What is the control mechanism for the sub fan? As mine comes on with ignition all the time.

 

In the fusebox there was a relay missing, maybe the previous owner removed it to stop the fan running fast all the time.

 

- On ignition the sub fan is always on at slow speed.

- Plugging a relay in "SUB FAN" makes the fan run at fast mode.

- Removing the "RAD FAN" relay stops the fan.

 

Before you mention it, the EFI loom is brand new, all connectors are perfect, and both coolant temp senders are brand new. :cool:

 

Is there a thermostat in the side of the radiator like on my Laguna?

 

Thanks guys.

no

If your electric fan is on all the time, typical cause is no signal being received from the ECU water temp sender. Take a look at the sender (top water pipe, right hand wire, typically yellow) and give it a wiggle to see if you can make a connection. Worse case, you may need to take it off and clean the connectors with contact cleaner. Very common problem...

 

HTH

 

Steve :)

just put the relays back in

its not just temp related, it also comes on when A/C is on and speed is less than 10mph (or some speed)

its not as simple as most cars, so dont let the temp sender throw u down the wrong route.

Download efec.pdf from here http://300zx.lostyourwatch.com/PDF/ then look at page 31 :)

just put the relays back in

its not just temp related, it also comes on when A/C is on and speed is less than 10mph (or some speed)

its not as simple as most cars, so dont let the temp sender throw u down the wrong route.

 

If engine temp is below 89 deg then the sub fan will be off regardless of speed or A/C

Thanks for all your suggestions guys.

 

After some more research i am thinking that the wires that run to the ecu for a controlled earth may be getting earthed somewhere along the way. Or the ecu itself is at fault. I may just wire the earths to a switch if the new replacement ecu doesnt solve it.

 

- The only way the fan can get power to run is if these wires are earthed.

- This can only be done by the ecu.

- With all relays in the fan wants to be high speed

- Therefore the ecu thinks:

1) A/C is on

2) coolant is above 100c

3) speed is above 40 kph

or

1) A/C is off

2) coolant is above 105c

- The only input irrelevant to others is coolant temp, which i know to be right... :confused:

- My dash speed readings are correct

- I never use A/C anyway

 

Thinking about it the wires running to the ecu arent shorted as its a brand new loom, ive read of the short occurring right under the fuse-box so i am going to test this today. If its not this, or solved by a new ecu, im stuck :(

Try a different ECU. Known a few ECUs to be damaged when being chipped and this causes the fan to run permanently ;) Do you have access to a conZult to check the ECU is seeing the correct coolant temp?

Thanks for the advice.Hopefully i can pop round a friend's next week to check with conzult. New ecu arriving this week so it may (fingers crossed) sort it. Although this one is chipped and the old one wasnt LOL :)

If engine temp is below 89 deg then the sub fan will be off regardless of speed or A/C

 

If the air con is switched on and insufficient air is passing over the condensor (ie car stationary )the pressure in the air con system will rise and when it gets between 15 bar and 17 bar the sub fan will come on to reduce the pressure in the condensor, if it does not come on and pressure is allowed to rise the high pressure blow off valve will dump the refridgerant.

 

Daveman

If the air con is switched on and insufficient air is passing over the condensor (ie car stationary )the pressure in the air con system will rise and when it gets between 15 bar and 17 bar the sub fan will come on to reduce the pressure in the condensor, if it does not come on and pressure is allowed to rise the high pressure blow off valve will dump the refridgerant.

 

Nice one Daveman, it's always nice to learn something new each day :hyper:

If the air con is switched on and insufficient air is passing over the condensor (ie car stationary).......

The fan is on with ignition switch, not air con, but:

.......the pressure in the air con system will rise and when it gets between 15 bar and 17 bar the sub fan will come on to reduce the pressure in the condensor

could a faulty "air con pressure sensor" (wherever this is!) cause the ecu to think pressure is high even when it isnt, or the a/c isnt even on, therefore keeping the fan on all the time. I found no mention of air con pressure in the manual or any research. Could this be it? Only mentions a Low Pressure Switch to drive the Compressor :confused:

 

Thanks daveman, new light on the subject!

I notice in the photo there is an earth lead disconnected. Is this part of the problem ?

I notice in the photo there is an earth lead disconnected. Is this part of the problem ?

 

waiting for someone to point that out, no, its connected, i just took the photo when i moved the fuse box to fit the BOV. :)

Have you tried -

1) Disconnect battery

2) Disconnect ECU

3) Reconnect battery

4) Ignition on

5) Fans going ????

 

That will prove the ECU or wiring.

Just don't reconnect the ECU with the power on or it will be ......

Sorry to hijack thread but is it necersarily bad to have the sub fan constantly running? I am having some overheating problems at the moment (90C+ in traffic and keeps rising steadily when idling) and thinking by removing the yellow connector I could have this extra fan on all the time to help my cooling before i get the problem fixed properly. What do you all think?

Have you tried -

1) Disconnect battery

2) Disconnect ECU

3) Reconnect battery

4) Ignition on

5) Fans going ????

 

That will prove the ECU or wiring.

 

Top thinking! Just did this and fan runs without ecu, so i know from the wiring diagram (and the fact my efi loom is brand new) that the short has to be between the relay and the EFI connectors right by the relay box, narrows things down a bit :)

 

Owe you a pint for that spark of inspiration.

 

But in typical british style its started raining so tests halt :(

 

Sorry to hijack thread but is it necersarily bad to have the sub fan constantly running? I am having some overheating problems at the moment (90C+ in traffic and keeps rising steadily when idling) and thinking by removing the yellow connector I could have this extra fan on all the time to help my cooling before i get the problem fixed properly. What do you all think?

Having the fan on all the time will not only wear it out faster but sap power. There is a link somewhere on how to have it on a switch, involves earthing ecu pins 19 (slow speed) and 6 (fast speed (TT only)) through a switch.

Owe you a pint for that spark of inspiration.

 

I'll take you up on that offer next time you're in New Zealand (or I'm in the UK) :D

Sorry to hijack thread but is it necersarily bad to have the sub fan constantly running? I am having some overheating problems at the moment (90C+ in traffic and keeps rising steadily when idling) and thinking by removing the yellow connector I could have this extra fan on all the time to help my cooling before i get the problem fixed properly. What do you all think?

 

Not such a good idea IMO. Removing the connector will run the fans as the ECU thinks the temp is way high but it may impact on other functions of the ECU e.g. low boost, EFI functions, etc.

 

As olliezx pointed out, a switch from the ECU harness is a much nicer way of fixing things, or even better is to get to the root of the overheating problem.

 

My radiator was dismantled and rodded - the guy recons the things was 40% blocked.

 

If you do go the switch way (which is always good for emergencies) you simply have to tap into the approproate wire and ground it. There is no risk of damaging the ECU using this method.

I notice in the photo there is an earth lead disconnected. Is this part of the problem ?

 

LOL

 

This is the problem, this earth isnt supposed to be there as OEM. Just opened up the relay box and this has been spliced into the relay earth. Probably the easiest way to purposefully make your fan run all the time.

 

Now im worried about the reasons why they did this :confused: maybe the actual problem is the fan doesnt come on properly...

 

Thanks guys for pointing me to the problem, but maybe this is coverning up a new problem :(

but maybe this is coverning up a new problem

 

Bugger !!

 

Time shall tell I guess. Have you got a good temperature gauge ?

I think i am going to reconnect the two wires that were cut and run the extra earth to a switch just in case the fan doesnt come on at all.

 

Fuse Box Chaos

 

There are other splicings within the relay box, is taped splicing OEM? I remember reading somewhere that it can be.

If the air con is switched on and insufficient air is passing over the condensor (ie car stationary )the pressure in the air con system will rise and when it gets between 15 bar and 17 bar the sub fan will come on to reduce the pressure in the condensor, if it does not come on and pressure is allowed to rise the high pressure blow off valve will dump the refridgerant.

 

Daveman

 

Hi Jeff,

 

Once again the service manual is wrong then eh.... :rolleyes:

 

Ollie,

 

Disconnecting the ecu may well leave the fans on anyway, the ecu may have to 'tell' the relay to turn the fans off.... ;)

Disconnecting the ecu may well leave the fans on anyway, the ecu may have to 'tell' the relay to turn the fans off.... ;)

 

The ecu floats the earth under normal circumstances and connects the earth when it wants them to run, so disconnecting the ecu will mean they wont have earth and wont run. ;)

 

In my case the earth was hardwired by somebody so it didnt matter if the ecu connected the earth or not, it was always there.

 

Any ideas on the other insulation taped joins being oem?

>> There are other splicings within the relay box, is taped splicing OEM? I remember reading somewhere that it can be.

 

in this case it isn't

they sure did a good job messing up the wiring there !

 

it could be your AC system is refilled with R134 some time ago.

One downside of this stuff is it makes the AC system run hotter and needs better cooling as the stock R12.

As a shortcut they sometimes "modify" the aux. fan to be on all the time.

 

see if you can restore the wiring to how it used to be ? Probably solves your fan problem also.