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#2411391 - 11/30/17 03:06 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By RapidRobert
I'm thinking I would toss in a regular MP dist/ECU for a quick test to see if that makes it dissappear. Wouldn't be hard to do with some jumpers. I keep coming back to capping/plugging the vac can hose makes it much better. We've checked that the can/hose ain't leaking & we've added back in the timing the can was providing & we've corrected the rotor phaseing.


Well isn’t possible that a broken valve spring would work better with less timing?
Take away the 10-12 degrees fromvacuum advance and your making it easier on it,
Seems logical to me.
Idk though I’ll pull the valve cover tonight and have a look at it.

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#2411622 - 11/30/17 10:42 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
Dave Hall Offline
pro stock

Registered: 01/21/08
Posts: 1509
Loc: Cotati, CA
Just a couple thoughts. The pic of the two plugs. They look pretty normal to me. #8 could be a bit rich but definitely not fouled. It may be just the pic but the gap looks pretty wide on those. I had a problem like you describe and found out that my plug gap was too wide. .025 should be plenty.

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#2411687 - 12/01/17 06:46 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
360view Offline
master

Registered: 01/18/06
Posts: 4226
Loc: USA
Did you re route the ignition wires exactly like the TSB shows?

Have you replaced #8 ignition wire and spark plug with "known good" substitutes?

Like i wrote in your previous post
looking at all 8 spark traces on an old Sun machine display
could eliminate doubts about ignition.
Those old Sun machines could also do a "cylinder power balance" test at 2500 rpm.

Looking at the valve springs, rocker arms and hyd lifter bleed downs is quite reasonable, as Magnums have been known to have problems in all 3.
A video boroscope makes this inspection quicker and easier but removing valve covers is also worth the time and gasket costs. Looking inside all 8 cylinders with the video boroscope through the spark plug hole is worthwhile. Are there deposits on intake valve stems?

Having down the static compression test on #8 is good. Your 155 is typical.
A "running compression test" also called a dynamic compression test
would also be instructive in spoting a bad valve spring or lifter,
and could even give a hint about intake manifold runner air distribution variation cylinder to cylinder.

Have all the previous worries about the Carb set ups been eliminated?

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#2412829 - 12/03/17 06:45 PM Re: Back with rough spot around 2500 rpm [Re: 360view]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By 360view
Did you re route the ignition wires exactly like the TSB shows?

Have you replaced #8 ignition wire and spark plug with "known good" substitutes?

Like i wrote in your previous post
looking at all 8 spark traces on an old Sun machine display
could eliminate doubts about ignition.
Those old Sun machines could also do a "cylinder power balance" test at 2500 rpm.

Looking at the valve springs, rocker arms and hyd lifter bleed downs is quite reasonable, as Magnums have been known to have problems in all 3.
A video boroscope makes this inspection quicker and easier but removing valve covers is also worth the time and gasket costs. Looking inside all 8 cylinders with the video boroscope through the spark plug hole is worthwhile. Are there deposits on intake valve stems?

Having down the static compression test on #8 is good. Your 155 is typical.
A "running compression test" also called a dynamic compression test
would also be instructive in spoting a bad valve spring or lifter,
and could even give a hint about intake manifold runner air distribution variation cylinder to cylinder.

Have all the previous worries about the Carb set ups been eliminated?







I removed the valve cover this afternoon and took a close look at both valve springs on cylinder 8 and I’m not seeing anything out of the ordinary compared to the rest of the springs.
I have a leak down tester that I have barrowed from a friend but I haven’t had time to perform the test.
I was told cylinder 8s valves need to be closed while performing the leak down test.
How do I determine when the valves are closed on that cylinder?
The plug gaps are set at .40 cause I am running a crane cams hi-6 cd ignition and a crane cans ps92 e-core coil.
I did another compression test on cylinder 8 while the engine is cold and it revealed 147-148 psi this time.
Is it normal for it to drop a few psi when it’s cold?
I haven’t ran the truck in a few days cause I’ve just been so frustrated with whatever the hell is going on with it.
So you reccomend I call a few shops and find out who has the equiptment to monitor ignition while it’s running and have them bring the throttle to 2500 where the rough spot starts and go from there?
Cause I’m throwing in the towel I have no idea what’s causing this issue.
Number 8s plug looking darker then the rest has me thinking it’s all connected some how.
One thing I can do is turn my chokes fast idle down a little bit more; throw a new plug in cylinder 8 and see what happens.
All plugs are brand new and my plug wires are also brand new.
Coil is brand new, distributor is brand new, timing has been verified with two different lights.
Timing mark on balancer has been verified with piston stop.
This is just strange and I have no idea why this rough spot is a lot more prominent when vacuum advance is connected.
With no vacuum advance it’s much better.

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#2412836 - 12/03/17 07:06 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
Dave Hall Offline
pro stock

Registered: 01/21/08
Posts: 1509
Loc: Cotati, CA
Just try a tighter gap. .040 to .025 isn't going to hurt anything. With high output ignitions the gap will only get wider over time. Start a little tighter.

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#2412845 - 12/03/17 07:28 PM Re: Back with rough spot around 2500 rpm [Re: Dave Hall]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By Dave Hall
Just try a tighter gap. .040 to .025 isn't going to hurt anything. With high output ignitions the gap will only get wider over time. Start a little tighter.


I’m running all 8 plugs at .040.
The cd ignition should have no problem firing that.
Most company’s reccoemnd .045 to .060 with cd ignition boxes and coils.
I’m turning the choke down a little bit and turning the fast idle down a little bit as well and I’m going to try and route number 6 and number 8 plug wires as far away from each other as possible.
I just don’t know how I’m going to accomplish that cause I only have the plug wire looms that bolt to the valve covers.
I know plug wire 6 and plug wire 8 cross each other but where the do cross is up near the distributor cap.

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#2412858 - 12/03/17 08:13 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33030
Loc: Lincoln Nebraska
.040" ain't an issue nor is 6/8 crossing each other (& crossing at a good angle as opposed to running parallel for a good length is the best). the problem is elsewhere.
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#2412886 - 12/03/17 09:16 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By RapidRobert
.040" ain't an issue nor is 6/8 crossing each other (& crossing at a good angle as opposed to running parallel for a good length is the best). the problem is elsewhere.


Well tonight I turned down the electric choke a little bit and turned down the fast idle a little bit and installed a brand new plug in cylinder 8.
I’ll drive it to work tomorrow and check the plug when I get home from work tomorrow night and see if that made a difference.
Cause every morning when I fire it up it is running off the choke and fast idle, its possible the choke being a little on the rich side and the fast idle being a little too high was causing the rich condition on cylinder 8’s plug.
And maybe the rough spot around 2500 is still rotor phasing or maybe it’s just my crane ignition box.
I’m going to call around to a few shops tomorrow and hopefully find someone with a sun machine or a spark analyzer that can hook up to my ignition and bring the Rpm up to 2500 and watch the ignition to get a better idea of what’s going on.

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#2413029 - 12/04/17 10:03 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
moparx Offline
master

Registered: 09/03/03
Posts: 8142
Loc: north of coder
what is the timing at 2500 ? i know you have initial at 18, and the total at 32, but what is it at 2500 ? [with and without the vacuum advance hooked up]
beer

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#2413041 - 12/04/17 10:29 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
krautrock Offline
pro stock

Registered: 01/27/03
Posts: 1551
Loc: central texas
you never said if you did anything to the carb. did you jet it down to clean the plugs up?

is it possible the carb is rich at idle and transition and lean once it gets on the mains (your jetting)?

the color difference on the two plugs you showed doesn't seem that drastic to me given you have a dual plane manifold.

if it were me i would jet the carb up 4 steps, let it get wamr, then set idle speed and adjust idle mix to the highest vacuum reading, then go see if it's still missing.
it's a simple thing to check.

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#2413155 - 12/04/17 02:27 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Well like I said I turned down the choke a little bit on the carb and turned down the fast idle a little bit and installed a brand new plug on cylinder 8.
Started it this morning and let it run on the choke and fast idle for about 10 minutes this morning when I first started it.
Left for work and to my surprise it felt a lot better at 2500 rpm in 2nd gear cruising down the road at 35-37 mph.
It wasn’t shaking nearly as bad and felt smoother.
I’m starting to think I just simply had the fast idle on the choke turned up a little too high and the choke was maybe opening a little too slow.
I do know that with this quickfuel carb when I first got it I was fouling plugs like crazy, like 3 or 4 plugs would be completely black and I realized the fast idle being too high was the cause of it cause with the engine idling on fast idle at night I could see the herders turning red and I called quickfuel about the issue and the guy said the engine was loading up with too much fuel on fast idle and to turn the fast idle and the choke down a little bit.
So I did that and I thought it was good but I’m thinking I didn’t have it turned down enough and it was still affecting cylinder 8’s plug.
Time will tell I guess I will run it a couple days like this and check number 8s plug after a few days of running it like I normally do.

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#2413981 - 12/05/17 09:46 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Well turning down the fast idle on the choke circuit as well as turning down the choke it’s self has seemed to help a lot here.
One thing I didn’t consider until tonight is should I try running a 1 step hitter plug?
Right now I’m running the factory rated heat range, but I am carbureted and I am also 3500 feet above sea level.
I’m wondering if maybe the combination of higher elevation and running a carburetor might call for a hotter plug?
It’s possoble right? I mean these engines were speced with the plug heat range with efi and sea level in mind.
Not 3500 feet above sea level and a carburetor.

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#2417540 - 12/12/17 04:40 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Issue is back and seems to be getting worse with the cold weather....
Now I’m back to thinking it’s an issue on cylinder 8 specifically.
Quick re-fresh, I have an awful miss around 2500-3000rpm it starts around 2000 rpm and feels like a slight surge then around 2500 it starts getting shakey and feeling rough.
Compression test on cylinder 8 revealed 155psi.
I removed the valve cover and couldn’t see anything odd with the valve springs on cylinder 8 but I’m convinced it’s an issue on cylinder 8.
Is there a way to diagnose a valve spring issue on a specific cylinder?

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#2417549 - 12/12/17 05:14 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
krautrock Offline
pro stock

Registered: 01/27/03
Posts: 1551
Loc: central texas
can you jet it up (richer) 4 or 6 sizes and see if it gets any better?


Edited by krautrock (12/12/17 05:14 PM)

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#2417600 - 12/12/17 06:36 PM Re: Back with rough spot around 2500 rpm [Re: krautrock]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By krautrock
can you jet it up (richer) 4 or 6 sizes and see if it gets any better?


I’ve already increased the idle feed restrictors up 3 sizes, I’ve increased the main jet 1 size, and I’ve decreased idle air bleeds 5 sizes.
There is no way this thing is lean.
I even took the carburetornoff thenither day tire it all down and cleaned it very well used 3 cans of carb cleaner and blew out every orfice in the carb main body and the metering blocks and put it back together with new gaskets.
I have a strong feeling it’s strictly cylinder 8 that’s the issue.
Another reason I believe this is cause of all the things I’ve read online with people having issues with cylinder 8 in particular.
But the compression test on cylinder 8 checks out.
So I’m kind of stuck not knowing what to do next to pin point what the issue is.
Tonight I’m going to hook my timing light up to number 8’s plug wire and bring it up to 2500 where it gets rough and see if the flash from the timing light is erratic.

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#2417643 - 12/12/17 07:54 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
So tonight I hooked up the timing light to cylinder 8s plug wire and brought the rpm up to 2500 rpm and sure enough you can see the break in the light from the missfire on cylinder 8.
So there is definitely something going on with cylinder 8.
I’m going to go around all the other 7 plug wires and do the same thing just to make sure there isn’t a miss fire on any of the other cylinders but I’ll bet money it’s just cylinder 8 cause like I said every time I pull the plug from cylinder 8 it also looks semi fouled with fuel and looks like it’s struggling to fire compared to the other 7 plugs.
So what are your guesses? Compression test reveals 155 on all cylinders including cylinder 8.
I’m back to suspecting a broken or weak valve spring again.

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#2417664 - 12/12/17 08:18 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33030
Loc: Lincoln Nebraska
Quote:
So what are your guesses?
I wondering if the oil rings are fubared on #8. A quick visual would confirm the spring ain't broken & did we check the seal? I was thinking we did. but if #8 blinks differently than the rest of em, plug wire or check the underside of the cap, the # 8 brass terminal. didn't we replace the plug wires?
_________________________
live every 24 hour block of time like it's your last day on earth

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#2417667 - 12/12/17 08:24 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
Originally Posted By RapidRobert
Quote:
So what are your guesses?
I wondering if the oil rings are fubared on #8. A quick visual would confirm the spring ain't broken & did we check the seal? I was thinking we did. but if #8 blinks differently than the rest of em, plug wire or check the underside of the cap, the # 8 brass terminal. didn't we replace the plug wires?


Yep brand new plug wires, brand new plugs, brand new cap and rotor.
And number 8’s plug is never oil fouled it’s always fuel and it even smells like fuel.
I’m seriously thinking valve spring.
Something is letting more fuel into cylinder 8 which is causing the plug to semi fuel foul.

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#2417668 - 12/12/17 08:28 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 648
Loc: montana
It’s ether the valve springs or a valve it’s self but if it was a valve wouldn’t that be showing something on the compression test?

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#2417673 - 12/12/17 08:34 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33030
Loc: Lincoln Nebraska
I would think, but the compression rings could be adequate & the oil rings can still be bad. First we gotta resolve the blinking light potential.
_________________________
live every 24 hour block of time like it's your last day on earth

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