86camaro383

iTrader: (3)

My 383 runs a little bit after I turn off the ignition. HELP!

There are only 3 things I know of that causes this, Engine is running to hot, timing is off, or idle is high.

My idle is at 800 RPMS

According to my gauge it runs 200* in driving, and in traffic it runs 220*
It doesnt boil over or anything, so I know its not overheatings.

My total timeing is 36*...(set up by the machine shop who dynoed the engine for me)

what else can it be?!

camaro8tysvn

iTrader: (1)

what kind of compression do u have is ur gas good, try high test

86camaro383

iTrader: (3)

Its 10.5:1 with alumium heads.

I did have 87 in there before i did the swap. I filled it up with 93 in there.... but that was only 5 gallons. I was going to get some octain booster tomarrow. I actally heard if the thottle return springs are weak, this can cause this....

Sonix

iTrader: (1)

what is your timing at idle? 36* at WOT sounds ok, but what is base?

rx7speed

also you could try changign the heat range of the plugs. if they are too hot it could cause a hot spot and ignite the fuel. where the combustion chambers worked over?

as was asked what is the initial timing?

84z28350

Had any work done on the heads?

Like mentioned above a sharp edge on the chamber or similar could be causing a hot spot and doing this to you.

Possibly something feeding power back into the ignition circuit after you turn it off?...

rx7speed

that's not nice. 57 is a good guy

though if you have a problem take it up with him in PM guy maybe he can explain what was going on.

86camaro383

iTrader: (3)

Honeslty, I dont know base timeing. The machine shop set it up for me when they dyno'd the engine. They told me total timing was 36*

As far as heads go, they are AFR 210 race heads. Im looking towards the octaine of the fuel....

Auggie

Well, the only way an engine can keep running is if it is still getting air and fuel. Did you mention if your engine is FI or carbed? You could shut off the ign. when the trans is still in gear. Did you mention if your is an auto or a stick.

Auggie

86camaro383

iTrader: (3)

Its auto and carbed. Could the octaine be a major role in this?

Called up the machine shop and they said it had to be either octain is to low and to try to cool down the engine a bit. Told them it runs 220 in traffic and 200 while driving. They told me to try to cool it down another 20-30 degrees. Any suggestions? Have a stocker rad with dual cooling fans and jegs High flow WP. Im going to start with swaping out the themo's for a 180 to a 160.

Auggie

Yah, I had the same problem. My 355 has 10.3 to 1 with steel heads and would run on using 92. I lowered the idle as far as I could and still keep the engine from stalling. The problem is that the throttle plates are still open a little and will draw into the engine air and fuel which keeps it running. So, what I did was to back off the idle adjustment screw all the way so the throttle plates were compleatly closed when I shut the engine off. I then installed another A/C idle solanoid (see pic) that I use for the engine idle. These solanoids are adjustable so the idle can be adj. when the compressor kicks on. Heres how it works: When the engine is cold you step on ths acc. peddle to set the choke. When you turn on the key the idle solanoid is energized but does not come in contact with the throttle lever because its on high idle. When the engine warms up and the choke opens and comes off of high idle and settles down onto the throttel lever and maintains hot engine idle. The solonoid is not strong enough to move the throttle lever (two springs) when turning on the key so when the engine is hot you must just touch the acc. peddle to allow the idle solonoid to extend and your good to go.

Auggie

84z28350

yes, if you did get crap 87 it could cause this.

You would be lucky if it didnt do it on good 87oct. Since you didnt get to add much 93oct your probably still way too low.

86camaro383

iTrader: (3)

Well I dont have a q-jet. I have a 750 Mighty demon. I did get a universal thottle bracket. Could it be possible that I put the thottle cable back to far causeing it to be open a little bit?

But if thats the case how come it only happens when its warm?

mystikkal_69

iTrader: (2)

are you running ported or manifold vacuum to the dist? if ported vacuum try using manifold vacuum and see if it still does it.

Angelis83LT

For the holley they sell what is called a dashpot... same thing as a selinoid thing that that guy did with the a/c thing.. not sure why he did it since there is a selinoid built specifically for that purpose...

The throttle cable more than likely would not be a problem. I would do the manifold/ported vac test too to see if it does any better. although at idle you have the most vacuum in the manifold, so it will increase the vac advance. The ported vac has no vac unless it is under load i think..

Auggie

Angelis83LT, the origional solanoid that came with the car (there was only one) is used to keep the engine idle rpm even when the A/C comp. kicks on and only has power (12v) when the comp. is on. The other solanoid that I added is for the engine idle speed and has power when the ign. key is in the run position. The engine idle speed screw is backed all the way off. When I shut the engine off the throttle plates close compleatly so the engine doesn't "run on".

Auggie

rx7speed

dashpot is only for when you let off the throttle. this way once the throttle hits a specific point the throttle will hit the dashpot and slow down and close at a slower rate. prevents the car from having a rich run condition when going from throttle to no throttle.

Angelis83LT

now. do you not think that having a rich condition could cause it to do that.. Especailly if he has any hotspots upon shut down... the extra fuel in the cyl could ignite and cause a deisel effect. ( and my original seleniod on my 84Z is charged when the ignition key is turned and has nothing to do with the A/C)

rx7speed

but here is the thing with the dashpot you let off the gas. let it idle for a second now your dashpot means nothing.

usually it is only a very momentary rich condition. and usually not enough to make the car continue to diesel. usually ppl don't go rev their car then as they let off the gas shut it off.

once the car has entered an idle state for maybe 2 seconds most the fuel should be gone

drag1LE

Try to up the octane first - it's the easiest thing to try and most likely the culprit.

I've a 388 w/AFR 210 heads and was at 10:1 last year and I had to run a mixture of 110 octane and premium pump gas (about 5 parts pump gas to 1 part 110). If I ever tried to run on straight pump gas, I'd diesel, but with the 110 mixed in, I never do.

gpbtt

When you build a custom engine with a larger cam you never worry about base timing (because it can be at 15 ,16 or more) You are only concerened with total timing and is should be around 36 and even can go to almost 40Each set up is different.......You need to run atleast 91 with your gas.........Having that 87 in there will not help...At this point get some booster and fill the tank with 91 and it should be fine.
We run a 383 making 500 hp that I hand built and we run a big cam........we tun 91 as a min and it is street driven with no problems..Total timing is 36.

Auggie

Angelis83LT, I have the L69 package so maybe mine is differant. I also have the 1984 Service Manuel with all the wiring diagrams and my solanoid is definetly used to maintain engine idle speed when the A/C comp. kicks on.

Auggie

smokingss

this may be totally off in your case, but i thought i'd just share..
Back when i built my 88 iroc, with a 383 as well(motor is just a coincidence in thsi case) i used the stock single electric cooling fan, but since the previous owner already ditched the ecm, I had to re-do the fan power wires. And when i first put the car on the road, i made the previous owners "half assed setup" work for me by just putting the main power wire for the fan in the ignition terminal on the fuse box. I planned on getting a relay setup that weekend though. Anyway, When i would turn the car off, it would "diesel" for a short time, then shut off. this was a brand new motor, perfect timing, cold or hot. Turns out, the electric fan would spin up, then when i would turn the car off, as the fan slowed down but was still turning, it was actually acting as a generator instead of a motor and it was feeding power back into the Ignition system, just enough to keep the car barely idleing. If i unhooked the wire, it would shut down fine. That little issue made me very confused for a few hours till i finally realized it. SO, like i said, this may not apply to you, but hey, every little bit helps i guess. good luck with getting it sorted out.

fb305svs

Wow - thats one hell of an intresting thing...

the only time i've had dieseling problems is in the very warm weather... all i ran was mechanical advance, no vacum...

midniteplowboyy

iTrader: (1)

What heat range plugs are you running? Might drop atleast a couple lower. Are they the correct plug for your head?

Have you checked your timing to be sure it hasn't walked on you and your balancer marks are right?

What size is your cam?

Are you running a vacuum advance, if not it would help keep the exhaust valves cooler at part throttle and idle (not ported).

Or you got a real bad batch of 87, you should have more problems wide open and part throttle if it was the gas I'd think.

86camaro383

iTrader: (3)

Well I threw some octain booster in there and filled it up with the 93, and it doesnt seem to be doing it anymore. It runs a steady 220*. Im going to throw a 160 stat in it to try to cool her down a little bit better.

paulmoore

Running an MSD ignition box will do the same thing sometimes. MSD came out with a diode that you put on the ignition positive terminal (I think) so that battery voltage won't back feed into the coil and keep the engine to run after the key is turned off.