348 rattling shutting down

Hi all,
new issue: my 348 sometimes does a strange thing.

Shutting down the engine by turning the key to 'off position', the engine does not stop immediatly, but continue to round for a while (3-4secs), rattling until it stops. The 'feeling' is like it deosn't want to stop and it's forced to do that by the lack of electricity.
It does this from time to time; normally it stops immediatly (i turn the key off and in less than 1 round the engne is off)

What is that????

 

The rattling could be your flywheel. You will want to have a look inside the perforated inspection plate on the bottom of the flywheel housing (aka the pumpkin). Look to see if you have grease all over the place. If you do then your are gopnna have to remove the flywheel and repack it, maybe even get the clutch rebuilt too. Go have a look and let us know what you find.

Oh yeah and fill out your profile while your at it.

 

Knock? It could be poor gasoline or fouled plugs. I have had the run on for about two or three seconds after driving at very low RPM for about thirty minutes on three month old fuel. New fuel, and some decent revs cured it.
BT

 

Sounds like cheap gas (relative term) to me.

 

+ 1 with ernie !!!!! try to restart the car right after you shut it down- does it do it then too ??????? happened to me --- ernie and jeff hit the nail right on the head ----- fly wheel......... time to repack with grease....

 

It's called "dieseling." http://en.wikipedia.org/wiki/Dieseling

For the engine to keep running it must have fuel and an ignition source, which means that you have at least 2 problem areas on your 348, probably more.

Fuel is still making it to your cylinders with your key off. That may just be recidual pressure, however...

And you've got a non-factory ignition source such as massive carbon buildup in your cylinders or on your valves...or...perhaps greatly fouled spark plugs or spark plugs that are the wrong temperature rating.

This needs to be fixed.

 

You need to diagnose dieseling from Flywheel rattle. FW rattle is short maybe 1 second and the car definately dies. Dieseling lasts for a couple seconds or more until the source of fuel is exhausted. You could have a leaky fuel injector or two still spilling fuel after shutdown causing this problem. A high carbon fouled motor us usually not a cuase of diseling but a symptom of bad fuel/hydrocarbon management. 348 run really clean. Erine and plugzit will attest to how clean these cars run. Ernie almost passed kalifornia smog without cats! Plgzit has about 50k miles on his 348 and when the plenum came off to put the 355 ITB's on the back of the valved where shiny clean!

 

I agree. He says that sometime his engine runs for 3 to 4 seconds after key is off, other times 1 second.

Offhand, I'd speculate that the difference is how he was driving (e.g. hot engine on the times when it diesels longer).

He'd just about have to have at least 2 leaky fuel injectors plus either major carbon buildup or the wrong heat-range spark plugs.

If he's got major carbon buildup in a 348 then he's got bigger issues going on. If it's just idiotic spark plugs, then it should be an easy fix for the spark side.

 

Yup the fat man speaks the truth. They run really clean, and as a matter of fact I was failing smog by only 0.1%, with one cat that was burned out. And, when we did the 355 throttle body swap on Plugzit's 348 the valves were clean as a whistle.

 

Yes, i didnt explain well before, but the feeling is similar to a 'dieseling' effect.As said, it comes from time to time, and is longer when engine is hot. If i shut down and restart and shut down again usually I have no problems.

 

Just for kicks, try running a bottle of fuel injection cleaner through it on your next fill up.

 

You know Ernie is right sometimes you can pull off a miricle with that stuff. I don't think it works that great at manufacturer recs.. I totally do it wrong by running the tank down to 1/8 and put in a full bottle of techron from chevron and then drive the car hard until nearly empty. Then I top off the tank and put another bottle of techron in. Amaziningly this stuff works. Otherwise pull the injectors and send them to RC engineering in torrance Ca. Ron is the undisputed fuel injector hero. He will clean, replace bad parts, and blue print your injectors to better than new condition.

 

That'll work. Of course, refurbished 348 fuel injectors are just $30 at rockauto.com, so that's another option.

 

Its true, techron really works

 

Thank you. Actually I am in europe, and chevronm is difficult to get in the shops. What about stp? Do you know it?

 

STP should be fine.