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Old 01-08-2012, 08:39 PM
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Pont V8 105,000 Miles, Misses at Idle

Only misses at idle. Has all the speed of turtle anymore. Are these signs of a tired timing chain?

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Old 01-08-2012, 08:47 PM
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Could just need a fine tune of the idle mixture screws to eliminate the miss.
Easy way to check a bad timing chain. Pop cap off distributor and hand crank motor each way and see how much rotor moves. Shouldn't move much.
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Old 01-08-2012, 09:09 PM
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Quote:
Originally Posted by Nuck Chorris
Only misses at idle. Has all the speed of turtle anymore. Are these signs of a tired timing chain?
If it only misses at Idle it could be a low cylinder, ie:weak rings or a burnt valve.
perform a compression test , that will tell you.
It could be as simple as a vacuum leak, but I trust you allready looked it over under the hood.
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Old 01-11-2012, 03:34 PM
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did compression test.
___________
!
1 151 2 145
3 151 4 145
5 155 6 150
7 145 8 149

Looks outstanding to me.

The plugs had some gunk on them. The #3 stood out because it had a fair amount of oil around the outer edge and on the metal washer. 7 had some black chunks stuck to the outer part of the ground stem.

I took a video of the timing test. Here's a link:
http://www.youtube.com/watch?v=er9nI...ature=youtu.be
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Old 01-11-2012, 04:25 PM
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How bad is the miss. If it is consistent you can try pulling 1 plug wire at a time until you find the offending cylinder then trouble shoot from there. None of those plugs look real bad. You could have a bad wire or idle mixture or timing could be off a little. You didnt say what year it was so any further troubleshooting will require more information
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Old 01-11-2012, 05:17 PM
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X2. Timing chain test shows a bit of slop but not bad. What do you run for a distributor? Vacuum advance hooked up where?
Oh ya!! If you value your life get rid of that flex fan. Potential fan explosion there!!
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Old 01-11-2012, 05:37 PM
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Here's another Video of Vacuum gauge, Engine bay, and exhaust. It's about a 2 minute clip. I don't think the video is very successful at showing the miss and the jolting vibration it sends through the car. Let me know what you think.
http://www.youtube.com/watch?v=JUT1d...ature=youtu.be
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Old 01-11-2012, 05:47 PM
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I'm running what I think is the stock distributor. Obviously newer cap and rotor. I just replaced the Coil with a Crane PS20. Set my Dwell to 30 the other day. My initial timing is set to 12 Degrees. Stock setup was Vacuum advance connected to a ported advance controlled through a TVS switch on the front of the manifold. I changed it to a manifold Vacuum Advance.
So the idea is that I should pull one plug wire at time, and the one time it does not get worse I've pinpointed my problem?
Forgot to mention it's a 69 Firebird.
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Old 01-11-2012, 05:48 PM
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Looks like # 4 plug has some deposits on it. Also the tailpipe on that side looked like it was way richer than the drivers side, as evident by the amount of water coming out (which as a result of a cold started engine).
One side of the engine must be richer than the other.
The engine didnt seem to be jumping like a miss, maybe the balancer slipped and it is vibrating due to that.
I have also had 350 C transmission that the torque converter went bad and shook the whole car, nothing wrong with the motor.
just talkin here , what ev
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Old 01-11-2012, 06:45 PM
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Adjust the mixture screws first. Then try unplugging the vacuum advance to see what that does. Could be firing on the next cylinder with too much advance at idle. Also try getting more air in the carb. That small air cleaner inlet could be part of the problem. Flip the lid over maybe.
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Old 01-13-2012, 12:02 AM
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Quote:
Originally Posted by Nuck Chorris
I'm running what I think is the stock distributor. Obviously newer cap and rotor. I just replaced the Coil with a Crane PS20. Set my Dwell to 30 the other day. My initial timing is set to 12 Degrees. Stock setup was Vacuum advance connected to a ported advance controlled through a TVS switch on the front of the manifold. I changed it to a manifold Vacuum Advance.
So the idea is that I should pull one plug wire at time, and the one time it does not get worse I've pinpointed my problem?
Forgot to mention it's a 69 Firebird.
Pulling one plug wire at a time should indicate which cylinder has the problem, providing you have a steady miss at idle.
A couple of maybe very obvious questions...have you tried a new set of plugs?
Have you tested the high tension leads?
One minor thing you might check - although it shouldn't really cause a miss - see how much you can pull the rotor up and down in the distributor. If it has worn enough it can cause erratic firing. It can be fixed by adding shims between the distributor gear and housing. If you have the distributor out, it's very easy to see how much slop there is. Keeping this to a minimum helps to give consistent firing.
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