Detonation sound on hot starts!

[mattb5150]

Recently I have been hearing a strange sound from the drivers seat when starting the truck. It only occurs when the engine is warm and sitting for a short time. While cranking and just before normal ignition I hear a sound sort of like detonation in a gas motor with not enough octane. Wonder if I have a leaky injector that is weeping fuel when the engine is off and when I restart the fuel in the cylinder ignites out of time? Truck seems to run fine otherwise, no oil in fuel. Just went over the 100k mark on the odo. Got this truck with 80k miles on it local dealer printed out service data and showed injectors were replaced under warranty at 35,663 miles. Any thoughts?

Matt

[Mark Rinker]

Every Duramax I have owned makes these 'pings' or 'marbles in a can' sounds at hot startup. None have ever come apart as a result.

Evidently, they are built to take it. Until the opposing flame fonts quit banging into one another, and the pilot injection system kicks in and starts to work, this is just a characteristic hot startup noise, IMO.

Sometimes it can be unnerving. However, the noises on COLD (-30F) startup worry me more.

I try not to listen. :)


(Upon re-read of your thread, if the sounds are actually happening BEFORE ignition, you may have raw fuel in the cylinder. Do you have any exhaust smoke at idle? I'd try treating your next few tanks of fuel heavily with your favorite additive. Seems too soon to be up for injectors, but a quick check of your balance rates on a TechII should tell the tale...)

[DmaxMaverick]

If it does this only when hot, after sitting for 10-30 minutes, but never cold or immediately after a hot shutdown, you have a leaky injector. Time for replacement.

[mattb5150]

When I say hot I mean engine up to operating temperature. This recently occurred driving to the store, shut off, run in grab a few items, come back 10 minutes later and whamo! I have Primrose which I haven't added lately but will try for the next few tanks to see if there is a difference.

Matt

[DmaxMaverick]

An injector cleaner may help, if the injector is just "stuck" a bit. I've seen/heard a few like this, including my own, and it wasn't long after the injectors were on their way out. If it's happening in less than 10 minutes, the leak is significant.

[mattb5150]

If I take it in to my local dealer and the balance rates are off I should get new injectors on GM right? Since the truck is still under the extended 200k warranty?

Matt

[DmaxMaverick]

If I take it in to my local dealer and the balance rates are off I should get new injectors on GM right? Since the truck is still under the extended 200k warranty?

Matt

You should, if it meets enough criteria for a replacement. The knock is only one symptom, of many possible. With a fuel knock, your balance rates should be off considerably, but they require a specific range. I recommend having a look at your balance rates before going into the dealer. If they don't warrant a repair, you'll be charged for the diagnostics, and be sent on your way. You'll need a Tech II (or equivalent, like Snap-On) scanner or Predator programmer to see the rates.

[mattb5150]

Had the injector balance test performed by a local shop with a tech II and they said the rates were within spec.

Matt