Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
My wife's 99 STS has surely tried my patience over the years! ....an understatement! I do have a few codes like an air inlet door movement fault and rear wheel sensor shorted, but nothing to point me to where to look as it almost seems to be in limp mode. It came and went a few weeks ago, but apparent it is here to stay this time. I chased a PO452 around for a day, until I realized it was an information only code, and causes no symptoms in performance. Fuel pressure is 45 -55 during operation, and the ignition control module tests as good. The number of cylinders affected seems to come and go.....up to speed at times with missing, and other times will hardly get out of its way! ....because the shifting is affected, my wife is set on it being a bad tranny, but think I have her convinced that engine problems is causing the shift problems.
As bad as it runs...I find it hard to believe that there is zero codes related....not even a misfire code. I need to research more to be sure if all or most of the pertinent sensor performance will show up as a code. My cousin has a shop with diagnostic equipment, but he seems to let his impressions of the problem, keep him from studying the data. I think he showed misfires that come and go, and mentioned something he thought wrong with spark advance. He was willing to bet on the ignition module, but had it checked last evening as good. Before I head back to his shop....anyone with any ideas? Jim
What do you mean by misfires come and go? like sometimes it's missing sometimes it isn't? Sometimes worse than others? I would start with a spray bottle and a salt water solution and check the wires for arcing then check plugs , from what I understand of your explanation it sounds like a basic tune up . How many miles on car and when was last tune up?
The vehicle should store intermittent misfire dtc's..
Since its intermittent on random cylinders, I would start by checking the 'main' stuff first.. Faulty coilpack, bad engine ground?
Very difficult for me to share an input with you guys, as I dont have the same vehicles in my country that you guys have.. So I have no idea what a STS is.. lol
Thanks for the replies. STS is an upgraded Cadillac Seville with the v8 DOHC 320HP Northstar aluminum engine. ....commonly known to "pop" the head bolts at the 100K mark!...DAMHIK!
update...no better with thorough cleaning of ignition module, but after cleaning two of the 4 grounds, along with several of the sensor connectors, it runs much better. Now I wish I had done one at a time, as one appears to be the culprit. I sprayed the ignition wires last night, and no noticeable arching ....more checking and inspection today!
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