Automotive question.

[Azrael256]

So, I've been working on a friend's '94 Olds Bravada.  We did all the usual tune-up stuff, and it's still running rough and dying at idle.  I'm thinking it's EGR valve time.  That one's going to be a total PIA since I have to take off the upper half of the intake manifold.  Not looking too forward to that, but I'll get it done.

Anyway, while inspecting the upper manifold to figure out what needs to be done, I noticed something.  He had mentioned that his cruise control didn't work, the blower didn't blow in all the vents, and so on.  Sounds like a vacuum problem, right?  So I find this little piece sticking out the back of the manifold, and it looks like three vac hoses run to it from the troubled accessories, and the little bugger is cracked up real bad.  So, problem solved, right?  Not so fast.  Nobody, and I do mean nobody can figure out what this part is.  It connects to a vac fitting on the back of the manifold by about 2" of hose.  The part itself is a central tube that connects to that manifold hose, then a small disc, maybe 1" in dia and 1/4" thick (a regulator of some sort, I presume), and then three  vacuum hoses connect to the various aforementioned accessories.  Two of the output fittings are (were, actually.  the fittings have come apart) capped off, presumably there for accessories this car doesn't have.  All fittings lie in the horizontal plane, two on either side, and one sprouting off the back end.  The whole part is about 3" long.  It's some sort of vacuum distribution part, obviously.  One line goes straight into the resivoir, one to the diaphragm on the cruise, and one disappears into the firewall (to whence I know not, but I think it's the blower selector thing).  I have asked half a dozen auto parts store drones, who pound away at their computers and then give me puzzled looks.  The Hayne's guide offers absolutely no mention of it, and I haven't been able to find a Chilton's that covers this vehicle.  This is clearly a key part, so you'd think somebody would have a clue what the heck I'm talking about, but you'd be head-pounding frustratingly wrong.

So, before I give up and put a bullet in that frappin' engine, anybody have a clue what this thing is called?

[Parker Dean]

A pic would be nice, but if I'm picturing what you're describing correctly it sounds like a part called a Cruise Control Check valve. Basically it serves as a combination one-way vacuum check valve and manifold. They come apart all the time, and can be found in the HELP parts section.

IIRC the 94 Bravada would have an injection system where the injectors are inside the intake. I forget what they call it, but it's like Central Injection something. Anyway, this system has the fuel pressure regulator and some plastic lines running to each port. Frequently the regulator leaks and you get rough running, black smoke, and poor economy. Same thing happens if the plastic lines crack. Kinda hard to confirm this is actually the problem without teardown, and even then all you'll find is clean areas where the carbon got washed off.

[Azrael256]

Ah, that's it.  I searched and came up with this, which looks almost exactly like it.  Thanks for that one

It does have that wacky injection system, but I've basically ruled it out.  I'll know more when I open up that wacky intake, but it's exhibiting classic EGR failure symptoms.  Rough idle, dies when you stop at a light, and surges at highway speeds.  I'll hit the EGR first, and if that doesn't do it, I'll move on to the injectors.  I'm praying that's not it, since it's soooo expensive.  That regulator isn't too bad, ~$50 IIRC, but the whole injector assembly is around $350.  Here's hoping it's just the EGR.  

I've already had enough fuel problems...  You know that little shrader valve that you hook the fuel pressure tester to?  Well, the core failed on it, and it started a nice little fire on what I thought was a plug miss...  turns out it was a crack in the plug wire.  I couldn't see the spark in the daylight, but that fuel sure as hell found it.  It toasted two plug wires, which was nbd since they were trash anyway, but it also scorched the plastic sheathing off a couple inches of accelerator cable.  The wiper motor housing took a bit of scorching, but it's just superficial.  Things got real exciting there for a few seconds, but if I learned anything from an idiot friend's combination backfire and needle & seat problem, it's to keep a fire extinguisher handy all the time.  He had just put a new insulator mat under the hood, and, not wanting it to get all burned up (it's flame retardant, moron), the first thing he did was pop the hood.  He was sans eyebrows and about half a moustache for a couple months.  And no, I haven't let him live that one down.

[brimic]

Looks like a Positive Crankcase Ventilation Valve  (PCV).  Do any of the hoses from it connect to a fitting on a valve/cam cover?    If this is what it is its a real cheap fix.

When the EGR system goes kaput, its an expensive fix, even if you do it yourself

[Sylvilagus Aquaticus]

Sent you a note, Az.

Regards,
Rabbit.

[Guest]

If the PCV doesnt fix it,  have a look at the throttle postioning sensor

[Azrael256]

Nah, PCV is fine.  I replaced the valve yesterday because he couldn't remember having it replaced.  The lines to it are new and tight.  We've been working over all the rubber on the car since most of it is deteriorating.  That fuel pressure regulator is actually sounding more like the problem.  He said it was dumping black smoke before this latest blowup.  This new problem is, without a doubt, the EGR.  The computer is howling about the EGR, the O2 sensor says rich (DUH!), and the knock sensors can't figure out when the cylinders are detonating.  All the other sensors I could find passed electrical tests just fine, both computer and me with my multimeter.  And it makes sense that a REALLY rich condition would gum up the EGR pretty bad.  Would've been nice to have fixed the fuel pressure problem before $100 worth of emission parts burned up.  *sigh*

Luckily, the EGR isn't *that* expensive ($40 for the valve and $50 for the solenoid), I just have to bring the whole thing in to find a replacement because GM decided to put no less than five different EGR systems on that particular vehicle.  I mean it, five different parts for the same engine code and transmission.  But, I suppose it's for the best.  I need to pull that plenum off to check the fuel injector system for leaks anyway.  I'm hoping it's the regulator, which comes in a kit with all the little O-rings and gaskets for the injector system for $25.  That, and with the plenum off, I can hose down the entire upper intake with B12 so it'll be clean and shiny.

Everybody pray for me.  Between flaming pressure test ports and dealing with the drones at the auto parts store who know nothing more than to pound on the computer (seriously, I've asked a dozen of them about that vacuum valve, and nobody could identify it), I'm almost at wit's end on this car.

[cfabe]

The part you posted is just a vacuum tee with some sort of regulator or check valve in it. It's purpose is to isolate the vacuum resevoir and any vacuum driven accessories from the engine vacuum during high-load (low-vacuum) engine conditions so that, for example, your vents don't change setting when you accelerate. You should be able to rig up something similar with parts from the parts store, tee togther the cruise servo, the accumulator, and the blower selector (you're correct on that, btw, the tube going into the firewall is for the hvac) and manifold vacuum with a check valve in the manifold line in the proper orientation. Should get the job done well enough without having to special order what's certianly at least a $20 part.

[Azrael256]

Well, I fixed it.  We popped off the intake plenum, and the pressure regulator was still bubbling fuel 2 hours after running.  The passenger side basin of the plenum was almost spotless, while the driver side was filthy.  We ran off to the store, and it turns out that the HELP! people have come out with a replacement regulator.  Good thing, too, since the Borg Warner injectory system was $315.  That regulator was $42.  I hosed out the entire plenum with a couple cans of B-12, and cleaned out the bottom half of the  manifold as best I could without disturbing any of the poppet lines.

The EGR problem seems to have gone away.  I think it was fouled badly with the incredibly rich exhaust, so I cleaned it up a bit and reinstalled it.  I don't know if it's going to last forever, but it's working for now, and it's a $175 part, so I'll go as long as it will work.  It has no vacuum diaphragm, just a solenoid in that one, so as long as the solenoid doesn't burn up, we're in good shape.  It shouldn't foul again.

We've got one error code, and it's the knock sensor.  I checked and found that the connector on the passenger side sensor was torn up badly, and it wouldn't stay on.  I'm going to see if I can find a pigtail to replace it, 'cause I REALLY don't want to have to attach a new connector behind the engine.  That's a royal pain.  When I hold the sensor on, the light stays off, and when I let loose, the light pops right on.

I also rigged up a vacuum check valve system per your instructions, cfabe.  Cruise control works now, and the AC vents all blow properly.  It cost me a whopping $12 for it, but that's including about eight feet of vacuum line that looked pretty old and cracked.  No reason not to replace it, so it's all brand new.

Just have to fix up the interior.  I'm going to need a new instrument panel, since most of the gauges don't work, and it's this solid-state LED thing.  The speedometer works, so it's relatively safe to drive, but I don't care for the idea of rolling around with no gas gauge or temperature sensor.  Looks like it's off to the junkyard for me.

Thanks for your help, guys.  Your information made that car run again.  I really appreciate it.

[Parker Dean]

The EGR problem seems to have gone away.  I think it was fouled badly with the incredibly rich exhaust, so I cleaned it up a bit and reinstalled it.  I don't know if it's going to last forever, but it's working for now, and it's a $175 part, so I'll go as long as it will work.  It has no vacuum diaphragm, just a solenoid in that one, so as long as the solenoid doesn't burn up, we're in good shape.  It shouldn't foul again.

Well, actually those like to stick internally. Intermittently. After a half-dozen or so rechecks you'll finally see on the data outputs that the thing is open like 10 percent closed throttle, but still no code.

I'm going to need a new instrument panel, since most of the gauges don't work, and it's this solid-state LED thing.  The speedometer works, so it's relatively safe to drive, but I don't care for the idea of rolling around with no gas gauge or temperature sensor.  Looks like it's off to the junkyard for me.

Quickest, half-assed way of getting oil/coolant temp might be getting some of those cheap gauge sets from the parts store. Just a thought.

[cfabe]

In my 92 bravada I did exactly as Parker describes with the gauges. For about $15 you can get an oil pressure and coolant temp gauge set. It doesn't look pretty but they work, and it's a lot cheaper than what you might find that digital cluster for. The digital cluster in these is a common failure, and actually if you look on ebay I think there's a guy who rebuilds them and/or sells repair kits.