1988 Bronco II cruise control vacuum routing

[hoverfish]

Hey everyone,

First-time Ford owner here. I picked up an 88 Bronco II XLT to use as a winter beater back in November. The guy who owned it before me was a "mechanic"... meaning there are a lot of things done on it recently, which were all half-assed. New brake shoes on badly worn drums, new hatch lift struts which are for a different vehicle and modified to (partly) work, and so on.

Anyway, he said the cruise control unit was leaking vacuum so he took it out and there was a replacement unit included with the truck. I figured out where it mounted and how the cable runs to the throttle body, but have no idea what the vacuum routing should be. The diagram under the hood makes no mention of a cruise unit, and no amount of Googling seems to help either. It looks like near the back of the intake plenum there's a vacuum line about the right size that's capped off, but I doubt that simply runs directly to the cruise servo... does it?

 

[rtg143]

The vacuum line runs from the manifold and has a tee in it with a line running to the brake pedal dump valve.

 

[hoverfish]

I finally got around to connecting it up last night. I connected a hose from the nipple at the rear of the intake to a tee, with one line running to the brake pedal valve and the other to the cruise unit. Started it this morning to go to work and it immediately revved and bounced off the rev limiter. Not having time to look at it I just yanked the hose off the intake and capped it. I guess next I'll try capping off the line to the cruise unit to eliminate the brake valve as the culprit and vice-versa.

 

[hoverfish]

Alright, so I had a little time to have a look at it... as soon as I start the engine the cruise cable is pulled opening the throttle all the way. I don't imagine this is normal behavior.

So, I have a hose running from the manifold to a tee, one leg of the tee runs to the brake dump valve and the other to the nipple on the fitting on the front of the can. Is that anywhere near correct? This causes a vacuum leak under the dash when I press the brake pedal, and what connects to the other nipple on the can? I can see marks where there once was something there.

 

[fastpakr]

I remember precisely this behavior when I had the cruise vacuum lines hooked backwards on my old Bronco II. Don't have that anymore to compare to, but more or less the same system is installed on my '92 F150. If nobody's answered this sooner, I'll try to take a picture tonight to show you the correct connections.

 

[hoverfish]

Judging by http://www.allfordmustangs.com/forums/attachments/5-0l-tech/139219d1315917216-1988-mustang-cruise-servo-replacement-6.jpg I see I have it entirely wrong... the nipple I was using is for the brake dump valve, and the "what goes here?" nipple is for manifold vacuum. Does that sound right?

 

[rtg143]

That would be correct. I was thinking of the tee in the side as you see it from the front. If the tee was how I mentioned, it'd cause a vacuum leak when the brake was applied. It's hard to explain without seeing it. My excuse anyway.

 

[hoverfish]

I connected everything correctly last night and tried it this morning... nothing. Back to the drawing board, I guess.

 

[fastpakr]

Check your local library. If they have a good reference section, you'll be able to find a Mitchell manual for domestic light trucks and vans for 1988 (or something close to it). There is a cruise control troubleshooting section specific to the vehicle that will have a logical sequence for testing each component so you can chase down exactly what's wrong.

 

[rtg143]

You may de able to read about it on Autozones website. They have online repair manuals.

 

[zekew64]

I know this is almost a year old, but here goes:

Basically, on the older Broncos and Rangers, the EGR system--if there is one--helps to control the cruise system. Hook up your vacuum connections per the diagram under the hood; this will take care of the EGR and fuel systems. After this, you'll have to hook up the one hose to the intake manifold. This will give vacuum to the inhibitor solenoid (a yellow combination electrical/vacuum solenoid), the accelerator solenoid (the immediate solenoid off of the vacuum tree that is red), as well as the vacuum reservoir (black, circular, round plastic thing; has two connections) and other electrical/hose connections. One hose goes to the inhibitor solenoid from the reservoir. The other connection goes to your brake pedal (auto) or your clutch pedal (manual/stick shift).