Intermittent power under load (1 Viewer)

[Seth_O]

I have a 93 FZJ80 with 305k on the odometer and approx 5k on a new head gasket and top end rebuild.

When under load and 2100-2300 RPM's I get a faint 'jerking'. Almost feels like bumps in the road, but you can feel the truck catch up on power in your stomach. If I get below 2k RPMs or above 2400, it doesnt happen. Or if I am coasting (so not under a load) then nothing. If in neutral on the driveway and in the RPM range - nothing. This is new behavior within the last 1k-2k miles.

This one has me stumped. No other issues with the truck at all, and no CEL.

Anyone seen anything like this?

 

[NLXTACY]

I saw that in a video...

Wait, sorry. Just saw the title

 

[livelarg]

I saw the title, thought you where talking about me!

 

[Seth_O]

Keep your couch and @LS1FJ40 out of this....we're talking tech here.

 

[Seth_O]

I saw the title, thought you where talking about me!

Apparently I need to change the title.....

 

[Willy beamin]

Motor mounts?

 

[livelarg]

Have you looked at your u-joints and pinions? If they are worn, they can bind up under load.
It’s the “bumps in the road” part of the symptoms made me think of that.
Good luck.

 

[Seth_O]

Motor mounts?

I can check them, but not sure that would give such a specific RPM range?

 

[Seth_O]

Have you looked at your u-joints and pinions? If they are worn, they can bind up under load.
It’s the “bumps in the road” part of the symptoms made me think of that.
Good luck.

I've thought about the u-joints, I'll check them for play.

 

[Funner]

Always do this over loads, under loads is just disgusting...waiting for my month long ban.

 

[Seth_O]

Thankfully the update allows me to change the title......

 

[LS1FJ40]

Keep your couch and @LS1FJ40 out of this....we're talking tech here.

It was his cat, not the couch...

What was the original title of the thread?!

 

[Seth_O]

It was his cat, not the couch...

What was the original title of the thread?!

"Jerking while under load." I should have thought of the audience before I posted that one.....

 

[LS1FJ40]

"Jerking while under load." I should have thought of the audience before I posted that one.....

Hahahahahahahahahaha

 

[bajaphile]

Is the jerking coming from the engine or drive-train?

The 93's use the VAFM / flapper door style meter after the air box right? I would probably check that first with a multimeter per FSM guidelines.

 

[Seth_O]

Is the jerking coming from the engine or drive-train?

The 93's use the VAFM / flapper door style meter after the air box right? I would probably check that first with a multimeter per FSM guidelines.

Great thought! That hadn't even occurred to me. I will check it.

 

[Tools R Us]

At what speed, is it speed or motor RPM dependent? Low/dry knuckle(s) can cause a grumble like running over highway rumble strips, most often at higher speeds and under load.

 

[Seth_O]

At what speed, is it speed or motor RPM dependent? Low/dry knuckle(s) can cause a grumble like running over highway rumble strips, most often at higher speeds and under load.

I only ever notice it on the freeway, so call it at speeds of ~65mph. I'll add checking knuckles to the list, that's a good thought.

 

[Ridonculous]

Try checking the intake hose between the MAF and the intake manifold. Look for cracks and make sure the wire hose clamps are tight. Removing /checking the air filter without removing this hose will cause it to crack and cause your symptoms. I had the same symptoms and this solved the problem.

 

[Seth_O]

Try checking the intake hose between the MAF and the intake manifold. Look for cracks and make sure the wire hose clamps are tight. Removing /checking the air filter without removing this hose will cause it to crack and cause your symptoms. I had the same symptoms and this solved the problem.

Was the power loss confined to such a narrow band? I thought about bad air flow but thought it would manifest all the time.