Dealing with the HAC & EBCV

[Chirpbark]

Since I live in a valley, I figure I might as well disable one or both of these... or should I?

Does the EBCV have a separate function of it's own, or are they interdependent? Hoping that disabling them could even cure the still rough idle, if not, at least it's less things that could go wrong.

How should I go about dealing with these, in a way where I could always hook them back up? This is what I'm looking at:

20140719_161559_544.jpg

Thx

[Petros]

the EBCV (the item on the left of the pic) is necessary for low speed operation, disable it goes full rich and you get really poor economy. the item on the right is the altitude compensator, it has no effect below about 4000 ft alt, disabling it will not affect driavlablity at low altitudes. but it is good if you ever go up in the mountains, it leans the mixture above 4000 ft, and advances the timing. This makes it more drivable and improves high altitudes economy. Check the FSM for some simple test to verify correct operation, not likely these are your problem, they are reliable and seldom cause issues, the car is designed to run with these items in place.

BEFORE you try and fix something, diagonse it first! It saves time and money. Pulling these things out (or anything else) will not liely fix it and will waste time, and more likely add new problems on top of your old ones.

Go study the trouble shooting guilde in the fuel system section of the service manual, and work down the list of system checks. they are not difficult and are much faster than trying to fix a problem by pulling things out that you do not know what they do.

If it runs rough you likely have a vac leak somewhere, these are not hard to find, there are many threads on this topic.

Good luck.

[Chirpbark]

Thanks, yeah I've pretty much narrowed the problem down to either a vac leak, fuel pump, bad ground, dizzy...

Dumb question: is the idle mixture screw the one closer to the radiator, parallel with the speed screw?

Could a broken HAC cause a lean idle, even @ low altitude? Could an EBCV as well? & can an off timing belt cause roughness only at idle?

[Petros]

a failed HAC would act like a vac leak. easy test, as is the EBCV, see the FSM. A timing belt off a tooth or two could cause a rough idle, but mostly it would run "normal" but get poor fuel economy. You have to pull the upper timing belt cover to verify it the belt is in the right place so you can check the timing marks on the upper sprocket.

Not very likely a marginal fuel pump would cause bad idle. If the pump was leaky and weak, it would cut out at high demand conditions (hard acceleration, long up hill grade).

check for vac leaks, get a copy of the vac routing diagram for your car and check all of the vac houses are routed properly and plugged in at both ends, look for cuts or cracks that would cause a vac leak. Use a can of carb cleaner spray with the engine idling and squirt it around the various vac operated equipment, the vac lines and the gaskets. when the engine speed changes when you spry it at one spot, that is likely the location of the leak. also, if one of the many vac diaphragms are damaged, they will act like a vac leak, those too are easy check. this is true with the vac advance on the distributor, if it is leaky just cap it off, it will run fine without it.

[irowiki]

Not very likely a marginal fuel pump would cause bad idle. If the pump was leaky and weak, it would cut out at high demand conditions (hard acceleration, long up hill grade).

This is exactly what my 83 is doing!

[Chirpbark]

After getting more acquainted with the car, its problem is that it really loses power at a stop, rumbles & dies, or wants to die. Although there is some vibration in park, it's way worse when braked in drive. Also noticed the AC gets way weaker when stopped or if the headlines are on. Alternator & battery are new & tested fine. It's a 100 amp alternator that most stores provide, though I noticed most the ones online or @ other stores are just 60 amp? Can a bad ground cause this exact problem too, or am I probably still looking at a vac leak?

[irowiki]

It might be as simple as your idle being too low. When the car is warmed up, what is the idle in park, and what is the idle in D with the brake applied?

There's also a vacuum device that increases the idle when the AC is on.

That seems way too large of an alternator.

[dlb]

when checking for vacuum leaks, don't forget to check every diaphragm. if one is ruptured, the hose going to it will just suck air right through and be a leak. just stick a clean vac hose on each diaphragm, suck, plug the end with your lip or tongue, and make sure it holds pressure. if it does not, the diaphragm is ruptured and should be replaced. until then, plug the hose that goes to it.

when testing the advance diaphragms at the bottom of the distributor, note that there are two ports on the upper diaphragm. one port has a smaller hole, that one goes to the HAC. to test this diaphragm, you must plug either port when you suck on the other, otherwise you will just suck air through the open port.

Dumb question: is the idle mixture screw the one closer to the radiator, parallel with the speed screw?

no, the idle mixture screw is located at the bottom of the passenger side of the carb. you can just get a screwdriver around the EGR to access it. however, this screw has a plug installed over it at the factory to prevent adjusting it. if the plug is still there, i would not mess with it since it should still be stock and fine. there is a procedure in the FSM on how to set the idle mixture but it's crappy and unclear.

the idle speed screw and fast idle screw are also found on the passenger side of the carb, closer to the firewall. the idle speed one looks like a normal screw and is lower down, the fast idle one is skinny and higher up.

after checking for vacuum leaks and ruptured diaphragms, try setting the idle, fast idle, and throttle positioner as per the FSM specs. it sounds like one or more may be a little out of adjustment. you should also check the AC idle kick-up diaphragm to make sure it is working and not ruptured. it's purpose is to increase the idle when the AC is on to compensate for the extra drag on the engine then.

let us know what you find.

[irowiki]

I also found that when in neutral with an auto, the idle needs to be slightly higher, because when in gear and the brake on, the engine gets dragged down by the transmission.

Also I've found that our old cars don't always like the factory idle setting, they're happier a little higher

[Petros]

ditto idle speed. try raising the idle a little bit, might solve the problem. if it is worse during cold idle, there is a separate adjustment for that, speed it up and see if the issue goes away.

[Chirpbark]

Thanks for the help guys. So far tightening the throttle position screw has made the most improvement, though it kinda feels like an artificial fix, as there's still vibrations & lean idling symptoms. I should mess more with the other screws as well. I think the mixture screw is plug-protected, there are two, stacked, port-looking ends, is the screw in the top one?

I've checked quite few hoses & diaphragms & no problems yet, so more to go.

[dlb]

the throttle positioner (on the front of the carb) only adjusts how long the throttle is held open after you let the gas pedal up. this is to reduce emissions. however, if the TP is set too tightly, it will actually increase the idle speed and not allow you to adjust the idle speed below a certain point when adjusting the actual idle speed screw. that's why i suggest starting with FSM specs. i personally like my TP adjusted quite a bit less than FSM states but it will give you a place to start and make sure the systems aren't fighting each other.

[irowiki]

How many miles on the car? Sometimes these old cars never quite run like they did from the factory. You may need to swap the carb. All three of my runners have required carb swaps.

[Chirpbark]

Only 156.8k, surprisingly

[irowiki]

I still wouldn't be surprised if the car wanted the idle set 100-300 higher to run smoothly!