Fuel pump inertia/kill switch location??????

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demarpaint

demarpaint

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Hi and thanks in advance. I would like to know where the inertia switch is located on my 95 Caprice Classic 4.3L. The switch that kills the fuel pump in the event of an accident. That is if the car even has one. I have intermittent starting problems where the fuel pump is not kicking in and the car cranks and cranks, and have reason to believe this switch is at fault.

It will run perfectly for weeks with no issue then won't start, then will start w/o issue. The fuel pump is new, and proper operation was verified on re-check by mechanic for same problem.

Thanks
Frank D
 
You need a wiring diagram for your vehicle to find out if there is an inertial kill switch. Other vehicles use a Main Fuel Relay controlled by ECU that stops power to fuel pump if no rpm's.

I know that some GM vehicles have a low oil pressure safety switch that disables starting if the oil pressure is low, or more likely if the switch is bad.

good luck
 
No luck, I checked before I posted.......Thanks, it was running fine yesterday, and is dead again now, then for no appearent reason will start right up run fine for a week or more and then not start. Mechanic can't find the problem, I might as well trouble shoot it myself. These switches go on the Fords, not sure about GM.

Thanks again!
Frank D
 
My 93 Suburban has the fuel pump through the oil pressure switch. Have replaced two fuel pumps and no fuel pump relays. I keep hoping it would be the relay as its a LOT easier than dropping the tank and replacing the fuel pump.

For a free wiring diagram go www.autozone.com choose your vehicle then select repair info then repair guides and you can get to wiring diagrams.

There should also be a fuel pump relay and fuse. The fuel pump relay provides about 5 seconds of power to the fuel pump regardless of oil pressure, then will cut out if not oil pressure. At least thats the way it works on my Suburban.

Next time it cuts out, have someone turn over the engine and just when they hit the starter give a pound or two to middle of gas tank with fist. It will shake up the fuel pump if its stuck.
 
Thanks for the replies, I checked the autozone link and oddly they don't show the 95 Caprice. I will punch the fuel tank in the morning, its not starting as of a few hours ago. I was bouncing up and down on the rear bumper.

I'd hate to think its the fuel pump, I just paid $350 to have it changed out about 2 months ago. I don't want to have it towed, and will probably have more success fixing it myself this time.

FD
 
I would buy a manual before I pulled the fuel pump again. They can be had on EBAY cheap. The websites do not list an inertia switch for the vehicle but do list the fuel pump relay. Maybe its not called an inertia switch.

If you walked into the service area of a Chevy dealer I would bet the service manager or a mechanic would tell you if there is a inertia switch or its controlled by oil pressure.

Maybe you could buy one on EBAY, but ask the seller to fax you the wiring diagrams before he sends it out, that way you do not have to wait.

I assume who ever replaced your fuel pump also replaced the strainer/sock on the end of the fuel pump, that prevents rust particles from getting into the pump.

Lastly some people say that people who keep the fuel tanks very low go through fuel pumps. Not sure I believe that, but I keep the fuel tank low and have gone through two in a year.
 
if you don't want to spend a lot of $, get a Haynes repair manual for $17.....they have wiring diagrams in the back.
 
Thanks for the info, the strainer and fuel filter were changed with the pump. Yesterday the car was dead in the driveway today it started.

I noticed the last time it didn't start I couldn't hear the fuel pump pressurizing the system this time it did. As it turns out I don't think this car uses an inertia switch to kill the fuel flow in the event of an accident. I'm used to Fords.

I am thinking the fuel pump relay might be bad.

I went to 2 local parts stores looking for Chiltons or Haynes manuals and no one had them for that car.

Any idea where the fuel pump relay is? I stopped by the mechanic that changed the pump and told him what was happening. His reply was unless it was dead while he had it finding the problem is almost impossible. I am not happy with that answer, and would take the gamble and change the relay myself.

If anyone has an idea where it is please let me know, I have a manual on order but it will be a few days before I get it.

Thanks,
Frank D
 
Your 1995 Caprice has no inertia switch. The fuel pump electric supply goes through the oil pressure switch, just like Donald's Suburban. The fuel pump relay is in the fuse block in the engine compartment -- near the passenger side hood hinge. There are three identical relays int hat fuse block. Swap the fuel pump relay for one of the others and see if that helps.

While you are looking at that fuse block -- a diagram of what fuses and relays feed what is under the lid -- look at the post that attaches the battery feed cable, toward the center of the firewall from the fuse block. It may be covered with a black plastic cover. If that post is white -- rather than yellow -- or has any signs of overheating, like the black plastic cover is melted, do not start the car until the post is replaced with a brass one. There have been fires that burned the car to the ground from the white, pot metal, post deteriorating. Any Chevrolet or Buick parts department can get you the brass post. There was a TSB on this.

For more information on your B-body go to http://www.impalassforum.com/ and click on the links to the forums. Lots of us have these cars (I have two), and have been there before you.
 
Two other thoughts, (again coming from my 93 Suburban)

1) The next time it does not start, spray some starter fluid down the intake and see if it at least starts for a second, then you will be sure its a fuel issue of some type. You might be lucky and it will keep running in which case the problem might have been the initial 5 second timer that gives the fuel pump power until the oil pressure kicks in.

2) The wiring from the fuel pump assembly comes out with 3 wires plus a ground. Two wires for the fuel sender and one for fuel pump power. The connector is very near the fuel tank. The ground just goes to a screw that is screwed to the chassis. This screw and the chassis can be rusty not getting a good connection and the fuel pump not get any power. With a wiring diagram and the wire color identified, you can pull apart the connector and with a DVM check for voltage on the fuel pump wire.
 
Also when your pump was replaced, was it just the pump or fuel sender assembly and the pump? If just the pump, was the short 8" harness to the fuel pump (inside the tank) replaced or did they just slip in a new pump? This short harness was included with my pump as there were some problem with the electrical connector going to the pump. If you replaced the fuel sender assembly, then it would have been replaced.
 
Donald that is all good advice for Frank. The ground for his fuel pump is in the trunk at the driver's side hinge. I think the tail lights ground at the same location, and that screw and those wires do deteriorate over time even in that relatively sheltered location.

Fuel pump in-tank wire harnesses are an issue for Caprice/Impala/Roadmaster (B-bodies) as well, but a separate wire harness is not available from Chevrolet. One has to spend several hundred frogskins (even at the good-guy discount price) to replace the entire fuel gauge assembly when the in-tank wires go bad. Checking the connectors in the fuel pump electrical supply and ground is a good precaution before replacing the fuel pump again. All that said it is not unheard of for brand new fuel pumps, even those from the GM parts counter, to go bad in short order.

Of course operating the car with low fuel levels will exacerbate the fuel pump issue. Many people don’t realize that fuel is the cooling medium for the in-tank fuel pumps which are so common on fuel injected vehicles.
 
Gentlemen thanks for the info here, is an update. As mentioned the car has no inertia switch. I took a chance and changed the relay, drove the car for a few days and got stuck yesterday. I was in an area where the car had to be off the street at a certain time. I had it towed in last night to the shop that changed the pump. My luck being the way it is, the car started for him this morning.

He claims he changed the complete pump assembly and screen when he originally did the pump in late December. In January he re-checked wiring etc because I had this problem. Now the situation is worse and he claims its not the pump. I said I would leave it there until it doesn't start for him, appearenty that is the only way he can trouble shoot the car.

Frank D
 
I refill the tanks on all my vehicles between 1/4-1/2 tank of fuel, I never let them get to 1/4 tank. This guy is one of the better mechanics in the area, and I realize trouble shooting intermittent problems can be a real PIA!!!!!!!!!!

Frank D
 
Well the car's been sitting at the service station since it was towed in Friday night. Saturday morning it started up and ran fine. Monday and today it did the same thing, he can't find the problem. I told him it could be a week, two weeks or longer before it happens again.

Other than finding another mechanic and going through this whole nightmare again or selling the car any suggestions? I want to leave it with him longer, but I get the feeling he's convinced there is nothing wrong with it.

Frank D
 
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