By Henri Le Hir

My Z is a 1992, "Continental European" Nissan 300 ZX Twin Turbo, 2+2 (!!) (left hand drive). All the tests have been done on this car. Hopefully, this applies to all the Z32 all over the world.

Special thanks to the "Jim Wolf Technology" Team, as Jim and Clark helped me understand a few technical points about this problem.

You probably have a failing detonation sensor if...

• When the car is warm, you only get about 7 PSI of boost.
• You put the ECU in test mode, and you get the dreaded code 34 (bad or missing detonation sensor).

If you don't know how to put your ECU in test mode, go there..... Twin Turbo Zs of Dallas (excellent site, with a lot of accurate technical info)

Tools required :

• A multitester (continuity tester, ohm meter).

The part that is "free to move", is going towards the ECU.

The part of the connector that stays on the engine block is going to the detonation sensor.

During all the following part, it's assumed that your car is a STOCK one, and that there are no special surgery done with the ECU.

If you ever tried to fix the problem yourself, cutting ECU wires, splicing connections, or whatever, REVERT everything back to the stock configuration before proceeding.

Do the following tests :

Using the multitester as an ohm-meter, test the connections going to the ECU.

• One of the wire going to the ECU should be connected to the "ground" of the engine. (a good "ground" can be found on any metallic part of the intake manifold)
• The second wire going to the ECU should have about 500 k Ohm resistance when tested towards the "ground" of the engine.

• One of the wire doing to the detonation sensor IS NOT CONNECTED (both US and EUROPEAN manuals are saying "connected to the ground", I've found this incorrect while testing the connection, as well as looking at the wiring diagram of the harness)
• The second wire should display about 1 meg Ohm resistance.

If you have a problem with one of the wires going to the ECU

• You're lucky....
• Check the wires between the ECU and the connector, at most, replace them.

If you have a problem with one of the wires going to the detonation sensor

• You're NOT lucky.
• Re-check the wires, one of them is NOT connected.

If you still have a problem with one of the wires ...You have the following options..

• Get your engine fixed by Nissan. This requires the removal of the engine, as the detonation sensor is located on the engine block, under the intake manifold.This requires time, so it's quite expensive. But it's what you should do.

• Follow the bypassing procedure.

WARNING : If Nissan's engineers decided to intall a detonation sensor on the VG30DETT engine, it's because they have a whole bunch of good reasons to do it. If you decide to follow the "bypass the detonation sensor" instructions, your ECU won't be able to "listen" to detonation anymore, and that could cause the destruction of your engine....you've been warned.

First of all, an additional test to be sure.

Required material :

• A one mega ohm resistor (1000 k ohm), should be able to find it at your local electronic shop (shouldn't cost more than a few cents), or recycle an old one. The one I used in my car is coming from an 18 years old TV set.

Actions :

• Reset your ECU (to delete all error codes).
• Plug the detonation sensor back.
• Start your engine for 10-30 seconds...stop your engine (so the ECU will analyse the car).
• Double check that you indeed have that code 34 showing up again.
• If you don't have the code 34 showing up, STOP IMMEDIATELY. Several things can trigger a "fail safe mode", a bad detonation sensor being ONE of them. Instead of "playing" with your engine, e-mail me with the symptoms, and I'll try to do a remote diagnostic.
• Reset the ECU (to delete all error codes).
• Install the one meg ohm resistor on the ECU side of the connector, as if you would make a short circuit with it. Do NOT use a plain wire, it won't work.

• Start your engine for 10-30 seconds.
• Stop your engine.
• Check the ECU code, you should get code 55 (all's fine folks).

If you still have a code 34, then the problem is NOT your detonation sensor. Either the wires going to the ECU are defect, or the resistor you've been using is NOT one megohm.

At this point, you will have to decide if you'll have your engine repaired (IMHO, the right thing to do), or fix it.

Bypassing the detonation sensor

Ok, you're still with me, so you take full responsabilities about the possible consequences of the installation.

Required material :

• The abovementioned one meg ohm resistor.
• Some electrical tape.
• A Swiss army knife or equivalent.
• A soldering iron (gas, or car battery operated being a plus), and some solder.

Actions :

• On the ECU part of the connector, remove the stock electrical tape to have an easier access to the wires
• Using the Swiss army knife, gently cut the insulation of the two wires. Do NOT cut the wires. Try NOT to remove the insulation at the same distance of the connector, to avoid a shortcut.
• Using the soldering iron, permanently solder the one megohm resistor between these two wires
• Re-apply electrical tape to prevent corrosion.
• Re-plug the connector.

• Start your engine for 10-30 seconds.
• Stop your engine.
• Check the ECU code, you should get code 55 (all's fine folks).

Note : The way the resistor is installed, if the detonation sensor suddenly re-starts working (due to an intermittent problem), the car will immdiately go back in "fail safe mode", and it's exactly what I want. If you don't want this, then you can either leave the connector unplugged, or cut the wire(s) going to the detonation sensor.

It's now time to test-drive your Z. As an insufficient engine temperature can trigger a fail safe mode as well, you need to have the engine warm, and then go for it. At that point, you should get your full boost back.

If you still don't have full boost, check your ECU again.

If you have a code 55 (all's OK), then it means that your Safe Boost Solenoid Valves might be defective.

They could be defective because "someone" cut a wire at the ECU not fully understanding all the relevant issues, or that the ECU is defect, or that the Valves themselves are out.

But there are as well other possible causes of a "fail safe mode"

Anyway, at that point, you should read the "how to install an electronic boost controller in a 90+ Z" (coming soon), and probably buy an EVC as well.

Zee you

Written by H. Le Hir / 980325@00:51 email 100031.1520@compuserve.com