Hi

I have a little question. When I turn the key in the 68´the engine don´t stop immidiatly, it takes some sec. before it stops... ( what is the correct tecnical term ? ) and what should I do to fix it??

it is a 1987 350 HO engine from a C4, I bought the car in California, and could it have something to do with the colder klima here in Denmark??

Thanks
Claus

 

Is it popping & chugging when you shut it down, and sound a bit like a diesel engine? (I would think you'd be familiar with the sound of that, seeing as how Europe has more diesel passenger cars than here in the States)

I've always heard that referred to as "dieseling", because of the way it sounds like a diesel engine. It's caused by improper tuning/timing. I had that problem in my old Ford F150, and it was due to the timing being off by 2 degrees and the engine running rich...

 

I thought it was lean conditions that caused dieseling...

 

Lean Carb, Improper Timing and Cheap Gas all contribute to Engine Run On or Dieseling.

 

Thanks for your answers - and yes it could sound like Dieseling

I had a friend i CA who bought the car for me, and he drove a few 100 miles and there wasn´t any problems...

How many degress should the timing bee?? ( is it the same on and old and newer Chevy engine ? )

Thanks / Claus

 

A couple years ago I had an issue where some wires coming out of the alternator melted together and the car wouldn't shut off. But that was it wouldn't shut off at all. Sounds like a different issue, but thought i'd throw it up there just in case.

 

high idle could also cause this. mine used to do it.

 

Hej Claus.

What ignition system do you use?, MSD has a solution for "engine run on" i dont know if it works on other systems as well.

But basicly its as easy as soldering in a diode btweeen connector #4 on the external voltage regulator and the alternator.

 

As PNK mentioned, it's also called "engine run-on"

 

I had the "run-on" problem in my 1971 vert with a 1968 327ci/350hp. I researched the issue and heard all of the above corrective solutions. I tried adjusting the timing w/o success. Then I noticed that my radiator overflow tank was empty, and at the same time I found a copy of the "original" recommended fueling instructions for these old cars that was on a lable on the original sun visor. It said to use at least 91 octane in the car. I had been using just regular 87 octane. I had read elsewhere else that putting better gas in the car could solve it too. So I put premium gas in the car and filled the overflow tank, and it hasn't run-on since then. So my solution was either a combination of the two fixes or maybe just one of them. I hope this helps you.

 

1. Iidle too high
2. Incorrect timing
3. Octane too low.

Most likely causes in descending order.

 

Thanks everybody

I´ll start by emptying the gaztank and put in fresch gaz.

The car came form California - and here in Denmark you can get pump gaz 92, 95, 98 unleaded and 95 leaded - what should I go for??

/Claus

 

92 or 95 unleaded should work for your engine.

 

Fellows:

He has an L98 there out of a C4 in his C3. That engine began life as a TPI setup. Look at it now. Different manifold and a carb to boot. This is a whole different game......

 

brdd,

Since I am new in this game - so is your coment ment in a bad or good way??

I must say that the engine runs smoothly

 

What I experienced with my '70 was that no matter how low I set my idle or what octane fuel I ran I still experienced run-on or 'dieseling' as it is popularly known. Everybody knows that fire needs three things to be fire- air, fuel, and an ignition source.If your Corvette is running a little hot (as un-rejetted older Vettes tend to do because of the higher oxygen content of modern gasolines) it can leave 'hot spots' in the combustion chambers upon shutdown.Also, your carburetor is a 'reactive' system, i.e., it continues to supply fuel as long as there is a vacuum signal being presented to it.....if your Corvette's labyrinth of vacuum lines have a leak somewhere, you now have the air-fuel-spark recipe necessary to cause dieseling AFTER you've turned off the ignition.
A simple band-aid for this is to install an 'idle-stop' solenoid which will close the throttle completely as soon as you shut off the ignition, but a better way is to find the vacuum leak and kill it at the source. In my case it was the vacuum switch in the console that controlled the heater valve and various AC functions- I was having to keep the throttle plate set more open than what should have normally been necessary to keep the engine at a happy idle because this valve was losing vacuum-also, the heater valve was open all the time because this vacuum switch was leaking rather than applying vacuum to the diaphragm at the valve.
There should be a vacuum tap on your intake manifold behind the carburetor (I noticed you have what looks like an Edelbrock Torker intake so I'm not sure in your case)- if you plug everything on this tap or just pull it out and install a well-sealed pipe plug into the opening and THEN notice a significant increase in idle rpm when you start the car you will have indeed verified that the primary cause of your dieseling problem is vacuum-leak related. You can then go about troubleshooting the individual vacuum components to find out exactly WHERE the leak exists. Dr. Rebuild (as well as others) sell a very clear and easy-to-understand little manual for troubleshooting this system....GOOD LUCK!

 

I'd agree except for #2. If the ignition is off, there is no timing Though, incorrect timing could result in a too-fast idle, which is the problem 99 percent of the time. If it's a stick, drag the clutch just a bit when you shut off the key. If an auto, leave it in drive, tho probably won't help much.

 

I don't think the fact that you have a L98 there is either good or bad, just different. I'm not a "motor guy" so I can't tell you what the differences are between what you have and what your corvette originally came with. If and when you start ordering stuff you need to know that you have a hybrid there. That engine was originally set up for fuel injection, so someone has seriously changed it. It is almost identical to the engine in my 91 coupe. A real torque monster and very reliable. If you have questions about the engine itself you should post pics and questions in the C4 technical area.

 

Logically that's true but I found that the timing being advanced on an MGB (which are complete b'stards for run-on with unleaded gas) caused massive amounts of run-on. I'm guessing that the timing being advanced caused localised hot spots in the chmaber (plug tip? Carbon?). Another thing to check is the grade of the plugs. Sometimes fitting colder plugs will help, but only in cases where the run-on is minor (I always run the coldest plugs that don't foul).

 

BTW, my bro and I have B's incl. GT, A's, a C, a Triumph, an AH Sprite, a couple of Midgets, and some other Brit oil leakers here and there. Whew. Talk about abusing yourself