85 Century - periodic rattle with "Service Engine Soon" light

[RonTruppa]

I just helped my girlfriend get this 85 3.0 L Century Limited. Old lady story: One owner (school teacher), 54K miles, drove it less than a mile to work 5 days a week. All proper maintainence was done, but a lot of brittle hoses, caps and wires.

CA car, but I went through it for smog check: new plugs, wires, dist cap & rotor, fuel filter, air filter & element, oil cap with bad leak, and oil, gas, and transmission treaments for 1,000 miles on highway. It passed easily.

One week ago, the coolant overflow starts bubbling (brittle seal in radiator cap), and the upper radiator hose bursted open spilling out all of the coolant. I replaced the hose, radiator cap, coolant, and put in a new fan switch (stopped working after overheating), but now I'm hearing a low "exhaust-like" knocking/clacking in the engine occassionally, accompanied by the "Service Engine Soon" light. It's usually at a low idle, but never at start up, only when the engine gets warm. And when the car is fully in motion on the street or highway I can see the "Service Engine Soon" light go on and off periodically. There's no temp gauge and the "Overheating" light works, but never goes on.

It's also pretty consistant when it's on regardless of the car's idle or acceleration, it doesn't get louder or quieter. Car works likes new and runs beautifully minus periodic tranny slippage b/w 1st & 2nd gear and a slightly rough idle. Any advice would be much appreciated!

[maximagirl420]

A similar problem with mine ended up being a loose belt. Plus, coolant ruins belts.

[luke146]

hI,i'D LIKE TO KNOW IF YOU GOT YOUR PROBLEM SOLVED.i HAVE SOMETHING SIMALAR TO YOU,MY MECHANIC WAS GOING TO RESET THE SERVICE ENGINE LIGHT,BUT I DON'T KNOW IF HE DID,I HAVE THE SAME TROUBLE.THANKS DAVE

[RonTruppa]

Originally Posted by luke146

hI,i'D LIKE TO KNOW IF YOU GOT YOUR PROBLEM SOLVED.i HAVE SOMETHING SIMALAR TO YOU,MY MECHANIC WAS GOING TO RESET THE SERVICE ENGINE LIGHT,BUT I DON'T KNOW IF HE DID,I HAVE THE SAME TROUBLE.THANKS DAVE

I have another posting on this subject (a few postings away from this one). The group advised me to check and/or replace my EGR valve in case it was stuck closed. I did that, but the EGR valve wasn't the problem. My mechanic and I came to the conclusion that the noise is definitely coming from the smog pump (CA car). I did the paperclip method to find out the error code on my Service Engine light is 44 (lean exhaust - problems are from bad vacuum hoses and/or the poor mixture of fuel/air from them). So I started the process of replacing mostly all of the vacuum hoses and fuel lines. The engine idle is running a lot better now with a lot more power, but the problem still occurs (even though it's less frequently now). My next step is to replace the hoses leading from the smog pump to the exhaust line. If that doesn't work I'll just replace the entire smog pump (which seems to be a very cheap item based on all of my current research). Also, when I disconnected the wires that are connected to the smog pump (during the noise and illuminated Service Engine light) it didn't seem to make a difference. So it could possibly be faulty or dead wiring leading up to the smog pump.

Hope it helps.