I think I'm havin a glow plug issue won't start when it's cold how do I check to c if the plugs are lighting? It has the rail connecting all of em together I Obo there kno to go bad so any help is good thanks
Glow plug issue
- Thread starter eutsey04
- Start date
there should be codes for the plugs if they are shorted, or if the glow plug module is not firing. If you want to manually check each plug you can remove the small wire going to each plug and take an ohm meter to each. Touch on end of the lead to the threaded part of the plug and the other end to the block and it should be around .8ohms if it's much higher than that it's likely shorted and bad.
good info right here, i had the same thing as OP and i did end up having two bad glowplugs and i still never got a code, are some newer models equipped with better GP controllers that throw codes easier?
federal or cali LB7? How cold is it when your trying to start it? The LB7 should start down to about 30 degrees without glow plugs with just a little extra cranking and some white smoke on startup. Much below that and they won't fire off without glow plugs. If it's a federal emissions LB7 they are known to have the drivers side connector rail rust out right in front of #8 which leaves just #8 working with no codes.
Lb7's have a buss bar that connects all 4 glow plugs together and has only one hot wire going to each bank. Unless it is a cali lb7 then it will have an individual wire on each plug.
Also something to look out for is that lb7 and lly glow plugs physically look the same but are not interchangeable so make sure you get lb7 specific plugs and not lb7/lly plugs like some companies sell. Been down that road.
01-04 federal trucks use a basic glow plug system with 1 relay that sends power to the #8 glow plug, a metal rail connects the drivers side glow plugs together, a wire runs from #2 to the #1 glow plug, and another rail connects the passenger side glow plugs together. The ECM only looks for basic resistance in the glow plug circuit, so if 1 works it will not code. Cali emission LB7's used a controller that would code if 1 glow plug failed(but it didn't always tell you which one), the LLY uses a controller to run the rapid heat plugs, and the LBZ/LMM use a controller wired in on the can bus I believe to run the glow plugs as well as coding for individual glow plug failures(tells you which one has failed).
so i think i did testing wrong, ive had the worst cranking problems and hard start at anything below and im thinking GP problem. so can you test them individually?
I would assume you could still remove the buss bar and perform the same resistance check? I have only messed with LLY's and LMM's so thanks for enlightening me there.
Yes, you can do it that way. I have also pulled them just for the heck of it and ohm tested on the bench. Then I apply 12 volts and watch to see if they are working. Pretty fool proof really.
Applying 12 volts will work on lb7's as they are a 12 volt system. But incase anyone with an lly+ truck wants to test glow plugs you can't just apply voltage to them unless you have a hefty 5 volt power supply because lly+ trucks use a 4.7 volt glow plug system. That's where my "lly and lb7 plugs aren't interchangable" statement came from:thumb:
Depends, LB7's use straight power to them, but the LLY+ vary the voltage as they are rapid heat plugs.
I thought they did, but I wasn't sure. Never heard of an LLY needing glow plugs before, mostly just CALI LB7's and LBZ's.