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I replaced all gp's less than 5k miles ago. Past few weeks ive had problems "cold" starting even in warm 70+ weather. When the engine is hot its starts no problem. Ive been using block heater pretty much every night... RIP electric bill. Starts easy after block heater, and after its hot i can kill and restart it no problems for a few hours until cools down.
All of my glow plugs give no reading, i watched a few videos and double check my method, still nada. Like i said they are all less than 5k miles old. (Autolite GP's) Just tested GP relay, with input reading 12.7v, output reading 12.43v. Someone said if the difference is less than .3v its good, so GPR should be good. I tested all 8 GP caps and they are all outputting between 12.27-12.3v.
Im pretty confused here, they should not be bad after <5k, and you would thing there would be at least a few that give a reading. What the heck?? Lol
Please tell me if I'm making a silly mistake somewhere...
My method for testing in pic: (yes my multimeter functions properly)
Thanks,
Josh
1991 f350 7.3 idi
Last edited by Joshseekins31; May 9, 2025 at 08:55 PM.
Most people use Motorcraft glow plugs. Autolite do not have a good reputation and 5k miles has been a common failure time for them.
On the ohm out, make sure you are only on the input connection where the wire is attached and then to the middle of the threads. 1 ohm looks correct, well good on a 6.9l GP. I think the 7.3l is same.
Move your red probe out to the tip where the wire connects and see what your reading is. I much prefer testing for amp draw. Most digital meters are not sensitive enough to get a good reading. They draw around 20-22 amps per plug.
Most people use Motorcraft glow plugs. Autolite do not have a good reputation and 5k miles has been a common failure time for them.
On the ohm out, make sure you are only on the input connection where the wire is attached and then to the middle of the threads. 1 ohm looks correct, well good on a 6.9l GP. I think the 7.3l is same.
Copy. Looking into motorcrafts.
Meter reads 1 ohm by default, even when not touching anything. It remains at 1 when touching any of the plugs, and the number doesnt change at all. I think if they were all truly reading at 1 ohm, the numbers would probably dance around a little bit before settling at 1.
Crazy short lifespan!! Im blown away that they are all toast after less than 5k mi. More accurately it was actually right around 3k. Wild. Guess i just need new ones then. Motorcraft it is
Move your red probe out to the tip where the wire connects and see what your reading is. I much prefer testing for amp draw. Most digital meters are not sensitive enough to get a good reading. They draw around 20-22 amps per plug.
I moved the probes all around an tried many different contact points, including what you mentioned. Still nada
actually 5,000 miles from autocrap glow plugs is very good.... from my experience with them they usually burn out after the first or second use.
for your 91, you want motorcraft ZD-29 glow plugs only.
That's pretty high for lead resistance. Usually they are around 0.1 ohm. So the way you were measuring resistance on the GP left only 0.4 ohm, subtracting the leads.
For testing GPs I use a 12v test light with alligator clip leads. Remove the GP connection and clip the lead on the GP. Touch the battery positive with the other end. Bulb lights up good and bright, GP is good.
actually 5,000 miles from autocrap glow plugs is very good.... from my experience with them they usually burn out after the first or second use.
for your 91, you want motorcraft ZD-29 glow plugs only.
That's pretty high for lead resistance. Usually they are around 0.1 ohm. So the way you were measuring resistance on the GP left only 0.4 ohm, subtracting the leads.
For testing GPs I use a 12v test light with alligator clip leads. Remove the GP connection and clip the lead on the GP. Touch the battery positive with the other end. Bulb lights up good and bright, GP is good.
Remove and replace any non Motorcraft GPs.
Tested them with a direct power supply from battery. They're all toast. Motorcraft on the way
thanks
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