7.3L cold start problem
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Senior User
Joined: Mar 2007
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7.3L cold start problem
I haven't had one of these trucks with the glow plug controller still connected before. The WTS light comes on about 10 sec and the WIF light comes on while crankings... that is normal correct? I checked each glow plug and found all to glow red in 5-7secs. Compression 350 psi. One glow plug connector was not connected, soldered the pin connector back on and reconnected. If I touch my test light to the connector on a glow plug it should light? I tried that at didn't get anything. Or is it just time for the old gal to get some manual attention?
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
Did you have the ground clip on the tester on the positive battery terminal?
Using a test light will only show the glow plug is not burnt out.
The best test is to check the ohms with a multi meter.
Good plugs should read between .5 and 1 ohm with one lead on the threads and one on the connector.
It does take a decent meter to read ohms that close to a short.
Over time as the heating element ages, the ohms go up.
Since the new style controller uses resistance feed back to time the heat cycle the higher ohms make the heat cycle shorter.
Higher ohms also mean the glow plug is not making as much heat as one with lower ohms would.
Indicator lights on while cranking is a bulb test.
Using a test light will only show the glow plug is not burnt out.
The best test is to check the ohms with a multi meter.
Good plugs should read between .5 and 1 ohm with one lead on the threads and one on the connector.
It does take a decent meter to read ohms that close to a short.
Over time as the heating element ages, the ohms go up.
Since the new style controller uses resistance feed back to time the heat cycle the higher ohms make the heat cycle shorter.
Higher ohms also mean the glow plug is not making as much heat as one with lower ohms would.
Indicator lights on while cranking is a bulb test.
Thread Starter
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Senior User
Joined: Mar 2007
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Thanks Dave.. No, I didn't check the ohms. I will have to go back tomorrow and test that. The WTS light stays on for about 10secs.. does that mean it is activating the plugs for 10 secs? or is the light on a separtate timer than the glow plugs? I looked up the photo in your gallery for the controller and put power to the glow plug terminal using a light guage jump wire and it fried the wire. Is that normal? is there a large amp draw for the plugs? How heavy of a wire would be required?
I have a set of 8 new sealed in the bag ZD1A.. I wonder if anyone here has a set of ZD9 they would trade me?
I have a set of 8 new sealed in the bag ZD1A.. I wonder if anyone here has a set of ZD9 they would trade me?
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 16
From: Nutter Fort, WV
Glow plugs start out with about a 200 amp draw if they are within spec for ohms.
The glow plug harness has two 8 AWG wires, one for each bank of cylinders.
Using a wire that small for that amount of current helps reduce the voltage supplied to the glow plugs.
The large draw is why a relay is used.
Are you working on the 1990?
To activate the 90 controller, supply a ground to the white wire terminal while the key is on.
The 86 and earlier relay needs power supplied to the purple wire terminal, key does not have to be on.
The glow plug harness has two 8 AWG wires, one for each bank of cylinders.
Using a wire that small for that amount of current helps reduce the voltage supplied to the glow plugs.
The large draw is why a relay is used.
Are you working on the 1990?
To activate the 90 controller, supply a ground to the white wire terminal while the key is on.
The 86 and earlier relay needs power supplied to the purple wire terminal, key does not have to be on.
