Failed Smog, again. High HC at Idle. - Page 6 - JeepForum.com

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post #76 of 118 Old 09-02-2012, 04:09 PM Thread Starter
Michaelgoesrawr
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I finally got around to doing a compression test and although the numbers are a little low, they are close enough together that it leads me to believe compression is fine.

D/W
1. 133/136
2. 130/133
3. 133/135
4. 125/128
5. 125/129
6. 125/130

I'm not sure if the motor was bored when it was rebuilt, but I think it was. So my logic says that those numbers are okay because it's a bigger cylinder. I didn't have any coolant in my oil the last time I checked it so I'm pretty sure the head gasket is alright. And my compression numbers, at least to me, means that there is no dead cylinder and that the ignition is cause for my miss. It has a new coil, cap, rotor, plugs and wires. It missed before the tune up so I'm thinking it's the ICM that Old4x4 pointed out earlier. It fires the injectors fine but since it's a two type system maybe it could be that. I'm hesitant to get a new one though because a duralast replacement is $46 bucks and if I don't need to spend it I don't want to. Haha. So with that information, anyone have any more ideas?


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post #77 of 118 Old 09-02-2012, 05:22 PM
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Well, I agree that those compression numbers are fine. Nothing to worry about there.

Can you post a video of the motor idling and missing?
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post #78 of 118 Old 09-02-2012, 05:27 PM Thread Starter
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Quote:
Originally Posted by plym49
Well, I agree that those compression numbers are fine. Nothing to worry about there.

Can you post a video of the motor idling and missing?
It's hard to hear in a video but there is a distinct pop. I'll do my best to get it.

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post #79 of 118 Old 09-03-2012, 03:31 PM Thread Starter
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Got the videos done today. Much easier to hear on the computer.

This is the exhaust at 1000-1500 rpm

This is the exhaust at idle

This is in the engine bay with varying rpm. I have no idea what that whistle is because you can't hear it in real life, just the video.

Hopefully this helps narrow it down so I can finally drive this thing again.

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post #80 of 118 Old 09-03-2012, 04:09 PM
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I am not sure what you are hearing as a miss.

The best might be a shot taken rock-steady of the engine at idle. No racing the motor and try to keep the camera still so we can see any shaking. I would also like to see angles from the distributor side.
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post #81 of 118 Old 09-03-2012, 04:17 PM Thread Starter
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I think me saying there is a miss is because I hear that pop sound and it makes me think there is a miss. I will get that video soon. I'll use the tripod this time.

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post #82 of 118 Old 09-03-2012, 04:49 PM Thread Starter
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Here you go.

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post #83 of 118 Old 09-03-2012, 07:31 PM
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It does seem to hunt a little at idle, but I do not see or hear any sign of a miss. Whatever you hear from the tailpipe can be caused by any other factors downstream of the engine.

BTW those stock air cleaners are notorious for rusting on the inside. They get hot, they cool down and condensation forms on the inner surfaces. It eventually rusts and if the pieces of rust get into the carb then your BBD plugs up and gets itself a bad reputation on account of an idiosyncrasy of the air cleaner design.
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post #84 of 118 Old 09-03-2012, 08:27 PM Thread Starter
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Quote:
Originally Posted by plym49
It does seem to hunt a little at idle, but I do not see or hear any sign of a miss. Whatever you hear from the tailpipe can be caused by any other factors downstream of the engine.

BTW those stock air cleaners are notorious for rusting on the inside. They get hot, they cool down and condensation forms on the inner surfaces. It eventually rusts and if the pieces of rust get into the carb then your BBD plugs up and gets itself a bad reputation on account of an idiosyncrasy of the air cleaner design.
That makes sense. I'll be sure to give it a scrub and paint it although I don't have the carb anymore. Is there a reason it hunts like it does and can I fix it? Lol.

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post #85 of 118 Old 09-04-2012, 04:05 PM
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Originally Posted by Michaelgoesrawr View Post
That makes sense. I'll be sure to give it a scrub and paint it although I don't have the carb anymore. Is there a reason it hunts like it does and can I fix it? Lol.
In general, many things can cause the idle to hunt. Some engines just do, notably earlier designs.

Aside form that, if you are in closed loop, it means that the ECU is making fine adjustments based on what it thinks is happening. Engine slowing down a few rpm? Make it faster. Oops, now to fast? Make is slower. Repeat constantly and there is the hunt.

If there is a lag in reading, if there is a lag in adjusting, if there is not a fine enough correction, then the hunting gets worse. Remember the old days of speed controls? (Probably not. ) You would set a speed, say 65, and the vehicle would hunt between 64 and 66. Totally annoying, they were.

So it is hard to say what you can do about it. maybe nothing. Maybe just throw a lot of parts at it. But the hunting by itslef should not cause you to fail smog, unless it is running crazy rich for that split second before it goes uber-lean.

It also seemed like your idle was set kind of high. Try backing it down to the lowest speed at which the motor still runs smoothly. That can help hunting on a carburated engine where the carb is operating at the transition of the loww-speed and mid-range circuits, not deciding where to be.
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post #86 of 118 Old 09-04-2012, 04:36 PM Thread Starter
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Makes sense. I'm trying to avoid throwing parts at it because that can get expensive quickly and I'd like to have money for gas lol.

It idles around 1200 when it first kicks on and then after a 20-30 seconds it'll drop to 7-800. I was under the impression that the lower the idle the worse the hc would be. Maybe the tune up solved my problem. I'll see if I get get a pre test in down and see what happens.

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post #87 of 118 Old 09-04-2012, 07:55 PM
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Quote:
Originally Posted by Michaelgoesrawr View Post
Makes sense. I'm trying to avoid throwing parts at it because that can get expensive quickly and I'd like to have money for gas lol.

It idles around 1200 when it first kicks on and then after a 20-30 seconds it'll drop to 7-800. I was under the impression that the lower the idle the worse the hc would be. Maybe the tune up solved my problem. I'll see if I get get a pre test in down and see what happens.
1200 on a cold is super high, especially in nice warm California. 7 to 800 is on the high side, too.

If it were my Jeep, I would be shooting for less than 1000 cold and 600-650 hot.

Running faster won't make it run leaner, it has no effect or could work against you. That might be your roll right there. The lower a carb engine runs, the more you are running on the odle circuit - and you have some control over the odle mixture.

Also, never asked this, what thermostat are you running? 180 minimum and ideally a 190 would be good.
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post #88 of 118 Old 09-04-2012, 11:41 PM Thread Starter
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I can bring it lower, but from my understanding per the smog results is that the slower the engine runs the more unburnt fuel there is. Evident by the pass at the 2500 rpm test.

Its hard to set because when I bring down the idle(impossible to regulate the fuel/air mix) it'll come down to 600 but then when I stop the change idle process per Howell it's more at 7+

I think it's a 180 but I have a 195 from my old motor that I can put in. It doesn't run as hot as the other motor which is why I believe it's 180.

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post #89 of 118 Old 09-05-2012, 03:45 PM
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Quote:
Originally Posted by Michaelgoesrawr View Post
I can bring it lower, but from my understanding per the smog results is that the slower the engine runs the more unburnt fuel there is. Evident by the pass at the 2500 rpm test.

Its hard to set because when I bring down the idle(impossible to regulate the fuel/air mix) it'll come down to 600 but then when I stop the change idle process per Howell it's more at 7+

I think it's a 180 but I have a 195 from my old motor that I can put in. It doesn't run as hot as the other motor which is why I believe it's 180.
If you are really in closed loop, there isn't any unburnt gas, unless something is wrong which gets us right back to where we started. All I can say is that the roll is probbaly due to the somewhat high idle speed.

The warmer thermostat will help, so definitely put that in. 195 is perfect.

Is your EGR working? That can cause flaky operation.
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post #90 of 118 Old 09-05-2012, 05:47 PM Thread Starter
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Yeah. The 195 isn't even a year old. Put it in last Christmas. The one in there works though. Just never seems to get up to that center line.

I have no idea if it's working or not. How would you test that? I also have the one from my old motor so if one doesn't I'm sure the other will work.

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