1991 Grand AM F/P INJ fuse blown


#1

The vehicle has 70,000 original miles. You guessed it - grandma’s car. My wife drives it now.

The vehicle’s 20 amp fuse blows on occassion. Usually after the vehicle has been driven several times in one day around town.

It is normally driven a few blocks to work and back. During this “normal” daily driving there is no problem of the fuse blowing.

The fuse blows only during “more than normal” driving. I’ll replace the fuse, drive a few car lengths - fuse blows. Leave the vehicle overnight (or two), vehicle operates correctly.

I did replace the fuel pump when this problem began. Did not correct the problem.

I have researched for a schematic and electrical diagram to help find a root cause, but have not found any available to purchase.

We do own a Haynes manual, but that does not have the detail I need for this problem.

Any suggestions are appreciated.


#2

The best way to find this problem would be to find out exactly what is on this fused circuit, then eliminate each thing one at a time.

What else stops working when the fuse fails? Unplug something and see if the fuse fails again. Then unplug something else. When the fuse stops failing you’ve found your problem.


#3

Most public libraries have free access to the ALLDATA web site. This site will provide a detailed schematic of this circuit.

Tester


#4

According to Mitchell On Demand (www.ondemand5.com) this is actually suppose to be a 25 Amp fuse. Not a 20 Amp fuse. Try putting the correct fuse in and see what happens. This should fix the problem


#5

I have the manufacturers wiring diagram and it is a 20 AMP fuse, do not put in a 25 amp fuse, you could cause serious damage. You don’t specify which engine you have but according to my wiring diagram both engine options use a 20 amp fuse for the F/P-INJ circuit.

Since this seems to be a somewhat intermittent problem it could be very hard to track down. The components in the circuit include… fuel pump relay, fuel pump, oil pressure switch, fuel injectors, ECM, and all of the related wires.

When you changed the pump did you change the sock on the pick up tube? Has a new fuel filter been installed?


#6

Thanks to everyone’s reply. I appreciate the help.
The engine is a 2.5 and carburated (sp?) not fuel injected.
I did replace the sock on the fuel pump but not the fuel filter.
Since I posted the request the car has run well - no fuse blowing.
But the car was driven short distances (wife’s workplace). There hasn’t been any long or frequent trips in a short period.
I will look up the references mentioned in the replies and keep everyone posted with the ongoing saga.


#7

I don’t think your engine has a carburetor. It should have a TB (Throttle Body) which has TBI (Throttle Body Injection). It looks much like a carburetor; but, it’s not. It does have a fuel injector which sprays into the throttle body.
The 20A fuse powers the fuel injector, the fuel pump, and the fuel pump/oil pressure switch. A wire to, or from, one of these components could have a bare spot. Check with an ohm meter, and wire wriggle tests.
(Will the problem of blown fuses return?)

PS. You may be able to get a detailed wiring diagrams, as willey has, from the dealer’s service manual (ask), or from www.alldata.com (through public library, or by subscription).


#8

Hopefully the problem will stay away but if it shows up again I would check for a damaged wire in the areas that Willey mentioned.