I posted this in 720 forum but figured this would be a good place as ell as it may not be 720 specific. Really need your help.

1985 720 4x4 4wd 5spd. Ok guys I figured out whats wrong with my truck but need your help to learn what to do to fix it. I posted earlier about my engine dying randomly and everyone said they would start with the fuel pump, well that is sorta the problem. Also the truck while running intermitently prior will no longer crank. Heres what I did.

1) Pulled fuel line off of carb cranked. no gas to carb. 2) pulled fuel line off of fuel pump cranked no gas. 3) hooked up fuel pump directly to battery worked like a champ. 4) hooked line back up ran off of battery fuel out at the carb like a champ

Now basically the parts work but my fuel pump will not run when i start it with a key. Now a couple times i turned the key up untill u crank and barely turned it past so that the engine didn't turn over but i did here the pump fire up for a few seconds tried to start nothing and couldn't really get it to do it again. Any thoughts? I checked wiring from pump all the way untill it goes into the passenger floorboard checked good, i also of course checked the fuse. nothing. Is there some mystery component that controls fuel pump at start up? all ideas welcomed and appreciated. Thanks in advance

Heres a link to original post:

zerothread/428239

I may have a similar problem on my 86 Z24. I should know tomorrow after I do the diagnostics.

One experience I have had is with Honda motorcycle fuel pumps which have fuel pump shutoff relay that allows the pump to pressurize the system when the ig switch is first turned on. Once the bike is started a pulse from the spark box (ecm) powers the fuel pump. But if the motor stops with the ig switch on the pump stops pumping - this is a safety feature. If the relay is bad it can be bypassed.

If there is a similar system on the 720 maybe it could be bypassed by a switch-hot wire from the ig switch or fuse box.

Of course you problem could be as simple as a bad connection at the fuel pump. Do we have access to a wiring diagram on here?