1993 Buick Century 3.3L MPFI OHV V6 - Fuel appears to be liquid and exploding???

[Deparneaux]

After taking out my last set of spark plugs (which were cold-to-mid range), I noticed significant carbon fouling (mostly gas – very little oil, most likely from valves). I then went to crank my engine, which has sat dormant for a little over two months, and when I did – bam! Loud, crackling explosive sound from inside the engine. It combined the sound of a backfire with a gaseous explosion going off. It was very nasty and concerning, so I pull out the plugs again and examine them. They reek of liquid gasoline, despite being brand new. It was an unusually large amount of gasoline – more than the injectors should have probably been releasing. That in particular caught my attention: the plugs are firing in the correct order and are of the right heat range and the engine has already been manually cranked to get oil flowing, but the injectors released seemingly WAY TOO MUCH fuel and it caused a massivemisfire/backfire/detonation (????). I understand that an engine will use more fuel than normal to start, especially when cold, but this was completely overboard and caused one of the most mechanically incongruous, blood-chilling sounds I’ve ever heard while working on vehicles.

My car normally drives extremely well – the previous owner ran very hot platinum NGK plugs that never once saw a drop of oil or carbon residue and were in seemingly perfect condition when I changed them. I replacethem with copper-resistor OEM plugs and in one start attempt the car is flooded with gasoline and gunk with injectors that appear to be pumping way too much fuel in, though no CEL is on.

I had a similar issue just once when I first replaced my coolant temperature sensor – when turning over the car for the first time to drive, I went to crank it and it cracked really loud with a massive backfire/miss. I checked the combustion chamber and it reeked of fuel and gasoline residue. I cranked it again and just seemed to happen to get lucky –it managed to start without further issue and ran perfectly until now. My car is a 1993 Buick Century 3.3L OHV V6 with MPFI (46,100 original miles – 1 previous owner). It uses the OBD-I system and has no CEL lights. Does anyone know how to rectify injectors pumping too much fuel, even though they’re connected (electronically to the PCM) correctly? Anyone else have this problem ever?

 

[HotZ28]

You may have a bad fuel pressure regulator. Have you removed the vacuum line to the regulator to inspect for raw fuel in the hose, or have you checked fuel pressure & pressure drop? Unless all the injectors are leaking the fuel pressure down when the engine is turned off, (not likely) they should not be the problem.