89 Ford Diesel 7.3 hard to start

Shortie · Sep 30, 2022

1989 Ford F250 7.3 Replaced glow plugs, I have added a relay switch, which I just replaced as well. Tested each glow plug all were getting 12V. Truck started great for about a week, now it will only start if it is plugged in for at least an hour. I am in NE Arizona present average temps are 75 daytime and 50 nighttime. If I park the truck for about 6 hours even with the warm weather it will not start until I plug it in for at least and hour. Bad glow plugs? Anyone experienced this.

Thank you, Shortie

chillman88 · Oct 1, 2022

It absolutely sounds like bad glow plugs. They can be tested with an ohmmeter. I believe they are all supposed to be less than 1ohm and should all be roughly the same reading. You want to check the resistance between the top where the wire goes and the hex shaped portion of the plug like where you would put a wrench.

franklin2 · Oct 1, 2022

Make sure to unplug the wiring to the glowplug when testing it. They are all wired together, so the meter will read through the other ones unless you undo the wiring.

It's suspicious you are getting 12v at the glowplugs when they are active. The glowplugs are a very large load on the battery system, if they are all plugged in and you take a reading, you more than likely will get something less than 12v. More like 10-11v. My dash gauge reads down to 8v when I am cycling my glowplugs.

chris142 · Oct 1, 2022

How's the compression? Mine will start after weeks with no glows down to about 60f.

franklin2 · Oct 1, 2022

chris142 said:
How's the compression? Mine will start after weeks with no glows down to about 60f.

Yes, but that is with a lot of cranking correct? If the glowplugs are working, it should start like a gas engine.

Jesus Freak · Oct 1, 2022

chris142 said:
How's the compression? Mine will start after weeks with no glows down to about 60f.

franklin2 said:
Yes, but that is with a lot of cranking correct? If the glowplugs are working, it should start like a gas engine.

I'm with you, I can have a 110°F heat index and I still got to have glow plugs to start.

chris142 · Oct 1, 2022

franklin2 said:
Yes, but that is with a lot of cranking correct? If the glowplugs are working, it should start like a gas engine.

Maybe 3-4 seconds of cranking is all. I don't want to burn out my starter

Jesus Freak · Oct 1, 2022

chris142 said:
Maybe 3-4 seconds of cranking is all. I don't want to burn out my starter

Amazing!

IDIBRONCO · Oct 1, 2022

Jesus Freak said:
Amazing!

Not really. I can do that with mine if it's above 95* and the sun's been shining on my hood for a few hours.

chris142 · Oct 1, 2022

Jesus Freak said:
Amazing!

Here it is fast as I can get the key in and turn it. It's 80F today.

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Jesus Freak · Oct 1, 2022

IDIBRONCO said:
Not really. I can do that with mine if it's above 95* and the sun's been shining on my hood for a few hours.

chris142 said:
Here it is fast as I can get the key in and turn it. It's 80F today.

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I crank my truck on oil, so to me it's amazing.

IDIBRONCO · Oct 1, 2022

chris142 said:
Here it is fast as I can get the key in and turn it. It's 80F today.

I'm impressed for 80*. I know that I can get mine to start with no glow plugs at 93*, but it's not that fast. I've never tried at cooler temps and I have no desire to.

chris142 · Oct 1, 2022

IDIBRONCO said:
I'm impressed for 80*. I know that I can get mine to start with no glow plugs at 93*, but it's not that fast. I've never tried at cooler temps and I have no desire to.

I think it mostly has to do with the compression. We All know that an engine with low compression is harder to start.

This one has never been overheated,no blow by and only 127k miles. It won't pull a wet noodle off a plate though.

rreegg · Oct 2, 2022

Hm just a thought OP but since you mentioned the voltage going down to 8(?) when cycling the glow plugs - are all the battery cables/terminals in good shape? Could possibly be ground related

chris142 · Oct 2, 2022

Here is another video after it sat all night. Currant temp is 72F... If yours won't start it's most likely low on compression.

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89 Ford Diesel 7.3 hard to start

Shortie

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