Intermittent power under load (1 Viewer)

[Ridonculous]

The biggest issue was climbing a hill and needing to accelerate to maintain speed. The tranny would shift down and the rpms would go up, but the engine would seem to bog down and not accelerate.

 

[baldilocks]

The 1993 engine ecu p/n -60220 is known to fault out. Is yours original? If so, borrow a newer -60221 ecu and slave it in for trouble shooting purposes.

 

[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.

I had a couple of mins today so I busted out the multimeter and followed the FSM for on-vehicle testing of the VAF:

It was 48* F when I tested and I got the following:

VS-E2: 287ohms (should be 200-400 ohms)
THA - E2: 3860 ohms (should be 3-4 KOhms)

VAF seems good. Have to check driveshafts and knuckles next.

 

[ppc]

On page EG-292 there is another test that is more relevant to your problem. It tests the output of the device under changing amounts of air flow.

 

[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.

Bringing this thread back to the top. I had time this morning to get back at it.

Knuckles look good, they appear well greased.

 

[Seth_O]

On page EG-292 there is another test that is more relevant to your problem. It tests the output of the device under changing amounts of air flow.
View attachment 1907932

Pulled the VAF and tested per the FSM. I got 260 ohms closed, 43 ohms fully open. I used a digital multimeter so not sure I could accurately see a wave, but the multimeter bounced up and down as I moved the door, so I assume its good.

 

[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.

U-joints look good, I greased them and the d-shafts regardless as it's been a while.

 

[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.

Pulled the intake hose and examined it closely, it's in good shape and free from cracks or holes.

 

[Seth_O]

The 1993 engine ecu p/n -60220 is known to fault out. Is yours original? If so, borrow a newer -60221 ecu and slave it in for trouble shooting purposes.

I took a look at my ECU, PN -60221. I should be gtg.

 

[Seth_O]

I also checked my intake manifold for snugness against the block. Bolts were tight.

Running out of ideas.

 

[baldilocks]

Pulled the VAF and tested per the FSM. I got 260 ohms closed, 43 ohms fully open. I used a digital multimeter so not sure I could accurately see a wave, but the multimeter bounced up and down as I moved the door, so I assume its good.

Since you are not 100% sure of the vafm, you may as well get ahold of a borrowed unit to try out, that is known to work properly, so you can be sure and either fix your problem or move on to the next possibility.

You can probably find a used one here in the Mud classifieds to purchase and then you will have a spare if you don’t need it this time around. I carry one with me on all trips. 300k miles is asking a lot from a part that works the way a vafm works.

 

[ppc]

Pulled the VAF and tested per the FSM. I got 260 ohms closed, 43 ohms fully open. I used a digital multimeter so not sure I could accurately see a wave, but the multimeter bounced up and down as I moved the door, so I assume its good.

Yes, a digital meter isn't going to show much other than the circuit is somewhat functional. An analog meter will show any dropouts as the sweep is done closed to open because the resistance should smoothly change. Picture that under normal operation, cruising etc. the vane is going to remain in a relatively small section of that sweep. That small area would be the most likely to wear, become contaminated.

Using another VAF to test would be the easiest way to eliminate the air meter as the cause of your problem. As somewhat of a last resort you could open the sealed cap on the top and spray the circuit board inside with electronic contact cleaner spray as the vane is moved open and closed.

 

[iansplatinum]

I also checked my intake manifold for snugness against the block. Bolts were tight.

Running out of ideas.

Did you ever fix this?

 

[Seth_O]

Did you ever fix this?

Nope. I'm not in a position to throw parts at it, and since it only affects me the very first acceleration of the day, I just live with it. I have some other issues that I have to prioritize, once I deal with those then I can rebook at this.