I spend the afternoon trying to clean up the grounds off the battery, installed a new battery, new ground connectors and underneath car cleaned up ground connection and hooked up ground wires which were disconnected. Just tried to jumper the relay to make it work and it would not kick on the fuel pump - where is the ground for the fuel pump relay?
That car has a ground wire wherever there is something that uses electricity.
The one that you're most interested in is a stack of 5 wires all on one bolt in the trans bellhousing. That would be directly below the wiper motor, driver side, usually seen from under the car. Almost impossible to access from above. Once its located, see if thats loose or corroded. That stack of wires has the ECM ground, a ground for the instrument cluster and most of the other engine management features. There will also be a small 1/4" strap that runs from the block to the frame.
That stack of grounds goes into the harness in both directions....some go to the bulkhead seal on the passenger side and others go to the big bulkhead plug next to the battery. If there is no outside sign of damage to the plug its probably not worth trying to pull it apart...the bulkhead seal for the harness on the other side is only a seal and simply seals the harness as it enters the cabin. That part of the harness is where your ECM grounds enter. It does
not come apart.
This almost has to be a ground issue. IF the pump ran with the oil pressure switch 2 wire plug jumped, but the pump will not run with the relay, that screams ground...question is, where?:confused
Something does NOT add up....the FP relay is not even necessary for the fuel pump to operate.
The fuel pump power system is redundant for this very reason. If the relay fails, the car still runs as long as there is oil pressure...only 4 lbs. The oil pressure switch (2 wire plug) is also called the "back-up" switch...for the fuel pump. It has nothing to do with anything else...Having oil pressure is just a simple way of indicating that the motor is running.
If the FP relay is bad, the motor will have to crank for a few seconds to build a few lbs of pressure to trip that switch and then the FP has to run for a second to create fuel pressure. Thats what the FP relay does so nicely, is to prime the injectors so you don;t have to grind the starter forever to get it to lite off..
If you jump the oil press switch, then you can take that fuel pump relay and throw it as far as you can and the car will still run. You proved this. All you did was simulate having oil pressure, which
did run the pump. Right?
So, the problem is within the relay circuit and if you have power to the relay, or use a jumper to supply power and it still does not run, that leaves the ground. A control ground or a common?
A jumper on the common would answer that, and confirming power from somewhere at the relay eliminates everything else, but the control ground. An inspection of the ECM plugs might not be a bad idea...Thats no more work than cleaning that stack of ground wires while laying under the car..
I already know that there are harness issues with the wild oil pressure readings....seen that, been there. That is a rotten wire (corroded or bad insulation) issue within the harness. Wiggling the bundle around will cause different readings on the gauge even with the engine off.
otfl
