Water on floor board on passenger side of 1991 Buick Century

Whenever I see a system which is leaking from more than one or two places, I do a head gasket check because that tells me that the system is experiencing above normal pressures. the wet floor is a heater core. whether it's a water pump or some other thing near it only you can tell. Actually it rarely happens, but the wet floor could be the hose where it meets the heater core at the firewall; again, only you will be able to tell the difference. if the hose connection looks dry, assume that it is the core itself.

I had the same problem on my 98 Century. Turned out when I had my oil changed, they dislodged a rubber "gasket" ( a foot long piece of rubber ) mounted on the firewall seam right in front of the passenger compartment air filter box under the passenger side windsheld wiper. It diverts water from the windshield so it doesn't flow into the fan blower box and onto the floor. It's a crappy design. If it's not in place all the water runs into the car. I had two inches of water on the floor, had to pull up and wring out the soundproofing, hit it with a hair dryer ( took two days to dry ), same for the rug. Put some silicone in the slot on the bottom of the rubber piece and set it on the firewall seam. You should see where it was originally. Good luck.

Hey Gary!

I have noticed this condition in a few cars and have found the solution to be one of the following in each incidence ;
Cause :The drain plug in the floor board was dislodged / missing.
(assume that someone had spilled or inundated the rear compartment floor pan at one point and dislodged the plugs to relieve the excess?).
Correction : reseal the plug holes (bung holes).
Inspection proposal ;
Lay on the ground and inspect the underside of the suspect area of the vehicle. Note the 2.5 inch diameter simetrical holes with black rubber plugs protruding them.
Note condition and presence of plugs.

The front right inner fender (plastic liner that isolates the splash from tread water exhaust) is compromised , allowing the water to flow from the tire to the interior rear floor pan via the hollow thresh hold under the doors (assuming they have not rotteed out yet) to the point in the upper structural pillar between the front and rear compartments.

Solution ; GREATSTUFF the area and paint with a matching paint color.

Sounds like the condensate drain is clogged. for this you need to jack up the car and support it with 2 means. from the bottom look up just inside of the passenger side frame rail on the firewall is a rubber hose sticking out about 1 1/2 inches stick a wire in there and clean it out. You will get water coming out when your done.

The resistors are located in the firewall just above the blower motor. they have a heavier gadge wire going to it. As for the water if it is not antifreeze then you have a leak in your cowl area by the lower windshield. I ran in to this problem on several gm cars such as yours it can be deficult to find good luck

Your heater core is bad. I would recommend a shop if you are a novice.

U need to clear the AC condensation drain, crawl under the car on the passenger side and near the base of the engine firewall u will find a drain pipe, (about 3/4") clear t and the water will stop going on the passenger floor.

Noise from the blower says that armature bearings were going bad. Water on floor is a separate issue, likely the drain on the firewall is plugged. I believe your blower motor can be removed from the engine side of the firewall...it's on the passenger side.

If you have the 4 cyl, look in upper engine area, end of valve cover, mounted in front side of water outlet.
If it's the 6 cyl, Passenger side upper engine area, below alternator, mounted in intake manifold.

I have the same problem with my 91' 318. Water is coming in from the outside air intake at the base of the front windshield, under the black vent covers. If the basin fills up, water enters the vent system throught the outside air intake. Solution: there is a drain line at the fire wall, easily accessible between the firewall and engine block. It drains water from the basin. It becomes clogged with dirt, and prevents water from draining. However, after further inspection of mine I noticed that during periods of HEAVY rain, even a clean drain line is inadequate to drain that volume of water and the same happens. See attached link. Good Luck

http://e30.bmwdiy.info/passenger-water-leak/index.html