When I turn off the engine sometimes
it sounds like it wants to start again type thing and a swoosh sound
doesn’t happen all the time

any ideas what this could be

 

Idle at too high, timing too far advanced?

 

timing is dead on

idle could be. Around 1100 rpm but settles out at 900

 

Idle should be around 600 RPM in drive, assuming this is an automatic transmission. I am just guessing since you gave us very little information.

 

that’s to low imo

I want good water flow and oil pressure

mine is a built 455 4 speed

 

Sounds like minor run on... how is the gas quality ?

 

not sure. I put 93 octane gas

 

Depending upon the year, the manual transmission idle speed spec is 650-750 RPM for a factory engine. Your modified engine may need different parameters than a factory engine.

What is your present idle speed and ignition advance?

 

idle speed is 900-1100

total timing is 34 degrees
idle timing 12-14

 

So when you turn the key off, you get some run-on, a.k.a. dieseling?

 

yes. I would say 1 out of 10 times

actually never heard of that term run on
But I’m assuming that’s what it is

 

Define "built 455".
Is the engine idling smooth at 1100 RPM's or still loping ? How much oil pressure are you trying to maintain ?.

 

1100 RPM sounds like way too high an idle speed and is likely the source of your problem. What are your cam specs?

 

Build is all your goodies
cam pistons 30 over etc

motor idles fine in any range

i just like to run it at 800-1000 rpm
oil pressure is good 35-70

 

not sure. I would have to look

 

That’s about the most generic, non-informative post I have seen in a while. My engine has an aftermarket cam and .030” over pistons, too.

Please provide accurate, specific information so we can actually help you.

What are your cam specs? Which .030 over pistons? What carburetor? What distributor, and what timing parameters?

 

I mean what would be the difference what cam or pistons I’m running ?

would high performance parts cause this more than stock ?

 

let’s assume I have a stock 455

 

Wow. Yes, a long duration cam and high compression pistons would be very different that a factory short duration cam and low compression pistons. Details are important.

 

Then set the idle speed to stock settings. Don’t try to out-think the design engineers.

 

Run on / dieseling is much like it sounds. As if the engine never shuts off or keeps trying to restart even though you already shut it down with key in hand. My 67 had it bad once with low octane gas, went on for a few seconds... horrible, the engine is jumping, convulsing, and sputtering.

You have a very minor version of it.

This very short video should match you to a T. And the 3 comments posted should seal the deal for you, which includes the solution.

 

thanks. Interesting

 

Sounds like you spent money on "goodies" that you have knowledge of their function. High performance parts can make a difference. Your preference to run the idle at 800-1,000 RPMS has little merit if it idles smooth in any range.
You have a 455 with "grocery getter" parts. "Grocery getter" is defined as a car that you run errands and get groceries with.

I have a 455 with a big cam that will smooth out between 1,500 and 2,000 RPMS. I have it idling about 1,000 RPMs.

YOUR idle is way too high, thats your problem. You don't need 35 PSI oil pressure at idle.

 

Just back off the idle speed. Since you don't know your cam specs, try 750-800 RPM in neutral. I'm willing to bet that'll solve your problem.

Don't worry about oil pressure. Anything over 10 PSI at idle will be adequate.

 

it did it at 600 rpm as well

I bought it like this

I didn’t build it

 

here’s my specs

 

 

Try what Bangscreech suggested.

 

Do you have an HEI distributor ?

 

yes

 

Ralph it's my understanding that oftentimes built engines are mistimed to an engines base information. And this often leads to disappointment in performance till the modified timing is achieved ?

 

I never suggested re-timing the engine. I did ask about an HEI distributor which often times has higher initial advance. Idle speed smoothness he said was fine in any range.

 

Ok, so, your idle is too high. If you MUST have that idle, you need an idle stop solenoid.

My car is messed up some, but my curb idle in drive is 650 and the park idle is 1000. It will diesel. The quadrajet has holes for a solenoid that mounts on the front left of the carb, and lines up with a tab on the throttle bracket. When powered, this solenoid extends. These can also be used for AC on idle boosting. The idea is that you set the slow idle screw to something like 500. Do that with the solenoid unplugged. Plug the solenoid in, and adjust its stud (it has flats like a bolt, screw it in or out) to get the idle you want. Wire this to ignition on power source. When you turn the key off, the ignition stops, but now, also, the idle drops from 1000 to 500. This closes down most all fuel, and allows the engine to shut off nicely. I shut my car off 15 times last week, and I may have got one or two extra firings out of all of them. Highly recommended.

 

You said this, then posted build sheets showing a 230 degree duration camshaft. That is a long ways away from a stock 455.

It’s hard to give helpful recommendations if you don’t give us accurate information.

 

any reason why it would run off per say ? Either cam ?

 

Not sure what you're asking here, but in general a big cam (and yes, your cam is a long way from factory) necessitates a higher idle speed, leading to increased risk of post-ignition. If a high idle speed is required or desired -- for whatever reason -- maybe look into an idle stop solenoid, as @Koda suggested.

 

Either all that, or just shut it off in gear and let it stall itself.

 

thanks.

 

Hi all,

before having rebuilt my 425 in my 1966 Starfire, I also experienced sometimes dieseling when shutting off. I checked the idle timing and it was fine. Then I checked the distributor advance weights and found out the advance mechanism was stuck (vacuum advance was okay though).

I pulled the distributor and made everything move nicely again, and for some months I had no dieseling any more. So you could check the rpm advance weights if they work and allow timing to be advancing at higher rpm. Because if not, timing seems good at idle but is too late at higher rpm (means, typical driving condition), and then heat up spark plug tips and other parts too much so that they might cause the dieseling effect.

In my case, unfortunately the problem came back after some months and I had to repeat the procedure. When I overhauled my engine last winter, I finally found the root cause (probably not very common, but still I want to share here):

My engine was not well maintained by the previous owners, had lots of oil sludge and completely broken valve stem umbrella seal fragments sitting everywhere. When I teared down the engine and checked all oil gallery's and plugs, I found that a small fragment of a valve stem seal made it even past oil plump and oil filter into the oil plug which should drain oil onto the camshaft/distributor gear in the back of the engine block. So the distributor including its advance mechanism did not get oiled properly and got stuck over time.

Ah, another possibility which also happened to me was that the harmonic balancers outer ring slipped due to a defective rubber layer (see the two pics at the end of my post). So the timing seemed right but actually was not! I first tried to add a mark to the right place on the outer ring but it kept moving. I finally fixed the issue buying a new balancer from damperdudes.com, can recommend them really. Fast service and excellent quality.

Just my 5 cents, maybe could also be explanations for your case.

CU, Steffen

Here I add some pics for illustration:


Advance weights before restoration, no surprise that the mechanism did not work smoothly


After cleanup


Valve stem seal fragments in my engine like crazy


They even clogged the oil holes down from the heads


Crazy amount of valve stem seal fragments pulled out from the engine


Clogged oil hole for distributor gear


Minor oil flow was still possible, but in no way as intended


Removed the fragment


Location of the plug, looking down into the block at the distributor flange


The plug is behind the sheet metal plug on the left


Second possibility: timing wrong even though mark seems right


My balancer rubber was defect and the outer ring slipped

 

thanks for the info