Back from dealership, still won't start

[cadillackid]

I never knew about the injectors not firing below 11 volts.. im thinking mine goes below 11 volts most always when im cranking... esp in cold weather.. I was readinfg somewhere that the injectors wont fire if the RPM is too slow.. but info is vague in my service manual about it.. I swear I read somewhere that it needs to see 160 RPM to start nbut thats awfully fast.. mich faster than it sounded cranking last winter when I started it at 0 degrees f without issues.. so not sure thats true..

theres also differences in the computers of the ford 7.3 vs the navistar T444e so its possible what we are reading gets mixed up between the 2.

theres also differences in the computers between the 94-96 and 97-up so some of the info on the web can be for those too..

there are 4 versions from what I can tell..

94-96 (3 box computers)
97-99.5(diamond logic)
99.5-03/04 (diamond logic enhanced turbo / torque / injector seats / split shot injectors)
Ford - its own deal.. later years used electric lift pump, higher RPM (different head gasket), different Cam..

-Christopher

[MeloYelo]

Originally Posted by cadillackid

I never knew about the injectors not firing below 11 volts.. im thinking mine goes below 11 volts most always when im cranking... esp in cold weather.. I was readinfg somewhere that the injectors wont fire if the RPM is too slow.. but info is vague in my service manual about it.. I swear I read somewhere that it needs to see 160 RPM to start nbut thats awfully fast.. mich faster than it sounded cranking last winter when I started it at 0 degrees f without issues.. so not sure thats true..

theres also differences in the computers of the ford 7.3 vs the navistar T444e so its possible what we are reading gets mixed up between the 2.

theres also differences in the computers between the 94-96 and 97-up so some of the info on the web can be for those too..

there are 4 versions from what I can tell..

94-96 (3 box computers)
97-99.5(diamond logic)
99.5-03/04 (diamond logic enhanced turbo / torque / injector seats / split shot injectors)
Ford - its own deal.. later years used electric lift pump, higher RPM (different head gasket), different Cam..

-Christopher

It could very well be that the mechanic who told me was mistaken/confusing the two. I figured if I can confirm it then I won't bother trying to crank it anymore until I find some electrical draw buttttt given what you said I'll keep the gamut of my search pretty wide.

[Trailer2]

160 rpm is about right. If the shop has a scan tool hooked to it while cranking they can monitor cranking rpm and injector pulse width. Does it smoke from the tailpipe? If you have smoke, you are getting fuel and injectors are firing.

[MeloYelo]

Originally Posted by Trailer2

160 rpm is about right. If the shop has a scan tool hooked to it while cranking they can monitor cranking rpm and injector pulse width. Does it smoke from the tailpipe? If you have smoke, you are getting fuel and injectors are firing.

I haven't checked for smoke, I'll plug it in for a while and then give it a go.

I DID find a blown 25a fuse coming off of the relay panel to the left of the pedals, and while down there firmly pressed down all of the relays to make sure they were well seated. There's a HELLA buzzer that's glitching out, making a nice high chime when its held and when pressure is released it's intermittent or not making contact.

Can anyone direct me what that fuse may be for and what circuit that buzzer is warning about?

THANKS FOR ALL THE HELP! I think I'm slowly getting there.

[Jolly Roger bus 223]

Sorry I don't know your engine? All my knowledge is for old school all mechanical stuff.
The buzzer could be your air pressure low air warning unless you already hear that one until you are up to pressure? Mine turns off at 90 psi which is my minimum.
An old school way to check the glow plugs or glow plug relay is to run a seperate or bypass wire directly from your battery to your glow plug bar or maybe for you the leaving side to the engine on the relay and connect that wire with an alligator clip/roach clip or whatever. Wait about 10-seconds and try to start but remove that hot wire as soon as you can.
I had an old excavator that the relay or wire was bad inside the frame so we ran a hot wire to the bar and just wire butted it when we didn't need it. Took to people to start it in the winter or after it set but once it started for the day it was the best we had.
It's worth a try.
Good luck

[cadillackid]

if your buss has air brakes and the air tank is below 75-90 PSI the low air pressure buzzer will be ringing anytime the key is turned on.
-Christopher

[Jolly Roger bus 223]

Originally Posted by cadillackid

if your buss has air brakes and the air tank is below 75-90 PSI the low air pressure buzzer will be ringing anytime the key is turned on.
-Christopher

Not trying to step on your toes?
The low air buzzer should be audible/buzzer when the air is below your systems acceptable level? For me it is 90 psi and I can't even release my brakes until it is at least 90 and playing with it if I step on my brake pedal at minimum release it automatically locks the brakes until the pressure is high enough to hit the road?
Usually minimum is 90 and my switch locks everything out which means a no go anywhere.
But that is my 86 bus and I can't speak for a newer bus?

[MeloYelo]

Thanks for the responses, my brakes are very much hydraulic not air. When I asked the dealership why they had to replace my low pressure hydraulic switch on the master cylinder while working on the fuel pump they told me it broke off while they were unplugging it, they said repeated start attempts can damage the brake sensor if they don't unplug it(?)... my suspicion is that they unplugged the buzzer because they were attempting to start it for so long with the sensor unplugged and that itnwas evidently screaming at them. Maybe I'm paranoid but going in for a no-start and leaving with brake related issues and a broken-replaced pressure switch makes me weary.