Buying another 97 Chevy K1500; Engine shakes really bad

[jasolhe]

So I found a 97 Chevy K1500 with 180k miles. Most of the stuff I can fix on my own because i did it with my truck. This would be
for my son.

Something this truck has that mine didn't is the engine shakes A LOT while running. I'm assuming bad motor mounts?? Trying to find a video
on swapping these out with the motor in - I GOT NOTHING!!!

Every issue is minor and I can fix except this. I can buy it for 1k cash.

How severe is this problem, am I right in assuming motor mounts, and can this be done without taking out the engine? Thoughts please! I won't buy
if it's going to cost a shop 3k to replace motor mounts on this dinosaur.

 

[rebelyell]

Is the motor misfiring ? Have you checked for misfire ?

 

[GoToGuy]

Crap tune up, plug wires mixed

 

[Scooterwrench]

Wrong flywheel/flexplate?

 

[Sean Buick 76]

I would bet it’s not engine mounts causing the issue but since you asked . Yes just use an engine crane to lift the engine 2-3” after removing the engine mount bolts between the mounts and the frame pads. The engine mounts are solid in these trucks, the part that wears out is in the frame pads. A least that’s how my 92 is, not sure if all of them are the same.

 

[jasolhe]

Is the motor misfiring ? Have you checked for misfire ?

took it for a 5 min test drive it did start misfiring once i reached 50mph

 

[jasolhe]

took it for a 5 min test drive it did start misfiring once i reached 50mph

the heavy vibration i noticed at idle in the driveway with the hood up

 

[rebelyell]

took it for a 5 min test drive it did start misfiring once i reached 50mph

First resolve whatever's causing misfire(s) and that'll probably end the shakes.
Continuing to drive while shaking will eventually wreck motor / trans mounts.
Others have already pointed at possible misfire root causes.

plug wires/routing/cap n rotor ... If this is a vortec motor ... they're notorious for failed cap & crossfiring. If ya buy a cap n rotor, pony up for AC Delco ... careful ! ... don't strip plastic distributor body's threads for cap's screws.

 

[HotWheelsBurban]

First resolve whatever's causing misfire(s) and that'll probably end the shakes.
Continuing to drive while shaking will eventually wreck motor / trans mounts.
Others have already pointed at possible misfire root causes.

plug wires/routing/cap n rotor ... If this is a vortec motor ... they're notorious for failed cap & crossfiring. If ya buy a cap n rotor, pony up for AC Delco ... careful ! ... don't strip plastic distributor body's threads for cap's screws.

Another good cap and rotor for the Vortecs is the United Motor Products set that Rock Auto sells. I have them on both my trucks and am very happy with them. We can drive in pouring rain and no misfires!
I second the idea to check the plug wire routing.#5 and #7 are next to each other AND adjacent in the firing order, and if the wires are too close to each other, misfires and eventually damage will happen.

 

[Schurkey]

"Good luck" finding decent motor mount cushions for a K-series GMT400.

OTOH, my truck still has the original mounts at 320,000+ miles, because I refused to install the cheap-crap aftermarket mounts; and I refused to install the Polyurethane inserts that look nothing like the originals.

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As for the engine shake, consider:

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
   
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
   
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.