12HT rough idle need ideas (1 Viewer)

[BigHighBlue]

Hello Legends! Some time ago I took my '87 with a 12HT swap off line for a while to replace the tie rod ends and swap the steering box which I exchanged for a reman 80 series box I bought from Rock Auto. After starting her up the idle was rough. You can noticeably feel it as well as it making a good bit of noise and rattling from loose parts like the roller fairlead. It seems to drive ok and once the rpms are above 750ish the roughness smooths out. It also seems ok initially when the cold engine idle up is engaged but gets rough once the engine is warm and the idle up turns off. In other words when the RPMs are higher it gets better.

One theory is that there's something about the new steering box that is causing added strain on the engine. If this is the case can I just turn up the idle and call it a day? Could the new box need to be adjusted somehow?

I've looked through the trouble shooting guide in the 12HT service manual and nothing seems to fit except adjusting the idle.

Any ideas or wisdom you can share will be greatly appreciated!

 

[duncanrm]

When its idling rough, is there an increase in exhaust smoke or does it stay much the same as your smooth idle?

 

[BigHighBlue]

I haven’t noticed any change in exhaust smoke. When I start it up there’s a small plume of “regular” smoke then it goes clear.

 

[mudgudgeon]

Is it smooth/normal under load? Such as accelerating away from a red light, or giving some poke to get up a hill?

If it's rough under load and blowing any white smoke, you may have air bubbles getting into the fuel lines.

Have you changed fuel filters recently? Or have any fuel lines been disconnected or disturbed? A cracked fuel line can suck in air without showing a visible fuel leak.

I don't see the steering box change having any impact.
There's also very little really to adjust on an 80 series steering box.

 

[BigHighBlue]

Is it smooth/normal under load? Such as accelerating away from a red light, or giving some poke to get up a hill?

If it's rough under load and blowing any white smoke, you may have air bubbles getting into the fuel lines.

Have you changed fuel filters recently? Or have any fuel lines been disconnected or disturbed? A cracked fuel line can suck in air without showing a visible fuel leak.

I don't see the steering box change having any impact.
There's also very little really to adjust on an 80 series steering box.

Yes I would say its smooth under load. I was giving it the beans this morning on the way in and no complaints. I don't see any white smoke at all. I did have a leak in the lines up to the fuel filter housing but I replaced the crush washers and bled it through the lines all the way to the injectors.

My theory with the steering box is that if the freeplay adjustment was too tight from the reman maybe the sector shaft is bound and causing constant load. Not sure if that's plausible or not. I'm going to remove the PS belt this evening and see if there's any change.

Thank you for your help!

 

[mudgudgeon]

My theory with the steering box is that if the freeplay adjustment was too tight from the reman maybe the sector shaft is bound and causing constant load. Not sure if that's plausible or not. I'm going to remove the PS belt this evening and see if there's any change.

I think an easy way to test this would be jack front wheels off the ground, and turn the steering wheel lock to lock without the engine running.
If there's any binding, you should feel it.

I think the adjustment would have to be extremely over tightened to affect the idle.

Also, its not going to have any impact at all while the truck is stationary and idling

 

[BigHighBlue]

I think an easy way to test this would be jack front wheels off the ground, and turn the steering wheel lock to lock without the engine running.
If there's any binding, you should feel it.

I think the adjustment would have to be extremely over tightened to affect the idle.

Also, its not going to have any impact at all while the truck is stationary and idling

Thank you. I'll have the truck on a lift this weekend so I'll try this out. Cheers!

 

[BigHighBlue]

Hello Legends! Some time ago I took my '87 with a 12HT swap off line for a while to replace the tie rod ends and swap the steering box which I exchanged for a reman 80 series box I bought from Rock Auto. After starting her up the idle was rough. You can noticeably feel it as well as it making a good bit of noise and rattling from loose parts like the roller fairlead. It seems to drive ok and once the rpms are above 750ish the roughness smooths out. It also seems ok initially when the cold engine idle up is engaged but gets rough once the engine is warm and the idle up turns off. In other words when the RPMs are higher it gets better.

One theory is that there's something about the new steering box that is causing added strain on the engine. If this is the case can I just turn up the idle and call it a day? Could the new box need to be adjusted somehow?

I've looked through the trouble shooting guide in the 12HT service manual and nothing seems to fit except adjusting the idle.

Any ideas or wisdom you can share will be greatly appreciated!

I solved it and it was the 80 box…the 80 box has an extra “ear” that the 60 box didn’t and in my case I had an old alternator belt that was stretched enough to let the alternator sit on the steering box and make the vibration that was driving me nuts. Pretty crazy find:

 

[mudgudgeon]

I solved it and it was the 80 box…the 80 box has an extra “ear” that the 60 box didn’t and in my case I had an old alternator belt that was stretched enough to let the alternator sit on the steering box and make the vibration that was driving me nuts. Pretty crazy find:

View attachment 3683446
View attachment 3683451

Good find!

 

[BigHighBlue]

Good find!

If you install the 80 box you get a built in early warning alert that it’s time to replace your belts!