Tried Glow Plugs

[TTM]

Hey Guys, How do I know if my glow plugs are getting weak? just lately when I go to start the truck after sitting a few days it seems to crank fine but after it catches it slowly chugs over (like it has no snap after it starts) then runs to idle then runs fine. The old girl has 255km (160k miles) and it has the original plugs. The truck has been starting fine for the last four years. :confused:

[Hubert]

There is a specification for the resistance the glows should read if you test them individually. Search other posts something like around 9ish ohms (but don't quote me)???

Cranking speed (battery strength), how long it turns over before starting (injecting fuel but not starting), injector health (not a good spray pattern or tired and not as sharp opening/closing), fuel quality, oil viscosity, and weather temperature all affect starting and the initial few seconds of running.

If all of the above are good then look at glows more carefully. How much money do you want to spend now or wait til later. At 160,000 miles injectors and glows are tired but if it cranks ok I'd drive it for now and save for maintenance when you can.

[Hubert]

Oh yeah and of course lift pump and fuel filter. The engine will run without a functioning lift pump but it starts harder especially if has sat for a while.

[Iain]

My truck did a similar thing after I installed a glow plug timer. I had 4 weak plugs on the drivers side that burnt out on the first try. The truck would start hard and barely run until you could get it rev'd up enough to start firing on all 8 cylinders.

You may have cooked your glow plugs if you have been trying to extend the glow time or they could have justed burnt out. Make sure you install the AC Delco 60G's. These are the best plugs for up here. They can go for years before burning out and can handle the extended glow times if you are running a timer like me.

How to check: Use an ohm meter to check your glow plugs, you can do this without removing them from the block. If the circuit is broken (put one lead on the glow plug prong and the other lead on the hex head where your socket goes) your ohm meter will read 0. If the circuit is good it should read about 1.0. Any plugs much less than 1.0 should be replaced. Any that read 0 must be replaced. Use a deep socket and you can get most of them without swearing too much!

Good luck!

Iain

[TTM]

Thanks guys for the info I can hear the lift pump hum after I shut off the truck so it should be okay, and I change out the fuel filter. I have a feeling though it's those plugs. I will test the plugs tonight for the proper ohms. Thanks for the those test procedues.

[TTM]

Just tested the plugs at lunch and "0" on the ohm meter on the first two on the drivers side. Going to replace them all. Driver side looks okay to do but the turbo looks like a PIA to get around. Any tricks for R/R for the plugs?

[Iain]

You should have an inner fender rubber flap on the passenger side. Take the passenger side tire off and take off the rubber flap (about a half dozen plastic clips). Look up through the rubber flap opening and you should see the glow plugs going through the heat shield. Unbolt the heat shields and the wires and then pull out the glow plugs (sorry, it has been awhile). #8 is a pain even then as you cannot see what you are doing. Put some Copper Coat on the threads on all glow plugs (Driver side too!) so they do not sieze up in there next time. If you can use a hoist it is best because everything is at eye level and it is easier to see in the tight spots.

[GMC Hauler]

I have done a current check on each plug in the past and seen current flow through each one. Can they short out? What is the normal mode of failure?

[TTM]

Thanks for the tips, going to do them in the next day or so.

[ZZ]

You may want to check the batteries as well if starts cracking normal and then falls way down.