'89 S15

bcrooms · June 6, 2022

My grandpa has an '89 S15 2WD 4.3L with 90k miles on it.

I've been driving it while my '97 K1500 is in the shop.

I've noticed that when I come to a stop while the truck is at operating temp, the truck begins to have a very noticeable vibration. Doesn't matter if the truck is in Park or Drive, it shakes all over. But once I start moving it seems to go away. Seems like something engine related. I can feel it under the seat, on the gas pedal, steering wheel, and I even see the front of the truck "shaking" somewhat.

I have a video of it that I can try sharing for reference.

I'm not as familiar with these trucks as I am the K1500s, so I'm not aware of common issues...

Any idea of where to start checking?

KARNUT · June 6, 2022

11 minutes ago, bcrooms said:

My grandpa has an '89 S15 2WD 4.3L with 90k miles on it.

I've been driving it while my '97 K1500 is in the shop.

I've noticed that when I come to a stop while the truck is at operating temp, the truck begins to have a very noticeable vibration. Doesn't matter if the truck is in Park or Drive, it shakes all over. But once I start moving it seems to go away. Seems like something engine related. I can feel it under the seat, on the gas pedal, steering wheel, and I even see the front of the truck "shaking" somewhat.

I have a video of it that I can try sharing for reference.

I'm not as familiar with these trucks as I am the K1500s, so I'm not aware of common issues...

Any idea of where to start checking?

Does it have AC and is it on? Could be the fast idle switch.

bcrooms · June 6, 2022

1 minute ago, KARNUT said:

Does it have AC and is it on? Could be the fast idle switch.

It has A/C and I've noticed the vibration with A/C on & off. I'm thinking a rough idle issue, but that's just my first guess. It also feels like it may be misfiring when accelerating from a complete stop. It's an A/T but feels like a manual.

Niners 365 · June 6, 2022

If you already considered the A/C not the problem like the other two mentioned in thier posts. The crank shaft sensor when it goes bad can do the same bit. As well as a clogged fuel pump.

I replaced my crank sensor at 130,000, it was doing same bit as yours. Then when my pump was failing, it did same bit. I am 4th owner of my 2003 S10 4.3 4x4. Everything started going out when I got it. I have litterally replaced alot of parts and hardware. Now she runs like she came off the show room floor..

Spiney Norman · June 7, 2022

It could just need a good tune up. Plugs, wires, cap rotor, filters.

Give everything under the hood a good looking over.

Check for disconnected vac hoses, loose or unplugged elec connectors.

RPM's at idle while in gear?

Niners 365 · June 7, 2022

22 minutes ago, Spiney Norman said:

It could just need a good tune up. Plugs, wires, cap rotor, filters.

Give everything under the hood a good looking over.

Check for disconnected vac hoses, loose or unplugged elec connectors.

RPM's at idle while in gear?

Vaccum lines are the worst. If these come loose, or break, they will cause major shaking and vibrations. To include not shifting correctly for automatics.

bcrooms · June 7, 2022

16 minutes ago, Spiney Norman said:

It could just need a good tune up. Plugs, wires, cap rotor, filters.

Give everything under the hood a good looking over.

Check for disconnected vac hoses, loose or unplugged elec connectors.

RPM's at idle while in gear?

I think it may need a good tune up and overall check up. My grandpa doesn't drive it much to notice any issues, but today it had the vibration a lot worse, with or without A/C turned on.

bcrooms · June 7, 2022

1 minute ago, Niners 365 said:

Vaccum lines are the worst. If these come loose, or break, they will cause major shaking and vibrations. To include not shifting correctly for automatics.

Another thing i've noticed with this truck (and it may just be me) but it feels very sluggish when accelerating from a complete stop. I'm not familiar with how these smaller trucks perform.

Niners 365 · June 7, 2022

14 minutes ago, bcrooms said:

I think it may need a good tune up and overall check up. My grandpa doesn't drive it much to notice any issues, but today it had the vibration a lot worse, with or without A/C turned on.

Start with the basics. Change all the plugs, wires, cap n rotor. Make sure to take pic of how the plug wires are b4 you start. Do one plug, one wire at a time.

Also change out fuel filter, usually below driver side inside frame area. See where that gets you.

garagerog · June 7, 2022

Brandon, as others have said a tune-up may be in order, but before you haul out the parts cannon on a truck that old with the vibration issues you've mentioned I would check the motor mounts for integrity.

bcrooms · June 7, 2022

2 minutes ago, garagerog said:

Brandon, as others have said a tune-up may be in order, but before you haul out the parts cannon on a truck that old with the vibration issues you've mentioned I would check the motor mounts for integrity.

I was going to check the engine mounts as well to make sure they're up to snuff

bcrooms · June 8, 2022

18 hours ago, Niners 365 said:

Vaccum lines are the worst. If these come loose, or break, they will cause major shaking and vibrations. To include not shifting correctly for automatics.

Yesterday, I took a few minutes to look over the engine and see if I noticed any loose hoses as a starting point. I did find the Pre-Heather Hose from the Air Intake tube to the driver's side exhaust manifold is very loose and not secured to either fitting (each end) could this cause a vacuum issue? I also checked the air cleaner while I was looking and it was relatively new, so I didn't change it.

But this morning after re-installing the air cleaner and pre-heater hose....the truck almost stalled a few times after first start. Once it warmed up, it was fine....

bcrooms · June 8, 2022

Just found this issue as well with the coolant

Niners 365 · June 8, 2022

7 hours ago, bcrooms said:

Yesterday, I took a few minutes to look over the engine and see if I noticed any loose hoses as a starting point. I did find the Pre-Heather Hose from the Air Intake tube to the driver's side exhaust manifold is very loose and not secured to either fitting (each end) could this cause a vacuum issue? I also checked the air cleaner while I was looking and it was relatively new, so I didn't change it.

But this morning after re-installing the air cleaner and pre-heater hose....the truck almost stalled a few times after first start. Once it warmed up, it was fine....

Check your vaccum hoses off your TBI from your vacuum canister. Check at the points of connections before you chase the line. 90 percent of time they break and the point of connection. Here is a diagram layout for you year emission vacuum to follow. Check them all.

If the one to your TBI from vaccum is damage, it will cause a hard start and die.

But dont give up on the tune up. 90,000 most sparkplugs are good for 60 to 70,000. Same with wires, points, rotors. Fuel filters are good for 60,000. Fuel pumps between 95,000 and 120,000.

Niners 365 · June 8, 2022

4 hours ago, bcrooms said:

Just found this issue as well with the coolant

Looks like you have two different coolants mixed. The brownish is the dacron made for newer GM vehicles. The green I would say was Prestone. I would drain all of it, keep all drain plugs open, run your hose thru the radiator, the fill tank, just flush all that out. Take top radiator hose off radiator side, leave other end connected to engine, turn hose on, have someone turn engine over for a couple minutes. This will flush out the mix internal in engine.

Let it sit till all fluid and water is down to a drip. Then put plugs back in, 89 shouldn't need dexron, but y pi y can use it. But you need to pick one and only use one. Those two combined after awhile will form a gell that seizes up your radiator and forms in your engine.