My 1995 Blazer (late '95 with OBD11) fuel pump won't turn off until maybe 10 seconds after key off. Pump starts with key on and stays on. The relay is supposed to be in the glove box and pulling both relays there doesn't stop the pump. I'm afraid of burning out the pump with it running all the time. Any other places that a fuel pump relay could be or suggestions as to what would keep the pump running if the relay is removed.

 

The oil pressure sending unit on your 1995 supplies an additional path for current to flow to the fuel pump when oil pressure is above ~7psi. If the switch sticks, the pump will remain activated even after the ignition is shut off. Replace the oil pressure sending unit. It is located next to the distributor at the top rear of the engine. CARQUEST by BWD Engine Oil Pressure Switch S4269P: Advance Auto Parts#

 

Many thanks for your help. I hunt and cannot find the switch which should be there. Feeling really stupid. BUT I'm now thinking what I hear is not the fuel pump. Don't hear what I think I should be hearing in the tank with the gas cap off. Any idea of what else could be constantly running back around the tank with key on and for about five seconds after key is off? Afraid that one of these moments something will burn out from constant running.

 

The link that I posted has an image of the switch so you'll know what you're looking for The sender is about 3" long. It's not easy to see the sending unit with the plenum and the distributor in the way

 

Again, thanks. Whether it is the pump that I hear or not, I have to find the switch and try disconnecting it. Refuse to be put in the class of somebody who can't find an oil pressure sensor. If I have to change it, going to be interesting trying to swing a wrench on anything there unless it's vertical, I'll get back with results when I get back to it.

 

Don't feel stupid about that. I'll join you.

When I got my "new to me" Bravada last month, it was exhibiting symptoms of fuel system problems, and there was a noise in the back that sounded to me like a loud, about to fail fuel pump.

It wasn't the fuel pump at all. The "ah ha" moment for me was when i hooked up a fuel pressure gauge. The "noisy fuel pump"noise started immediately when I tuned the key on, but it was a couple seconds before the real fuel pump primed.

Here's how I found my noise. I turned the key on, so the constant noise was going. Then, I started pulling one fuse at a time. If the noise persisted, I put the fuse back and pulled the next one.

For me, the noise stopped when I pulled the fuse for the rear wipers. I turns out that my rear wipers are not only broken, but for some reason, the rear wiper motor was getting power all the time when the key is on. Having the wiper switch in the "Off" position didn't stop it. I haven't even looked at that situation yet, it's way down on the prioritized list of "things to fix" for me now. I just pulled the plug on the wiper motor and put the fuse back.

Oh, and if yours is like mine (mine is an early 1996 Bravada), the fuel pump relay should be in the glove box. There should be three small relays in there, and one larger one. The fuel pump is the left most of the three small ones. I know this because I pull my fuel pump relay every day when I shut it down for the night. I've got a small leak somewhere inside the plenum (probably one or more of the "poppet valve" nozzles), and it won't start in the morning if I leave the system pressurized. I just picked up a gasket set, and I'm gong to look at fixing it for real soon, but for now, pulling the fuel pump relay and letting it die of fuel starvation, then turning the key off is a workaround that gets me a good start in the morning.

 

[QUOTE=Racer_X;664883]Don't feel stupid about that. I'll join you.

When I got my "new to me" Bravada last month, it was exhibiting symptoms of fuel system problems, and there was a noise in the back that sounded to me like a loud, about to fail fuel pump.

It wasn't the fuel pump at all. The "ah ha" moment for me was when i hooked up a fuel pressure gauge. The "noisy fuel pump"noise started immediately when I tuned the key on, but it was a couple seconds before the real fuel pump primed.

Here's how I found my noise. I turned the key on, so the constant noise was going. Then, I started pulling one fuse at a time. If the noise persisted, I put the fuse back and pulled the next one.

For me, the noise stopped when I pulled the fuse for the rear wipers. I turns out that my rear wipers are not only broken, but for some reason, the rear wiper motor was getting power all the time when the key is on. Having the wiper switch in the "Off" position didn't stop it. I haven't even looked at that situation yet, it's way down on the prioritized list of "things to fix" for me now. I just pulled the plug on the wiper motor and put the fuse back.

Hot Damn!!!!!!!!!!!!!!! You got it. Seems like the switch for my non-working rear wipers has a problem. Blessed silence now. Don't know how long I'd have had to play around before I found that.
Many thanks to you and Capt. Hook. Now back to stuff that's really broken.
Life is good.

 

Just an FYI: 95 & 96 have totally different fuel injection systems, and computer controls.


On your 96, I would suspect an external leak at the fuel pressure regulator, or a leaky line, before a stuck, (open) poppet nozzle. Doing the pressure and leakdown tests at the service port, and at the fuel filter outlet, (or fuel pump) would tell you if the leakdown is excessive, and narrow the cause down to the plenum or the pump. If leakdown in the plenum is excessive, it would confirm your theory. You can visually check the lines and fuel pressure regulator after removing the plenum. You can also visually check the nozzles for leakage, but it requires pulling them out of the manifold. Checking the regulator for an internal leak is a bit more involved, but that wouldn't cause flooding after shutdown.

 

Hi,
As I explained above and hoped that it got to you lest you waste more time on my "stupidity", my issue was solved by Racer_X and it wasn't the fuel pump making the noise but the rear wiper motor running to not drive a non-functioning rear wiper.
I do thank you for the help.

 

That's true for most 1995 models, but not for all of them.

Every GM assembly plant switched over to full OBD-II engine controls and wiring before the VIN's changed. There are vehicles out there with "S" (1995) in the year position of the VIN that have 1996 engine wiring and PCM's. Some plants rolled out OBD-II cars for a few months with 1995 VINs, some for only a few weeks.

The opening post said this:
I read that to mean that his PCM (ECU or whatever you want to call it) is under the hood on the passenger side, by the coolant recovery tank, and that his OBD-II connector will yield real data when connected to an OBD-II (only) scan tool.

If that's what he has, his wiring is virtually identical to my 1996.

If he has an early 1995 with the PCM under the dash and the 12 pin ALDL or the 16 pin ALDL connector that looks exactly like an OBD-II DLC, but isn't really OBD-II, then you are correct and his wiring is different from my 1996.