Zulu31

Hello all,

This is my first post here. I'm new to the Nissan world, but definitely not to the automotive scene in general. I'm acquiring an '88 300ZX N/A tomorrow, and well, it doesn't run currently because it has very old gas in the tank and:

- The original ECU got soaked, and was replaced with an '85 ECU (not sure why they didn't just get an '88). I read that in '88 the injector impedances changed and therefore the ECU output signal is different than the previous ones. Is this true?

- Could this be why it does not start?
- Are there other ECU differences that I should be aware of?

Also, on z31.com I found a table of ECU part numbers (resources:z31_ecu_list [Z31.com]). I just wanted to be absolutely sure that "23710-25P00/A18-A00M84" is the correct ECU for this Z and is the one I should find for a replacement.

I look forward to learning a lot from this project, and wanted to say thank you in advance for your help!

NismoPick

Welcome to ZDriver!

My z31 ecu zip file would be helpful in your case. It contains docs and ecu comparisons by year for the 280zx Turbo Z31T ecu upgrade.

(Right click and save as)
https://www.zdriver.com/forums/attac...cu-swap-v3.zip

In a nut shell, the 88 n/a ecu is high impedance, zirconium o2 sensor. The 85 n/a ecu is low impedance, zirconium o2 sensor. Maybe (hopefully) they installed a resistor pack somewhere in the harness? If they ran it for any long length of time without resistors, they probably burnt up the injectors.

Zulu31

Thank you for the warm welcome and the great info, it'll definitely come in handy. I'm sure the current owner did not put a resistor pack in the harness. We spoke a lot about what he had done since he got it and he only mentioned finding an 85 ECU and plugging it in. I'll have to find a set of injectors likely then I guess, at least I know in advance now. Is there a resistance check or something I can do on them to know whether they're still ok or not?

NismoPick

You can ohm check the injectors with a multimeter. Low impedance will be 2-4ohms, high impedance is usually 11-14ohms. Anything outside of that range will mean they are likely toast. If he didn't do any changes, then you probably still have the side feed high impedance. Look under the plenum and look at the injectors to see if they are side or top feed... I actually have a spare set of low impedance top feeds, but you'd need the top feed fuel rails too.

rogerz

zulu. check out our z club website and come to a meeting. ZCCW.org we are having a get together at LeMay musuem on Sat 26. Our next meet is at the XXX drive in Issaquah.
We have members from Stanwood to Tacoma so we shift our meetings around. We are a friendly bunch and glad to give advice. 240 to 370 we have members with all those.

Zulu31

The injectors are definitely still the high impedance side feeds. Thanks for the offer, but i'd rather stick with the ones that are there and just get the correct ecu to match these ones. He mentioned that after he put the '85 ecu in, he drove it up and down the block once and would start it from time to time, but that was it. So I'm hoping they may not be fried. I'll make the resistance measurement sometime this coming week.

Zulu31

Good to hear there's a solid group around! I'll definitely look into making one of them once I get the ol' girl running and driving right of course. There's A LOT of work to be done, especially on the interior. I'm hoping once I get the correct ecu and drain/fill with new fuel, I won't run into too many mechanical issues but we'll see.

Thanks for the invite

Zulu31

Wait a second, I just found this:

"Low impedance ECU driving a high impedance injector should operate normally."
It mentions that there is only an issue when a high impedance ecu (88-89) is running low impedance injectors from the earlier years, which mine is the opposite. The 85 ecu that I have is a low impedance and the 88 side feeds are high correct? If this quote from that site is true, I shouldn't need another ecu.

XenonZcar.com Z31 Fuel Injector Differences, ECU and O2 sensor and Interchange Information

Zulu31

Update:

- Went ahead and got a Federal 89 N/A ecu and plugged it in. It wants to start more than before. It used to not have any combustion, and now there are a few cylinders firing at random times.

- Ohm tested the injectors, and they're 13.6 so within specs

- Reattached a lone yellow wire to a sensor on the passenger side of the engine that had been cut for some reason

She still didn't want to stay running. It really wanted to, but wouldn't stay sputtering without the starter's help. I looked over the ignition system one last time and found the distributor cap was loose as hell. Both of the two bolts were very loose, enough for me to be able to rock the cap back and forth.. I was excited to say the least, after finding what I thought to be the reason she hasn't started all this time, especially being something so simple. I tighten both cap bolts, hop into the driver's seat, turn the key, and.. The starter decides to not engage the flywheel. It spun, but it didn't push itself out to grab the teeth on the flywheel. So, I'm not entirely sure whether or not the distributor cap was the fix. I guess I need to replace the starter before I can find out.

I really want to be able to drive this thing!

NismoPick

Have you run the ecu diagnostic codes?

Zulu31

Not yet, I'll have to look up the process and how to read the lights. I'll do that one of the days this week.

I am a little worried that the teeth on the flywheel may be rounded or ground down. When the starter did engage, it would intermittently make a grinding sound, and then re-catch on the flywheel and resume cranking the engine. We'll see if it's messed up once I get the old starter out and can take a look at the teeth. Is there an inspection cover anywhere that I can take a peek at it beforehand?