Cruising on the highway last week I heard a pop/tick noise and it seemed to die for a split second then come back. Did this a few times within a couple miles. Has run rough all over and backfires when reved since then. Haven't looked that deep into it yet, but the research I've done points to a vac leak or timing problem as the most common causes.

So far this is what I do know:

No changes in the setup, basically left alone for quite a while now aside from changing the fast idle speed around the time winter hit

Distributor looks to be in the same position is has been and that bolt isn't loose

Although I haven't tested it with ether yet, the one vac line it has looks to be connected and as it was before this issue

The plugs look good to me, nothing broken and the tips are clean, maybe a little "dirty" looking on the ceramic. I've also pulled one wire at a time as I did last time I had a problem that ended up being a busted plug. Each plug made it run even worse when pulled from the cap.


I've also read about things like jumping timing, but I'd like to exhaust all the typical things first. Hopefully I've got some troubleshooting time before the next snow hits <img src="/forums/images/graemlins/drunk.gif" alt="" />

Forgot to mention the backfire is through the carb, not the exhaust.

I had a simialr experience with my 2.6L. I pulled each plug one at a time until I narrowed down the culprit cylinder. I then removed the valve cover and found that the last Camshaft Bearing bracket had broken in two, allowing the camshaft to move upward and not opening and closing the valves properly. It was a simple fix, but you might check into that.

-Austin

you can check the timing pretty easy by pulling the valve cover off, then putting the crank at tdc on number 1 both valves closed in the front and make sure that cam dowl hole is at 12 o clock. If it isnt then it's jumped a tooth.

I suppose it's also possible of a bad ignition componet also.

On the timing thing, would a compression test tell me if the cam timing is off? I could loan a tool one of those and get a better idea maybe.

About the TDC thing, just stick a straw in number one and rotate motor until its as far up as it'll go? I'm guessing it could be on the wrong stroke so if it is that dowel will be 180 off?

Also pull all the plugs and hold throttle wide open, pull coil wire off and crank a few times?

once you remove the cam cover you can see the sprocket. rotate the engine until the dowel pin is at the top and turn the crank till the timing mark is TDC. The dowel should be at 12 oclock as mentioned. Then look over everything else up there.
Look for a broken valve spring, the rockers. Look at the end of the rockers to see if a lash adjuster broke out of the end. Make sure the jet valves are working freely. They have light springs and can get buggered up.

I suspect a jet valve has come apart. This squirts compression pressure and combustion fire out the carb.

Would that be obvious once the valve cover is removed? I just need to make room in the garage, pull it in and start taking it apart.

Yes, it should be obvious. You may have to remove the cam sprocket bolt (only if you have the little metal shelf for the gear to sit on, or the tensioner will expand and you can't get the sprocket back onto the cam because the chain tightens up) and loosen up all the rocker arm shaft bolts and let it come off (use cut off rubber glove fingers to hold the lash adjusters in the rockers) the cam, and any broken jet valves should pop out. You may get enough slack to check by backing off the adjuster nuts, but it's just a quick to take off the rocker shafts.

If the cam sprocket slips down too far, there's a fix with a half inch dowell about 2' long, end whittled to a tapered wedge and hammered in between the two sides of the chain, driving the tensioner back in.

Would a cracked distributer cap cause this?