Topic: spark knock

[jlabean]

i decked the head .015" on my 1995 YJ 2.5L, now it has spark knock very bad. is there any way to turn my timing closer to 0?

[FourbangerYJ]

By spark knock, do you mean pinging? Does it do it all the time or just under a load?

[chardrc]

the computer controls the timing.. but i think i red somewhere that you can move the crank position sensor to trick the computer into changing the timing

[warpedredneck]

does your jeep use a egr?
if so make sure the ports(tube) are clean and clear
also make sure the egr still works
egr's introduce exhaust into the combustion chamber to reduce chamber temps(pinging/detonation)
hth

[JeepGeek666]

My Jeep....with the 2.4L engine had some pinging under load (up hills and heavy acceleration etc.) and switching to mid grade gas cleared that up for me.    I think I might need to run hotter plugs?  My plugs were changed once ar 30K and again at around 80K along with the wires.....but, I use mine as a delivery vehicle so it idles a lot and tons of stop and go.    I did a fuel induction cleaning this past summer, been using Mobile 1 10w-30, mid to high octane and a can of Techron fuel injector cleaner every other month.    So far so good.   

[chardrc]

we found that when we went to Colorado with our Rubicon if we ran regular it would ping under load so we had to run mid grade or premium to stop the pinging at high altitude, I guess what I'm saying is that if you live in the mountains the thin air could be part of the problem... or i could be totally wrong. 

[Jeffy]

we found that when we went to Colorado with our Rubicon if we ran regular it would ping under load so we had to run mid grade or premium to stop the pinging at high altitude, I guess what I'm saying is that if you live in the mountains the thin air could be part of the problem... or i could be totally wrong. 

The thing you have to consider with like Mile High state and other high alt. places is that the air is thinner up there.  This means your engine gets less air with every cycle.  This is also why when you buy gas in CO. their regular is not 87 octane.  It's 85, IIRC.  Their middle grade is 87 and top grade is 91.

Less dense air means less pressure in the cylinders which your compression ratios will be off.

Maybe the computer backed off too much causing a leaning condition.

At least with a OBD II vehicle you can cheaply tap into the computer with inexpensive scanner.

[chardrc]

The thing you have to consider with like Mile High state and other high alt. places is that the air is thinner up there.  This means your engine gets less air with every cycle.  This is also why when you buy gas in CO. their regular is not 87 octane.  It's 85, IIRC.  Their middle grade is 87 and top grade is 91.

Less dense air means less pressure in the cylinders which your compression ratios will be off.

Maybe the computer backed off too much causing a leaning condition.

At least with a OBD II vehicle you can cheaply tap into the computer with inexpensive scanner.

that makes sense... on a side note there is more difference in the gas between Mn and CO than octane... the MN gas doesn't work well in Co... basically the gas likes to boil in Co.. took us 3 years of going in our willys to finally figure than one out... always wondered why it ran the worst the first day out then got better... But i guess we ( or just me) should get back on topic now....