Better idle with vac advance removed

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Tiger38117
Posts: 1
Joined: Tue Oct 16, 2018 10:45 am

Better idle with vac advance removed

Post by Tiger38117 »

Hello all...new to the forum but long time Wag fan owning a few over the years. Having an odd problem with my latest one. This is a bit long but trying to give all the info.

1987, almost totally stock. Has an aluminum radiator w/ electric fan and an electric fuel pump. 111,000 miles. Until recently, she ran like a top. Smooth idle at about 650, smooth acceleration & cruise. Timing at 12. 21 inches steady on a vacuum gauge. 12 mpg. Drive it about 50 miles a day.

A few weeks ago, the water pump bearings started howling. That is a project I would normally do myself, but I had a lot of balls in the air at the time so I sent it to a shop so it would get done. Not long after that job, it started stumbling at idle, the kind of stumble that feels like the igntion was turned off for a split second. It was not rhythmic it was random. Eventually this deteriorated to the point that it would die at every stop, had to shift into neutral & give gas at a stop to get home.

Started nosing around looking for vacuum leaks or other problems. Rechecked the timing( it was fine), thats when I discovered that with the vac advance line disconnected & plugged, it ran smooth again. Vac advance on the dizzy holds vacuum and pulls advance like it should, so I dont think it’s a leak there.

Did some research and seemed like replacing the ignition module was a good idea based on my symptoms, so I did that (Rock Auto). This made the issue better...it wouldn’t die at a stop anymore, but still idled rough with vac adv attached, smooth without it. It drives “fine” with no advance, just with less throttle response & worse mileage as you would expect.

Still reading a steady 21nches on vac gauge with advance plugged, it will bounce around 20-21 when the advance is attached. I have checked all the vacuum hose routing, everything is attached to match the diagram under the hood.

Anyone have any suggestions or solutions from their own experience? Possible CTO issue? I have seen a diagram for “simplified” vacuum routing that eliminates the high temp CTO, considering trying that to see if it helps, anyone tried that?

Thanks!

letank
Posts: 4010
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: Better idle with vac advance removed

Post by letank »

welcome back...

a slight bounce is usually ignition related... recheck your spark plug wires to be fully plugged at spark and distributor as well as the coil wire, may be the engine is running on 7 cylinders

otherwise test the integrity of your vacuum advance, may the canister is leaking.

simplified vacuum, run on manifold vacuum
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)
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TeaBag
Posts: 147
Joined: Wed Oct 09, 2013 1:22 pm
Location: Chicago

Re: Better idle with vac advance removed

Post by TeaBag »

It seems like you have narrowed it down to a vacuum problem. When the advance is disconnected, the problem is resolved-right? So, stay on that path. It must be something in the Vacuum circuit. You can take the CTO out of the equation by running a vacuum line from the manifold to the Dizzy. Might use a new hose to make sure that's not the issue. If that doesn't work, check the Vac canister on the Dizzy for leaks.

440sixpack
Posts: 332
Joined: Sun Jul 31, 2016 6:31 am

Re: Better idle with vac advance removed

Post by 440sixpack »

1987 is after the smogger crap came about, so you should be running ported vacuum on your distributor if it's still stock.

Ported vacuum will not effect your idle at all.
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