Compression Ignition Addict
Join Date: Jun 2006
Location: Columbus, OH
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This stuff might help....(sorry..long!)
I just went through the same exact problems that you guys are having..here's how I fixed it, and also some FACTS about the glow plug system on a 7.3L (I say Facts cause I was fed quite a bit of BS before I finally got my truck fixed!). First the facts: (some of this stuff may have already been said).
1. The "wait to start" light has nothing to do w/ the actual glowplug operation.
2. If your dash voltmeter gauge goes instantly all the way up on a cold morning, your glowplugs are not getting any juice. Since I fixed my truck my volt meter goes up slowly and until the plugs shut off it won't go all the way to full charge. (Those plugs can pull 100 plus amps pretty easy)
3. Before buying anything, go have BOTH your batteries LOAD tested. Just cause the motor will crank doesn't mean your batteries are strong enough to crank the motor AND heat the glowplugs (or they won't heat up enough..).
4. The Glowplug relay looks similar to the intake air heater relay (Brown in color, round..looks like a solenoid), only it's shorter. It's on the passenger side valve cover and it's the rear-most relay. With the AAA discount at NAPA it's 64 dollars.
5. There is a 9 - pin connector towards the back of the valve cover on each side of the motor that connects the injectors and the glowplugs to the rest of the truck. You don't need to remove your valve covers to test the glowplugs. Unhook the connector, the outter most 2 pins on each side of the connector are the glow plugs, the inner-most 4 pins are the injectors. Use an ohm-meter to test the plugs, a reading of 0.5 to 2 ohms is good. Zero or Infinity (open) ohms is definitely a bad plug.
Now for how I actually fixed my truck: It turned out to NOT be the relay OR the glowplugs (even though I ended up putting a new relay on it). I had my batteries load tested, they were good, HOWEVER, when I checked BOTH ends of my cables for corrosion, I found that my ground cables on the block side were all rusted and dirty. I cleaned all the connections on the main battery cables and where they connected to, that was step one. Next I took all the wires off the glow plug relay (Since I'd bought a new relay in haste) and found that the main power wire to the plugs (big wire) was also VERY dirty and corroded. I cleaned all the relay wires and the posts on the old relay and put it back together and it worked! Turns out all it was was just dirty connections on the battery cables and relay wires! But I learned one heck of a lot of stuff in the process, which was way cool. I hope this helps!
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