Engine Performance problem
1995 Chevy Corsica 6 cyl Front Wheel Drive Automatic 142000 miles
I've had a lengthy problem with this vehicle and no one has figured out what's wrong with it. When I'm driving on the interstate I start to lose power after a while, that is the car is still running but pushing the gas starts decreasing in how much it accelerates the car until the car stops completely. The engine makes a whirring sound like a very loud dustbuster or a blender if I floor it. There's also a rotten egg smell, which I've been told is hydrogen sulfide forming in the catalytic converter from sulfur in unburnt fuel. First mechanic I take it to says its the converter, so new converter. Second one says it's the fuel pump, because it's an internal fuel pump this means new pump and tank. Next mechanic tells me it's leaking coolant out of the intake manifold gasket(a common problem with this engine). At this point I've spent so much not fixing the car that I begin repairing it myself because I don't have the money to continue to pay someone else to, and I've never worked on cars before.
I replaced the gasket which was indeed leaking and put in a new one that's not supposed to leak (I recently had to open it back up again and it didn't appear to have failed like the last one though the ATV on the ends of the engine may not have been adequate enough). Of course replacing the gasket doesn't fix the problem. So after rooting around some more I figure out that it's probably a misfire causing unburnt fuel to accumulate and get into the converter. The car has never had a tune up as far as I know (it was used when I got it) so I started doing that, new air filter, fuel filter, pcv valve, spark plugs, spark plug wires, new o2 sensor, even threw in a fuel pressure regulator for the heck of it. No change. So I cleaned out he fuel injectors thinking they might be dirty. Nope. Malfunctioning EGR valve? Nope. Clogged manifold intake port from the EGR valve? This time yes, but not the cause of the problem. I did a compression test on it and it came back about all about the same. All looked to be in a fairly normal range, with psi < 180 (maybe closer to 165-170) and greater than 150 although, Cylinder 2 would not go above 150 and cylinder 1 would not go above 155ish. I tried running it and applying gas while parked to listen for an audible misfire, but it doesn't sound like it's misfiring to my untrained ear. There is popping out of the exhaust when I take my foot off the gas, but that's it. It holds a rough idle though. The spark plugs showed no signs of fouling when I replaced them, they were clean and didn't look whitish so I figure they probably weren't overheating, or if they were that could be attributed to the intake manifold gasket. One of the ignition coils did appear to have plating coming off and had a slight brownish tint compared to the others. I haven't done any other diagnostics on it. Would check OBD but from what I've read my model came out between OBD I and OBD II and uses something like OBD 1.5.
Most recently I started trying to clean off some of the carbon build up, cause there seemed to be a lot but other than that I'm out of ideas.