1990 F150 5.8 problem is,, no initial timer switch igniting fuel pump relay and/ or fuel pump switch, we have gone thru everything, can the computer be causing the problem?? or any sugestions,, everything else works, was intermittant now wont work at all. Like I said we have done everything to find the proble, we are missing something small but hidden,,
Did you check the fuel pump relay connector?, this connector tends to accumulate lot of rust that makes bad connections and can't get the right voltage for closing the switch and the pump won't start. also check the fuel shutt off switch and it's connection.
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First check for spark at any of the sparkplugs,if you have spark next check fuel pump fuse and relay then check fuel pressure.Turn ignition switch on and listen for pump it should come on for 2 seconds then shut off.
The fuel pump draws far too much current to be allowed to go through the ignition switch. It would melt. So there is always a relay. And the ignition just turns the relay on and off. The relay should be in the fuse box I would assume, but I don't remember exactly on a Saab. As a temporary test, you can plug jumpers into the relay socket and run to a toggle switch. But of course this is not a good permanent solution because you can forget and ruin the battery, or it could stay on in an accident.
I had the same problem, I was the Igniter in the distributor, controls power to fuel pump and spark to plugs, I changed coil, fuel pump only to find out it was so simple, try changing the igniter in dist.
from the ignition switch or the starter, power is taken fromeither of these points to fire the fuel pump on start. This is what charges the fuel system so that you can start. then your fuel pump goes into run mode.
If someone can make a power check on the wiring going to the fuel pump with the engine is being cranked, you can possibly solve your problem.
To my knowledge, there is no separate switch to activate the fuel pump. The fuel pump is one of the many electrical devices powered by the ignition switch when turned on. This is necessary since the fuel pump must be active if and when the engine is running. Due to electrical design, that is to reduce current passing through the ignition switch, a relay is used to along with the ignition switch.
Often, this relay would be among the many relays in the fuse/relay box in the engine compartment pretty close to the battery. However, in your particular model and to my knowledge, it is under the dashboard. More particularly, the fuel pump relay is under and to the right of the glove box above the ECU. There would be two (2) other relays in that area and the fuel pump relay is the last almost hidden.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
You can get wiring diagrams from autozone.com -- they have parts of repair manuals online. I have the smae problem but the person I got my 88 fox gl from wired up a switch going to the fuel pump that you have to leave on while driving. I"m probably giong to fix this soon. It looks like the wire powering the fuel pump relay comes from the ignition switch. So if the pump side of the relay is good, but aren't getting power, you may want to see if your ignition switch isn't providing power on one wire, going to the fuel pump relay.