Cadillac Repair: 1991 Sevelle STS, negative battery cable, ac delco

Question
Hello; My 91 STS has an intermitten miss at a low idle and once in a while during lower rpms. It feels like a suttle vibration when it occurs. I tried to pull the DTC but came up with none. My first thought is that it is electrical. Do you know of any other 4.6 liter engines with this problem. Any advice you can give me would be greatly appreciated. Thanks in advance,    Larry

Answer
Hi Larry,

       You kind of have me confused because they don't make a 4.6 liter engine in 1991. What year and engine size do you have that way I can better answer your question?

       What I would suggest is to start out by replaceing the sparkplugs and wires. Make sure to use the recommended AC Delco plugs that the engine came with or you could create more problems. Also if you have the 4.9 liter engine replace the distributor cap and rotor if it has more than 30,000 miles on it.

       If you have the 4.9 liter engine they have a problem with the negative battery cable end where it attaches to the engine gets corroded and can cause a miss. If it is located on the engine mount and not under the starter bracket bolt then remove the cable and sand both sides clean, remove the starter bracket and sand it clean on both sides where it attaches to the engine as well as the engine around the bolt hole, bend the bracket slightly to allow the cable to be placed between the engine and the bracket and tighten everything up. If there isn't a braket there then just get the correct size metric bolt(M8X1.25 aprox. 3/4" long) and attach the cable to the engine. Hopefully that will take care of your problem. If not then the injectors will need to get tested for flow and resistance. My dad had a '91 that we put in a bottle of the Valvoline severe injector cleaner in the gas tank and that cleared up a sluggish problem he had...might also work for you if some injectors are restricted and not flowing enough gas.

      Past that are hooking up a scan tool or monitoring the computor sensors through the dash and see if they are all ok.

      Let me know what you have and what happened if you need more help. Bill