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Discussion Starter · #1 ·
1st post: all respect to the grey and grizzly!
My first Cummins. Wrenched on many of my prior Ford 6.9/7.3 idi's, P-strokes, etc. Minor Soob expert.

Just bought a '97 2500 4x4, 47re, ext. cab. 350k miles. Price was low due to a very particular shaking problem.
Conditions:
  • Only between 1600-1800 rpm's. Not above, not below (unfortunately, that is smack-center 55mph in O.D.),
  • Occurs in all gears but only during low to medium acceleration,
  • Does NOT occur at all during WOT, hard-accel, while climbing through gears,
  • During WOT, truck seems to accel slowly through 1st & 2nd, but when it shifts into 3rd gear it suddenly has much more accel power.

Anyway, needed a tow vehicle, it seemed to drive okay outside of 1600-1800rpms, and the price was essentially half comparable market. Convinced it was trans-related, I bought it and immediately drove it "home" the 600-miles from SF to Baja. Above/below 55mph in OD ran very smooth; no issues & >18mpg. [What is typical City/Hwy mpg's?]

However, yesterday my trusted local trans shop said that he has owned/driven many 5.9's and he isn't convinced that this is a trans-related problem and that compared to others mine is noticeably under-powered and the throttle response isn't "normal". He enlisted a local Cummins specialist to ride-along for a diagnostic test-drive. He, also, was uncertain which system is causing this rpm/throttle-specific violent shaking. The fact that it instantly corrects itself above 1800rpms is confounding to all of us.
Consensus: given that I've already purchased a Goerends 3-disc TC/rebuild kit/shaft & Transgo Shift Kit ($$$), proceed with the trans rebuild and go from there. Regardless whether or not the shaking turns out to be trans-related, given the discounted purchase price and 350k miles there's no harm investing in a rebuilt & upgraded trans for long-term reliability.

In anticipation that the shaking problem is neither cured nor diminished by the trans rebuild, I'd appreciate any knowledgeable input:
  • Fuel-system related? Injection pump? I've had to pull/flush entire fuel systems before [WVO-converted Fords, bad-gas sedans, etc]. However, to me this does NOT act fuel-starved = above 1800rpm's runs very smooth,
  • At around 1600rpms it abruptly starts bucking HARD then around 1800rpms stops as quickly as it started. Given the distinct effect of throttle-velocity, combined with no GRADUAL vibration increase-decrease, I'm inclined to eliminate driveline suspects: wheel-balancing/rim/tire/front-end/brakes/diffs/bearings (I'll review symptoms of drive-shaft imbalance).
  • Harmonic Balancer?

I know zero about Cummins control systems.
I need a reliable tow vehicle YESTERDAY.
Any qualified input greatly appreciated!!!

Caveat: I commited to this purchase while suffering from undiagnosed covid; very foggy-headed, usually fair judgement downgraded to poor... ("Fully" recovered now, but NOT fun).
 

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Check the rear drive shaft, make sure it is straight, check carrier bearing and mount, and also check U-joints for play. I would have pointed you toward tire vibration, but from what I read in your post, it doesn't vibrate when power is applied.
 

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Discussion Starter · #3 ·
Definitely not driveline/train related:
My trans guy just rebuilt the 47RE AT, disassembled/inspected the Tcase, and inspected all ujoints/driveshaft & suspension components... all okay.
Replaced all fluids with HQ synthetics: AT/Tcase/Diffs.

The shaking is actually WORSE post trans-rebuild, lol. He thinks the new transgo shift-kit and Goerends 3-disc TC is putting additional load on an engine with a fuel-supply related power-loss issue, and [now] when power drops-off between 1500-1800rpms the engine is working even harder to send adequate power to the rebuilt trans. All seems plausible to me and I trust Manuel's integrity 100%.

Anyway, tomorrow the truck goes to a local cummins injection pump specialist.
With the Trans/TC & drivetrain now eliminated from the 'lineup', the injection pump is now the main suspect. To avoid duplicating the labor to R&R, it makes sense to me to have this guy install a known-good rebuilt unit and just take mine as a core.
Questions:
- What are the common mods to the injection pump to bump the HP? Links to pertinent threads here would be greatly appreciated!
He has offered to make mods to increase power from stock and I'd really like to arm myself with greater technical knowledge when engaging him re upgrades.
- Fuel Plate. An acquaintance mentioned that he got a 100hp gain from a fuel-plate upgrade. Links to relevant threads would be apreciated!
Is that an upgrade that should be done during the inj. pump R&R to save labor?

Many Thanks!
 
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