Engine noise after deiseling event! Help!

[CST10]

I recently had a deiseling event on my 68 c10 250 engine. Never happened before. I use premium gas all the time and timing set at 8* BTC. Anyway, after I started it up and drove on home but notice a slight ticking noise. I don't remember this noise before. Couldn't pin point the tick with a stethoscope or by ear.

What could it be? Any ideas? Looking for advise how to check for damage OR what could have been damaged.

Hopefully it's a lifter or rocker or just my imagination running wild.

[swamp rat]

I'd say your timing is out, or if your engine is a stock build you are burning Ppremium gas for nothing, both can cause detonation. was the tick on acceleration? Dieseling is also an indicator of a timing issue.

[CST10]

Never deiseled before at the current timing setting and fuel. Premium should suppress knock but the tick increases as RPMs increase. I've only noticed it idling in the shop. Opened the hood and increased RPMs while in neutral and tick increases also. Have not driven it since I noticed it yesterday.

A mechanic I trust indicated that it could be carbon build up in the cylinder and a piece broke free and stuck to the top of the piston making the noise when on compression stoke. He also said it could have damaged a lifter and colapsed or a cracked rocker.

Just wondering if anyone one else had the same issues and what was the problem.

Thanks

[CST10]

It's a stock built 250 engine. Never been rebuilt with 22k original miles

[GASoline71]

Stock I6 should not need Premium fuel. If you must run a high octane, you can even cut back to 89.

Another thing to look at is exhaust leaks. Many a small "tick-tick-tick" that increases with RPM turns out to be an exhaust leak. Could be at the donut seal.

Gary

EDIT: I thought I was seeing double... I was in the engine and drivetrain section and saw this post and couldn't figure out where my response was. No real need to post in multiple forums.

[CST10]

Thanks for the info. I'll check the exhaust for leaks too. Didn't think of that possibility.

[CST10]

UPDATE:
I pulled all the plugs, appears to be running on the lean side. I then fired it up and checked for exhaust leaks and didn't find any. Then I was finally able to narrow the ticking noise down to the mechanical fuel pump. Shut it down and it deiseled again. Decided the check the timing and found that it had move to 4* ATDC, I had set it at 8* BTDC when I did the HEI upgrade a few weeks back. Checked the dizzy hold down bolt and found it barely snug. Loosened it up adjusted timing back to 8* BTDC without VA hooked up. Adjusted the idle speed then the idle A/F mixture. Shut it down. No more deiseling. Drove it for about 20 miles, still no deiseling and fuel pump noise is a little quieter.

Thanks everyone for the advise.

[MagmaJct]

Very few things cause dieseling. One of them is not ignition timing. Think about it, dieseling occurs with the ignition turned off. That is, unless one is considering the temperature of the spark plug if the timing is too advanced. I suppose then it's conceivable timing can contribute, if the plug is hotter than normal.

I have recent experience with my truck dieseling, I'll share for further reference. Driver's side donut had been leaking for some time. Truck is driven infrequently, so it hadn't been an issue. I ended up finally doing the repair, and found the idle to be rough afterwards. In a pinch I upped the idle speed to compensate.

Know what happened? It started dieseling! Warmed it up, adjusted the fuel mixture, set the idle. Now it idles great, doesn't diesel. Exhaust leak is gone, sounds wonderful!

In my experience, dieseling is caused by incorrect fuel mixture and/or high idle speed. (I am curious, if the high idle speed directly causes dieseling, or if it has more to do with the alternator back-feeding the ignition?)

As an aside, my old VW Beetle has a idle stop solenoid in the carburetor to prevent dieseling and wasted fuel from being sucked into the intake between the time the ignition is shut off and the engine stops rotating.

[CST10]

I agree with you. May be the timing and plugs might have been the issue. After I set the timing and cleaned the plugs. I also decarboned the engine using the water trickle trick then lowered the idle down and adjusted the A/F ratio.

Been driving it as my DD all week. Never has had another dieseling issue again.

Don't really know which one corrected it, guess the fuel carb adjustments made it go away.

Engine runs so quite now you have to open the hood to see if it's running if your in a spot where you can't hear the exhaust note. Got a quite muffler on it.

[MagmaJct]

Ooo, quiet muffler eh? What kind do you have? Unlike perhaps 95% of truck owners out there, I prefer quiet!

I've got a set of Turbo mufflers from the PO, not a fan of them, but being broke is my motivation for keeping them!

--Mike

[CST10]

I got the biggest diameter and length round shape muffler the shop had. I asked for the quietest one they had and they said round ones with the longest length and diameter makes them quiter. It's just a no name brand stock style muffler. Not a turbo or anything. I'll be under the truck tomorrow and see if they got a name on it, don't remember one being stamped but may be I over looked it. Think I paid $40 installed.

[Longhorn 70]

Glad you got the dieseling under control. Kind of a bummer that you don't know which resolved it. But don't look a gift horse.....

I did the quietest on mine too.... Went to the shop I always go to. Asked the guy for the quietest 2.5" inlet and outlet. Run then from the headers and dump them right before the rear end. They are quiet in the truck. Outside I am told they are noisy but I don't hear it that much. They are ovals tucked up tight.

[CST10]

Well this old I6 is a quite motor to begin with. Now the 462 bob in the 70 is another story. Couldn't make it quite unless you turn the key off. Lol.