I have a problem with my 93 300zx TT Auto.

 

When starting from cold it runs fine on all 6 cylinders.

 

However, when it is hot the 6th cylinder stops working. I have tried swapping plugs and coil packs and eliminated those at this stage. The problem always stays with the 6th cylinder.

 

I have checked compression and that seems fine too.

 

What else could it be?

Could be a connection issue on the injector or the injector itself going open circuit when hot although that would be rare, what you need to do is test the injector resistance with a test meter when the fault is happening, it could be an ecu output issue too.

 

Have you actually checked for spark at that cylinder, ie coil pack with spark plug lying on the engine to see if it is sparking, the ptu can fail on individal cylinders when hot

 

Jeff TT

Edited October 26, 201114 yr by JeffTT

The problem that first only appeared to happen when the engine was hot, is now happening from cold.

 

The car only runs on 5 cylinders.

 

The 6th cylinder (nearest to the battery) is not working.

 

I have re-checked the spark, and it seems good.

 

I have put a screwdriver against the injector, and there seems to be a strong ticking noise, as heard on other injectors.

 

I have checked compression again, and all is fine.

 

When you disconnect the connection of the coil pack whilst running it makes no difference to engine speed at all, so it is definately that cylinder.

 

Any ideas what this could be?

unplug the O2 sensors see if it makes any diffrents

 

Mark

Sounds typical of a cooked PTU.

 

They will generally do it when hot as they are on thier way out then fail that cylinder completely.

 

It is also worth noting 300zx's don't like thier plugs being unsettled you'll often see green corrosion/ white powdery corrosion on the pins, if they have been in for a long time the connection point usually remains, but unsettle and plug back in its is easy to make problems worse, so i'd first try some electrical contact cleaner on all the pins. clean them all up including ptu pins and injectors.

 

If that doesn't fix it i would suspect a bung ecu, perhaps somebody local to you will let you plug on thier PTU to narrow it down but it is your most likely suspect given the behavior.

I do not think it is corroded plugs, as they were all replaced around 200miles ago. The spark on the plug seems good too.

 

The problem happens when the car is COLD now as well as HOT.

 

If there is a spark, is it still possible that it could be the PTU?

As Jeff said it could still be an injector, although you are hearing the ticking, the noise from the other injectors will be travelling along the same rail, so may sound like its working. Check the injector plug for corrosion and use a multimeter to test the output on the plug itself.

Can only be one of these, injector/ injector plug, coil pack/ connector plug, PTU.

Also check the harness wires to both inj and coil pk plugs for chafing