My 1990 300zx Twin Turbo build by megaDan

7 minute(s) of a 731 minute read

I appreciate the encouragement and I'm glad that taking the time to document my progress is in some way enjoyable to others.

I've been continuing to put miles on the Z. Funny how more power and no problems will do that....I've got almost 1300 miles already on it this year, which is the same amount I drove all of last year. The more I drive it, the more it pushes me to address the few remaining creature comfort issues I've already discussed in this thread. Cruise control, and air conditioning. My last update described doing some of the physical troubleshooting of the cruise control system. None of those checks resulted in any smoking guns. Someone made a very detailed post on twinturbo.net years back that also included some electronic trouble shooting methods. By the end of these tests, I should know if the problem is in the vehicles wiring, or in the cruise control unit itself.

Since I rebuilt the unit a few years back after I had it powerdcoated, and it didn't work upon reinstall; I figured I screwed something up on re-assembly. There were some very very small brass washers within the unit that I wasn't 100% sure were back in the correct place. Imagine my surprise when I applied 12V to the vacuum pump and it ran. Grounding the remaining pins on the pump itself resulted in the throttle cable retracting. Woah! Given that I was now sure the unit itself worked, and I didn't change anything in the wiring; either I've screwed up the reinstall every time I've tried it, or the speedometer signal from the transmission is no longer working. My speedometer is intermittent, which makes me think its transmission related. Despite this, I trudged on with the remainder of the electronic troubleshooting; this time I was verifying that the wiring going to the cruise control module was intact and the steering wheel controls worked. Unfortunately it appears the module changed over time, so the pinout provided in the forum post did not exactly match my pinout, which also didn't match the pinout in my service manual. After spending some time checking wire colors and finding power/ground I managed to determine where/what each pin was and confirmed that everything was functioning as intended.

The only remaining check was to jack the car up, lower the back half of the transmission and directly check the output from the speed sensor. I figured going for a test drive would solve the same purpose, be easier, and be a heck of a lot more fun. I pulled out of the driveway, got above 25mph, turned cruise on, and set my speed.....IT WORKED! Hot damn. I love the seating position in this car, but the go-pedal really is only made for someone with a size 6 foot. As my feet are about twice that size, my right foot ends up sitting at a 30* angle from the floor. It's natural now that I've been doing it for years, but its still not exactly comfortable for hours at a time. I'm very excited to have this operational again.

I mentioned a few paragraphs up that the Z has been running great...which is mostly true. However I took it to Madison this past Saturday, and was encountering a stumbling upon reaching high boost, but only intermittently. First guess was boost leak at injectors because the wideband was giving a lean condition rather than a rich condition which is typical with boost leaks in other areas. It didn't happen all the time, so I drove it out to cars and coffee in lake mills on Sunday. And C&C is the highlight of my month. The weather was gorgeous and my Mini isn't worth showing. We had a great morning out there and the turnout was spectacular, but the problem got a bit worse on the way home. My friends and I attempted to take backroads home, but the the suspected boost leak had gotten worse. Phooey.

Later on Sunday I did a boost leak check and sure enough, heard a large amount of air being released from under the intake manifold, right near the injectors. The insulator actually blew out. You can see this if you look closely.

Gross

I repositioned the leaky insulator and added a bit of RTV as a quick fix to keep the car driveable. Turns out it wasn't successful. Taking the car for a test drive resulted in a leak from an injector on the opposite side. At this point I started to become somewhat concerned as this was an entirely new problem. In my mind, these insulators were new! I installed them when the fuel rail went in. When I really started to think about it, I realized that even though they were 'new' and installed by me.....this was 10 years ago now! Holy cow time flies. I thought about it some more, and realized that I could see cracks forming in the rubber insulator. With these being tucked down under the intake manifold, they've probably heatsoaked a few thousand times and have likely aged quite a bit. I found a Viton alternative at Z1 and elected to try these instead of the standard rubber insulators.

The new insulators were delivered yesterday so last night I pulled the fuel rail again (just a 5 minute process) to swap the new ones in.

New insulators!

I removed the old ones, and 4 of the 6 showed major signs of aging. They were still soft, but definitely cooked. You can see the cracks pretty easily.

Probably not a good thing. Ignore the RTV :-)

This is what a new Viton seal looks like

Upon installation of the new seals, I couldn't find evidence of any air escaping past the injectors. I was dealing with two separate leaks on the old ones. Fortunately (or unfortunately, depending on how you look at it), sealing up the injectors showed me where my other boost leaks were hiding. This surprised me a little bit, because I had the intake system locked up tight before my dyno day. We've had both freezing and hot temperatures since then, so I'm assuming the temperature fluctuation led to hose clamps losing their grip. I found a few of them that were definitely not as tight as I left them a month and a half ago. It's still not airtight, but if I bring the system up to 5psi, it's a good 30 seconds or so before it bleeds down to zero which is tight enough that it won't affect power, driveablitity, or affect the measurements the ECU takes for airflow/fuelling. And I was right, the test drive was a blast.

I do need to spend some time re-learning how to adjust my boost controller. I attempted to set it to 1bar on the low setting, but it blows by that. The lowest I can get it to stop at is 1.3bar. Too much boost isn't a bad thing, but I'd like to figure out how it works.

However. Next priority is absolutely getting AC working. I'm having problems sourcing an idler pulley. I can grab one for $150 on ebay or from a dealer, but I'm willing to keep looking for a $20 partout or junkyard option. As soon as I have my hands on this I can charge the system and see what happens.