If the engine is original it will be the first of the injected 3.5's and a build date later in the year as 86 is when they crossed over from Carbys to EFI. If this is the case, then they don't have liners to slip and are far more tolerant of overheating than the 3.9 these were introduced in and a better engine IMO.
As for the cause of the issues - if it's backfired the flapper could be damaged in it - fairly common problem from what I'm told. These early EFI systems are not the greatest and not sure what spare parts are like to get to be honest. What caused the backfire could be a separate issue which may also need looking at.
I'm no expert on these early EFI's as my 86 is the last of the Carbys, but I stuck a 3.9 with 14CUX EFI in it anyway, so skipped all the fun of the older stuff. Have fluffed around with a couple but not in a major way. Hopefully there are others here that are more conversant with these units.
Bookmarks