"85 bronco II with some issues

[bonedoc]

Hey, I have an '85 bronco II, Has a new 2.8L, with about 20,000 miles on it and an A4LD autotrans. The trans has about 15,000 on it. drivetrain is all stock except for a 4" rough country lift and 31" Cooper sst tires. Motor has headers and a 2 1/2 inch exhaust, no cat. Having problems with hesitation on the motor and to boot it is intermittent. Some times the truck has no hesitation, put the pedal down and it takes right off with no problems pulling, other times it is horrible and just bogs. You then literaly need to mash the pedal to the floor to get any rpms on the motor but it quickly upshifts and bogs again. Any ideas...we were thinking that it ultimately was the carb. looking at swapping in a holley 350 cfm 2 barrel. Holley has a throttle position switch and auto choke conversion that will work for this application. Has anyone done this or tried it?

The other issue is the trans, when cruising at 45 to 55 mph, it constantly goes in and out of overdrive, constantly up and down...gets annoying. Someone told me it sounds like the throttlr position sensor, anyone have any suggestions?

I love the truck, drive it everyday, the steering it horrible and scary at times but I think that is just the cheap rough country lift, I plan on putting in a james duff 5 1/2 inch stage 3 lift with superlift superrunner steering system this spring.

Thanks everyone

know enough to be dangerous!!!

 

[martin]

Check the hose to the power valve, it might be cracked or otherwise damaged.

 

[bonedoc]

thanks will check that!

 

[ForOffRoadDriving]

it sounds like you may have a vaccum leak, possibly from the modulator valve on the trans up to the carb, which could be the explaination of both symptoms. the best bet would be to nip a chunk off from every vaccum hose on the motor and head to the store and get new lengths of hose for each, assuming that they werent all replaced when the motor was rebuilt.

 

[adsm08]

yeah, sounds like a leak to the tranny's vacuum modulator, when it bogs down its leaking and thus in the wrong gear.

 

[bonedoc]

thanks everyone, huge help!

 

[cckc135r]

Something else you might try is to disconnect the plug that controls the TCC function then go for a drive to see if it still does it. It's located on the driver side of the transmission toward the front of the trans. The 85's still utilized hydraulic shifting for the 3-4 shift. I have the same set up (2.8 A4LD 85 4WD B2 XLS) and mine was doing the same thing. I now control the converter lock up function by using a switch mounted on the dash. Check the tech area too as it details this problem and shows 3 different ways to control the TCC function. (TCC=torque converter clutch) I thought mine was overdrive going in and out too but turns out I have an old engine, old trans, poopy carb, bad vacuum, and an oil filled EGR tract that are all causes of this very annoying problem. 2.8's are known for going through valve seals which in turn can and does cause problems with the TCC function. Hope this helps some and keep us posted on your progress.