90 Excel: unexplained loss of horsepower & runs rough
 

My 90 Excel has over 250,000 miles on it, so just about everything has been replaced at one point or another. But, the engine has always been very reliable, starting up without problems and running smoothly. Recently though, while waiting in a traffic jam, the engine started running very rough, causing the whole car to shutter. It also started running sluggish with a very noticeable loss of power and I have to stay in lower gears longer. While the engine idles, it shutters and begins to stall. I checked timing, sparkplugs, rotor & cap, converter, and I added a fuel system cleaner to the gasoline. The computer isn't throwing any diagnostic codes either. The air filter was recently replaced in a tune-up, so it's not likely the problem. This is a real stumper, any suggestions out there?

Other notes: the fuel pump and filter were replaced less than a year ago, but the new pump has already started making a menacing "whirring" sound, even before the loss of power.
:The exhaust is a constant problem--at the same time this event occured, the exhaust imediately behind the converter dissolved. That's how I was able to check the converter for blockage. The pipe was repaired, the engine trouble remained.
:I'm always pleased when I take this little car to the pump, it is very fuel efficient. But I think this problem is affecting fuel efficiency.
:Still startes up right away, even in cold weather, just wont continue to run without extra gas.

RE: 90 Excel: unexplained loss of horsepower & runs rough
 

Could be an ignition coil block

RE: 90 Excel: unexplained loss of horsepower & runs rough
 

you cat converter is likely plugged from the top

had the same thing with my 88, ran like i was pulling a trailer, also made strange load type noises.

the 88 and 89 model had a recall on the purge valve which when not working can damage the converter.

hope that helps

Jim

RE: 90 Excel: unexplained loss of horsepower & runs rough
 

Just before the pipe dissolved, the weave flex part between the heatshield and the cad converter developed holes. Shortly after that was replaced, the pipe behind the converter gave out, causing the converter to hang down and sound like a really loud lawn mower. To fix the pipe, the converter was removed and looked at and through from both ends. I could not see any blockage. The problem is slowly getting worse too.