So I have the weird one. The odd man out. The one-year-only 1984 Corvette. And it has problems. Weird ones. Here's the full story -maybe someone can make something of it.

Took it in to Boston one day for job-related training. I noticed it was loosing power a little bit on the highway. Thought it was weird, but chalked it up to the fuel injection, which has never quite been right and always needed cleaner, etc. On the way back, the problem began to gel -the car was experiencing a problem at high RPM. More like it couldn't get there. At lower RPM, it would drive OK, and shift through the gears correctly. Give it gas, and it would run up to about 3K revs and actually LOSE power, the motor staying at 3k and the car slowing down, even though the enging was running like blazes but not going anywhere. Couldn't persuade it to go any faster. It began to gradually overheat, too, but I chalked this up to it being 90+ out and goddamn Boston traffic.

As I drove home, the problem became more pronounced; the car was growing weaker, the motor getting hotter still -beyond the point it could be chalked up to a hot day. I could not get above about 55 no matter what I did to it (before, it could go fast if you sped up gently to avoid high revs) and it began to seriously lose power. I made my exit, and it stalled out at the first light, and nearly overheated. I got it started again and got going. It sat for a while as nobody had time or money to look at it. It still drove, but badly. It was put into storage for the winter after failing (badly) state inspection (one month shy of the cutoff date in MA for all cars 95 and older never being smogged again).

This month we pulled it out of storage and took it promptly to the mechanics, where an old Cadillac tech familliar with vintage high-tech cars had a look at it. He figured out some problems -it had had the wrong spark plugs (apparently GM cars and Bosch plugs do not get along well, as not only were they out of place in this car they had been out of place in the Buick I was driving at the time too, due to some sort of weird system that applies current backwards to the cylinder on the exhaust stroke... if that makes sense), and the wrong wires, and two of the wires had burned through. The connectors for the computer were fouled and the computer was essentially out of the loop, hence why it was not throwing any codes. He said when this happens, the car enters a "limp mode" where fuel is dumped wholesale into the engine (explaining the ****-poor mileage I got througout this ordeal) as this will suffice to run the motor so you will not be stranded. All this was rectified.

I took it home last week and, after checking fluids and applying the injector cleaner the mechanic reccomended, first drove it in earnest on Sunday. On the drive home from the shop I punched it -and it redlined and shifted up with a vengance, just like it should. On Sunday, however, the old problem reared its ugly head -the car would not get over 3,100 revs no matter what you did, and got attrocious fuel economy. It still had plenty of power below 3,100 and did't seem to overheat (held a steady 170°f on the highway, climbing to about 200 when I got off, which then dropped to 180° in town), confirming the power loss was caused by the loss of two cylinders! I could actually go quite fast as long as I kept below 3,100 revs.

I tried to determine if this was a transmission issue or an engine issue by holding it in gear and running it up that way, but when I hit 2,800 revs in 2nd an evil sound happened so I upshifted, and again the evil sound occured at 3,200 in 3rd (a sort of grinding noise which I couldn't pinpoint). This sound does not happen when you leave the selector in overdrive. The trans fluid was dark when I checked it (it needs to be changed) so I discountinued this behavior lest I do something uncalled-for. I am at a loss to explain this behavior in a car.

The capstone happened when I took it to work yesterday. I had decided to drive it around gently and let the injector cleaner work its magic (the mechanic said put two bottles through, so the next fill up will be Shell high-test with the second bottle). Then, for no good reason, when I go to get my lunch, it will not start. 11.9 volts showing, but no cranking, not even the click-click-click you usually get from a just-flat battery. However, I notice an unusual sort of rhythmic clicking comming from the dash. At first I thought it was just the balky, horrible cassette deck (the sound system deserves, and will get, its own thread), so I ejected the tape. Sound still there. I took out the key -still clicking. Weird. Called my girlfriend to get a jump and went back to work. After losing a big sale because a customer couldn't make up her mind, I went outside to fiddle with it some more, and maybe pin down the clicking. Not under the hood, so I open the passenger side door, as it was from that side of the car. Suddenly the clickling stops, so I put the key in the ignition and sure enough, she fires right up. So I call the girlfriend and tell her I don't need a jump, and take it home to swap it for my Suburban. I am not even sure this is related.

As it sits my best guess is the computer has somehow lost its mind/come unplugged again. (In the past the car had bad problems with water incursion and the moisture got into and ruined a lot of things.) Does this behavior fit? And what about that cliky-clicky-no-starty business? Is it even related? This is the first time it's ever done that to me!

 

First thing you need to do is charge or replace the existing battery and check out the charging system, low system voltage can cause all sorts of strange issues with computer controlled engines. Once the electrical system is back to normal check the ECM for codes.
Your power loss sounds like a possible clogged cat, if it was misfiring previously that may have caused the damage, your mechanic should be able to verify that by testing with a vacuum gage, good luck.

 

OK here's some more info -the mechanic said the cat was OK, although when I change the transmission fluid I will evaluate how easy it will be to remove the cat. I have done some exhaust work before, but some cats are a weird shape and I don't trust the bendy pipe in a car like this.

The battery is fairly new and in good shape, and there is no problem with the charging system AFAIK. Remember, when the clicking sound went away it started right up, so the clicking had both drained the battery some and kept it from starting. This car used to have a bad battery in it so I know what it should be doing at what voltage!

 

If it's rev limited the problem is in the engine, not the A4.

Rev limited can come from clogged exhaust, inadequate fuel delivery and/or bad ignition.

The cat can be tested by measuring pressure in front & in back of it; the pressure diff should not exceed a few psi. Of course replacing with a "test pipe" will do the trick too.

 

If I were you, start the car and leave it in park and see if the rpms go up normally and slowly with the gas pedal. If the engine does this it's okay.

What your problem sounds like to me is the clutches inside your automatic are burned and worn. This would explain the brown fluid. Does the trans dip stick and the fluid on it smell burned? It could be your torque converter too. Maybe it's time to go to a transmission shop. All the symptoms you describe sure sound like the transmission needs a rebuild.

 

OK guys -here's the skinny. Tonight I took it out for a brief run after work -it started right up OK after sitting since monday afernoon so there is no electrical problem as far as I can tell. I revved it up in the driveway and was first able to reach 4,200 revs, but then it fell off to 3,200 and I couldn't get it higher. So it is doing this with the transmission out of the loop. The mechanic had said the trans was solid and I do know that the GM automatics rarely go wrong anyway. It does definitely need new fluid and filter, though -this may explain the evil sound I noticed on the highway when holding it in gear, or it may not. I am leaning towards fuel delivery at this point, or possibly air delivery, although I do not know if that could make such a profound difference. Tomorrow I will take the filter off and run it that way in the driveway and see how high it will rev breathing free.

 

Sorry for the double post but I have more info.

I played with it more today, and found a few things. Taking the air cleaner cover off seemed to help, and there was a vacuum leak up at the front in the form of a small tube that had rotted and come away from its fitting. Clamping this tube made the car run better immediately -and lo and behold, there are dampers that control the airflow into the air cleaner which are -wait for it- vacuum-actuated! All starting to make sense now. It will rev high sitting in the driveway just fine. I got it up to the top of the green zone in the tach but didn't want to push it higher as it's unloaded sitting in the drive. Took it out for a quick run for gas (and put the next bottle of injector cleaner in it) and it would rev to about 3800 and seems to be running much, much better in terms of power, fuel economy, and when it shifts. Didn't get to do a lot of driving tests and I'm leaving for a brief holiday tomorrow so I will be away from the car until tuesday. I will have internet access so I can keep up.

 

Cool, you found your problem. Keep looking around for other vacuum leaks there might be more.

I'd still be a little worried about the brown trans fluid though. Well, I don't mean to scare you on that. You said you're going to change it and the filter. So, you should be in good shape there after the new fluid. The brown fluid maybe is the original from the factory and never changed in all the miles. I'm not sure if you ever mentioned the miles, but they're probably up there.

Anyway, good going on the investigating and finding the vacuum leak.

 

keep an eye on your tranny, that is not healthy.

 

I would doubt that this is the original fluid, the car belonged to a Corvette collector who looked after it properly until he became disabled. Then someone broke into it by chucking a stone through the driver's window -to steal the roof. The the stone cracked the dash, so it had no speedo when we bought it. It now has the dash pannel from an 85. It had a roof and window when we got it. I am definitely going to change the fluid and keep an eye on everything, but it is not totally resolved yet. My dad seems to think that the vacuum advance might be screwed up, and there is of course the issue of where that hose actually went versus clamping it. We shall see how this goes.

 

I have an 84 also that I blew a head gasket on. I'm in the process of putting the motor back together but with TPI not CFI.

After doing some extensive reading on this vehicle, one thing I hear often is that the fuel pump on the 84 needs to be changed. The recommended pump is from a 1985. These have higher fuel pressure but can be lowered via fuel pressure regulator. I believe the recommended pressure is 13 psi.

I firmly believe this was what took out my head gasket. Too much driving on a lean motor caused extensive cylinder pressure thus causing high cylinder temps.

My recommendation is change the pump.

 

OK, sorry for the grave-dig but I've made progress with this car and have new(?) problems. I changed almost all the vacuum lines on the driver's side; they were rotted badly. The charcoal cylinder and cylinder solenoid were changed with replcements from some random Chevy that looked right; the original is impossible to find and I assume any other pulls from an 84 will have perished just like mine did. The replacement had the valve right on it; but it was the same valve. The canister itself, however, has an open bottom with a sort of fiter, the old one had a solid bottom with a port that had a Y-piece and two hoses comming out of it going nowhere. I couldn't find these hoses on the diagrams in the shop manual, so I assumed they comprised an intake of sorts and the filter was a different take on this idea.

Anyway, changing these lines and the canister helped performance immensely. I couldn't change one line that disappears into the firewall somewhere into a blob of epoxy, but it was actually in acceptable shape so I left it alone. Car ran pretty well, had the same lack of power and no upshift at very high throttle, but in any sort of ordinary driving it was fine. Then the other day it started to slowy get worse, and now it is pretty much back where it was.

When changing the valve-cover gasket on the passenger's side I found a small brass-looking vacuum valve sort of thing, with a line comming off of it leading to a solenoid valve. The lines are some sort of specialty thing, real fine solid tube with rubber ends going into a special fitting on the solenoid valve, it will be difficult to change or replace, and the rubber ends have perished and cracked. I "fixed" one with electrician's tape, but it's still very loose. I may try doping the ever-living **** out of it with high-temp sealer, and see if that "fix" makes it better until I can get a replacement part. What is that part and where else should I be looking? I'm guessing I blew a vacuum line somewhere; are there any hidden ones I should be looking for, or likely points of failure? I've also heard I can bypass the charcoal cylinder but I've also heard I can't; is there some easy way to "jump around" it for testing purposes?

 

I just think you are barking up the wrong tree with vacuum.

Your problem lies with the computer going into limp mode.

There is a bad sensor somewhere that is causing this. Have you ever touched the O2 sensor? MAF sensor?? Coolant temp sensor??

 

I've never touched those sensors... Is there an easy way to test them for faults? Are some cheap enough to just "shotgun" them? The coolant temp sensor seems OK, car always reports coolant temp which is alway more or less in line with where you'd think it'd be in relation to the oil temp...

 

Oh, the '84 doesn't have an MAF sensor, it uses a speed-density system, and I have no idea how that works... I have lined up the O2 sensor for $20 and we'll see what that does... But the vacuum lines are definitely part of it; changing them helped fixed the problem the first time.

 

Not sure that is the case. You wriggled some wire while you were messing with the vac lines.....now that sensor or wire has returned to the "Shorted" state and you have your limp mode issues.

There is something that is tripping that in the Computer......

I'm not smart enough to help you....but I ask good questions

 

Have you looked at the injectors? Mine would die over 3000rpm, changed the injectors to ones out of a 454 truck and what a differance. I had more power through the entire rpm band

 

Yeah, my injectors are rooted and I know it; they need to be rebuilt. I wouldn't be surprised if it had something to do with them too. What trucks had cross-fire injection to get the injectors out of? I drove it at lunch and it was better but still crappy. I'll pour in some injector cleaner and hit them with carb & choke cleaner, which seems to do them some good.

 

OK, many appologies for the double-post but I have updates, since I drove home from work. I had to drop off a set of keys with a co-worker and made a drive into Lowell, about 5 miles or so I'd say. The car was kinda OK at lunch, but tonight it was absolute rubbish. No power, stalled all the time, could barely move from a stop, got hotter than normal, couldn't rev over 2400 at max. There was a tremendous heat comming from the tunnel, such that I could feel it through the carpet, my trousers, leather boot, and sock! There was a kind of rattle at times, too. I am begining to rule out the transmission in all ways as it would shift smoothly when it was actually at a shift point that fell in line with its limited rev band. The motor wouldn't rev over 21-2400 in or out of gear. I had a theory that it might be a plugged catalytic (a buddy of mine had a car with a piece of baffle or something broken off in the cat which would sometimes plug it up and sometimes not), but when I looked under the car it wasn't glowing or anything to suggest it was faulty.

 

You have a clogged Cat!!!

The screens are falling around inside the Cat....sometimes they are clear and sometimes they are impeding the flow......When they are impeding the flow....that is your heat build up.

I bet you, if you looked at the cat next time it acts up.....it would be glowing red.

If there was a way to keep the 02 sensor in place...I'd suggest you drop the exhaust from the header on back and then go for a drive......but the O2 sensor bung is on the pipe just after the header ends.....

I'm not real sure how to test this theory without major changes to the exhaust. If you have access to a "real" muffler shop......I'd go spend a $100 and get a bypass test pipe put in place of the cat.....just to see if this is your issue.

*Edit*
OK, I read your whole post where you looked under there and no glowing.......But I'd still take the exhaust loose at the Headers and see if you can get the RPMS you need while just sitting in the garage ........don't kill yourself, open the door...