Glow plug logic
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Fleet Mechanic
Joined: Feb 2007
Posts: 1,252
Likes: 113
From: Mandan, ND
Glow plug logic
97
Key on, WTS goes out, volts low (relay is sending power somewhere...) and after 30 seconds, crank no start.
BUT...
If I WTS, light goes off cycle key WTS goes out, cycle key, WTS goes out it fires right up.
I thought the WTS had no connection to time glow plugs run. But yet it seems it does. ??
If glow plugs were still going after WTS goes out, why when I wait 30 aeconds does it not start?
I know something pulling a lot of power, cycles as the engine heats up when running. Always thought it was glow plugs, but now not so sure.
New starter and new cables. Cranks likety split (fast).
???
Key on, WTS goes out, volts low (relay is sending power somewhere...) and after 30 seconds, crank no start.
BUT...
If I WTS, light goes off cycle key WTS goes out, cycle key, WTS goes out it fires right up.
I thought the WTS had no connection to time glow plugs run. But yet it seems it does. ??
If glow plugs were still going after WTS goes out, why when I wait 30 aeconds does it not start?
I know something pulling a lot of power, cycles as the engine heats up when running. Always thought it was glow plugs, but now not so sure.
New starter and new cables. Cranks likety split (fast).
???
Logistics Pro
Joined: Mar 2007
Posts: 4,583
Likes: 841
From: knoxville, tn
When starting cold, don’t put too much emphasis on the WTS light. Watch the voltmeter. You are correct when you notice the draw on the system. That is the glow plugs. When the voltage jumps up, they have cycled off. Then try to start it.
if you feel it still struggles to start, ohm out the glow plugs to see if they are still in good shape. You can also jump the two large lugs on the relay if the relay is not working.
if you feel it still struggles to start, ohm out the glow plugs to see if they are still in good shape. You can also jump the two large lugs on the relay if the relay is not working.
i ain't rite
Joined: Mar 2005
Posts: 65,561
Likes: 5,595
From: Marlboro Mental Hospital.
i am going to say you have a few bad glow plugs if you have to cycle the key three times to start. what happen is cranking the engine ot see if it will kick builds heat in the cylinders. do it enough times and it will eventually fire off.
Lead Driver
Joined: Apr 2016
Posts: 7,210
Likes: 1,341
From: Bahstun
WTS light is just a timer based on temp. GPs saty active for 30 seconds to 1 minute and can turn back on in colder weather if AIT is connected.
If glow plugs are not working right, WTS timer doesn't know this info and says ok when GPs are not really hot enough
Pull Valve cover connector and ohm out outer pins to ground and you should have 1 ohm on each.
Also do this free cleaning
https://www.ford-trucks.com/forums/1...ou-cranky.html
If glow plugs are not working right, WTS timer doesn't know this info and says ok when GPs are not really hot enough
Pull Valve cover connector and ohm out outer pins to ground and you should have 1 ohm on each.
Also do this free cleaning
https://www.ford-trucks.com/forums/1...ou-cranky.html
Lead Driver
Joined: Sep 2002
Posts: 9,550
Likes: 2,034
From: North Texas
You may have weak batts or starter too. Consider the upgraded glow relay also, inexpensive enough.
Easy to test the commanded 'ON' time with a $4 test light clip the output to the small GPR terminal from PCM (should be pink) and poke the pointed end on Pos of batt. Key on, time it with a watch.
Agree 100% with all other suggestions. The WTS is simply a suggestion.
Easy to test the commanded 'ON' time with a $4 test light clip the output to the small GPR terminal from PCM (should be pink) and poke the pointed end on Pos of batt. Key on, time it with a watch.
Agree 100% with all other suggestions. The WTS is simply a suggestion.
Thread Starter
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Fleet Mechanic
Joined: Feb 2007
Posts: 1,252
Likes: 113
From: Mandan, ND
OK, once again I did a ****ty job explaining what I am seeing and what I have done.
Batteries, cables and starter and new and perform well.
I have ohm'd the glow plugs in the past, but will check them again.
I have done the test light thing on relay, functioning as expected (stays on like you would expect it to until engine temp is up enough).
So, if the glow plugs are powered up like the relay says they are, waiting 30 seconds (glow plugs still powered) results in no start. But if you cycle the key 3 times every 10 seconds, it starts.
Perhaps bad glow plugs that heat for a little bit but then fail? Then heat again when power is removed and applied again?
Batteries, cables and starter and new and perform well.
I have ohm'd the glow plugs in the past, but will check them again.
I have done the test light thing on relay, functioning as expected (stays on like you would expect it to until engine temp is up enough).
So, if the glow plugs are powered up like the relay says they are, waiting 30 seconds (glow plugs still powered) results in no start. But if you cycle the key 3 times every 10 seconds, it starts.
Perhaps bad glow plugs that heat for a little bit but then fail? Then heat again when power is removed and applied again?
i ain't rite
Joined: Mar 2005
Posts: 65,561
Likes: 5,595
From: Marlboro Mental Hospital.
put a small led light in the cab one side to ground, one side to glow plug output of the relay.
if the light is on power is going to the glow plugs.
if cycling the key every ten seconds or so will get it to eventually start, you will either see power going to the glow plugs turn off, or the glow plugs are bad.
i see WTS light go out after around 15 seconds or so, but the glow plugs remain powered for up to 1 1/2 minutes depending how cold it is.
i also use a white rogers "stancor" relay. parts store chinesium relays are pure garbage anymore, i have seen 5 in a row bad out of the box.
if the light is on power is going to the glow plugs.
if cycling the key every ten seconds or so will get it to eventually start, you will either see power going to the glow plugs turn off, or the glow plugs are bad.
i see WTS light go out after around 15 seconds or so, but the glow plugs remain powered for up to 1 1/2 minutes depending how cold it is.
i also use a white rogers "stancor" relay. parts store chinesium relays are pure garbage anymore, i have seen 5 in a row bad out of the box.
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Lead Driver
Joined: Apr 2016
Posts: 7,210
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From: Bahstun
Wonder if you have a IDM or PCM power relay issue. Their contacts wear out over time and can make for weird starts.
CPS wire can break and do similar. Does tach always work when cranking?
CPS wire can break and do similar. Does tach always work when cranking?
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Fleet Mechanic
Joined: Feb 2007
Posts: 1,252
Likes: 113
From: Mandan, ND
129k
Anything below 50 it struggles (when dead cold) unless plugged in.
What I am having trouble grasping is there is a good load on system with key on. Can see volts decrease when relay snap shut. Why would volts drop like a load is on, if glow plugs were defective?
My logic (could be faulty) is that if the glow plug is faulty it will be an open circuit, hence no load.
Following my perhaps faulty logic is that if all the glow plugs were faulty, there would be very little voltage drop (load) when relay engages.
OR...can a glow plugs still draw a ton of amps, bit not heat up? That seems counterintuitive...
Anything below 50 it struggles (when dead cold) unless plugged in.
What I am having trouble grasping is there is a good load on system with key on. Can see volts decrease when relay snap shut. Why would volts drop like a load is on, if glow plugs were defective?
My logic (could be faulty) is that if the glow plug is faulty it will be an open circuit, hence no load.
Following my perhaps faulty logic is that if all the glow plugs were faulty, there would be very little voltage drop (load) when relay engages.
OR...can a glow plugs still draw a ton of amps, bit not heat up? That seems counterintuitive...
Thread Starter
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Fleet Mechanic
Joined: Feb 2007
Posts: 1,252
Likes: 113
From: Mandan, ND
put a small led light in the cab one side to ground, one side to glow plug output of the relay.
if the light is on power is going to the glow plugs.
if cycling the key every ten seconds or so will get it to eventually start, you will either see power going to the glow plugs turn off, or the glow plugs are bad.
i see WTS light go out after around 15 seconds or so, but the glow plugs remain powered for up to 1 1/2 minutes depending how cold it is.
i also use a white rogers "stancor" relay. parts store chinesium relays are pure garbage anymore, i have seen 5 in a row bad out of the box.
if the light is on power is going to the glow plugs.
if cycling the key every ten seconds or so will get it to eventually start, you will either see power going to the glow plugs turn off, or the glow plugs are bad.
i see WTS light go out after around 15 seconds or so, but the glow plugs remain powered for up to 1 1/2 minutes depending how cold it is.
i also use a white rogers "stancor" relay. parts store chinesium relays are pure garbage anymore, i have seen 5 in a row bad out of the box.
Thinking about this, I should check voltage at output of relay. If significantly different from input of relay, it may indicate a bad relay.
I see with Complete Performance has that White Rodgers relay in stock...
i ain't rite
Joined: Mar 2005
Posts: 65,561
Likes: 5,595
From: Marlboro Mental Hospital.
a few bad glow plugs will screw up the computer. it senses power draw. if the glow plugs are only drawing 140 amps it will turn the relay off faster than it would drawing 200+ amps.
diesel orings is the cheapest i have found for a stancor relay.
https://dieselorings.com/products/16...low-plug-relay
diesel orings is the cheapest i have found for a stancor relay.
https://dieselorings.com/products/16...low-plug-relay
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