2 dead cylinders 258

[st0rck]

Heres the lowdown:

3 & 4 cylinder initially had 10psi compression (throttle floored, all plugs pulled)... while engine runs, you can pull plug wires and no difference in the way the engine runs.

Pulled the valve cover, found two bent pushrods (one on #3 and one on #4 I have no idea if it was intake/exhaust #3 was front valve, #4 was back valve).

Installed brand new push rods (84 AMC 258 push rods are 9.72in I believe)

Fired her back up... idles OK but once you put it in gear, it bogs down hard and until you get her moving she will die under any kind of throttle. Once shes moving, anything more than half throttle and I pops like crazy.

Prior to putting the valve cover back on, I turned the crank over by hand (clockwise facing the front of the car) and verified that all of the valves were in fact moving up and down with the push rods (I did this to verify proper installation, rule out stuck valves, and rule out worn lobes on the camshaft)

Re-checked compression on #3 & #4 cylinders and it comes back at 150psi each. Nearly perfect, but alas has not fixed my problem. The plugs were pretty fouled on the two cylinders even though I just replaced them literally less than 200 miles ago (200 miles of actual drive time there has been quite a bit of idle time in there) so I replaced them. Problem still persisted.

I am running out of ideas. I have replaced the coil, plug wires and plugs. I know that my vacuum advance on the distributor does not work but I would think that would effect all of the cylinder and not just 3 & 4. The distributor is the only thing that I have not replaced.... Someone help... I'm running out of places to look... (any money to fix those places!)!

[Ryan]

if vacuum advance isn't working, then your timing is off the more you increase throttle. Have you double checked timing to make sure it hasn't moved / slipped?

[st0rck]

I checked the timing... it was set @4 btdc but i bumped it to 8 since im running the 1bbl carb setup... i just got a new distributor/cap and rotor tonight and am going to put it on tomorrow and see how that goes... but i still dont understand why i can pull 3&4 plug wires and the engine still runs the same? Is there another way to test for a dead cylinder?

[Ryan]

if you pull 3 & 4 and no change, then cylinders are dead. That can be from shot compression, but also could be from bad spark plug / plug wires / distributor / ignition control module.

[st0rck]

Compression is @ 150psi both cylinders... replaced the spark plugs while troubleshooting so they are brand new... just purchased a new diatributor/cap/rotor button and am going to put that on today to see if anything changes... is there a way to test the ignition module? Plug wires have less than100 miles on them but they are fairly cheap suppression wires (xact 7mm)... resistace was good on them but with the new distributor on i am going to swap some of thr plugs around and see what i get and buy a better aet if that fixes the problem... more to follow i will post again after my findings!

[Ryan]

on the ICM, the electronics inside can fail intermittently, so until it goes south, hard to test.

on the compression, with it being that good on both cylinders, the problem is most likely electrical (ignition related)

[davpratt]

Check to be sure the vacuum advance plate is properly in place in the distributor. If the vacuum plate moves up and down the pickup coil may hit the rotor. If it does that cylinder will miss fire. It can fire to early or late.
I had that problem with a 79 CJ5. I had to add a piece of metal to hold down the vacuum advance right where the vacuum advance control rod enters the distributor. The rotor is a maginet and it will pull the pickup coil toward it.

[st0rck]

Problem solved! Meant to post yesterday but once I got the Wagoneer up and running it was on to the lawnmower (successful as well). I attribute the MAIN problem to be a self inflicted error. I got a tech manual from a good friend of mine who is huge into AMC's and was looking through it quite puzzled...

Turns out, whoever had the car before me had the plug wires on the distributor cap wrong (hense the bent rods I discovered upon removing the valve cover). When I put new plugs on, rather than research on the internet the proper location I did one at a time with the way they were previously setup. Needless to say, my 2 dead cylinders (3 & 4) were swapped. DOH! Luckily I was able to figure it out prior to re-bending the new push rods I installed.

I did take yalls advice, and since I knew for certain my vacuum advance on my distributor was shot I went ahead and got a new (new re-furbished that is) distributor, and a new rotor button/cap to boot. She fired up and is now happily running on all 6 cylinders for the first time since I've owned her! There is a "slight" exhaust leak off the headers into the downpipe that is much more pronounced given the added power but she runs great! Thanks for all the help everyone and steering me in the right direction!

[Ryan]

awesome, and a great testament to making sure wires are going to the right spot in the correct orientation!