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1979 AMC 304 Rough idle.

1979 AMC 304 Rough idle.
It really sounds like the ignition control module has given up. The goop oozing out and the overheating icm pretty much give it away. I am sure it runs better when you first start it up also. When the pickup coil in the distributor gives up it runs crappy also. You have a number of choices for a repair, I would suggest not buying one of those cheap versions of the icm and the ground wire for the icm is the black wire that goes into the distributor and a better place for it to go would be directly to the battery negative post. A poorly grounded icm will not last long.
 
:agree:

Also check the OEM horseshoe connector on the coil. It is a well known area for intermittent contact issues.

LG
 
Ok. New ign. module on. It doesn't have that noticable cough at idle. It is still spitting under load.

Carb is rebuilt. I set the idle screws seems like 3 turns out is where it likes it best. I did by ear. I adjusted screws out half turns until idle stopped rising then went back one half turn at that point.

Timing. I'm lost. Emission tag says in first box to left, "ignition timing - + 2deg. BTDC @ RPM. Box next to that one says 5 deg. @ 750. Ok with the vacuum advance plugged and the engine at 750 rpm, the timing mark is flashing at the 3rd point from the bottom or left of the TDC mark on the timing tab. That would be a neg. 10 deg. right? Where the heck is it suppose to be? Is the emission tag a +5 deg. or -5 deg.? So is it minus or positive 2 deg. of 5 deg.? I'm lost here.
 
Hope this helps-Look at post #4.
304 timing - JeepForum.com

Hint-Anydangtime you work on the electrical system like the ign. Disco the POS(+)lead from the battery.

:chug:

LG
 
Ok. I think I'm close. I decided since setting it at 5 deg. BTDC made it worse and 10 deg BTDC still has the same problem but not as bad, I took the timing further out.by 5 more degrees. At adjustment, it's setting at 15 deg BTDC now. I took it out and drove it and it did.pretty good. I would say great but my dang shift knob came off and I still don't know exactly where I am really on timing. But it didn't sputter or spit one time and I bogged it down pretty good. I'm getting there but I still have more to look into.

For example. Tell me, on these crankshaft dampers, do they have a rubber ring built into them? I ask this because it is entirely possible that if it does, the damper may have slipped at some point in it's life. I've had this happen to me before on a chevy damper. When they slip, the timing mark is off.
 
As promised the old valve next to the replacement:

IMG_0322.webp

The top (white) tube spike goes to the carbon canister. It can be turned to the position needed. The bottom "T" attaches to the two vent lines from the fuel tank.

Timing is a spooky thing, especially if you only know enough to be dangerous. What you are seeing on tags are a setting for emissions. That rarely means it's where the engine will run or perform the best. I've been told to advance the timing until the engine starts to ping under load, then back it off a few degrees. That makes me a little nervous, I set mine to ~12.5*, it runs well there. But turn it back to 5* for emissions. One thing to know. Even with vacuum leaks or essentially gone the distributor will advance at driving speed, the centrifugal advance is mechanical and will advance the timing by itself.
 
Last edited:
Torxhead said:
It really sounds like the ignition control module has given up. The goop oozing out and the overheating icm pretty much give it away. I am sure it runs better when you first start it up also. When the pickup coil in the distributor gives up it runs crappy also. You have a number of choices for a repair, I would suggest not buying one of those cheap versions of the icm and the ground wire for the icm is the black wire that goes into the distributor and a better place for it to go would be directly to the battery negative post. A poorly grounded icm will not last long.
Click to expand...

I will keep these things in mind. Thanks.
 
Hedgehog said:
As promised the old valve next to the replacement:

IMG_0322.webp

The top (white) tube spike goes to the carbon canister. It can be turned to the position needed. The bottom "T" attaches to the two vent lines from the fuel tank.
Click to expand...

Ok, I've yet to see anything like that under the Jeep. Since I've got most of my running issues answered, I'll have to check it out. Thanks!
 
Hey while you guys are around, wanted to say thans to evryone who's helping me out here. Lot's of good info you just can't get in a manual. I really appriciate the input.

I also wanted to wish you all a Merry Christmas too!
 
You guys are quick. I've edited the picture post to add advice on timing issues. Please drop back and check it out.

Gotta go, Christmas duties ahead tonight.
 
The roll over valve is up inside, the driver side rear wheel well.
LG
 
I have always giving my stuff as much timing as they can take with out pinging.
 
Hedgehog said:
As promised the old valve next to the replacement:

IMG_0322.webp

The top (white) tube spike goes to the carbon canister. It can be turned to the position needed. The bottom "T" attaches to the two vent lines from the fuel tank.

Timing is a spooky thing, especially if you only know enough to be dangerous. What you are seeing on tags are a setting for emissions. That rarely means it's where the engine will run or perform the best. I've been told to advance the timing until the engine starts to ping under load, then back it off a few degrees. That makes me a little nervous, I set mine to ~12.5*, it runs well there. But turn it back to 5* for emissions. One thing to know. Even with vacuum leaks or essentially gone the distributor will advance at driving speed, the centrifugal advance is mechanical and will advance the timing by itself.
Click to expand...

I agree. When you try to set the timing according to the emissions tag and it's that far off, well it throws you a curve. You start doubting what you're doing. I had to step back and just go to the old trial and.error phase. Sometimes you just get lucky. I got lucky today.
 
I thought I'd share this pic also of the melted ignition control box.

I'm still getting a cough through the exhaust on a load. It's not all the time. It's worse when the engine is cold or not warmed up enough. I fiddled with the timing again moving it around and wound up back to the original setting. I also tinkered with the idle mix screws sense this happens mostly when taking off in 1st gear. To describe it, it's like when you're taking off and you ease into the gas as you let the clutch pedal out near the point where the clutch is almost all the way engaged it will kind of bog or something and cough, not an actual backfire just like a misfire. Like I said it doesn't do it every time and I think it depends on how much you slip the clutch. So something is still not right. The only thing left is a compression check, double check the harmonic balancer to make sure it hasn't slipped on the rubber ring, the coil grounding itself and the ignition pickup coil in the distributor.

What port does your vacuum advance line run to on the intake? Mine runs across to a sensor on the intake on the passenger side front of the intake. I wonder if the vacuum pot on the distributor is bad also? I know those sometime stick or just go bad. Not sure on the old jeeps, but on some old cars they would freeze or just not work.

As you can see in the pic, this ignition module got pretty hot for some reason. If this thing got that hot, could this have effected the pickup coil?

20161224_193106.webp
 
Yes-it could.
Have your alternator check'd for voltage output. You want 13.5-14 vdc at most.
LG
 
Before you fiddle with anything else, replace the ignition box. You are grasping at straws until that is done.
 
Lumpy Grits said:
Yes-it could.
Have your alternator check'd for voltage output. You want 13.5-14 vdc at most.
LG
Click to expand...

I'll have to look at the manual to see if they show you how to do this.

Being it's intermittent, it makes me want to think pickup coil or if these distributors have mechanical advance weights, maybe the springs are weak or weights are sticking or something. I'm about to just go buy an HEI. Almost. They have their weak points too.
 
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