I have a 90 model seville with the 4.5 engine. While stopped in traffic I noticed the engine was misotice at highway sing. It misses at idle and low speeds. Do not notice at highway speeds. I have replaced the plugs and wires, added fuel additives, cleaned the os sensors, dist cap. But the miss is still there. All the injectors seem to be working according to the mechanic. However he said it was getting to much fuel. The new plugs are already sooted up as is the o2 sensors. The converter is also getting red hot. I am almost broke and cannot afford to do anymore process of elimination repairs. The only code I am getting is a 0048 or it may have been 0049. I still have the car @ the shop and cant check it. Any help would be great, thanks!!!
It's obviously running rich. The most common cause seems to be leaking injectors but it's hard to check them without pulling the fuel rail with the injectors attached and running the fuel pump, watching for drips. Other causes can be a bad fuel pressure regulator, failed O2 sensors, a restricted catalytic converter, or a very dirty air filter.
E048 (EGR fault) and E049 (A.I.R. system fault) are two separate systems. Verify which of those codes you are getting and note whether they are current or history.
Automobile(s): 1988 Allante' (sold), 1984 Eldorado, 84 Sedan DeVille
Re: 1990 Seville enginemiss
If the A. I. R system is not diverting air back to the air cleaner once the engine temp is up to normal, that air will super heat the cat. converter. The smog pump supplies air to the cat when cold to shorten the time it takes to reach cat. temperature. Once in closed loop 80 % of that air is diverted to the air cleaner. So have him ck that 1st. The smog pump air acts like a bellows applied to a fireplace fire. More air bigger the fire becomes. That car can be monitored thru on board diagnostics to read the fuel trim values in regards to left bank vs. right bank. If the fuel trim is higher on one side then , most likey, thats where a dripping injector is. If the fuel trim is even left vs. right then probably not an injector problem. The fuel pressure regulator diaphram can rupture causing unregulated fuel into the injector rail. Simply remove the vacuum hose to it just after shutting off the engine. There should be NO fuel dripping from that hose. If there is, replace the regulator and fuel saturated spark plugs.