I have a 86 sedan deville and and I found a ho alternator for a 89 sedan deville and I was wondering if it will fit. The engine size is different mine is a 4.1 and the other is 4.5 will the alternator fit and not mess up my cars computer
First you need to look at the back of the thing, and if the connectors are the same then it ought to work just fine. If the connectors are different, you will need some custom wiring work, but they are all pretty much the same family so it's only some minor work. I looked at using a 140 amp alternator from the 4.9 but it is not at all the same connectors, and although my electrical guru said it could be made to work I did not want to go that far.
As for physical fit, the mounting holes should be the same and that is about the only that will matter for these cars given the placement. It might be slightly larger but if the holes are the same then the tensioner should adjust to fit no problem.
I'd also suggest you look at some online parts sites and see if the 4.1 and 4.5 alternators are really any different. They may be identical.