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Idle and timing issues

Thought I would check my ignition timing on the 1990 256 YJ. Checking at

700 rpm showed only about 3 degrees advanced. I advanced it to 9 degrees. I had to back the idle screw almost all the way out to get it back to 700 rpm. The strange thing is that now after letting off the gas, the idle is very rough and about 300-400 rpm higher. After a varying amount of time 5 to 20 seconds, the idle drops to about 700 and smooths out. When the idle smooths out and drops to where it should be, there is a click somewhere on top of the engine. My guess is that it is a solenoid. Anyone know what the computer might be doing after coming back from high rpm to curb idle. It doesn't seem to be the sol-vac that is doing it.

The good news is that the Jeep is way more responsive and has never run better. If I could just get rid of the rough faster idle period I would be a happy camper.

I have checked several times for a vacuum leak and so far no luck.

Also I am somewhat confused about the procedure for timing adjustment in my Haynes book It says to disconnect the electrical connector from the CEC sys switch located on top of the valve cover. What is this? It also says to increase the idle speed to 1600 rpm and the the timing mark should appear stationary. Does this mean that there should be no advance between spec idle at 700 rpm and 1600 rpm? It seems there was some advance on mine as you went to 1700 rpm, which I attributed to the a centrifugal advance. When I checked and reset the timing, I only disconnected the vac advance, but not the CEC system switch since I could not find out what that was.

Guess I am missing something here.

Aloha from Maui Joe

Reply to
Joe and Joann
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The book way is for the computer run carb 258 engine. At 1600 rpm, your mechanical timing is full advance and then the computer takes over. I believe the distributor vacuum line should be off and plugged too.

My guess is that click you hear shutting off the vacuum leak (high idle) is the defective PCV/canister solenoid that sits just behind the carb. These never did work, so the fix is to pull it and just put a plain T fitting in it's place.

My CJ7 with no computer messing up the works runs best at about 7-9 deg advance at 700 rpm with a ported vacuum signal. But, when I killed the computer, my timing had to be advanced by about 10 degrees to run manually.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Joe and Joann wrote:

Reply to
Mike Romain

Thanks Mike, but I am still confused about the 1600 rpm. With the vacuum advance disconnected and plugged, is there a mechanical advance that happens between 700 and 1600. In any event, assuming I disconnect and plug the vacuum advance, do I set 9 degrees BTDC at 700 or 1600 rpm?

Mike Roma> The book way is for the computer run carb 258 engine. At 1600 rpm, your

snip

Reply to
Joe and Joann

The distributor has a mechanical advance on springs and weights that maxes out at just under 1600 rpm from what I understand, then the computer takes over so the base timing is way down. No computer and set the timing at idle at 7-9 deg with vacuum off, whichever sounds smoothest, otherwise go by the hood sticker or book at 1600. You can play there by a degree or two to to get the smoothest idle.

You are supposed to oil the felt pad in the center of the distributor under the rotor every time you change the cap and rotor. If you open it up and grab the rotor, it will turn under a spring load or it needs cleaning and oiling if it's grabby.

Mike

Joe and Joann wrote:

Reply to
Mike Romain

Ignition timing is 9 degrees BTDC @ 1600 RPM, with distributor vacuum hose disconnected and plugged and vacuum switch assy on firewall electrically disconnected.

If you set it to 9 degrees at 700 RPM, it's way too advanced.

The click you hear is probably the PCV shutoff solenoid when the ECU goes into idle mode and energizes it.

Reply to
bllsht

Reply to
tim bur

Reply to
L.W.( ßill ) Hughes III

On a 258?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"L.W.(ßill) Hughes III" wrote:

Reply to
Mike Romain

Reply to
L.W.( ßill ) Hughes III

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