'89 Bronco II 2.9 running rich

[jmaynard]

I'm driving an '89 Bronco II XLT I bought out of a guy's barn, where it sat for over a year, for $125. I've put about $1200 of repairs into it, mainly replacing all the fluids and rebuilding the brake system. It's running fairly well now - except that the mixture is quite rich. It's pumping a lot of unburned gas out the exhaust, and as you might expect, gas mileage sucks.

I found and fixed one vacuum leak (the vacuum delay valve in the line going to the cruise control servo was bad and leaking), and can't find any other signs of a vacuum leak. Spraying the vacuum lines with carburetor cleaner made no difference in engine operation, as you would expect with a vacuum leak.

I'd cut the vacuum hose before the failed valve, folded it over, and tie-wrapped it closed. When I pulled that hose off of the intake manifold fitting, I got a dribble of gasoline out of it, which suggests that there's too much fuel being fed to the throttle body injector.

Where do I start? I've got a 1500-mile trip planned for this weekend, and would really like to have the truck running as well as could be expected for one of its age and mileage (203K) before I go...

 

[heptofite]

bronco II doesn't have a throttle body injector, it uses multiport batch fire injectors.

your fuel pressure regulator is ruptured, replace it.

 

[jmaynard]

That sure seems like it would fit the described symptoms, especially since the vacuum line going to it is connected to the same manifold fitting as the brake booster and cruise control servos are.

Only one problem: Where is the goofy thing? I traced the vacuum line going back and down, and it disappears behind the engine on the passenger side.

 

[Spitfire1975]

FPR sits on the fuel rail. Drivers side. It is in plain sight and has 2 fuel lines coming in one side and an S shaped vacuum line coming out the backside and hooking up to the vacuum tree.

It is right next to the schrader valve that you use to test fuel pressure.

 

[jmaynard]

Found it, finally. I was looking on the frame near the fuel filter, not on top of the engine where it really is.

I'm pretty sure that's the problem. I pinched off the vacuum line; the engine ran a bit smoother and I didn't smell unburned gas, and when I let go, the engine stumbled and a great big cloud of unburned gas came out the exhaust. I'll replace it this afternoon, once I make the 50-mile drive to the nearest store that has one.

Update: Just what does it do, anyway? If the engine runs with it ruptured, it ain't regulating... Can I block off the vacuum hose to go get the replacement, or should i just leave it as it is? Or should I leave it parked and take my roommate's car?

 

[heptofite]

ultimately that's up to you, if the engine is running super rich, you may cause damage to the cats, but if you've already been running it like this, and you're just gonna go to the store and buy a new one, go for it.

I probably would, personally.

 

[adsm08]

If the room mate is will to let you take his car I would. If he isn't go ahead and drive yours, you probably aren't going to break anything that isn't already broken.

The regulator just keeps the rail pressure at a certain point. Driving with it ruptured simulates full throttle keeping pressure at running max and dumping lots of fuel into the cylinder.

 

[jmaynard]

Well, the replacement will be in tomorrow morning, so I won't need to run mine before I can replace it. Even so, I've driven 1000 miles (or more!) with it like it is, so 10 more probably won't make a difference.

I was more concerned about driving it 1500 miles this weekend and dumping lots of unburned fuel out the tailpipe, making the trip more expensive than it needs to be. I agree: if anything was going to break, it would have done so by now.

That does explain the vacuum booster and vacuum delay valve in the cruise control line both getting destroyed, though: attacked by gas fumes. Given that, I expect to have to replace the vacuum booster again, though that's a fairly simple job.

Now, if I can just find that vacuum delay valve...no longer available from Ford, and I can't find any aftermarket replacements, so it's time to go junkyard searching...

 

[heptofite]

Well, the replacement will be in tomorrow morning, so I won't need to run mine before I can replace it. Even so, I've driven 1000 miles (or more!) with it like it is, so 10 more probably won't make a difference.

I was more concerned about driving it 1500 miles this weekend and dumping lots of unburned fuel out the tailpipe, making the trip more expensive than it needs to be. I agree: if anything was going to break, it would have done so by now.

That does explain the vacuum booster and vacuum delay valve in the cruise control line both getting destroyed, though: attacked by gas fumes. Given that, I expect to have to replace the vacuum booster again, though that's a fairly simple job.

Now, if I can just find that vacuum delay valve...no longer available from Ford, and I can't find any aftermarket replacements, so it's time to go junkyard searching...

if you can't find one, take me a picture of where it is on the truck, there's an 89 at the pick-a-part next door to my house, i can go down there and strip one off if you need it.

 

[robertc1024]

You might check your brake booster too. A lot of folks on here have had FPR's leak and the gas gets into the brake booster and melts a lot of seals. No personal experience, but that's what I've heard.

 

[jmaynard]

I've already replaced the brake booster, and know what it's like when it fails...it hasn't since I replaced it, but I'll be keeping an eye on it.

 

[robertc1024]

Doh - sorry I didn't see that in your previous post.

 

[jmaynard]

I replaced the fuel pressure regulator this morning, and then set out on a 100-mile drive each way to get the stupid little vacuum delay valve. Just got back home. No glitches, no clouds of fumes out the tailpipe, idles and runs well. Looks like it's fixed. The cruise control works better with the delay valve in it, too, instead of a straight piece of vacuum hose (which the old valve was, effectively).

200 miles and $2 for two of those little valves. Whee.

 

[heptofite]

Awesome, looks like you're good to go.

now throw out that 7.5 and D28, slide an 8.8 and a 35 under it, get a lift, and run 33s.

 

[jmaynard]

I'm not looking to take it offroad...if I do anything in the way of a mod to it, it'll get a 4.0. The 2.9 is a definite step down in power from the last vehicle I had, and it's taking some getting used to.

Who knows? Maybe when I get ready to sell it, someone from here will buy it...