Hello!
I just bought a 1984 Cadillac Eldorado Biarritz convertible. It has 80,000 miles, a HT4100 v8 (4.1L), and the gm 4 speed auto transmission of that era.
I drove the car home after I purchased it in a private sale. After about 40 miles or 1 hour, the car had a single large misfire, then it stalled. Up till that point the car ran smoothly and the engine did not skip. I let the car rest and drive it again, maybe another 20 minutes, then it happened again - a single misfire then a stall. After letting the car sit for 10 minutes, I could get about 15 minutes of driving before the next misfire. The car runs great except when this happens. It is not overheating. There is no coolant in the oil. After a timed period of rest, the car goes like normal, until it doesn’t. I had someone drive the car, and I followed - when it misfired, some flames came out of the tail pipe.
I myself did a tune up, I put on spark plugs, a distributor cap and rotor, spark plug wires, an oil change, a new air filter, and a PCV valve. I plan on putting on a new EGR valve. I told my mechanic the story, and he told me to take the gas cap off to see if it runs okay and just needs some air, he said it might be running lean. I have an appointment with him in 1 month.
I still need to test it. I haven’t driven it long enough to backfire since. I put porous cheese cloth over the fuel filler head with rubber bands. Do you have any advice????? Please help!
Also is there a good gas additive to clean out the carbs ( or injectors I guess, I don’t really know ) and maybe to clean up carbon???
Thank you!
I had an 83 SDV with that engine and it's only a matter of time before it goes belly up. I've owned 7 Caddy's from 76 t0 97 and that one was the only PITA in the group. Many guys replaced that engine with a Chevy 305 and got many years out of the car.
Unfortunately those engines are prone to severe internal problems like head gasket failure, eating camshafts and timing chain, oil pump failure, distributor gear failure, even head bolts pulling out of the aluminum block, frequently leading to catastrophic engine failure.
Hopefully you won't experience any of these problems. Any of these engines that have survived nearly 40 years have probably had these issues fixed along the way.
What did your old spark plugs look like? Any carbon fouled or burnt? ow old is the ignition module (could be cutting out when it gets hot)? That engine uses a computerized throttle body fuel injection system. Of course it is pretty crude by today's standards. If the ignition checks out and the engine is mechanically good you probably have a fuel injection problem.
Techron is a good fuel system cleaner.
Hello, and thank you for responding!
So when I bought the car, I read up on the engine before hand. I took a coolant system pressure pump to test if it had any leaks. I pumped up the system to 15 pounds and let it sit for 20 minutes. The needle did not move. So at this point, gratefully so, I would say that the head gasket, can shaft, and other overheating/ problems that come from a mixing of coolant and oil are not to blame. When I changed the oil, it was just dirty, there was no gunk and it was not milky.
The spark plugs really didn’t look all that bad. The left bank looked fine, the right bank looked a little ashy or white to me. I will check out on the ignition. The repair manual says that a backfire could be from ignition timing. I will try Techron, thank you. My mechanic and father both suspect that it is a fuel problem after hearing the symptoms.
Thank you again!