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Ok fellas, I have something seriously wrong under the hood of my '89.
The last couple times I've driven, there's been some sort of rattley sound coming from the engine or exhaust system area--hard to tell. It went away when she warmed up, which suggested exhaust. Like something loose expanding when hot enough to tighten up.
However, things seemed to go real wrong real fast. Today I had to drive out of town for a client meeting and I checked under the hood after starting to try to find the culprit. No luck but I did find a flat plastic cap/lid sitting on the wonderbar, which I did not recognize and wondered if it had been there the whole time I was recently working on my alternator upgrade bracket project.
I made the trip out of town just fine but after visiting some people on the way home, the car got a lot more rattley on the last start-up to head home. And then, as I was driving along, I suddenly discovered that it wouldn't rev over about 1600. I also started getting more induction noise. I had checked the air filter housing in cursory fashion and found mothing obviously amiss.
But.. that's when I realized that the lid I had found was the cover for my bosch MAF. Something else I noticed is that my AC system was all iced up, even though I had not been running the AC and in fact had the heater on (although it didn't seem to be working quite right.) Also... at the rear of the car I noticed that both tailpipes were emitting, along with the typical exhaust idle sound, what sounded like air being let out of tires. A high, loud hiss. Coming from my exhaust?!?
I made it home in "limp mode" with my coolant and oil temps higher than they ought to have been, given the barely off idle RPM, the cool night, and the low load. I also noticed some preignition rattle occasionally.
So WTF is going on here? Could it be two separate issues? MAF and AC system? Or is there some way they could be related? I don't even know where to start diagnosing things under there.
EDIT: It was a distributor carbon button failure leading to unburned fuel in the exhaust leading to destroyed cats.
Last edited by ThickLizzyVetteswerv; 05-13-2024 at 12:42 PM.
Sounds to me like your catalytic converter failed and has plugged up and restricted your exhaust flow. The no power and won't rev combined with the hissing noise from the exhaust, seems to be the likely cause.
When the Puff converts go bad they make a Nasty solid Rattle/Banging noise in the Exhaust system, so testing/Confirming. First one is easy. Cold car take a rubber mallet or a large fist hit the exhaust system listen fee a sound like rocks in the pipe. If you got rocks you got problems, so isolate where.
Next get car safely off the ground and take off the center converter you will probably find that the forward converters are now piled up on center converter clogging it or itself is also destroyed
Thanks, guys. I agree that this seems like a likely cause of at least some of these issues. Namely the banging sound and lack of revs. Currently researching options for a replacement y-pipe to eliminate the pre-cats entirely. (I suspect the issue is with the drivers side pre-cat)
This leaves the mysterious MAF lid ejection as a question, as well as the iced up AC components when the AC wasn't even turned on. Could I have a seized AC clutch? I don't know if it's related, but I've always found that turning the AC on causes a very noticeable drag on the engine. Also, it doesn't blow cold consistently .Sometimes it works great, sometimes it seems to hardly work at all (like when it's real hot out and is needed the most.)
No, I actually had the heat on. And this is another whole thing. That electronic heat control seems like a big liability. I had the heat on but it sure didn't feel like it. I had to push a few different buttons, turn it off and on again, to get it to start putting out heat. Could a malfuntioning heater control circuit be keeping the AC engaged even when it doesn't indicate it?
Don't assume such issues are related, you can be really chasing ghosts if you do.
The failure mode for the climate control system is Defrost On. Even if it's set hot, and heat on at the same time, it turns on the AC.
You can also check AC operation by looking at the clutch for the compressor. It freewheels when the AC is off, and drives the compressor when it's on (although it cycles when it's on). Usually a green and black wire for the compressor clutch for the 1989.
Having said that, it still shouldn't ice up more than just a thin layer of frost. Not sure what part of the AC system is icing up, you didn't say. It shouldn't unless there are problems with the AC system, or perhaps moisture-rain entering the evaporator at the firewall if that's where it freezes up. For "what to check", if it's the larger metal suction line freezing up it's likely caused by clogged up air duct to the finned condensor ahead of the radiator, clean out leaves and debris here as it can really accumulate.
For the other issues, you have good advice here about what to check. Not sure what the problem is with the MAF or cover, who knows, put it back on.
Another good piece of council. I'm not assuming everything happening here is related, as I know that would be imprudent. I'll take them all item by item in my diagnoses.
It was the air dryer (the aluminum canister at the front of the engine bay) and the lines coming off it that were frosted over when I had the heater on, or at least thought I had it on. It sounds like the frost isn't unusual--it's just that it was happening when it wasn't supposed to be on that troubles and baffles me. Perhaps it's in failure mode or perhaps I had it on a setting that actually does turn it on; I admit that I'm not clear on all the buttons of that damn electronic control affair. I'll deal with that after I've dropped my exhaust and figured that part of this problem out..
You guys were right. My passenger precat was totally gone and the drivers side was half full of busted up chunks. The main cat was totally backed up with crap. I took it all apart, cut the pipes just behind the precats, cleaned everything out, and welded it all back up. Hopefully I'll get it reinstalled tomorrow and check function.
I got the exhaust system reinstalled and the car runs and drives again. The emptied out precats create quite a ruckus, which I'm not terribly stoked on, but that can be dealt with later.
The real problem is that I seem to have lost about 100 hp. She pulls off idle just fine and exhibits that great L98 torque we all love but when I floor it, there's a lot of noise and no performance at all! It's totally gutless now. And I can't say for sure but I suspect it's running hotter than typical.
Also, the first shakedown run I did involved a stop at a print shop and I swear I got a whiff of rotten eggs (sulfur) when I stepped out of my car. I haven't smelled it again since then, though, so I'm not assuming my cat is dead just yet.
Anyone have any ideas about why the car now feels gutless? I'm basically green when it comes to fuel injection systems so I don't know my way around this car's engine bay at all, when it comes to the induction.
Could it be in some error mode that needs to be reset? Is that a thing?
The failure of the CATs were likely caused or exacerbated by the unburned fuel going out the exhaust. This is most likely caused by faulty ignition component. Use a laser temp probe on the exhaust at each primary to see which cylinder. Could also be caused by a faulty leaky injector.
The exhaust system is clear now. I have a bowl full of honeycomb crunch I pulled from it, along with 4 mesh fabric rings that must have been part of the structure of the precats.
I acknowledge the validity of the overly rich condition as a cat killer, as this happened to my truck (which lead to me buying this Corvette, actually) but something tells me that's not what's going on here now. I think my precats were in pretty bad shape when I got the car 1.5 years ago, as my neighbor commented way back about how there was rattling when I backed out of the driveway. I'm certain this was precat chunks. It's a 150k mile car and I think they were probably the original precats so I chalk it up to old age.
But it had passed California DEQ before I bought it and it passed Oregon DEQ just fine as well. And it has run well the whole time I've had it with no variation, up until now.
It "seems" like the final catastrophic precat failure I just had, which totally plugged the exhaust and prevented revving over 1600 rpm caused some sort of lingering condition where it's now gutless on WOT. But that's only my superficial observation as an uneducated C4 engine guy. Perhaps they are unrelated. But I don't know where to start diagnosing. I will hit each exhaust port with the laser and report findings.
Okay, thanks for that clarification. So wouldn't unburned fuel in the exhaust trigger an error code? Looking at a list of possible codes, it seems 44 indicates overly lean exhaust and 45 is overly rich. I shorted my A and B pins and didn't get any error codes at all--just code 12.
But I don't know how reliable that is and if it means I can rule out unacceptable exhaust. There is only one sensor in the exhaust system, after all, and it's only monitoring one bank of cylinders.
I just attempted to get exhaust runner temp readings but it's no slam dunk. They all seemed about the same.
One thing that has becomes apparent: there's a fairly loud mechanical ticking sound coming from the lifter valley area. Could this be a failing injector?
Okay, thanks for that clarification. So wouldn't unburned fuel in the exhaust trigger an error code? Looking at a list of possible codes, it seems 44 indicates overly lean exhaust and 45 is overly rich. I shorted my A and B pins and didn't get any error codes at all--just code 12.
Un-burned fuel is un-combusted fuel by definition, it wouldn't show on the o2 sensors as neither lean nor rich... not a lot of OBD on 35 year old OEM ECU's. Most likely cause is ignition system with one or two cylinders not combusting the air-fuel mixture. Bad injectors are not the likely cause, but it's possible.
I don't know about a new noise symptom, could be many things, address one problem at a time and you may solve multiple. If the injectors are ticking, they are working. You can take a long screw driver and place the handle on your ear, and touch different parts of the engine with the other end, and it works like a good stethoscope if you don't have one. Ticking is common for valvetrain issues, but can be other things such as an exhaust leak, faulty accessory, broken piston ring, grounding ignition wire, etc.
Okay, it sounds like I should focus on the ignition for now. I guess the next step ought to be to check all the plugs. Oh goodie.
I'm also wondering at this point if the fact that my MAF sensor cover lying on the wonderbar does in fact indicate some issue with that component or if it was really just a minor coincidence. Does poor performance at WOT suggest MAF issues at all?
As of my last drive around the area up to operating temp, the only real issue seems to be that it falls on its face when I floor it. The catalytic converter is 100 degrees F hotter at the back than at the front and the car starts, idles, and drives normally at part throttle.
Oh, also: When I was just under the hood, I again witnessed what seems like inappropriate frosting of the AC system lines and canister. With the auto climate control turned OFF, why the hell is my AC system doing anything at all? I realize this almost certainly doesn't have anything to do with the other stuff going on but it's really annoying me.
I'm just throwing this out there, but could the lack of power be caused by a stuck clutch on the AC compressor? I would check that before I dove too deep into other causes. If the AC clutch is engaged when it shouldn't be, unplug it and see if it releases. This will tell you if the problem with the clutch is electrical or mechanical.
So I pulled my distributor cap and found this. Just wanted to confirm that there's no way this would have had anything to do with sluggish performance and unburned fuel getting into the exhaust system, right...?!?
I haven't pulled any of the plugs yet but I reckon I'll be buying a new set along with the new cap and rotor.
You guys have really steered me in exactly the right directions here so I want to express my gratitude to all of you for taking the time to provide council.
When I'm done messing with the ignition system I'll try unplugging the AC clutch when it's misbehaving and see what happens. Workin' through the queue here!
04-11-2024, 11:30 PM
Big Trouble in Enginetown
