally replaced my dry-aged seats! Great for steak, not for leather. Despire a fair bit of additional complexity due to the electronics and work required for foam repair; the second seat took about half as much time as the first.

The upper outer bolster foam was in pretty rough shape; likely due to me trying to fit my 6'5" frame into to the cockpit. I was looking for some sort of batting or fill to attempt a repair when I remembered that the foam is identical between passenger and drivers side. I have a spare passenger seat which looked to be relatively untouched in the bolster area. Upon disassembly I found the foam to look just about new.

I shouldn't need to clarify which is the replacement.

I was surprised to see the foam this worn when the leather itself was still intact.

Not much else to go over; the process was pretty simple and even easier the second time after learning some techniques from the passenger seat. My goal was to finish them up last night so I could take the Z into work today; but nothing but rain in the forecast killed that plan. I got the driver's seat installed this morning and took the TDI instead

I was too excited to bother with good lighting or removing the Ttops to get a quality picture.

Ditto

I knew I was starting this project off on the wrong foot with a) amateur (if you can even call me that) installation and b) not replacing the seat foam. I absolutely want to do things right the first time, and my mentality with regards to the Z as I continue to mature is to do it once and do it right. Unfortunately paying for professional installation with new foam was just not in the budget. The Z is very much a 20' car. If it looks good from 20' away, I'm happy. I think these seats meet that criteria. Are they perfect? No, Do they look a hell of a lot better? Yes . Are they good enough where they won't bug me in 5 years, also yes (I'm pretty sure). This was a fun project and I'm really happy with how they turned out, and honestly I think they're even a little better than I had expected. They match the current OEM+ interior and they've improved comfort an order of magnitude at least.

Hopefully my next post will be a brief introduction to an 06 JCW....

We've had a TON of rain recently, so despite taking two weeks to finish the seat recovering project; I really didn't miss out on any driving days. I took the Z downtown yesterday for the first drive since finishing the seats. Going from aged slippery leather to soft novasuede is fantastic. They're super comfortable and the suede provides a great amount of friction to keep the occupant stuck in place. No pictures, but it was a great first drive.

In other news:

4 years ago: Thrilled to be back in the mini game for $800

4 years and 3 days later! It always helps to placate a peeved wife with frozen custard.

Medium length story short, my buddy met another mini fanatic (but non-gearhead) at a local meetup who had plans to trade in his 06 for a new Clubman. Knowing I'm always looking for a deal, he gave the guy my contact info when he told him the trade-in offer. After two months of waiting for his car to be built and one very brief test drive in a rainstorm, we finally finished the transaction on Saturday.

The good:
2006 (Last year for the hard-topped Gen 1)
One owner
New runflats
Dealer serviced
Everything intact and present (JCW badges/accessories/etc)
Supercharger replaced last year
Interior a 9.3/10
Exterior a 9.5/10

The 'bad':
Occasional limp mode due to throttle body or throttle pedal sensors. Troubleshooting will be aided via the silver mini
Needs brakes bad
Needs some other common failures addressed soon
140k miles

The great:
All original factory JCW w/210hp package with all documentation
Purchase price less than double my $800 silver mini.
Rust free. Underbody is VERY clean, and rust recall was performed as late as possible into the recall window by original owner

Having 4 cars that the wife can't drive doesn't make sense. It also doesn't make sense to have a mini as a dedicated winter vehicle as they are notorious for frozen window seals and latch mechanisms. I'd love to replace the dying TDI with the silver mini, but I think the 300,000mi TDI will still be a better winter vehicle. I'm not sure how to proceed yet...