Hey guys I really need help diagnosing whatever the hell is going on with my truck.
It's a 91 short bed 1/2 ton 4x4 truck.
I have a 300hp crate 360 magnum in it, I have a non lock up A-518 trans in it.
I have a very strabge vibration issue going on, in every gear I get a vibration that comes on at about 2500rpm and it's at it's worst at 2500-2800 rpm then it some what smooths out if i step on it a little more, but it's still there, at higher rpm it just seems like it takes longer to circulate if that makes sense.
This vibration at 2500 rpm is like a quick womp womp womp womp type vibration, I can feel it in the gas pedal and in the steering wheel.
For the longest time I thought it was drivetrain related, but I'm realizing that isn't the case because of how it's rpm sensitive and speed sensitive.
It still vibrates the same even in park or nuetral.
Transmission was re-built a few years ago and the dumb asses at the shop put the wrong converter on it, they put an la 360 converter on it and I caught that fairly quick.
They then put the correct converter on and I thought all was well there, trans shifts fine, no leaks anywhere, I don't see any abnormal amount of wobbling at the converter and flex plate while idling or while holding it at 2500 rpm.
I don't hear any strange noises coming from the transmission area and converter area.
I'm at a loss with what's causing this.
Brand new alternator and ps pump and brackets, new belts, I've removed the belts and the vibration is still there, new radiator fan, no fan clutch, I don't see any strange wobbling at the harmonic balancer and it is the original
Balancer that came with the engine from mopar.
I'm about ready to pull my hair out over this vibration and I don't know where to start.
I was thinking start at ignition since that's easy and cheap, I tested my ignition coil which is a crane cams lx91 e-core style coil, the numbers are .07 for primary resistance and 4800k for secondary resistance.
The ignition is brand new, crane cams hi-6 cd ignition, rev limiter is set to 6200 rpm.
Distributor is a brand new firecore 50, timing is 16 initial and 32 total.
I'm out of ideas and need some advice or some strategy to pin point whatever this is.
Oil pressure on engine is good, don't hear any strange knocking sounds or anything like that.
The last warm compression test I did each cylinder was at 150 psi, that was done while engine was at operating temp and last time i did it was a couple years ago.
I can perform another one if need be.
Please help.

unless it is an ign misfire & I have my doubts, it is strickly eng related, are you sure the right TC/dampener are on there? unless the factory balancing is way off but I'd think the above first.

Yes I can post pictures of them if you'd like me to.
I've verified the converter is the correct converter for the 360 magnum, it's dark maroonish red with the weight on the one side of it.
The flex plate is an La style flex plate.
I tried posting pics and it wants me to use a URL?

Once you enter the verbiage into the box, click on "File Manager" right below the text box then upload pics. Using the image link above the text box requires an externally hosted pic.

I'm using an iPhone, does that make a difference?

Here is some info that my brother Dog posted awhile back: 5.9 mag balance is different from a LA 360. 5.9 uses an OE 5.9 flexplate/neutral converter. magnum imbalance is in the flexplate. LA 360 imbalance is in the converter. You've got some of this covered/dealt with but I wanted to get it out all there (more info the better). EDIT after (re)reading I wonder if they used the common LA plate as opposed to the 5.9 specific one?

Yes it looks like the common la flex plate with the magnum weighted converter.
Which from my understanding works, it can work both ways, you can use a nuetral balance converter with the magnum weighted flex plate or you can use the stock la flex plate with the weighted magnum converter.
From my understanding Chrysler did it both ways, the early 93-95 magnums got the la flex plate with the magnum weighted converter and then in 96 they started using the nuetral converter and magnum weighted flex plate.

.

Are you sure it's a 5.9? My 400 Ford $500 pickup was really a 351M as I found out when the 400's pressure plate wouldn't work on the flywheel. Later I discovered that it was a 4" stroke so it really was a 400 by means of a crank and piston swap. So it could be a 5.2 masquerading as a 5.9. That seems pretty unlikely but a lot can change in 20+ years.

It's not the ignition but the real way to find that out is to use a timing light on each spark plug lead and watch the flashes. Even at 3000rpm, a miss in the flash pattern is pretty easy to see. Once you have put the ignition to rest, everything else you said points to a fundamental balance issue.

That means it must be something attached to the crankshaft. Period.

When you wisely ran the engine without the belts and the vibration was still there, it eliminated everything that was not attached to the crankshaft at that moment.

The description of the vibration being worse through a band of rpm is right in line with descriptions of 360s with 318 converters or neutral balance flywheels.

It helps if we stop referring to a 5.9Mag motor as a 360. Magnum engines have enough different parts that even though they share bore and stroke with certain LA engines, they are not LA engines.

It is important to restate that the values for factory imbalance in 360s and 5.9Mags is different. The 5.9Mag uses a smaller amount of imbalance.

IMHO you will be removing the engine and discovering which of the several incorrect combinations you have.

Good Luck!

R.

Im absolutely 110 percent positive it is a 360 magnum.
I still have the receipt from the dealership my dad bought it from as well as the installation instructions.
It's a 300 hp crate 360 magnum purchased in march of 2003.
I don't think I'll need to remove the engine to figure out what's going on, maybe the transmission to see if the flex plate is bent or broken.
I will go around the converter to flex
Plate bolts and make sure they are tight.
The shop that did the transmission wasn't exactly sloppy, they were just over confident not listening to me when I said it's a magnum so the balance is different.
They acted like it was your standard 360 and put that converter on it.
They fixed it without charge once they realized the bad made a mistake.
The timing light on each plug wire is a good idea.
What do I look for in the light strobe to see if one of them is Miss firing.
I was also thinking I could have it put on a scope to watch the ignition events to verify if all 8 cylinders are firing correctly.
Could it be a damaged plug wire that's causing this? Could the ignition coil it's set cause this? It's literally rough feeling at about 2500 rpm, the higher I rev the engine the slower the vibration is to come around.
I know the harmonic balancer on the front of the engine is correct, and I know it's a 5.9 magnum without a doubht.

with it up on a fast enough idle so it is in that rough idling zone, put the clamp on each plug wire one at a time & squeeze & hold the trigger on the gun & look at the blinking light to see if it "misses".

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Sometimes it's the simplest of things, your driveline "vibration" sounds just like the "shop truck" I bought off a bunch of ASE Certified mechanics who did an engine swap/torque converter swap and could never figure out the cause of the slight driveline vibration, so they "dumped" the truck on me, after 5 minutes of ownership, it was "cured"....firing order, 2 cylinders crossed wires, 4 ASE mechanics and a month of on and off troubleshooting, they over looked the obvious....so rule out the simple things before you go tearing stuff apart

Deffenitley, that's why I'm going to rule out ignition first.
In almost wondering if it's a bad plug wire or if it's my ignition coil.
The coil in running was in a truck that had caught on fire.
My dad had a 75 w100 and the wiring at the amperage gauge caught on fire and that's what burned down the cab.
They got the fire put out before it damaged the engine and under the hood.
But I'm wondering if maybe that coil got hot in that fire and it works but not exactly like it's supposed too.
I'm not sure if a single coil system like mine can affect an individual cylinder or two, but the last time I had my spark plugs out cylinder 7 and cylinder 8's spark plug were questionable.
Not fouled but looked like they weren't firing as well as the other plugs were.
Could a coil cause something like that to happen if it's on it way out?
Something is telling me to try a new coil just because of what I seen with number 7 and number 8 plugs and the fact that the coil I'm running was on a truck where the cab burned down.
The ignition in running is a crane cams hi-6 cd ignition box with the crane cams lx91 e-core coil. I measured the coils resistance and didn't see anything that jumped out at me really.
I guess you could say the secondary resistance of the coil was a little low at 4800 and the primary resistance was .07-1.0 which is ok.
I've been trying to find online what my specific coils resistance should measure out at.
Plug wires are Taylor thundervolt 8.2mn, they are only a couple years old but some of the boots are torn from taking them on and off as much as I have over the years.
Maybe this issue is ignition, it's just strange how it runs so smooth untill 2500 rpm and then all hell breaks loose with the vibrations.
I thought it was drivetrain related for the longest time, but being that it's strictly rpm dependent I've changed my mind.
That and I'm running a 500 dollar 1350 series cv shaft with all spicer yokes and u-joints and my pinion is 1-2 degrees below inline with the shaft which is exactly where you want it to be with a cv shaft.
All U-joints are tight, and output shaft bearing on t-case is tight.

Is it possible for a single coil system to only affect a couple cylinders? It should affect all cylinders not just one right?
I'm thinking maybe the coil is fine below 2500 rpm but at 2500 and up it starts acting up and that's what I'm feeling?
Like I said Idk, I tested resistance to the coil and primary reisistance is .07-1.0 and the secondary resistance is 4700-4800.
Maybe I should my plug wires and start testing the resistance on them, maybe I have one that just went haywire and it's causing bad missfires.
I haven't been able to even look at the truck the last couple
Of days I've been so pissed off at it, but I'm going to start poking around tonight.
I'm going to start with hooking my timing light up to each plug wire and seeing what the strobe looks like at 2500 rpm.
I'm really hoping this is just an ignition issue, if it is at the trans then I suspect the flex plate because I know the converter is correct, I've compared it to pictures of the magnum weighted converters and it looks identical.
And if it was the wrong converter wouldn't i fee that vibration all the time including at idle?
And also if the flex plate was bent bad enough to cause this vibration wouldn't I see some
Wobble to it?
I had my wife hold the throttle at 2500 rpm in nuetral and I couldn't see anything abnormal at the converter and flex plate.
Looked completely normal. No wobbling, no strange sounds, nothing.

external parts "Wobbling" from loose/eccentric/out of round parts would be different/visible on that specific part as opposed to vibration coming from the crank being out of balance either from the wrong tc/plate or wrong bobweight amt when it was balanced.

In these pictures you'll see I have the correct magnum weighted torque converter, first picture is my torque converter, second picture is from a guy o line that pulled a factory trans from a 1995 Dodge Ram 2500 with a 5.9 magnum.
My converter looks identical, the weight looks the exact same.
Third picture is a little crack that I found in my converter by the teeth where the starter Engadges, I'm going to guess that the starter was sticking at some point and smacked the teeth on the converter while the engine was running and that caused this crack.
I don't think it's causing my vibration but it will need to be addressed at some point.


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