Check the operation of all of the fuel injectors. You should be able to hear each one clicking if you use a piece of hose as a makeshift stethoscope. Check for proper operation of the Fuel Pressure Regulator. Make sure the pressures are correct and that there is no fuel getting into the vacuum line connected to the FPR.
You may be able to switch the bad injector with another cylinder and see if the misfire follows the injector.
Usually i would suspect an ignition problem (Bad plug or wire) first and then a dead fuel injector second. Either can cause a misfire on a constant cylinder.
Lastly i would do a compression check to make sure that you don't have a bad valve or a dead cylinder.
after i replaced all of the plugs i did run it for a while. since it did not help, i removed the plugs and did a compression check. the compression check was fine, but i noticed that every plug looked new and clean except #3 was discolored. today i had to drive the car, so i took a spark plug out of a different cylinder and put it in #3. after my drive, i removed the plug and that plug was now discolored. that cylinder had good compression. it seems like that is the cylinder causing the problems. i would really like to replace that injector if you think that it is a good idea. do you know of any websites that might show the whole procedure? thank you for the help! i really appreciate it. i would switch around 2 injectors, but it looks like a big job to take apart and put back together.
It really isn't a big deal to get the fuel rail out. If I remember correctly (if I forgot something, someone will chime in):
Remove the air box
loosen power steering pump bracket and pull out of the way
disconnect throttle cables and detent cable from throttle hammer
remove diverter valve and any piping that's in the way
remove heater hose attached to t-stat housing
remove any vacuum lines running over the fuel rail (EGR, brake booster, etc)
disconnect fuel lines at fuel rail
unhook injector harness (one for each bank)
unbolt fuel rail and lift it out.
Automobile(s): 58 Coupe Deville, 77 Coupe deville, 90 Deville
Re: 1990 cadillac deville
You may have to disconnect the battery and remove the alternator to move the PS pump. First I would check for leaks with either around the injectors with the air cleaner on the car. I assume you have no codes... A bad O2 sensor will cause problems like this also and will not set a code. I went round and round with my 90 Deville before I found that a NEW Bosh O2 sensor was the problem. If you need injectors I would recommend Fiveo Motorsport, $300 for a set of 8. Good luck!
is there anybody that can test the injectors? i cant afford to get all of them. i hoped to replace the one and test the others. i also am really stumped on my 90 and 93 devilles. they both make a growling noise like a power steering pump would make. they have made that noise for years and i keep worrying that i might break down on the road sometime. the power steering is fine. since it is doing that on both cars, is there a certain problem that cadillacs are notorious for or just a coincidence? i bought the 93 thinking i might need a transmission in the future, but then after only having the 93 for maybe 6 months. that one started to make the same noise. nobody can tell me what that might be. i did see a vcc engagement code come up a few times, but it isnt there every time i clear the codes or disconnect the battery.