Hi,

Can anyone identify the part circled on this pic?
It has a single electrical connection that goes into the wiring harness but I can't find any reference to it in the Nissan R30 manual.

The reason for asking is that the engine runs very rough when cold, misfires and backfires on acceleration as if there's a problem with the timing. When warmed up, it runs perfectly. The vacuum line shown in the pic goes to the advance on the distributor.

cheers,

JohnH

BCDD.
Boost Controlled Deceleration Device.

_________________
Regards, Graeme
Just trying to help...
http://nissanman.shutterfly.com/
graemes@internode.on.net

Many thanks...

Have just been reading up on what it does and doubt that it's got anything to do with the rough-running-when-cold problem. Where is the diagram from? One of the PDF's in the manuals thread perhaps?

Still think it's an advance/timing problem but thought if the advance was faulty I'd have the problem all the time, not just on a cold start. Have replaced the old vacuum hoses with new ones. I need to check the vac advance but don't have the gauge and pump (on eBay for $80+ but I'll only use it a couple of times).

cheers,

JohnH

My guess is that one or more of the following are faulty: -
1. Thermotime switch.
2. Cold Start Valve.
3. Water Temperature Sender.
I gather that the Engine Temp. gauge works OK?
If not then you might have a faulty thermostat

Images are from the Haynes Datsun 240Z, 260Z, 280Z Repair Manual.
Same hardware, different car model.
I don't have an MR30 Manual, one of the few that I haven't tried to source

Vacuum advance doesn't have any effect on a cold engine.
The vacuum motor will only attempt to advance the spark when the car is cruising at small throttle opening or coasting with a closed throttle.
Purely an anti-emissions device, not essential for normal operation.
Mind you the vacuum motor MUST be connected to the correct connection on the throttle body.
It MUST be a PORTED signal, only exposed to engine vacuum AFTER the throttle plate has opened and exposed the port.
If you connect the vacuum motor to manifold vacuum then it will attempt to advance the timing when it is not required, i.e. at idle

_________________
Regards, Graeme
Just trying to help...
http://nissanman.shutterfly.com/
graemes@internode.on.net

1. Thermotime switch. <= suspect this, will test (multimeter battery is flat - just when I need it)
2. Cold Start Valve. <= car starts every time, think this OK
3. Water Temperature Sender. <= temp gauge is working OK

Thanks for your help... still learning...

JohnH

The ECU uses a different sensor for Engine Temp. than what the Temp. Gauge uses.
If your gauge reads reasonable, the ECU may still be getting a "cold" reading from it's own sensor thus enriching the mixture too much or for too long.

"Still learning"?
Aren't we all??

_________________
Regards, Graeme
Just trying to help...
http://nissanman.shutterfly.com/
graemes@internode.on.net

Tested the thermotime switch. 56 Ohms on one pin which is within specs. The other pin was open (infinite) and should be zero when cold. Fortunately I have a spare which tests OK so will use that. Reading the manual, the thermotime switch seems to only interact with the cold start valve and that valve only operates for initial startup so I'm not sure why the engine was running so badly. Anyway will swap the part over and see how it goes.

Edit: (next day). All good, thermotime switch replaced and now running smoothly. (note to self: keep collecting spares!)

Many thanks,

JH

I still have a few crates of L24/R30 spares too
Thermotime switch is my first thing to check on a 'new' R30...

_________________
R30 skyline hatch TURBO project

another note to self: MAG86 has crates of L24/R30 spares (and no R30 any more)

JH

hmm... spoke too soon, still chugging after a cold start then suddenly perfect after about 5 mins driving. No further problems when restarted warm.

Temp sender checked and within specs. Air regulator OK and hoses OK. Cold start valve is the next suspect on the list.

Tested the ignition coil (which looks really old): secondary winding resistance = 12.3 kOhm (specs 8.2 - 12.4),
primary = 1.3 Ohm (specs 0.84 - 1). Will replace it.

JH