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  #1  
Old 07-19-2014, 08:15 PM
davidmij davidmij is offline
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Default motor is missing at low RPMs

I was testing my car out and missed a powershift from 2nd to 3rd. It revved to about 6K, but that shouldn't be a problem in and of itself. Anyway, I drove a couple of more miles back to town and when I came to a stop I noticed the motor was missing a little. I don't know if this is related to the rev, but thought I should mention it.

If I drive it at low RPMs it misses, but if I get it up to wide open throttle it runs fine.

I pulled a plug (#8) and noticed it was blackish. I decided to go through all the plugs one at a time to see if a fouled plug was the problem, it wasn't. I noticed that plugs from cylinders 4, 8, and 1 were blackish, I think the others were OK color wise. Another thing I notice is that the primary side of my Edelbrock 1407 is a little black too. Is this an indication that I have my idle set too rich?

Next I tried all the plug wires, but no help.

I decided to listen to each side of my exhaust, they are independent sides with cheap little 18 inch glass packs. I couldn't really tell anything sound wise, but when I put my hand over the exhaust I noticed the drivers side felt noticeably cooler than the passenger side. I have no idea if this means anything, it's just a rookies observation.

Any advice on what to look at next? Or even a troubleshooting flow chart type process?

regards, Dave J
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  #2  
Old 07-19-2014, 10:30 PM
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simplyconnected simplyconnected is offline
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Dave, armchair troubleshooting isn't going to be of much help on this one. Pull your valve covers off and look.

We can play, 'you could have' all day but the real answer is a mechanical failure. You are right, 6,000 rpm's is not a biggie IF you were developing HP. Sounds to me like you were not.

Idle speed tells us a lot more than high rpms. A black spark plug may point to the cylinder that is at fault, but keep troubleshooting. There is more to this story. Take videos and let us know what you see when running the engine with the valve covers off.

BTW, now you know why I run with an automatic trans. It has never missed a shift and it never stops developing HP through all the gears. - Dave
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Old 07-20-2014, 12:07 AM
davidmij davidmij is offline
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Thanks Dave, so if I pull the valve covers I can run the motor and video at the same time? I would have thought that it might make a mess? My lack of knowledge coming to the front once again.
I did take pix of the plugs, here they are.

Is the slight blackish primary's an indication of anything? I was thinking carburetion because of the miss at low RPM's and then it's OK when I get to "all in".

I missed the shift from 2nd to 3rd at about 5200, it shot up to 6000. It pulls really well all the way from 2500 - 5500 rpm.
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File Type: jpg P1030364(1).JPG (119.5 KB, 65 views)
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  #4  
Old 07-20-2014, 01:31 AM
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Quote:
Originally Posted by davidmij View Post
I was testing my car out and missed a powershift from 2nd to 3rd. It revved to about 6K... ...when I came to a stop I noticed the motor was missing a little...
Things normally break at high rpms but rarely at low rpms.

You can take the valve cover off the side you suspect is bad and run the engine. The idea of taking a video is so you can watch it many times because you will not notice everything the first time.

Pay attention to the rocker arms:
Are any broken? (Yes, I have seen a broken rocker arm.)
Do all of them go all the way up and down, or is there one that is 'lazy'? The pushrod side should travel ~1/2" but the valve side should travel ~3/4"
How do the lifters sound?
Do you see oil coming out of each one?
Are all the pushrods straight when you spin them?

I do this test with the engine off and the rocker shaft loose or removed: Next, take a rubber mallet and hit the valve stems. The intakes should all sound the same and the exhausts should all sound the same. If one doesn't return or if it is hard, (you can tell the difference) then the valve and guide need work. This can happen if you floated your valves, one hung open and the piston closed it (causing a bent valve stem and/or broken guide).

Another check is to blow air into the cylinder: Gut an old spark plug and weld a male air hose fitting in the base. Screw it into the spark plug hole and rotate the engine so both valves are closed. Turn on the air and listen. If hissing sounds come from the carb you have an intake valve problem. If sounds come from the exhaust, the exhaust valve is bad. If sounds come from the bottom of the engine (through those oil return holes in the heads), your rings are blowing by.

A simple compression check will tell you which cylinder is bad but it won't tell you 'why'. - Dave
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Old 07-20-2014, 09:50 AM
davidmij davidmij is offline
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Thx Dave.
I'll try these things when I get some time. I'm tied up today on other "must do" chores. I may take a day off work and do it.

I'll also resize my pictures of the plugs that didn't post and try to post them.
Only one of the plugs was actually a little shiny so I'll start on that bank.

thx again, Dave J
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  #6  
Old 07-20-2014, 10:40 AM
Joe Johnston Joe Johnston is offline
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Quote:
Are all the pushrods straight when you spin them?
This is the first thing I would check
(Been there and done that over revving thing more than once!!)
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Old 08-03-2014, 01:36 AM
davidmij davidmij is offline
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Finally got a chance to do some troubleshooting today. I ran the engine and pulled the plug wires one at a time on the drivers side. When I removed 5,6,or 7 the motor got worse. When I pulled number it stayed the same, thus it appears that number 8 is the problem.
I tried a new plug (again) and it didn't help. I checked the spark coming out of the plug cap by holding it close to the head and it arched, thus showing that I have spark.

Next I pulled the valve cover and checked it out, everything looks good to me. I ran the engine and oil is flowing as I think it should. The number 8 very end valve has a very very slight ticking sound. I could hear it faintly with a stethoscope.

One at a time I made sure the valves were seated, then tapped them with a rubber mallet. Each one sounds the same and snaps right back.

I posted 2 videos at this link. (The first video is an old one with the old motor) In video 3 it was running with the choke on at first - at 50 seconds in I turned off the choke and it was idling. I don't see anything, but I'm not very good with the camera. I guess next I'll need to find some one with a welder and try to rig up the spark plug test.
Any thoughts at this point?

thx, Dave J

https://plus.google.com/photos/10149...P-5_a-_v-Pf7gE
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  #8  
Old 08-03-2014, 05:06 AM
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Quote:
Originally Posted by davidmij View Post
...I posted 2 videos at this link...
What you have is good, but I need to see more.

Pull back with your camera so I can see your distributor and the wires. I want to see 1-5-4-2-6-3-7-8 (both banks).

GO S-L-O-W with the camera AND your engine speed. If you need to move around, do it slow and don't get too close. If you stop, count to four before moving the camera again. I can tell more from a little farther back than I can looking at two valve springs. I see your pushrods rotating but you went too fast to see the middle ones. High rpm's make the video a blur.

The engine doesn't sound as healthy as it should. I definitely hear a miss in your exhaust but I cannot tell which side it is coming from. You narrowed it down to #8. That may be true but you may have other issues as well.

Get a propane torch and turn it on but don't light it. Wave the nozzle around #8 intake manifold/head separation. If there is a leak, your rpms will increase. BTW, if compression is good on #8, I'm not convinced your spark is right or your vacuum is not leaking. A simple vacuum leak will make your engine run bad because the air/fuel ratio will be different at each cylinder. The propane torch will find a vacuum leak very fast.

So, start a good distance above the distributor and pan slowly down the wires to each bank. Keep your rpms low and let's see all the valves from the front to the back of each bank.

Cell phones are ok for slow video. Camcorders run at 30 frames per second (FPS), much faster than cell phones (15-24 FPS). Again, move slowly to get the best video. - Dave
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Old 08-03-2014, 10:20 AM
davidmij davidmij is offline
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Will do Dave, thanks.
I forgot about vacuum leaks. I have noticed a couple of times while driving it that the power brakes feel off every once in a while. I don't have the back up air canister in the car so low vacuum could be a real possibility.

I'll try to get to it soon. Right now it's early here and I don't want to annoy the neighbors with a loud car at 7am.

thx, Dave J
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Old 08-03-2014, 02:12 PM
davidmij davidmij is offline
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I don't know if these are much better Dave, I think some people are just better with video than others.
It's weird, but it seems like it's running somewhat better now. I had pulled the brake booster line for pictures and forgot to plug it back in when I stated the car. When I noticed it, I plugged it back in.
Back when it first started missing I had to turn up the idle about 2/3's of a turn to keep it running around 650 rpms at idle. Now this morning, after unplugging and plugging back in the brake booster line, it idles at 900 rpm. So I turned the idle back down to about 680 rpm for this video of both banks. There is a definite clicking from the passengers side, but I can't tell where or which lifter it's coming from. I watched all 16 lifters and they are turning nice and true.
https://plus.google.com/photos/10149...P-5_a-_v-Pf7gE

I'm using my camera that has built in HD video. The trouble is Panasonic uses their own weird video format. So I have to convert it to MPEG - when it converts it it loses quality.

thx, DAve J
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