Knocking YJ

[RR14]

I have this knocking noise that happens on acceleration, it does not do it when idling. I checked the timing and set it to 16 degrees like the specs say to. Set the timing by plugging the vacuum line that runs to the distributer and unplugging the electrical wire on the valve cover like the book said to. I noticed that the timing goes of once I plug all the stuff back in, not sure if that's normal or not? Any ideas on what this could be?

 

[69jeepcj]

When you hook up your distributer vac line, that activates your vac advance which will raise your timing around 10* and will fluxuate depending on the vac your engine is pulling. This is why they tell you to unhook the vac line. 16* seems like a lot of timing for a 6cyl.
I did some looking and it seems that if there has been a nutter bypass then set timing anywhere between 4* btdc and 12* btdc that doesnt cause any pingging . If no nutter has been done set it to 9*, or 16* for high alttitdes.

 

[RR14]

Okay I'll try playing with it between the 9 and 16 degree marks when I get off shift Saturday. I don't think it has the nutter bypass. Thank you

 

[PoliceMonkey161]

What year is your YJ? 16 degrees is a lot of advance at idle. It's not unheard of if you have certain modifications, but I have feeling that you are experiencing pre-detonation (pinging).
Do you know if any mods where done to the engine? HEI, carb upgrade, or is it fuel injected? Also, you may want to figure out if it does in fact have a Nutter Bypass (would not be fuel injected) as this would change your under the hood nomenclature for specs.

 

[RR14]

It's an 89 stock carb and stock engine as well from what I can see. I'll double check the nutter bypass when I get off shift in the morning. The ignition all looks stock too.

 

[PoliceMonkey161]

Nutter bypass or not, 16+ degress is to much. What wire are we unplugging on the valve cover? Regardless, try plugging your vaccum line and setting your timing to let's say 8+ (you will likely need to increase your idle speed once you drop down to 8). Connect everything back up take it for a test drive.

 

[RR14]

Messed with the timing finally yesterday no more knocking/rattling at the top of the gears, I am getting some just past the start to midway thought gears thought. It speeds up pretty good now though. Timing is at about 8 or so thinking maybe I need to give it a little more maybe to get the low end noise out maybe?

 

[PoliceMonkey161]

Ok, so that seems better for you. Another trick you can try to further reduce your pinging at lower RPM's is try using a higher octane fuel. If the pinging continues, consider that it may be some lose rust/debris in the catalytic converter or muffler. This is harder to truly diagnose, but it can sound a lot like a lite pining sound.

 

[RR14]

Well seams that the middle grade fuel helped some. Seams that the noise is getting less and less with more drive time. Hope next time I go try and get it to pass emissions the co goes WAY down so I can pass!!

 

[PoliceMonkey161]

Well seams that the middle grade fuel helped some. Seams that the noise is getting less and less with more drive time. Hope next time I go try and get it to pass emissions the co goes WAY down so I can pass!!

How bad are your emissions? There are a few things you can check and possibly adjust to lower emissions.

 

[RR14]

Co was at 94 and the limit is 24 I believe. Dunno if the fact that the jeep had been sitting for at least a year after I bought it had any play in it not passing or not

 

[PoliceMonkey161]

With your emissions being that high, I don’t think that sitting for a long period is the only problem you have. I would start with, has a Nutter bypass been done? If so, was it done correctly?
Even more importantly, check your EGR valve. If it is still on the engine and someone did the Nutter bypass only to leave it connected in its stock set up, that is probably part of the problem. You can reuse the EGR valve but it needs the vacuum lines re-routed. Even if no Nutter was preformed, check the valve for proper function (i.e. the diaphragm still modulates with increased RPM’s). If possible, take it off and clean it and the seating surfaces. A deflective EGR will cause rough idle problems as well.
The next thing to consider with regards to emissions is now old are the plugs? Are they gapped correctly? Do they appear black (running rich)? You may even consider a higher out-put coil so you can open the spark gap up more. More spark= more fuel burned off/ less emissions.

Keep us posted….

 

[RR14]

Well went to emissions and PASSED! CO went from 94.0 when I failed last time to 6.0 today... Put new plugs and wires this morning and threw in some ISO H.E.E.T in the tank before I left o the emissions place. So with that and rebuilding the carb helped a lot

 

[PoliceMonkey161]

Awesome!