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#2410271 - 11/28/17 04:57 PM Back with rough spot around 2500 rpm
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Well I’m back with the same issue that has had me pulling my hair out for months now.
Everything I do seems to make it a little bit better but nothing I have done has completely eliminated the issue.
I didn’t want to create another post but I’m just lost and have no idea what’s causing it.
It’s a 300hp crate 360 Magnum, roughly 25-30k miles on engine.
Dualnplane M1 4bbl intake manifold.
Quick fuel super street series 680cfm vacuum secondary carb.
Firecore electronic vacuum advance distributor.
Crane cams hi-6 cd ignition with crane cams Ps92 e-core style coil.
Taylor thundervolt 8.2mm plug wires.
Ngk bkr5e spark plugs brand new indexed and gapped at .40.
Timing is 18 initial 32 total all in by 3400-3500 rpm.
Vacuum advance on manifold vacuum to add 12 degrees timing at idle for a total of 30 degrees at idle.
Issue is I have a rough spot around 2500 rpm and I have not been able to determine the cause.
First I though it was bad plugs and wires, so I replaced them, it helped a little bit didn’t eliminate it, next I tried a new coil, I did have a crane lx91 coil I bought a brand new crane ps92 coil didn’t notice a difference.
Then I thought it was rotor phasing, I’ve verified rotor phasing is correct on my current firecore distributor.
I have verified the timing mark on the balancer with a piston stop.
I’ve verified timing with two dial back lights bothnare within a 1/2 of a degree of each other.
Then I pulled the distributor and put stiffer advance springs inn to slow the advance rate down from all in at 2400 to all in at 3400.
That seemed to help but again did not eliminate the issue.
Then I pulled the plugs again to look at them and seen that cylinder number 8’s plug was semi fouled, not totally but it was darker then the other 7 and a slight smell of fuel to it.
So tonight I am doing a compression test on cylinder 8 with engine warm to see if there is an issue there.
If compression checks out then i don’t know where to go next.
Maybe the crane ignition box? That’s the only piece I haven’t tried swapping out.
But I’d like to confirm it is the issue before spending money on another ignition box and going through the trouble of wiring a new box inn.
I have a steady 20hg of vacuum at idle with vacuum gauge.
I did a compression test about 7-8k miles ago and all 8 cylinder cranked out 150 psi even across the board with carb wide open and engine warm.

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#2410282 - 11/28/17 05:19 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
Cab_Burge Online   content
I Win

Registered: 08/23/03
Posts: 30536
Loc: Bend,OR USA
The motor is talking to you about it not liking something at that RPM, understanding what is saying Is the hard part whistling AKA aside, I would try reversing what you did with the mechanical advance and have it all in by 2000 instead of 3400 RPM. twocents
If that doesn't fix it try replacing # 7 spark plug with the next hotter range plug and see if that helps it or not scope Maybe you have a intake gasket sealing problem on # 7 work Is that plug shiny or dull looking?
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#2410297 - 11/28/17 05:44 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
at 2500 does it stay rough from then on as high as you rev it? is that part or WOT or cruise. I would measure the vac & fuel psi & timing at that exact point when it starts to act up. Yes do a compression test & maybe a leakdown & try the new plug first & see if the new plug straightens it out for awhile. Describe the roughness (shakeing/missing). EDIT if it dont continue to be rough from 2500 on up, how much more RPM does it continue to run rough?


Edited by RapidRobert (11/28/17 06:21 PM)
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#2410321 - 11/28/17 06:29 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
astjp2 Offline
master

Registered: 01/18/11
Posts: 4126
Loc: Utah and Alaska
Transmission issue?
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#2410420 - 11/28/17 08:46 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By RapidRobert
at 2500 does it stay rough from then on as high as you rev it? is that part or WOT or cruise. I would measure the vac & fuel psi & timing at that exact point when it starts to act up. Yes do a compression test & maybe a leakdown & try the new plug first & see if the new plug straightens it out for awhile. Describe the roughness (shakeing/missing). EDIT if it dont continue to be rough from 2500 on up, how much more RPM does it continue to run rough?


It’s hard to describe the rough spot, I just know it happens in every gear at the same rpm.
Starts around 2500 and continues on up as far as I can tell.
It almost feels like a driveshaft vibration and sounds like one in the cab specially when I get the rpms up higher around 3500-4000 rpm.
Seems like it takes a little longer to cycle once im at a higher rpm around 3500-4000 rpm if that makes sense.
At 2500-3000 it seems like its cycling pretty quick and the higher the rpm goes up the slower it gets but it’s still there.
You can feel it in the floor boards in the steering wheel, in the seat.
I know this isn’t a drivetrain issue becuause it’s rpm dependent not speed dependent.
I have a 1350 series cv shaft for a rear driveshaft, pinion angle is set perfectly at -2 to -3 so that the pinion is inline with the shaft while driving.
For the longest time I thought this was drivetrain related but now I’m convinced it’s not.
My converter is correct I’ve verified that, flex plate is correct.
Balancer is correct.
And like I said since it’s rpm dependent the drivetrain theory kind of goes out the window.
I’m convinced it’s in the engine somewhere, ether ignition or there is an issue with one of the cylinders.
Its just strange cause the last time I did a compression test all cylinders were dead even at 150 psi.
Below is a pic of the spark plug that came from cylinder 8.
The plug on the left cane from cylinder 6 plug on the right is cylinder 8.
All the other plugs looked just like cylinder 6’s plug.
Cylinder 8 was the only one that didn’t look right and smelled like fuel a little bit.
I’m heading out right now to pull cylinder 8’s plug and do a compression test.
The engine is still warm from driving it home from work.
I’ll report back with what it puts out, last time it was 150 and that was only like 6-8 thousand miles ago and I never abuse this engine.
I baby it big time.
So I don’t see how compression could have just dropped in one cylinder all a sudden.


Attachments
47E4CCB8-C0FF-4B45-8200-64594AE5A38A.jpeg




Edited by pjc360 (11/28/17 08:53 PM)

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#2410469 - 11/28/17 10:09 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
Can you bump the original post back up so we can reread/refresh our info?. A balanceing issue? just crossed my mind.
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#2410480 - 11/28/17 10:21 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By RapidRobert
Can you bump the original post back up so we can reread/refresh our info?. A balanceing issue? just crossed my mind.


I’ve verified the torque converter and the flex plate, they are correct.
I have the magnum weighted converter and a standard la style flex plate.
I just pulled number 8’s plug with the engine warm and the brand new plug I just put in it a couple of days ago is already looking like it isn’t firing right just as before.
Did a compression test on that cylinder with engine warm and carb wide open cranked on it that way for about 5-6 seconds and it’s reading 155 psi.
I’m at a loss with what’s going on with cylinder 8.
I suspect cylinder 8 is causing the rough spot.
Should I pull the valve cover and inspect rocker arms and valve springs?

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#2410490 - 11/28/17 10:37 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
I’m leaning towards a bad valve spring on cylinder 8.
But what I don’t understand is why I’m not seeing something obvious with the vacuum gauge hooked up.
But it makes sense, only cylinder 8’s plug isn’t firing correctly all the others look pretty good.
It idles fine and drives perfectly fine below 2500 rpm.
Once you get up to 2500 or higher it just gets rough.
I’m seriously thinking valve spring on cylinder 8 but the only thing that has me wondering if that’s really the case is the vacuum reading at idle appears fine.
Maybe I should hook up the vacuum gauge and sling it up to 2500 rpm and watch it and see what it does then.
Cause from what I’ve read online about bad valve springs and the symptoms I’m having it sure makes sense at this point.
Specially with cylinder 8 pumping out good compression.


Edited by pjc360 (11/28/17 10:39 PM)

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#2410501 - 11/28/17 10:53 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
Just thinking out loud, I'm wondering if a badly worn guide/valve stem/seal is letting the plug, oil foul almost immediately, the compression would still be good as would the valve spring. when you put the new plug in there is it still running rough IMMEDIATELY? (before the plug has time to foul) If so I might be wrong but I keep thinking a "balancing issue".
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#2410517 - 11/28/17 11:14 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By RapidRobert
Just thinking out loud, I'm wondering if a badly worn guide/valve stem/seal is letting the plug, oil foul almost immediately, the compression would still be good as would the valve spring. when you put the new plug in there is it still running rough IMMEDIATELY? (before the plug has time to foul) If so I might be wrong but I keep thinking a "balancing issue".


I’m just not seeing where the balancing could be off and why that would be affecting the number 8 plug?
Like I said i have crawled under the truck and removed the converter inspection plate and verified that it is a weighted Magnum converter.
And a La style flex plate.
The engine still has the balancer on the front that came with the engine from Mopar.
And the number 8 plug isn’t oil foiled, it’s fuel.
This just doesn’t make sense to me, but I have a strong feeling the rough spot I’m feeling is connected to what’s going on with cylinder 8.
Would it be a good idea to have the engine hooked up to some kind of monitor to watch the spark events to see exactly what’s going on?
There has to be way to determine whatever is going on here.


Edited by pjc360 (11/28/17 11:20 PM)

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#2410523 - 11/28/17 11:28 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Where would you have me start to rule out a balancing issue?
I’ve wondered the same thing in the past but like I said I’ve looked at the converter and the flex plate and have compared them to other Weighted magnum flex plates and my converter looks identical to the magnum weighted converter right down to what the weight looks like and where it is on the converter.
It’s easy to see it’s a standard La small block flex plate.
Then the front like I said still has the balancer that came with the crate engine from mopar.
And if it was a balance issue why am I not feeling anything below 2500 rpm?
Wouldn’t I be feeling it all the time.
This just has me baffled.

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#2410565 - 11/29/17 05:02 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
PhillyRag Offline
enthusiast

Registered: 05/02/06
Posts: 233
Loc: Phila
Would it be a good idea to have the engine hooked up to some kind of monitor to watch the spark events to see exactly what’s going on?
There has to be way to determine whatever is going on here.

I've used a timing light on plugs that are suspect. Just shine the light on a clean paper/cardboard piece while increasing rpm's. Up to a certain rpm, your eyes will notice a misfire or erratic firing. Start or with #1 for reference then proceed to #8. If it's erratic with a new plug, then problem is upstream of the plug. Just some off-the-cuff thoughts here.

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#2410683 - 11/29/17 10:45 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
So I talked to a mechanic friend of mine and he said that if there was a weak valve spring the compression test doesn’t always reveal that.
He let me barrow a leak down tester and said to make sure the valves are closed on cylinder 8 and test it.
He said something is allowing more fuel into cylinder 8 and that he agrees with me that it does sound like a weak valve spring.
And he said that could most definitely be causing the rough spot im feeling.
He said it sounds like the spring is ok at idle and lower rpms but it starts revealing its self around 2500 rpm where the rough spot comes on and it could be allowing the valve to stay open to long drowning the number 8 plug in fuel.


Edited by pjc360 (11/29/17 10:46 AM)

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#2410693 - 11/29/17 11:22 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
krautrock Offline
top fuel

Registered: 01/27/03
Posts: 1631
Loc: central texas
in that other post you said you got rid of the vibration by swapping in a new distributor. is that correct?

now the vibration is back? i see you posted a thread about fouled plugs and the #8 plug being darker.
did you make adjustments to your carb to clean your plugs up?

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#2410806 - 11/29/17 02:26 PM Re: Back with rough spot around 2500 rpm [Re: krautrock]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By krautrock
in that other post you said you got rid of the vibration by swapping in a new distributor. is that correct?

now the vibration is back? i see you posted a thread about fouled plugs and the #8 plug being darker.
did you make adjustments to your carb to clean your plugs up?



Well what’s throwing me off is why are the other 7 plugs looking perfectly fine but cylinder 8’s plug is looking like it’s struggling to fire.
This rough spot has been there for a long time and I’ve just kept throwing parts at it trying to figure out what’s going on.
Everything I have done has made it a tiny bit better each time but it’s never been eliminated all together.
New plugs, new wires, new distributor, new coil.
Timing is set at 18 initial and 32 total.
I’ve verified it with two different lights, both dial back lights I have show 1/2 of a degree of each other.
When I un-plug the vacuum advance it gets better.
That’s what led me to believe it was possibly a rotor phasing issue at first.
But I’ve verified rotor phasing on my new distributor and it’s fine with and without vacuum advance.
The only area I haven’t really checked out is the heads.
Compression test revealed 155psi on cylinder 8 with engine warm and carb wide open cranking on it for about 5 seconds.
I’m going to remove the valve cover and do a leak down test on cylinder 8 and hopefully that reveals something cause this is driving me insane.

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#2410833 - 11/29/17 03:22 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
Quote:
Everything I have done has made it a tiny bit better each time but it’s never been eliminated all together.

When I un-plug the vacuum advance it gets better.

Compression test revealed 155psi on cylinder 8 with engine warm and carb wide open cranking on it for about 5 seconds.
I’m going to remove the valve cover and do a leak down test on cylinder 8 and hopefully that reveals something cause this is driving me insane.
I reread back thru the old thread. with these changes/adjustments makeing it better it would not be the balancing. unplugging the can changes (4) things: reluctor gap/Rotor Phasing/timing/rotor tip to cap terminal air gap (related to RP) but the RP is corrected which gets the best rotor radial air gap & iirc you bumped the timing up to make up for what the can took out correct? there might be a ring issue causing the fouling but iirc you said it was fuel not oil? How the can capped is helping things & getting #8 to fire is on my mind.
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#2410868 - 11/29/17 04:11 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By RapidRobert
Quote:
Everything I have done has made it a tiny bit better each time but it’s never been eliminated all together.

When I un-plug the vacuum advance it gets better.

Compression test revealed 155psi on cylinder 8 with engine warm and carb wide open cranking on it for about 5 seconds.
I’m going to remove the valve cover and do a leak down test on cylinder 8 and hopefully that reveals something cause this is driving me insane.
I reread back thru the old thread. with these changes/adjustments makeing it better it would not be the balancing. unplugging the can changes (4) things: reluctor gap/Rotor Phasing/timing/rotor tip to cap terminal air gap (related to RP) but the RP is corrected which gets the best rotor radial air gap & iirc you bumped the timing up to make up for what the can took out correct? there might be a ring issue causing the fouling but iirc you said it was fuel not oil? How the can capped is helping things & getting #8 to fire is on my mind.


That’s whats on my mind as well.
I’m just going to do a compression test on all 8 cylinders and a leak down test and go from there for right now.
Everyone else I have chatted with about this seems to agree that something is causing number 8 to get more fuel.
And they all seem to think it’s a valve or valve spring problem.
I’m also going to remove the valve cover and see if I can see anything out of the ordinary.
I have a feeling whatever is causing this is something that’s not so obvious but will make sense once it’s found.
It’s just finding it that sucks.

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#2410975 - 11/29/17 07:08 PM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
Quote:
I have a feeling whatever is causing this is something that’s not so obvious but will make sense once it’s found. It’s just finding it that sucks.
We're gonna have a good laugh when we find it, as in THAT was it!.
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#2411020 - 11/29/17 08:34 PM Re: Back with rough spot around 2500 rpm [Re: RapidRobert]
pjc360 Offline
mopar

Registered: 11/23/11
Posts: 650
Loc: montana
Originally Posted By RapidRobert
Quote:
I have a feeling whatever is causing this is something that’s not so obvious but will make sense once it’s found. It’s just finding it that sucks.
We're gonna have a good laugh when we find it, as in THAT was it!.


Check out this article, this guy was having the same issue I was having except he was having problems with cylinder 6 and he had his computer throwing a miss fire code.
It ended up being a broken valve spring on cylinder 6 and the tech said historically it’s cylinder 8 that has issues with the valve springs.

https://www.justanswer.com/dodge/192b9-2001-dodge-ram-1500-truck-5-9l-v8-my-problem.html

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#2411233 - 11/30/17 10:00 AM Re: Back with rough spot around 2500 rpm [Re: pjc360]
RapidRobert Offline
Circle Track

Registered: 11/20/03
Posts: 33336
Loc: Lincoln Nebraska
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.
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