7.3l diesel turns over but does not fire

[wapiti]

i have a 99 7.3l and after parking it for a week it would not start. Cranks but never fires. wait light does come on so i replaced the glow plug relay to no avail. so i checked the volts on the 10mm posts (glow plug relay), the battery side is hot (12 volts) but i never get a read on the other side (testing with a multi meter while my wife turns the key on). I pulled and tested all the fuses, none ar blown

also and very weird, decided to check the fuel filter bowl, it was empty. filled it up and replaced the cap. removed the air filter cover and sprayed a few shots of wd40 while my wife turned the engine over, not even a hint of a fire. may have two problems at the same time??? can't hear the lift pump after turning the key on either, could this impact the glow plug relay?

[dray8165]

No - the glow plug relay is not on the same circuit as the fuel pump. The fuel circuit is a loop. From the tank, to the filter assembly, out the pressure regulator, and back to the tank. If you have a dry filter assembly, something is wrong there.

The small terminals on the glow plug relay are different than most standard relays. One of the small lugs gets 12V+ when the key is on - the PCM then provides ground to the other small lug when the key is first turned on and leaves the ground there for 20-120 seconds depending on oil temperature.

The correct test would be to see if the large lug going to the glow plugs gets 12V+ after the key is turned on - if not -then back track the problem.

If it were me, I'd track down the fuel issue first. Once you know you've got fuel, then you could always plug it in for a while to see if it starts when warm. If it does, then go after the glow plugs system.

[wapiti]

i mistated in my original post. the large lug that goes to the glow plugs was tested and it does not gets any juice. i've actually tried two new relays since the problem happened assuming that the first purchase was a bad one. also, i've been told that the relay is for cold weather cranking - it's been mid 70's all week.

[jethro]

to test the GPR jump the 2 large terminals with a piece of heavy wire that will manually work the glowplugs if that does not work try tracking down your fuel problem first. also does the tach have readings when your cranking???

[wapiti]

yeah, i crossed the large lugs to no avail. as for the tach? it does not move. if the problem is fuel would it not have tried to start while spraying wd40 in the air intake?

[jethro]

the cps may be bad as well if the tach does not move when cranking

[wapiti]

well, i replaced the CPS - still no fire. I did reach up and hold the fuel pump while my wife turned key on. It did not pump! Any chance that the glow plug relay and the fact that I do not get 12 volts on the glow pug side when I turn the key on and the fule pump can be related electronically? seem kind of suspicious that I'd be having two problems at the same time when considering that it was not exibiting and problems when I turned it off a week ago.

[dray8165]

Like I mentioned above - I would completely ignore the glow plug issue until you get the fuel issue resolved. Check your owner's manual - on mine (2003) the glow plugs and fuel pump are on different fuses. After confirming your fuel pump fuse is good, I would get under the truck, use your voltmeter, and confirm you're getting voltage to the pump when the key is first turned on. If you are - you've got a bad pump. If you aren't, make sure your inertial fuel switch isn't thrown (again, in the owner's manual). The bad news about the fuel pump relay is that it is behind the radio - so let's hope its a fuse or a bad pump.

[wapiti]

Thank You Dray - after your comments I went back to sqaure one. Pulled all the fuses and rechecked - I found a blown 30amp fuse, appears that the fuel filter heater was the culprit. It had ground out, I replaced the fuse and cut the heater element down to the rubber. Back on the road again.

[dray8165]

You are very welcome. And now you've got at least 8 months before you'll need to get your glow plug system functional!