Alot of backfiring !

[bearsden]

Got my head back from the shop and installed everything. After checking things
over again and again I fired her up. She turned over for awhile before she fired but when she did she started back firing a lot. I've double checked evrything and everything looks good.All vacuum lines are connected etc.It feels like a timing issue,but I'm just not that knowledgable about that.Can you give me a clue where to start? It barely idles before it dies andI don't want to keep running it in the event there is something wrong.Any help would be appreciated!!!! thanks.....Again.

 

[NorthwestCJer]

How much did you take apart? Did you take out the distributor?
Let us know what process you did to make the repairs.

 

[Texian]

check and make sure you have the firing order correct. also the dist. is set right.

 

[bearsden]

no distributer,the head had been done recently but they didn't replace the freeze plugs.PO ran just water through it and they rusted out.I had them replaced and the head checked out and resurfaced.new head,exhaust and intake gaskets.I didn't do anything to the valves as i figured they were good.I put the rocker arms,push rods,and all bolts back in there original places.I did take the plugs out and replace them.I asked for a set of plugs for a AMC 258 i6 / 4.2l 86cj at auto zone and installed those???? wrong stuff? any recommendations?

 

[Texian]

if not a ignition problem I would wonder about the valve adjustments then.You could have intake valve open at the wrong time.

 

[bearsden]

i did not mess with the valves at all and don't know how to adjust them but will have to do some reading...I appreciate the help!! would those different plugs i put in do something that drastic?

 

[Texian]

I gave you what appears to be bad advice on valve adjustments,you can only tighten the capscrews down to 21 ft. lb..

 

[Texian]

I take it you used a new intake/exhaust gasket and torqued to spec in the correct sequence. Vacuum leak on intake ?
I would think it would have to be either or a combination of wrong firing order on plugs,vacuum leak,bad valves or being held open,leaning out on fuel.

 

[hole]

Did you label the plug wires before taking them off? It sounds like the timing is off 180*. Pull #1 plug and tap the starter with your finger covering the hole, when you start to feel alot of air blowing past your finger, your at the start of the compression stroke. Check the timing marks on the dampner and line them up to 0. Pull cap on distributor and see if the rotor is lined up with #1.

 

[Jimbos76cj]

Back firing from a motor is normally a sign of a timing issue.

1) Pull the spark plugs and rotate the motor till the number one cylinder is TDC on the compression stroke. Dont just go by the timing mark. Theres 2 TDC times in a 4 stroke motor.Best wat to tell is pull the valve cover and watch the rocker arms as you rotate the motor. when you see the number one intake rocker open then close continue turning it until the mark reaches TDC. you are not at TDC on the power stroke. If you cant take the valve cover off you can place your finger over the whole and feel for it to build pressure when you feel it start to build pressure that means the piston is on its way back up to TDC.. again watch for the timing mark to reach TDC.

2) Once the pison is at top dead center on the power stroke.Before you remove the cap make a mark on the distributor body where #1 cylinder terminal is. Pull the cap off the distributor and see where the rotor is pointing. Make a mark in the body of the distributor where the rotor is pointing, make sure you can see it with the cap on. The terminal mark and the rotor mark should be close but not spot on.. they should be a few degrees apart.

3) If they are not close to each other then you have an issue with your timing. Either the distributor got bumped and moved or when you put the plugs and wires back on one or more got moved out of position.

If they are far apart put the cap back on and see what terminal is closest to the mark from the rotor and make that your new #1 cylinder and verify your firing order is correct. Remeber you want to start with the terminal at least at where the rotor is pointing. Again I would mark what terminal I planned on using for #1 on the distributor body, then rotate the distributor body so the mark from the terminal I plan on using is lined up with the rotor (cap needs to be off to do this).

Confused yet? Ive gotten into plenty of arguments especially when installing HEI's on 360's that the number one terminalo needs to point to the number 1 cylinder.. thats a big lie. When installing in a AMC v-8 the vacuum advance gets in the way of the power steering pump.. I use this method to find move it out of the way.

One other issue you can have is if your machinist took alot of material off your head then you may have your intake valves staying open when they should be closed. ou would have had to have alot of material taken off to cause this to happen. If you didnt remove your timing chain I would start at the Dizzy. Timing is usually the first thing I check because its easy and free..

 

[NorthwestCJer]

Sounding to me like you have a couple plug wires crossed. Check the easy stuff first. And double check it!

Good luck.

 

[JR74CJ5]

I like what they said. Check your timing and you firing order / plug wires.

It's happened before and will happen again. Good news is if it's just that, like they said it's free to fix, and you're good to go.




~ Jr

 

[bearsden]

So can I try turning the dist.Slightly to see if that helps? I did notice when i put the rocker arm back on that the very last valve it was a little loose. the pushrod was straight,but the rocker arm had some play.And it wasn't like that when i took it off. I was told that a loss of oil pressure might have done that since it had sat for awhile. everything was torqued according to the book and i did label all the wires prior to dissassembly and they are all on right. thanks for the help ! i'll need more !!!

 

[bearsden]

i did label everything to the tee....but i do like to have a few budlights while i work. But i don't get too crazy. Its got to be the valving.I'll double check hoses tonight then if all else fails pull that dang cover off.......................................again. thanks for the help!

 

[Blazerstud]

I had the same problem and it ended up being my ignition module. It's the little sliver box on the drivers side inter fender. 29.99 at autozone. There should be two plugs going into it. Check to make sure you didn't get one lose while working to the head. Hope this helps.

 

[bearsden]

i will definately check that,I'm out of town for a little bit all i can think about is getting home to get that darn thing going.........it's killing me.I did triple check all the vacuum lines and plug wires again. I did get it to idle but it backfired like clock work every couple seconds....thanks for the help!