1980 304 misfires under load

[corliss]

Gents, I have a strange one for you all. Got a 1980, AMC 304 that under a hard acceleration misfires and wants to stall, when this is occurring the tach is jumping around like crazy. The weird part is by just turning off the ignition and restarting the engine it runs great until you give it a lot of pedal going up a hill. If I drive it real easy this problem doesn't occur. Any ideas?

 

[Cheepjeep85]

is your vacuum advance hooked up? have you checked the timing? have you replaced any of the ignition parts at all?

 

[corliss]

Cheepjeep 85, yes the vacuum advance is hooked up, although I didn't try sucking on the line to see if the vacuum pot leaks. I did replace the coil but everything else is original since 1980 (except the normal stuff like plugs, wires cap and rotor a few times since new). I'll put the timing light on it to see where it is at as I can't say I've checked it lately.
Thanks for your thoughts, any others?
Whatever is causing this restarting fixes it, bum starting does not, the ignition needs to be turned off and back on, starts right up and runs great until I put it under load.

 

[Cheepjeep85]

sounds like a control module problem to me, does it still run after it starts acting up or die completely.

 

[IOPort51]

Accelerator pump??

 

[corliss]

Cheepjeep85, The control module is something I was thinking could be the problem too. To answer your question, I pump the gas to try and keep it going to a place I can pull over safely to turn the ignition off and restart it as after it runs perfectly. The other thought I have is a vacuum leak when the emissions system senses load, like EGR opening or a bad diaphram?
IO, Off a stop it accelerates as it always has, no loss of power which I think is when the accelerator pump does it's thing. Thanks for the thoughts guys.

 

[Cheepjeep85]

it just seems like it is definately something electric if you cut off the ign.and turn it back on and its back to running fine. could be egr i guess, only time i've ever had problems with an egr is on a diesel, and when they stop working the motor won't hardly run.

 

[corliss]

Thanks Cheepjeep 85. I'll check the vacuum lines, electrical connections and the timing for starters. I'll price out the control module just in case. Thanks again.

 

[kicknjeep]

I'm with IO on this, how old is the carb? ever rebuilt/replaced?. deff sounds like fuel issue, fuel filter?

 

[Cheepjeep85]

well the it could be the carb but it doesn't make sense to me if you cut it off and back on and it runs fine. i mean if it was a carb issue you'd think that when you were trying to restart it, it would stumble and act like it was flooded or didn't have enough fuel.

 

[IOPort51]

A couple of more ideas to cloud the water.
I have never "vapor locked" so I am not real up to speed on the subject but if the fuel line is a bit too close to the exhaust manifold will this cause any thing like these symptoms??
#2 the Tach is bouncing all over the place, the tach is driven by the ignition so if the tach is going on and off does it also make sense that the ignition is also? perhaps just a bad connection at the coil??

I am reaching pretty hard for possibilities here.

 

[kicknjeep]

I have seen some control modules act this way but for a very short period before going completely out. had a 79 AMC 304 act pretty much way and after carb rebuild it ran fine. Not saying it is for sure the problem just something to take a look at! some other good advise here as well,good luck.

 

[Cheepjeep85]

well a carb rebuild is around $15,an ignition module is $31.99. both fairly cheap and easy to do, but start throwing parts at it and even cheap stuff can get expensive. rebuild the carb, which it probabaly could use any way if that fixes it your done, if not move on.
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Ignition-Control-Module-BWD_5240484-P_194_R|GRPTUNEAMS_554110309___

 

[Old Dog]

My guess is either the module or the coil.

 

[CJ7Troy]

I just went through this very problem, I had replaced my control module while chasing what eventually turned out to be a bad pick up coil. I had to replace the distributor 3 times to get a good pick up coil (frustrating). The engine cranked and ran great while parked, driving down the road, it stumbled and backfired when putting the old foot in the carb. I could feather the throttle and it ran ok. I noticed the tach was jumping while checking the idle and timing. I ordered a new module and the same thing. Then I put the original 35 year old module back on and it runs like a race car. I carried the new modules back and asked about what happened, I was told that either the new one or the old was solid state and I would have to special order a control module from specialty products if my old one ever went bad.