How to adjust timing?

[thehulk]

I am an idiot, but I feel the need to adjust my 87 wag's timing because after starting the wag, the idling engine dies when I put it into drive. Then, when driving the **** thing the engine has been pinging when I give it gas to accelerate; but the pinging dies off while just cruising along.

And, after going through alot of everyones' posts, it seems that the timing is generally the first place to start with.

Any suggestions on how to do this?


Am I wrong?

[Darin]

You probably want to consider getting the Spark Knock kit mentioned in the technical library / engine section. I am installing one tonight along with a complete tune up. this kit is basically a non standard egr valve and I think a different timing setting as well. Sounds like timing alone doesn't take care of this. Good luck.

[joe]

Engine warm. Disconnect and plug the vacuum hose going to the distributor vac advance. Hook a timing light to #1 plug wire(front drivers side) and shine it on the timing marks on the timing chain cover and see where the mark on the pully is when it lights. To change the timing loosen the dist hold down bolt "slightly" and turn the dist a bit either way to advance or retard the timing. I don't know the specs for an 87(?) but it should be somewhere around 8-10 degrees BTDC(before top dead center). Re-connect the vac hose to the dist.
Timing too far advanced will cause pinging(a bad thing) but it shouldn't cause the rig to stall when you put it in gear.
Your timing may well be off some but I'd look for a vacuum leak before you try adjusting anything. When was the last time you replaced all the vacuum hoses? It could also be a carb/choke thing too. When it's running rough you getting any black smoke from the tail pipe? Do get the timing in spec and make sure your plugs, wires etc are ok before messing with any carb adjustments though. You can get a carb really out of whack trying to fix a spark problem by adjusting the carb.

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Regards,
-joe
63 2-dr Wag, 72 J-4000, 73 J-4000, 82 CJ-8

[nograin]

Hulk,
There is another very similar thread to this (how to adjust timing) pretty recently I think.
The timing specs are supposed to be on a diagram under the hood. If not, I can look up for you in the TSM, but its better to go by the sticker.
The 87 also had a vacuum rerouting "fix" that was recommended. I think the spark sensor fix was for the 6 cyl. not the 8s.

That all said. Your initial advance (thats what you set in the specifications) is probably OK. Go ahead and check it as -joe said. Preferably with a tachometer. Next question, Does it ping when you floor it? This is the key. If its OK at wide open throttle (no ping)when driving, and pings at part throttle acceleration only, then your inital advance is probably OK. (explaination later). If not, you'll have to reduce your inital advance, assuming you have no vacuum leaks sufficient to make the mixture too lean. So yes, check for vacuum leaks first.
If it only pings at part throttle, then its time to suspect vacuum advance, and EGR. Like I mentioned above, AMC had a fix for the vacuum line arrangements for 87. EGR pluging up is another good one. Also, I should mention that AMC recommended changing brands and grade of gasoline to address pinging (its right in the owners manual!)

Oh, the explanation.
Idealy, the spark plug ignites the fuel mix when the piston just reaches the top of the piston. Right? In reality, it is known that the explosion takes a little time. That plus other factors, make it better on most modern engines to fire the spark plug before the piston gets to the top. Follow? So thats why its marked Before Top Dead Center.
Now, the faster the piston is moving up, the earlier the flame needs to be started. So, up to about 2500 rpm, the timing advances with engine speed. For example, at 500 rpm timing is set at 12 deg BTDC, when the engine is at 1000 rpm its maybe 20 degrees, and at 3000 rpm its at 34 degrees. How fast it increases is controlled by springs and weits in the distributor.
AH, so whats that vacuum line? Thats because under very light load (cruising), its known that advancing the timing even more will be more efficient and get better gas milage. The vacuum line pulls on a diaphram and gives as much as 15 or 20 degrees additional advance. So at 3000 rpm, the total might be 34 + 20 = 54 degrees.
The ping you hear is too much advance under that condition. Basically the piston getting pushed back the wrong way for a fraction of a second because the flame front was started to early.


As the engine speed increases, the advance (thats the A on the timing mark) increases. Also, as the vacuum signal to the distributer increases, it too advances the timing.

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