88 7.3 won't start

I have replaced bad glow plug and repaired leak in fuel system. I only have 8.4 volts to the solenoid on injector pump. Glow plug light stays on for 7 seconds. I replace fuel filter, could I have air in the line to the injector pump?

Thanks for any Help!!

should have a little more voltage to the injector pump, check the wiring.

It sounds like you might need 2 new batteries and or cables. The amperage draw of the diesel's on cranking is enourmous ... thats why there are 2 batteries. If the ground cables look like crap, replace them too. If you know how to do a voltage drop on the cables do it or have a friend crank it over and with your bare hand grab the ground cable close to the block/frame where it is grounded. If it gets hot fast, the cables are no good. You need all the availible volts/amps to crank the engine over fast so that the compression will build enough to support combustion.
In addition, in 1986-88, somewhere in those year models, the glow plug controler was located in a bad spot and would short out due to water ingress. The controller would literaly keep the glow plugs on until the timer ran out and burn the tips off the glow plugs. If you have been cranking it without starting she will burn off all the diesel and really smoke (white) for a few seconds. If after a few more cold starts and it still pumps out white smoke you more than likley have a few bad glow plugs.

Keep us posted please.