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Discussion Starter #1
My truck wont fire first try & it only got down in the 40s then when it started next try a lot of extra smoke which looked like fuel came out the exh, r my glo plugs bad or relay ?
 

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Test the relay. Take a multimeter and touch one terminal to the negative post of one of the batteries and the other to one of the two big posts on the relay. One should be dead the other live. Now turn the key to the "wait to start" position and go to the other post. It should now also be live. If one or both of them are not live the relay could be bad. Hopefully I explained that some what understandably. To test the glow plugs pull them out and take a jumper wire and touch it to the glowplug and the negative post of the battery. Then touch the glowplug to the positive terminal of the battery. If the plug glows red it is good, if not it is dead. Either they work or they don't. Again hopefully that makes sense.


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Discussion Starter #3
the glow plugs make sense but the first part of your reply dont, my truck turns over fine very fast just dont fire when its colder, & its not even cold yet...
 

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If you look at the GPR there are like 4 studs. The two bigger ones are the two you test. One should have a constant 12v even with the key off. That is what I said to test first. Then once you have confirmed that the other post that should of had 0v while the key was off should have 12v with the key on. If not then the relay is bad. Hopefully that makes more sense.


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Set the meter on DC volts. Put the black probe on one of the negative battery posts. Put the red probe on one of the "big" terminals on the relay. Then put it on the other. One of them should read 12V (aprx) and the other should read zero.

Now turn the key to RUN and do the same exercise. Now, the terminal that showed 12V above should show something less, probably about 11V, and the other terminal should show _almost_ the same voltage. The _difference_ between the two (also known as voltage drop) should be no more than 0.3 volts.
 

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Discussion Starter #6
Set the meter on DC volts. Put the black probe on one of the negative battery posts. Put the red probe on one of the "big" terminals on the relay. Then put it on the other. One of them should read 12V (aprx) and the other should read zero.

Now turn the key to RUN and do the same exercise. Now, the terminal that showed 12V above should show something less, probably about 11V, and the other terminal should show _almost_ the same voltage. The _difference_ between the two (also known as voltage drop) should be no more than 0.3 volts.
what does the relay have to do with not starting right away ? yes im a dummie... the volt meter does jump around a bit if that is anything pointing to that..:dunno:
 

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the relay supplies power to the glowplugs, no power to the glowplugs= no heat in the cylinder to help start. which would cause hard starts and lots of smoke
 

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Discussion Starter #8
the relay supplies power to the glowplugs, no power to the glowplugs= no heat in the cylinder to help start. which would cause hard starts and lots of smoke
now u tell me lol .. where is exactaly is the relay & or what does it look like ? Is it the starter relay ?
 

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The glowplug relay is on top if the motor right next to the fuel bowl.


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now u tell me lol .. where is exactaly is the relay & or what does it look like ? Is it the starter relay ?
The starting circuit and the glowplug circuit are two completely seperate things. If you find the glow plug relay maybe you can have someone else turn the key on and you can at least see if you can feel it click..then you can go to the voltmeter/test lamp method
 

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the easy thing to do first is open your hood. turn your key "on" and you should hear an audible click from te relay when it goes on.. no click - probably a bad relay - also - you cannot just test to see if there is current on both sides with a test light to make sure the relay works. so you have to use a meter i suppose and get correct voltage on both sides.

although uncommon - a relay can still pass current and not trigger "on" which it what it does when you hear it click. i had a starting problem for months when i first got my truck, and nobody told me about how to correctly test the relay. $500 mechanic bill for glow plugs and still woudlnt start over a $35 relay.. expensive lesson.
 

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Discussion Starter #13
I shouldnt have to plug it in till it gets below 30 anyhow It got down to 37 I went to my truck this morning & left the key on longer than the wait to start said so & it started right up, same thing after work the wait to start light goes off fast , but if I keep the key in that position longer it starts right up, does that mean anything ??? Thanks ..
 

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I shouldnt have to plug it in till it gets below 30 anyhow It got down to 37 I went to my truck this morning & left the key on longer than the wait to start said so & it started right up, same thing after work the wait to start light goes off fast , but if I keep the key in that position longer it starts right up, does that mean anything ??? Thanks ..
The glow plugs stay on for 2 minutes or so after the WTS light goes off.
 

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Discussion Starter #15
ok I will do checks on relay or just get a new one not much money anyhow, & that will get one thing out of the way.. Thanks for input..
 

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ok I will do checks on relay or just get a new one not much money anyhow, & that will get one thing out of the way.. Thanks for input..
and you "shouldnt need" to plug in your truck until the weather is 0 or below.. thats really whats its made for. people just plug them in for the convience and to make it easier on the truck.. AND - if your truck starts easier when you leave the key foward for a while - then i would say the relay is working.. maybe then its time to check the glow plugs themselves.. if not - maybe theres nothing wrong at all..

your wait to start light - has 2 cycles, a long and a short. like mentioned above they will stay on longer than the light does.. sometimes people run an actual indicator bulb that goes on/off with the glow plug cycle so they know exactly when they are on and off.

so just to be clear - the relay controls when ALL the glow plugs go on and off.. so if some are working - they should all be working.. if they arent then its either a harness or glow plug issue.
 

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That video is just plain wrong. No voltage on the switched side does NOT necessarily mean a bad relay. If there is any problem with the trigger circuit (fuse #22 blown, break in either wire going to either of the small relay terminals, PCM or PCM ground problem), the relay won't trigger, even if it's a perfectly good relay. Also, when you turn the key to RUN, because of the load of the glow plugs themselves, the voltage at either big terminal will be less than 12 volts, probably closer to 11 or 11.5 (more on this below).

although uncommon - a relay can still pass current and not trigger "on" which it what it does when you hear it click.
Indeed, and it's actually not that uncommon. This is where the critical "voltage drop" test comes in. Rather than just a crude test light or "is it hot" test, you need a voltmeter that measures tenths of a volt. Either a digital, or an analog with a fairly steady accurate needle. Turn the key to RUN and measure the voltage on the hot side, then on the switched side. As said above, voltage will be less than 12 because of the load, but the important thing is the _difference_. The switched side will be lower, but if the difference (aka voltage _drop_) is more than 0.3 volts, the relay is bad. Indeed, it closes, makes a clicking noise, but can't provide the power to fully light the glow plugs.

AND - if your truck starts easier when you leave the key foward for a while - then i would say the relay is working.. maybe then its time to check the glow plugs themselves..
Still could be either one. It may be doing what you describe above, but providing insufficient power to the GPs. They'll still light, but they'll be like a "dim bulb". Imagine the heating elements of a toaster not getting enough juice. They'll glow, but not as hot. It'll take longer to toast your bagel. Same possibility here; weak relay, GPs running at less than full power, so it requires longer run time (pause with the key in RUN) to start. One of our GPRs did this; voltage drop was something like 0.8 volts, it still triggered, but "underpowered" the GPs.

your wait to start light - has 2 cycles, a long and a short.
Actually, it's a variable cycle, anywhere from about 10 seconds to just 2 or 3. It's based on the EOT (engine oil temp); the hotter the engine, the shorter the WTS time. Same idea with the glow plug run time, but the range is from two minutes down to about 30 seconds. There are graphs charting the WTS time and GP run time as a function of EOT posted as pictures on one of the PSD forums (possibly here on the org; I don't remember).

BTW, even a cheap $10 Harbor Freight meter can do the above. Every now and then they go on sale for $4-$5. At that price, I have one in each glove box, one in each tool box, one in my home office, one in my work office, etc...
 

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I shouldnt have to plug it in till it gets below 30 anyhow It got down to 37 I went to my truck this morning & left the key on longer than the wait to start said so & it started right up, same thing after work the wait to start light goes off fast , but if I keep the key in that position longer it starts right up, does that mean anything ??? Thanks ..
Ya that means you need to cycle the gp's longer :laugh:

I have NEVER plugged my 7.3 in.... even with it being below -0*f.
 

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Discussion Starter #19
I will say I cant hear any clicks under the hood when even my wife turned the key on... its been starting fine matbe it had a bad day now its fine lol ! I still will start with a relay cause they dont cost much..
 
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