I need help: detonation sensor error 34 and misfiring

[jesper]

Hello. First of all, i have been reading for over a year on this forum and learned a lot, and also fix a lot thanks to the people in this excellent forum, thanks for that!
How ever, now i had to register, because i really dont know how to move forward here...

This is what its about:

Bought my 300zx last year. It did not run good. Hard to start, especially when warm. Always smelled gas.

First, temp sensor connector to ECU was bad. That solved the hard to start part, and running rich.
Then i calibrated the TPS, that was totally off. Sorted some low rpm stuff.

Then i found two problems. First it sometime lossed power. After diagnostics i got error code 34.
Also it some time miss fired. Not for long. Never on idle, but it seems to come when i've been driving for some time, not hard, but like at red lights and in slow traffic, so my guess is that it comes when the engine compartment and the engine is getting warmer with not so good cooling.
I have also heared, especially when running at the same rpm on the highway that it kind of missfires (i am from sweden so it is hard to describe sometimes correct) - what i mean is that you can hear that sometimes one detonation was missed out, not that smooth engine sound..

So, this spring when it was time to get it out, i did the detonation sensor re location with a new detonation sensor, tightened it with 20NM (i read that some where). And for a bit it worked.
But now it is coming back. Now i am out of ideas, because when reading all the forums on the detonation sensor the answer to all problems is to replace the sensor. Nothing else. But my problem is still there. It goes in safe mode, when turning off the key, and then starting the engine, it works and boost as normal. Then these missfireing came back. Not often, but after a days driving maybe i get them 1 - 2 times for a couple of seconds. Always in the end of the day. So i thought these things maybe was related to each other, but today after it miss fired, i gave it some throttle, miss firing went away and the engine boosted as it should. I am running the car on 98 octane petrol, just to sort out that it actually pre detonates for real, but i cant hear it does (and i know how it sounds).

So: what should i look for in regards to the safety boosting?
1. How do i check timing on a car like this. I am 47, and it was a loooong time since i checked timing on a car (read distributor and carburettor age).
2. Can wiring between ECU and detonation sensor be an issue?
3. Did i use the right torque when relocating the detonation sensor?
4. Any other pointers?

What should i look for in regards to my intermittent mis firing?
1. I have new spark plugs NGK PFR6B-11B. What gap should i set when having the Z1 upgraded ECU?
2. Can it be related to other things than ignition?

Any help appreciated, Jesper from Zweden!

[rgregoryb]

Welcome!

Go up several topics on this forum to the "everything you need to know about the Z32'" it will answer some of your questions.

[DCaff300ZX]

Welcome!
Definitely check the "everything" sticky as it has a LOT of helpful stuff, most important is the FSM you can download and use for info and tests regarding a lot of what you ask about. I've used it a TON for my cars, it either helps you out immediately or points out a larger problem the best way possible- accurate tests.
Honestly I would begin by looking at, and in my case, replacing the PTU harness. It has several places where corrosion causes issues and really can't be cleaned well and was the final answer to my own misfire and boost-loss issues in conjunction with replacing the IACV and harness...both corrosion casualties. Corrosion of the connectors is the #1 issue to work past, then checking sensors, then larger components...the basic route the FSM will take you on. Also be SURE to check your injector harness and connectors for corrosion, it could be your issue as well.
Good Luck, and ask away with any further questions!

[jesper]

Hello and thank you for you answers.
Now i think i have tried to read up on it all, and i have planned to check the following:

Whats done:
[*]Found the issue with intermittent misfire, it was the connector of injector on cylinder 1. So thats sorted!
[*]New detonation sensor relocated to the upper plenum bolt. Know it is not ideal, but plan to fix this winter.
[*]Removed the connection between harness from car, and resoldered a detonation sensor connector directly on the harness.
[*]New spark plugs NGK PFR6B-11B, car had NGK PFR6B-11 and the smoothness change of how the engine runs is massive. So thats good but did not solve the problem.

To-Do
Check wiring:
[*]According to service manual section EFEC page 51, error code 34 is a short or open circuit. I did not realise that this involves the complete circuit but just focused on the sensor.
[*]According to service manual section EFEC page 133 i should check detonation sensor connector terminal A - ECU terminal 23. Then Ground - sensor connector terminal B. But B is only signal shield right? It is not connected to the actual detonation sensor, right?
[*]According to service manual section EFEC page 174, pin 23 on the ECU should be in the range of 2,5 Volts. I guess it should measure the same on terminal A on the detonation sensor also?

When this is sorted (because the car ran just fine last summer) i will check
[*]Leaks on the intake side (from the 6P-guide)
[*]Ignition timing.

Am i on the right track here?








Have not checked ignition timing yet

[DCaff300ZX]

You should check the timing ASAP as it's very important and an be informational if off, and also check the CAS as there can be issues with it and the connector- tests in the FSM.
You seem basically on track, but not having been through what you are doing specifically, I can't comment on your specific questions. If you stay with the tests and charts, you should be able to eventually find your way to your problem area, if not the solution unless it is very complicated (quite possible; been there) and the test results might trigger someone's memory of that specific scenario.
Damn Z32's are NOT easy to diagnose when things get sticky, stick with it!