I know, I know...here I am with another question.

Last night after drivin around for about 20-30 mins i came home to park the car and when i turned it off, the motor starts making this really lound rumbling/thumping sound...weird example but kinda like when a washing machine is off balance but way louder. It even makes the front of the car move a little. What could it be? Does it sound serious?

 

May be very minor, or may be death. Impossible to know for sure from the description.

Try a set of spark plugs first.

 

Spark plugs could make it sound like that after turning it off?

 

Possibly.

Sounds like it's "running on" after you shut it off. That's caused by fuel still being fed into the motor whenever the engine is turning (carbs do that), and something in the cyls is hot enough to keep igniting it even after the spark is turned off. Built-up carbon gunk on the plugs often gets hot enough to glow red-hot and will cause that.

Other possible causes are idle speed turned up too high or a vacuum leak.

 

Ah...thanks...i did turn my idle up a few days ago due to it stalling when i gut the ac on but it was fine for like 2 or 3 days until this started happening...ill change the plugs/wires sometime this week and ill go play with the idle a little later. Any other suggestions?

 

stupid but check out if theres any coolant in the car...

 

Time to SeaFoam the car and then stop using cheap gas. Buy 89 octane at a minimum.

 

Ill look into the seafoam thing and i do plan on switching gas....got the spark plugs changed and the noise has stopped for now...I'll update tomorrow. Thanks sofakingdom

 

First, you must understand that octane rating is + - 2 points so 87 octane could actually be 85. And, if you do the math, running 89 instead of 87 (cheap stuff), if you drive about 15,000 miles per year, will cost you about.............................$2.00 more per week. So, is it worth $2.00 to not have to make posts like you did? Can you give up one Big Gulp at 7-11 per week in exchange for a better running car?

Yes folks, cheap gas costs you more in the long run and is $2.00 really a lot of money each week?

math---- mid grade is 10 cents more per gallon. 300 miles per week at 15mpg (around town mpg) equals 20 gallons times 10 cents = $2

 

Lol thats all fine or whatever and i said i did plan on changin gas eventually anyway...so no disrespect, but whats with the math lesson...i was just trying to get my car to stop what it was doing and Sofa's post has stopped the problem so far.

 

Well..after driving the car all day today the sound has returned...idk whats goin on...would it have anything to do with the gap in the plugs...the guy at the store told me they were "pre-gapped" should i pull them and have them gapped properly or should i check something else?

 

Always at least double check the gap. They have no idea if it was done with any quality control or not, just at least check it just so you know it was right to prevent from having to do what I am about to say: Pull em and check em.

But I don't think that is your problem. Check engine temp if engine is running hotter may cause run on.

Timing may cause run on

Rich running carb may cause run on

poor fuel quality may cause run on.

All or only a few may cause this you know your car and hear the noise maybe get a recording of the noise would help. How long have you owned it?

 

let's be sure of the descritpion. If you turn off the key, the engine continues to sputter until it finally coughs and shuts off; is that the complaint?

If so, seafoam it and change your fuel. If that isn't the symptom, then please be clear.

As to your response to my "math lesson"

Automotive forums are to help everyone and here was a chance to point out the problems that can occur by running cheap gas. Most folks think they save big bucks but in the end, it costs more. So, the math lesson wasn't just for your own edification

Some day maybe you'll have a chance to tear down an engine that didn't have the cooling systemflushed, or oil changed regularly and ran cheap gas.


Please let us know if my description is your symptom

 

Details on the engine? Have you done anything with ignition timing recently? Whats your hot idle speed?

 

Were did he go?

 

I just bought the car...havent really touched much except the fuel pump, fan relay, and spark plugs...I believe its the original 305 with a carb and hedman hedders on it. I have no idea what u mean by hot idle speed...but idlin it says its around 39-4500ish rpms...either that or the gauge is just broken....i've been turning the car off in neutral and then putting it in park and it doesnt do it then...i turned it off in park this morning and it didnt do it...it only happens every now and then but i dont want it to screw up the internals...could it?

 

Sounds like run on to me. Aside from the stuff listed about the idle may be to high causing it as well. Try Seafoam why not it will clean things up nicely. Was it bought from a lower altitude person that may be an issue as well.

When you put your foot into does it rattle, might be timing is too advanced.

 

My engine does that when i turn it off in Neutrel (have to keep my idle higher because of the cam). Just turn it off in DRIVE if you want it to stop for now it will probly work.

 

ya it only does it when i turn it off in park...i also turned the idle down a little and it hasn't done it since but who knows...and what do you mean rattle? my exhaust kinda makes a rattling noise when i rev it high in park but thats about it...and as to the altitude thing...idk what u mean...i bought it from someone about 20-30 mins from here so i doubt altitude has anything to do with it...and i dont think it gets much lower than here in Louisiana

 

Pardon me. I was thinking high altitude setting in lower altitude or vis-versa. (got to remember to type all my thoughts :-P)

I was referring to the rattle aka timing ping?

 

Idk...i havent had the timing checked yet and idk how to check it myself. Ill have my mechanic take a look at it next time i get the car over to him. All i really know how to do is play with the lil idle screw

 

I am sure you could Google it. It is an elementary procedure. But make sure you know this person checking it because he might stick it to you, with a list of necessary and un-necessary stuff to do to it.

 

Im sure i could do it myself as long as there arent any special tools required...are there?

 

Timing light to start with possible a distributor wrench would be helpful and a manual to know the timing, and a friend standing over your shoulder that has done it before.

 

Ok...ill just take it to my mechanic and let him check it out for me...ive known him for years and hes worked on every car ive ever driven

 

The symptom you are having is commonly known as "run-on" or"dieseling". Anything that causes high cylinder temps can cause dieseling. Lean fuel mixture, timing too advanced, high coolant temp, manifold air leaks. Buildup in the cylinders is what allows run-on to begin with. Carbon build up that is heated by high cyl temps ignites fuel that is drawn in from the carb as the engine continues to turn. Decarbon the cylinders with Seafoam. Have timing checked. Have carb set on a 4 gas analyser to verify proper fuel mixture and repair any vacuum leaks. Check cooling system for proper operation.