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engine "shimmys" at idle with AC on

d9103365

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I have a 77 cordoba 400/4BBL. Whenever I'm at idle and the AC is on, the engine seems to shimmy a bit as if its struggling. This goes away once i start moving. It also seems to heat up a bit during this time, and oil pressure goes down....all of this corrects itself once I get moving. I've seen this problem on some of my other mopars before...what is the cause?
 
What's the idle rpm with the ac on and in gear?
 
It sounds like maybe the compressor is about ready to take a powder. Or maybe the clutch is "grabby". If I remember correctly those compressors are basically a V-twin, you might have to pop the heads (for lack of a better word) and take a look inside. Checking for a broken piston, bad bearing (if there even are any) and proper oiling.
I dont know how you would go about checking the clutch, but I'm sure somebody here does.
What I would do is: 1) Place a medium sized glass on the aircleaner. 2) Place two garlic-stuffed queen olives into the glass. 3) Fill glass with chilled vodka. Allow contents to be shimmied (not stirred). 3) Find a comfortable place to watch the Cardinals lose another game and blow ANY chance they might have had at 1st place.
Yeah, i lack ambition.
 
fan clutch?

My guess was that it may be the fan clutch having a problem. I seem to have a bit of an airflow issue...even w/ AC off, car heats up a little at idle on a very warm day. It tends to cool down when its moving. At night, its not a problem at all.
 
Just an idea, check your timing just idling in park, no air. Put it in gear and air on and see if the timing changes.
 
I have a 77 cordoba 400/4BBL. Whenever I'm at idle and the AC is on, the engine seems to shimmy a bit as if its struggling. This goes away once i start moving. It also seems to heat up a bit during this time, and oil pressure goes down....all of this corrects itself once I get moving. I've seen this problem on some of my other mopars before...what is the cause?

Here is what I believe is going on. The Chrysler V2 compressor takes power/ rpm's from the engine. That power robbed from the engine brings down your rpm's from where it normally is. The idle solenoid is supposed to kick up the idle, preventing the engine from stalling with the compressor running.
With that said, remember that when the compressor is doing it job, it is taking warm air from your passenger cabin, super heating it through the compressor and venting through the condensor, which is in front of your radiator. Now your engine needs to be cooled, but at idle it's not getting the benefit of large amounts of cool air being passed through both the radiator fins as well as the condensor fins, hence your temp gauge going up at idle.
When an engine gets warmer the lubricating oil tends to thin out and with the extra heat from the forementioned sources, you will get a lower reading on your oil guage as well as the fact that the engine is idling at a lower rpm and that means the oil pump is moving slower also since it's mechanically driven by the camshaft via the distributor drive gear.
 
An engine in a good state of tune shouldn't stall when the ac kicks on....even on the ones before the idle kickup became the norm but an engine that's already idling too low may have idle issues with the ac on. That's why I asked what it was idling at. Need to know what it is with it on in gear and with it off in gear. Just cannot diagnose this problem without knowing that little bit of into....then we can go from there with asking what the vacuum is at no load idle and loaded idle etc etc.
 
Here is what I believe is going on. The Chrysler V2 compressor takes power/ rpm's from the engine. That power robbed from the engine brings down your rpm's from where it normally is. The idle solenoid is supposed to kick up the idle, preventing the engine from stalling with the compressor running.
With that said, remember that when the compressor is doing it job, it is taking warm air from your passenger cabin, super heating it through the compressor and venting through the condensor, which is in front of your radiator. Now your engine needs to be cooled, but at idle it's not getting the benefit of large amounts of cool air being passed through both the radiator fins as well as the condensor fins, hence your temp gauge going up at idle.
When an engine gets warmer the lubricating oil tends to thin out and with the extra heat from the forementioned sources, you will get a lower reading on your oil guage as well as the fact that the engine is idling at a lower rpm and that means the oil pump is moving slower also since it's mechanically driven by the camshaft via the distributor drive gear.
That's exactly why I asked if it had an idle kick up solenoid.. The ones I have seen are adjustable, and without a tach reading we can only assume or guess that the poster has exceptable idle in gear without the A/C in the on position. This just leads to the question "what changed"? Most likely it's not the solenoid, but if the compressor is aging and drawing a bit more power to operate, the only solution at hand would be to replace the unit or increase the idle solenoids actuation a bit to compensate.
 
Here is what I believe is going on. The Chrysler V2 compressor takes power/ rpm's from the engine. That power robbed from the engine brings down your rpm's from where it normally is. The idle solenoid is supposed to kick up the idle, preventing the engine from stalling with the compressor running.
With that said, remember that when the compressor is doing it job, it is taking warm air from your passenger cabin, super heating it through the compressor and venting through the condensor, which is in front of your radiator. Now your engine needs to be cooled, but at idle it's not getting the benefit of large amounts of cool air being passed through both the radiator fins as well as the condensor fins, hence your temp gauge going up at idle.
When an engine gets warmer the lubricating oil tends to thin out and with the extra heat from the forementioned sources, you will get a lower reading on your oil guage as well as the fact that the engine is idling at a lower rpm and that means the oil pump is moving slower also since it's mechanically driven by the camshaft via the distributor drive gear.

All of the above is true. These compressors were not the smoothest running to begin with. I remember my dads '73 318 wagon ran a little rough at idle with the A/C on, so did my '72 318 Dart. It's a question of how rough. It shouldn't have too much of a profound effect but it is noticable. If that's the case then I wouldn't let it bother me.

If the cooling system is up to snuff it should be able to handle the additional heat load. You may notice the gauge rise and drop a bit as the fan clutch kicks in and out but it shouldn't ever overheat.

All of this will obviously be more pronounced at idle (especially in gear) when the car's not moving and the rpm's are down. No real air flow across the radiator, additional heat load, additional engine load, slower coolant flow, it all stacks up.
 
what you feel is the revolution ( or cycling ) of the compressor, it is common on these cars to do this. When I bought my Magnum new in '78, this bugged me, dealer basically dismissed it as the "shaking' ( or cycling ) of the compressor at a certain RPM range.

Basically they stepped up the idle a tad. If you can find a late 70's Mopar with the Nippo compressor and fittings, swap it out and the problem's gone.
 
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