Sporadic Ignition Timing when the Engine's at Temp

[FreedomMachine]

I'm pretty new, I didn't know where to going to talk about this, but when my Eagle has been up to temp for a few mins my timing at idle starts to bounce around between 11 and 8 deg or just misses a cylinder.  Just to be clear while its running cold it the timing is perfect, it doesn't miss or bounce around more than a 1/2 deg max.  I've changed the cap, rotor, wires, condenser, and spark plugs.  I already bypassed the computer, which seem to help while the engine was cold.  It seems to me the ignition control module is over heating or going bad.  Are the ignition control modules in Eagles known for going bad?

Here's a link to my best attempt at a video of my timing.  The quality is poor but I thing you can get the gist of the problem from the video.

DO NOT watch if flashing lights irritate you.
http://www.youtube.com/watch?v=enJUT5BQDBE

[Prafeston]

I think mine is doing this too. When I was doing my timing I noticed the light didn't seem to be very consistent. I just chalked it up to the cheap timing light I purchased on eBay.

Could it be I was just missing on Cyl. #1 sometimes?

[FreedomMachine]

When I checked the timing when the engine was cold the light was right on, keeping perfect time and never missing.  when I hear the engine start to run poorly, I check the timing and it's bouncing around and missing.

here, i just went out checked my timing again with the engine cold and took a video of it.  You can see the notch is in just the right place when the light flashes. The dark periods in the video are just periods when the light was flashing between the frames of the video.

http://www.youtube.com/watch?v=iX5FmwNy6ZQ

I wasn't willing to let my Eagle warm-up tonight since that could take 20 mins and my neighbors are going to bed, but it doesn't seem like my instruments are to blame here.  What could cause this?

[Bird-o-Prey]

I would check all of your vac lines for leaks first.  It is the easiest step to start with as a vac leak will play havoc with smooth idle.  It could also be the EGR not working properly as that doesn't come in to play much untill your engine has warmed up.  It's a place to start.  Good luck!!

[carnuck]

Knock sensor messing with timing unless it's been de-computerized and bypassed.

[GRONK]

Looks like it could be several things.  Stock dist w/ comp controlled Carter?

I would check vacuum 1st, air fuel second, ensure everything is properly grounded.  Could also be leaking diaphram in EGR  or an improperly configured advance to dist.

Probably ignition or vacuum related though.

[FreedomMachine]

I'm using the original Carter and would like to keep it, but I have bypassed the computer.

Alright, I want to look it to the ERG to see if that is the problem. What are the symptoms?

I re-did all the vacuum line a few weeks ago, but I didn't check the EGR.  I just hooked a handheld vaccuum pump directly to the EGR line and it din't hold any vacuum.  Is that a positive check that the EGR is bad/leaking?

[GRONK]

If the EGR won't hold vac replace it or block it off temporarily.  This is probably your issue.

When the CTO opens up at temp it routes vacuum to the EGR.  If the EGR is leaking, you now have a vacuum leak that is not present when cold.

[FreedomMachine]

The engine started great while cold as usual but plugging the port didn't change anything after the engine was up to temp for a 10 minutes.   I checked from the carb to the EGR and the line was air tight.  I check all of the lines while the engine was hot so the CTO valve was open and I check that it was open.  Needless to say the ignition timing was still being erratic.  I also put it in drive with the parking brake on and it started knocking like crazy.

With EGR line plugged and the timing still acting up, could this be an ignition control problem?   I've heard of ICMs start to die because of high temperatures under the hood.

[rohnk]

You can get a can of freeze spray from Radio Shack or an electronics store. When the engine is at temp, spray the ICM with the freeze spray to cool it down. If that is you problem, this test may show it.

Also, I don't think the EGR is really needed anymore since the computer is bypassed. Not sure about that though.

Coud it also be the wrong vaccum line hooked up to the timing advance. Manifold instead of ported?

[GRONK]

If you did the ECM Test Bypass, the distributor should be ported vacuum vs manifold vacuum as it was factory.

[HappyPappy]

  Is it possible it could be the timming chain?

[ammachine390]

The EGR valves on these cars will NOT hold vacuum, even when they are working correctly if the engine is off or at idle. This is because they EGR valves on Eagle are the Positive Back Pressure type and will not hold vacuum until exhaust back pressure is high enough. While the EGR is not needed, there is really no reason to delete as it keeps combustion temps down, which can help prevent pinging, and can also increase the mpg a little, and keeps the air a little cleaner.

As for the timing, I was thinking ignition module as well. Also, is it possible the trigger wheel in the distributor could be really dirty with grease or have a broken tooth?

[GRONK]

I just went out and checked Tootie and she holds vacuum at EGR when not running at all.  Looks like a newer EGR installed.  I can see the diaphram move too when i apply vacuum.

[ammachine390]

I just went out and checked Tootie and she holds vacuum at EGR when not running at all.  Looks like a newer EGR installed.  I can see the diaphram move too when i apply vacuum.

That's interesting, they should not hold vacuum, except at higher rpms when the exhaust back pressure is high. That's how EGR operation was controlled, it should only turn on when there is ported vacuum, higher back-pressure, warmed up engine, that way it was more or less limited to only activating during cruising.

Maybe somebody changed it, and put a Negative Back Pressure type on, or yours is defective?

[GRONK]

Could be.  Curious though, how does the EGR dictate backpressure.  I understand the CTO and the ported vacuum.

[ammachine390]

Could be.  Curious though, how does the EGR dictate backpressure.  I understand the CTO and the ported vacuum.

Basically, the pintle is hollow and has a hole at the end of it, the exhaust pressure can travel up the hole, when the pressure is great enough, it overcomes a spring, and seals the vacuum chamber, so that vacuum can move the pintle and allow egr flow. Pretty interesting how it works.

It's explained here in the 1982 Jeep TSM, on page 74. I think the same exact thing is written in my 81 TSM, but I don't have it for reference. This is a big file and takes a while to open.
http://oljeep.com/gw/82_tsm/Part%201%20Section%20J.pdf

Here's another site that explains it and can open a lot faster.
http://www.tomco-inc.com/Tech_Tips/ttt26.pdf

[GRONK]

Interesting.  Never knew.

[FreedomMachine]

I added another ground to the ICM and there was no difference.  I replaced the ICM and there was no difference.  I check the ignition and pick-up coil both were nominal . The timing is bouncing around after the car warms-up. I can see the vacuum advance isn't doing anything strange. Could the SSI in the distributor be over heating? would that cause misfiring?

Has anyone else had this problem before?  

[ammachine390]

Maybe try taking the distributor cap off and make sure that the trigger wheel and pickup is still clean/ok. Also, there is 3 wire harness that goes into the base of the distributor, the black wire is a ground for the ignition system, which is connected inside the distributor to the engine for a ground. Its been known to corrode causing misfires, make sure its clean.