06 M35x Engine Diesels on cold start...

[Oblivia]

Just bought the 06 M35x two week ago. Occasionally, in the morning, it diesels on the first start. Simple turning off - then restarting - cures the problem. Only a minor annoyance at this point. Car has 30K and just had 30K service done by Infiniti dealer prior to purchase. Still under warranty, but it is an intermittent problem, so I will probably have tough time documenting it. Any suggestions? Maybe a video camera? Any thoughts on what might be causing it? Runs great otherwise, and no other problems.

O.

[New2Import]

What octane are you using? Bump it up cures that problem. Get some Techtron injector cleaner and use high octane gas.

[Oblivia]

Using 92 octane - premium. Should run on either, according to manual. If it were an injector problem, why only on cold start? Not really "cold" either, here in WA state - only occurs after sitting overnight in garage. Its been in 50s & 60s here in at night. Could it be some sort of sensor or condensation problem that is "cured" once the engine diesels for a short bit?

O.

[jwheaton]

Sorry to threadjack, but what does "diesels" mean?

[Oblivia]

To me it means running poorly (roughly) with no power, even if you give it gas (via gas pedal) still no response - faster or slower - justs runs really roughly at low idle speed. Old diesels ran like this when you would turn the ignition off, they would keep running and you would have to starve the engine of fuel to get it to stop. The difference is the M35x turns off if you push "off". And on restart, everything works fine - no problems. Almost like it is shaking off condensation on a sensor or something. Once it runs, you can start/stop it all you want, still works fine, until you leave it set over night. Hmmm.

O.

[ken in az]

Sorry to threadjack, but what does "diesels" mean?

Diesel by itself means "compression ignition" igniting the air fuel mix without the use of a spark plug.

On a gas engine this normally happens with carburated engines when you shut off the engine, the carbon deposites in the combustion chamber will remain hot enough to ignite the fuel and continue to run, albeit horribly, until all the fuel in the float bowls are drained of fuel OR you starve or flood the engine to kill it.

Diesel can also mean "pre-ignition" which is when the fuel ignites befire the sparkplug fires durring normal operation, or it could also mean "detonation" where the fuel literally explodes rather than a controlled burn. this is when you hear the pinging noise from under the hood while under load.

The worst of all three is pre-ignition and detonation at the same time. This is normally where the most engine damage occurs. Think of 2 sticks of dynamite going off at the same time, the resultant pressure waves meet the cylinder pressure skyrockets and tends to break things - ie cracking pistons, ring lands, rings, bending rods/cranks - all the good stuff really.