I'm reading where some of you are having problems and are having little luck with replacing suspected items. I know I am new here, but troubleshooting electrical stuff is somewhat up my alley. If anyone wants my approach to systematically checking this circuit, just say so. Otherwise, I'll keep my mouth shut.

dtl

 

Any help would be great.

 

OK, I'm going to do this in stages, as time permits. Also, please remember I haven't had time to locate some of the components involved on my own truck, which at present is not having any problems beyond a slightly noisy power steering pump.

A quick glance under the hood last night confirms the existence of a heavy gauge yellow wire attached to the battery side if the starter solenoid. Make sure the ring terminal connecting it to the solenoid is corrosion-free, as well as the attaching nut. Per the diagram posted by the illustrious Dave F., this is the beginning of the run circuit that is to be inspected for the symptom of fuel pump non-op after engine startup. The fusible link in the yellow wire should not be far away from the solenoid, probably wrapped up in the factory black tape. It may look like rubberized solid block.

This link needs to be tested. Ground your test light and pierce the insulation of the yellow wire on the side leading "away" from the solenoid. If no light, then you have immediately found your problem; the link is blown. However, if you *do* get a light, you are not entirely home free, and I'll tell you why.

These links, especially ones in high-current, full duty-cycle applications, will deteriorate in performance over time. There are several factors that contribute to this. I have seen them fail to pass current just when cold, or just when hot, or just when the wire is twisted or hanging a certain way.

Also, since this yellow wire is big and constant 12v, the possibility exists that it has been tagged onto for add-on circuits, perhaps a power amp or lighting or trailer wiring or whatever. This will overtax the fusible link's original rating. If you are aware of such tag-ons, you should remove them to eliminate those as possible contributions to the problem. It appears that this yellow wire travels around the firewall area a bit, so look closely.

As all the vehicles in this forum have over 20 years on them, my suggestion is to replace that link anyway, preferably with a pushbutton (resettable) circuit breaker of the same value as the original link. For trouble shooting right now, you can bypass or jump the link. The right way to do this is with a heavy-gauge inline fuse holder wih a 30-amp or so fuse and alligator clips on the ends. This way the circuit is still protected against downstream problems that may have blown the link in the first place. Keep in mind that even if the link tests good with no load, it might still be failing.

Attach your link's bypass and test run the truck. If it still shuts off, we move on.

dtl

 

After looking at the circuit I check the fuse links and jumped out the oil switch and jumped out the safety switch then I pulled the relay and jumped the contacts and the truck runs great so I guess the Relay contacts are bad. Thanks to everyone who helped.

 

Well, jumping the relay's heavy wires does not prove the relay itself is bad. The line from the pressure switch provides 12v to the relay's coil contacts, and of course if that is not happening as the engine starts, the relay has no signal to operate. Also, if the ground wire for the relay is not secure, it will likewise not operate.

However, for the age and cost of the relay, it does not hurt to replace it. Use contact cleaner on the terminal ends or use new connectors if they are corroded, and pack a little dialectric grease in them for insurance. Remove your other jumpers one at a time and test after each one.

If all jumpers are removed and your system works fine, then either the relay's coil or one of the contacts failed. For general info, relays that are subjected to high current loads that are too close to their ratings may actually have their contacts "welded" together. In this fuel circuit, this would result in the fuel pump operating continuously without the engine running.

As this is a constant-duty relay, money spent on a name brand like Bosch or Potter-Brumfield is well spent. Cheapy relays will eventually fail again. The common value for these are 30 amp, and the style you want is an SPDT, or single pole/double throw. Always mount relays with the wires pointing down so condensation can drain out. If you can't see a drain hole next to any of the terminals on the bottom, then that relay is not rated for "exterior" use.

For those who wish to divorce the fuel circuit from the oil pressure switch, temporarily or otherwise, remove the red/yellow wire to the relay. Now run a new wire over to the red wire on the duraspark module and tag on. This wire should be the ignition run line. Test with a light to make sure it shuts on and off with the ignition key. Do not use a crimp-on Scotch-Lok connector. Strip some insulation from the red wire and solder the new wire to it, or if you must, cut and use the right size butt connector.

The relay coil only pulls 1/3 of an amp while in use, so there is no duress on that Duraspark circuit. Personally, I think the factory's use of an oil pressure shutoff is a good one. If the factory switch has failed, new ones that do not carry a Ford dealer's price tag can be used. Here is a link to Summit's 13-dollar universal 7-pound switch's wiring diagram:
http://static.summitracing.com/global/images/instructions/sum-g1438.pdf

I'm sure there are others at the local parts store.

Beyond the relay, the next component to check would be the in-dash tank selector switch.

bhs34, I'm glad you've got your truck's prob narrowed down!

dtl