258 Pinging

I just finished timing my 258 a couple of days ago, since it was hard to keep idling and pinging. I got it tuned back where it should be and it drove just perfect. No pinging at all, even in 3rd where it had always pinged when <2000rpm it accelerated just perfect and didn't make a sound. I was really happy until I took it for a little longer drive, after keeping it around 55-60mph for 5-10 minutes it started pinging again in 3rd when my rpm's were <2500. What could be causing this??? Could it be my vacuum advance??? Any help is greatly appreciated.

 

Recheck the timing. Could be it changed on you. Also, are you using the same gas?

 

What is the timing set to? What about the possibility of carbon buildup in the cylinders?

 

No Clue on exact timing.... When the engine rebuild was done, the tab for the timing marks was not put back on. I have been timing using vacuum. I get it to around 14.5" and ensure it is steady.... As for Carbon buildup, it is possible, but this engine only has ~3500mi since the PO had it rebuilt. I have checked since my drive and the vacuum gauge is showing aroung 13.5" and the needle is not steady, however the distributor has not physically moved....

 

You could try one of the two other old-fashioned timing methods I know -- they work best combined:

Advance until it kicks on starting, then back off bit by bit until it doesn't.
Find a steep hill and drive up it. If it pings, it needs to be retarded a bit.

Or something like that ... I still use this method in combination with a timing light when first setting the timing after having a distributor out.

 

Couldn't agree more. For a high tech engine like the 258, this is the way to go.

 

I agree also. Just back the timing off a tiny bit and you should be good to go.

 

I don't know what year your engine is. Mine is out of an 83 and I had problems with mine pinging like yours.I noticed the P/O had the EGR valve plugged off.I reconnected it to a ported vaccum source and no more pinging. I had also retarded my timing to try and get rid of it. Just something to check. good luck Bob

 

Other ideas:
- go to the middle pump instead of the lowest octane.
- slightly richen the mixture (rejet).
- check that the EGR system is working properly (as per Bob).

The EGR cools the combustion, so if there's no exhasut gas added, the high temperatures will cause pinging.

Lynn's right about deck and head surfacing. Always check your surfaces before you send the block or head to the shop, and don't let them routinely surface! If you tell them to do what's needed, shops will routinely surface. There's no need to surface unless the head or block is warped!

More details? Year? Original carburetor? Smog systems still present?

 

Man, thanks for all the great info. I will try re-timing altough from the last post I will check the timing after the engine has cooled first. To add smoe more information. The jeep is a 73 Cj'5 the 258 is from a 76 Cj-7 (according to the PO). There are no emmisions on it what so ever. He added a high lift Cam, Edlebrock performer 4bl 650cfm carb, holley electric fuel pump and Petronix Ignition to the engine when he had it rebuilt. He was running 108 Octane Gas with 4 Bottles of Outlaw Octane booster when I boght it. I dropped the tank to clean it and started back with plain 89 (middle) in hopes to time it back down to use 87 eventually. This is my 4th total tank of gas since the cleaning and the 3rd of 87 octane. I have been re-timing this thing since I bought it and thought I finally had it, but this is the first time the timing seems like it changed during a drive. I have all the info on the rebuil and I know he had it done at a "High End" machine shop according to him. High end meaning he paid WAYYYYYY tooooo much ($3500). I will research this some more and post my findings.

 

87 octane is too low for this engine. I think that the factory specs call for at least 89.

 

Thats weird mine will run with 87 all day long with no pinging. I have my timing set at 7* BTC.

 

I also run 87 without a problem, but I do not have as many modifications.

 

If the PO was running high octane fuel, hopefully, he was doing it for a reason. The only value in running higher octane fuel is to reduce detonation. Boosting octane when pinging isn't present is a waste of money. Fill up on super and see what happens.
If you have 13.5" hg at idle, that kind of stinks unless you have a lumpy camshaft. When timing with a vacuum gauge i'd try and get a baseline by advancing the timing to my max vac reading, and then retard it a bit. That's still no replacement for an accurate tdc mark and a dial back to zero light, as base timing is only 1/3rd of the battle. Most of the time on the old junk we are playing with you also have to account for mechanical and vacuum advance, which is never that close when an engine has gone from stock to a modified configuration. Not to mention that everything is probably not working as designed, which 30 year old vacuum diaphragms and weights might not be.

 

I'm amazed at the knowledge on this board.

 

He was running the high octance for "More Power" according to him. He used the jeep for offroad only, he trailered it to places to 4 wheel. I want a more rounded vehicle. I love to take it to play in the mud and on the rocks, but I also like to take the top down and drive the 25mi to work... I was trying to lower the maintenance level on it, and going to 89 would not be horrible, but there is no way I could try and hunt down the Ultra High octance and carry Octane Booster around (like he had it set). As for the cam, I have the specs somewhere around here. I will post them....

 

Here is the info on the Cam I have....

 

Do you have any specs on that cam? What's on it for an exhaust? Something tells me that if the PO was running 108 octane gas, he was having a detonation issue also. Higher octane fuel is harder to ignite so it helps prevent pre-ignition also known as detonation. Basically, the gas is igniting too soon. This can be a result of too high compression, too high combustion chamber temps, or timing that is too early. The reason I asked about an exhaust is that headers can help lower combustion chamber temps since they scavenge better than manifolds. You could also put a thicker head gasket in, or actually put 2 in, I've seen that done on race engines successfully.
Another thing I noticed, is that your engine is WAYYYYYYY over carbed. That 650 isn't doing you any favors at all. A 258 spinning at 5500 rpm with a 90% volumetric effeciency (which is pretty high, probably closer to 80-85%) can only possibly use 370 CFM of carb. Anything over that number is overkill. I'd suggest a 390 CFM 4 barrel Holley. It will substantially increase your throttle response since the venturi velocity will be much higher. It will also atomize the fuel more completely and promote better combustion. That means more power and better mileage

EDIT: I was typing while you were posting I see the cam specs. It's pretty aggressive, but not rediculous. If it's got some low gears in it like 4.11's or 4.88's you'll be fine. You just want to keep the RPM's up a little bit to keep it in the power band.
The PO is completely wrong about running higher octane fuel for more power. The higher the octane the HARDER it is to ignite the fuel. Get the octane too high, the engine can't lite/burn it, and you actually lose power. You only need as much octane as absolutely necessary to prevent detonation.

 

I agree, the PO did some wierd things... This was his first "Project Car" he built race bikes and traded one for this. The Carb is way too much, it is just hard to justify scraping a carb that is <18mo old, when I have so many other things I need to buy for this. I am begining to thing the Thicker head gasket may be the way to go (or 2 as you mentioned), but want to check the timing now that I have not driving it in a few days. Another question, do 258's come with Harmonic Balancers? This one does not have one and I found that kind of odd. Once again thanks for all the great input, I have found out things I never would have considered looking at. This board is a true lifesaver....