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  #46 (permalink)  
Old 10-02-2010, 11:12 PM
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Quote:
Originally Posted by Greg T
If I remember correctly, GM used the solenoids to allow the throttle blades to close at shutoff to prevent deiseling. The runon was caused by RETARDED ignition timing for purposes of emission controls. This is what I said way earlier in this thread. If you retard the initial you have to open the throttle more to maintain the desired idle speed. Open throttle = runon. ADVANCED initial allows for the throttle to be closed and prevents runon. I have to laugh when people need 50+ responses to the question or problem and then ignore the advice. RETARD THE CAM TO MFG RECOMMENDATION. And advanced cam will close the intake valve sooner which raises the cylinder pressure, which CAN promote detonation and runon. If all else fails, I'll bet the intake has an internal vac leak. Pull the intake and reseal it.
The cam has been advanced like it is for a good while (a year). Before I blew the engine, I had NO dieseling problem at all. It was non-existant even when I ran REGULAR 87 octane gas, NO DIESELING and the cam was still advanced the same 3*. Even with 10-12* initial timing, there was no dieseling problem. If the cam being advanced was the problem, it would have shown itself previously.

After the motor blew and rebuilt, I put everything back EXACTLY like it was. At first there was no problem, then after about 1000 miles, I started getting the dieseling.

That's why I'm not going to go through the trouble of pulling the engine apart just to retard the cam 3 degrees, it wasn't a problem before so there is no reason it should be a problem now.

The possible internal vacuum leak from the intake you mentioned, that there has me thinking. Maybe my next step is to pull the intake and replace the gaskets. Why would in internal vacuum leak cause this? Is there any way to diagnose it?

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  #47 (permalink)  
Old 10-03-2010, 12:00 AM
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Now that I think of it, the car has been using oil. I havn't been able to figure out where the heck it's going since the car doesn't smoke. I would loose about a quart every 1000 miles. It doesn't drip either. Reading around, someone said this is a symptom of an internal vacuum leak.
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  #48 (permalink)  
Old 10-03-2010, 12:11 AM
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Quote:
Originally Posted by cobalt327
If you are willing to do an easy experiment, I may have a solution for you.

Before starting the engine, completely close the throttle blades by backing off the idle screw so the engine will require you to keep your foot on the throttle to stay running.

Warm the engine up completely, so that when you shut it off it should diesel.

As you are about to shut off the engine, just as you turn the key to "OFF", release the throttle completely so the throttle blades will shut completely and see if this stops the run-on.

What you want to try to duplicate, is how a key-switched idle speed solenoid (shown below) would function- that is, when the key is on and the engine running, the solenoid extends to become the default idle stop. When the key is turned off, the solenoid retracts and will allow the blades to fully close exactly when the key is switched off- and that's what you want to duplicate w/how you let off the throttle at the exact same time you turn the engine off.

I missed this post. I will try this when I get the chance Cobalt thanks.

Last edited by kyle86; 10-03-2010 at 12:22 AM.
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  #49 (permalink)  
Old 10-03-2010, 07:20 AM
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Quote:
Originally Posted by kyle86
Now that I think of it, the car has been using oil. I havn't been able to figure out where the heck it's going since the car doesn't smoke. I would loose about a quart every 1000 miles. It doesn't drip either. Reading around, someone said this is a symptom of an internal vacuum leak.

As I said, pull the inatke and reseal it.
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  #50 (permalink)  
Old 10-03-2010, 08:47 AM
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Quote:
Originally Posted by kyle86
I missed this post. I will try this when I get the chance Cobalt thanks.
You're welcome, although this was mentioned (but more in passing, not in any detail) earlier.

This fix assumes you have no internal or external vacuum loss, but I'm sure you realize that the engine would need to be otherwise correct- and STILL dieseling- before using the solenoid.

Good luck.
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  #51 (permalink)  
Old 10-03-2010, 02:42 PM
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Quote:
Originally Posted by adantessr
Cobalt, I believe is right on the point there as ignition timing has nothing to do with dieseling once the key is turned off . As for having to back off the timing more than before to avoid pre-ignition, I'm not sure on that . I wish I could remember the application on the electric idle solenoid, but I do remember GM ran a lot of them .
LOL . Even as I was typing this I thought I might be getting myself in trouble . I was also thinking how retarded timing does make the engine run hotter and require more throttle opening . I don't mind a bit in being called on my goof ups . It just helps to keep me on my toes for the next time . Thanks, Seriously :-)
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  #52 (permalink)  
Old 10-03-2010, 02:48 PM
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You think that maybe an internal leak on the intake manifold could be sucking oil and causing carbon build up on the valves? That could be the cause of your dieseling problem Greg T mentioned. Something inside the chamber has to be getting red hot to keep igniting the next cyl. after the key is shut off.
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  #53 (permalink)  
Old 10-03-2010, 03:16 PM
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Quote:
Originally Posted by sqzbox
You think that maybe an internal leak on the intake manifold could be sucking oil and causing carbon build up on the valves? That could be the cause of your dieseling problem Greg T mentioned. Something inside the chamber has to be getting red hot to keep igniting the next cyl. after the key is shut off.
Oil from bad guide seals or from bad intake gaskets tend to carbon up the back sides of the valves, not nearly as much on the chamber side- although there could be any number of things that would act as a glow plug in the chamber.

The head gasket and intake gaskets would have been changed, from the "before" engine that didn't run on, to this "after" engine that DOES. If the head gasket has an overhung flame ring, or the intake gasket is leaking, either could account for the chances of having dieseling- but for a chamber hot spot causing dieseling, the chamber hot spot would also be causing preignition.

I would suggest looking carefully at the plugs to see if any look lean, or oiled more than the others.
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  #54 (permalink)  
Old 10-04-2010, 10:37 AM
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Quote:
Originally Posted by kyle86
Is there any way to diagnose it?
You could see if there is excessive vauum in the crank case. Unhook and block pcv valve. You could then either hook a vacuum guage up to crank case via the breather hole, or dipstick tube, depending on how its layout or put a very thin nitrile work glove over the opening and see if it pulls on it. You could have the tail pipe emissions checked. Another way of diagnosing, is to use a smoke machine. You pressure up either the intake or crank case side, to see if smoke bleeds over to other system. There is another tool called the First Look Sensor also, That uses an Oscope to measure the pulses either in the intake, crank case or exhaust, to isolate a leak ...But these are shop tools usually Silver bullets are hard to come by in many instances.
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  #55 (permalink)  
Old 10-06-2010, 11:49 AM
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The spark plugs are very oily. Especially the threads. These are from the passenger head, I havn't pulled the driver head yet.







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  #56 (permalink)  
Old 10-07-2010, 03:13 AM
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Quote:
Originally Posted by adantessr
Cobalt, I believe is right on the point there as ignition timing has nothing to do with dieseling once the key is turned off . As for having to back off the timing more than before to avoid pre-ignition, I'm not sure on that . I wish I could remember the application on the electric idle solenoid, but I do remember GM ran a lot of them .
They are still running them with all of the "fly by wire" throttles. When shutting turning the key on you hear the throttle plates open and when turning key off, you hear it slap closed. My '05 Silverado does this...

Yumm... Oil! Cuz she's definitely eating it!

Last edited by Caballerokid; 10-07-2010 at 03:19 AM. Reason: Edit:
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  #57 (permalink)  
Old 10-07-2010, 05:46 AM
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Besides for anti dieseling, the same type solenoid was used as a 'kicker' for the AC. When the AC would be engaged, the solenoid would energize and kick the idle speed up to compensate for the drag of the compressor.

These were mainly on the '80-back GM's w/small engines, V6 and such, especially those that used the loaf-of-bread shaped A-6 axial AC compressor.

If an application was needed to get one from the parts house, ask for a 1980 Malibu w/the 229 cid V6. They used an AC idle speed kicker solenoid. It's adjustable and has enough strength to move the throttle by itself when it's energized, in other words, you do not have to depress the throttle to "set" it, like a choke- it sets itself.
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  #58 (permalink)  
Old 10-07-2010, 10:13 AM
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After looking at those plugs Cobalt, do you still think that the solinoid might be his problem? I can just imagine what the valves look like. Nothing like oily carbon to get yer motor turning when the key is shut off. If not a leaky intake gasket, he has a major problem elsewhere.
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  #59 (permalink)  
Old 10-07-2010, 10:24 AM
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Quote:
Originally Posted by sqzbox
After looking at those plugs Cobalt, do you still think that the solinoid might be his problem? I can just imagine what the valves look like. Nothing like oily carbon to get yer motor turning when the key is shut off. If not a leaky intake gasket, he has a major problem elsewhere.
All the solenoid might do, is help the symptom, but would not be a cure- that's for sure. As I said earlier,
Quote:
Originally Posted by c327
This fix assumes you have no internal or external vacuum loss, but I'm sure you realize that the engine would need to be otherwise correct- and STILL dieseling- before using the solenoid.
Those plugs sure aren't extended tips, are they?

But yeah- there's oil coming from somewhere, MUCH more than normal.
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  #60 (permalink)  
Old 10-07-2010, 11:56 AM
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They look like the equivalent of AC 44T's or 45T's.
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