I fixed this issue on my Riv and learned a few things in the process that I wanted to share, based on my general impression of recent problem posts.
Problem was I had a P0104 code pop up quite a while ago. It's "insufficient flow." Checked the EGR valve and although it was clean (no soot buildup at the valve) it did not actuate properly (this can be checked with a Tech II) and as well the passage in the throttle body was cruddy (may have had accumulation of tar due to low flow? I don't know, I just cleaned it all out and replaced the EGR...)
So I replaced the valve and the car ran fine, no codes, for months after that, then reappeared.
Now, the '96 and later Series II SC engine has "digital EGR." The EGR valve is operated by a signal from the PCM based on sensor readings. There's a MAP sensor among them. One reason for a P0104 can be a MAP sensor gone bad. This happens, but not so often and is easily checked by checking for a sensor reading with a scan tool.
My MAP was reading - but erratically.
So I "took a dose of my own medicine" and looked in the FSM. How does this thing work? The upshot is that there is a vacuum harness connected to the supercharger bypass solenoid, the fuel pressure regulator, the MAP sensor, and a vac bleed on the manifold. It used to be GM #24507329. The harness has pre-bent nylon tubing with little flares to hold a set of rubber tees in place. Since the EGR is "Digital" and it gets its input from the MAP, I figured I'd track back from the MAP to the SC bypass and check the lines and fittings. Pulled off the engine sight shield (the gray shell with "3800 SERIES II Supercharged" on it) and started looking, from the back at the MAP sensor. The fittings were old and hardening - you know, they way they look when you know you could replace them but if you don't disturb them they will probably be OK. The nylon lines looked fine. I used a mirror to look at the manifold vac bleed nipple fitting, and felt it with my fingers. It was hardening too. At this point I am thinking I need to find some little rubber fittings, and I continue. When I got to the tee at the fuel pressure regulator - yuck.
What I found was the rubber tee in the manifold at the fuel pressure regulator was cut, the likely culprit being the spark plug wire retainer clip. Many years ago when I replaced the plug wires, I also reinstalled the OE clips that neaten and hold the wires in order as they are routed from the coil pack over top of the supercharger. What appears to have happened is that over time -- over the course of several years -- the clip had rubbed against the vacuum tee and finally had cut it. When I pulled on the tee to inspect it, it broke at the cut. So I pulled out my cellphone and called the local GM dealer's parts counter and asked if they had any of those little rubber tees. Got a junior counterperson and although he was trying he was making no real progress. After a minute or so I said, hey, I have an old parts fiche (borrowed for another project from friend who also has a Riv) and help look this thing up - a rubber tee, it might be in the "out of fiche calls" with the other shop and service parts, like spark plug wires, and gaskets. So he's looking on the computer and I'm looking on the fiche, we're not finding anything. Another minute has gone by.
Now, a rule of thumb I like to heed is that time is money - both mine and other people's. And he's at work at a parts counter that's often busy. I said tell you what, we'll make this a race. I will look on my fiche and you look on the computer and whoever finds it first, call the other one. He's already pulled up my VIN and phone number so we're off to the races. Off the phone, I look real hard on the fiche. Then I found the problem -- nomenclature that made sense only after you knew what it was.
I found the tee by trying to look up "vacuum," not finding it there, then looking up the supercharger sub-assembly, not finding it there either, then looking at the explosion pictures of the engine assembly until I found the thing. Being small, it took a while. It was under "ENGINE ASSEMBLY, MANIFOLD AND FUEL RELATED PARTS."
Clear enough.
The tee was shown as attached to the nylon tubes - uh oh - so I looked up the number and called Parts back. Asked for the clerk, got the supervisor. Told him that I'd spoken to the clerk earlier, who no doubt is now onto something else. Supervisor calls clerk, I say hold on I have the number for you - I think I do anyway - he says OK I give him the number. He says it's superseded by 24508742, and is discontinued and he can't find one at the moment, but he might find it tomorrow. So I ask, is there any chance that there might be a tee that fits in the shop supplies? He says probably, so I say I'll stop by to see if we can match the tee up (and then I'd of course pay for the shop supply and a little for their trouble).
At this point I still have a leaky vac harness that is setting false P0104s. I put a little dry gas (alcohol) on a rag, wipe the cut tee clean, then wrap it with "amalgamating tape." Amalgamating tape is a rubber tape that you stretch and wrap around stuff, and it fuses to itself. It is not adhesive, it's kind of partially cured synthetic rubber. When stretched and tightly wrapped around any surface it will become a solid mass of rubber. It can be used to seal hoses, water pipe leaks, insulate terminals, connectors, cable, and wiring. It can also be used for underground wiring, hi-voltage repair, in conjunction with, or in place of heat shrink tubing. and when you stretch it it fuses back to itself. More about it (and free sat-tv in the UK) at this LINK. So in this application, I used it to over-wrap and seal the vac fitting. It worked, although I did not know it at first.
With the fitting wrapped, I hop in the car and drive to the dealership. I stop in at the dealership and counter supervisor says it was not terribly busy so he made come calls and found a cache of the manifolds at a GM supply depot at this LINK. And quoted me a price. I order it. Not because it's cheap but because it replaces all the goofty custom-rubber-fittings-that-are-dried-out on the vacuum harness and, if I reposition the spark plug wire clip, won't fail (well, at least won't get cut) for another ~15 years.
I figure I'll try to find a vac tee cheap while I wait for the part to arrive. Hop in the car, start car - SES light's out. So I've solved the P0104 EGR problem -- sort of. Rube Goldberg would be proud (my tape job is effective but not neat) and Murphy is biding his time... I mull over going home and decide that since the AutoZone is closer than the house I'll cut my risk and go to AZ to find a vac tee.
BZZZZT. Waste of Time. After dealing with the AZ counter help (who have improved much over the past ~year by the way since they hired an ex-Marine supply room manager - he's not a yeller, rather it's that he gets how the kidployees tick and encourages them to motivate themselves to focus on what's important to customers... ) The problem at AZ is they just don't have any such part. I go to the next block, there's an old-line CarQuest franchise there. And I am thinking to myself that I should have gone there in the first place, they are *way* better at the "get me back on the road" thing. This CarQuest has fewer tools, but carries parts for my vintage tractor... anyway, I tell the counterperson what I am looking for. He looks a little puzzled. I tell him "well the car is outside" he says "let's have a look." So we go out, I flip the hood, he goes Oh and goes into the back and gets a similar vac tee. Edelman 767222. The ports are smaller than the one I had on - BUT - this may not be an issue. He opens the pack, says "put it on and see if it fits." I say OK, put it on and it fits the fuel injection pressure regulator fine. I go back in, he rings it up, I go. Turns out though that the vac harness from GM, all in, is cheaper than overhauling the harness with shop supplies (at $9.93 for a little rubber vac tee the $$ adds up real fast... and it probably cost them 99 cents... oh well, a buck for the part and ten bucks to hold it for me until I needed it...).
I got home, put a little black RTV smear on the vac lines and fuel regulator nipple, and installed it.
What I learned:
Hard parts for the Riviera continue to disappear; the Riv-specific ones are gone and the rest are vanishing as the last model they were in becomes ten model years old or so.
GM is automatically transferring NOS inventory to Vintage Parts, which will help. However, if you want anything from Vintage Parts for a GM car, my understanding is you have to get it through a GM dealer. The hassle is that although the counterpeople are supposed to know how to use VP, many (probably for what they think is good reason) won't.
If you can disassemble it without destroying it you can probably fix it instead of replace it.
AZ still really is not the place to go for "shop supplies.' Almost anyplace else (O'Reilly, Advance, NAPA, CarQuest, Auto Value) is better.
The cheapest way to really keep a car on the road still seems to be to buy OE parts at the best price you can get and do the work yourself, unless there is an aftermarket modification you want/need.
Vacuum sucks.
Albertj
