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Glow plug problems. Really need help.

4K views 30 replies 11 participants last post by  willep74 
#1 ·
Ok guys (and maybe gals), I'm having some troubles with my 1988 Ford F350. The truck has been sitting for a number of years without running and the glow plugs fail to heat up when the ignition is turned on. I have tried cycling the key several times and it just does not want to work. Now if you plug the block heater in for abour 2 hours the thing runs like a top. I have changed all the plugs to brand new MotorCrafts as well as changing the relay for the glowplugs. The relay is receiving 12 volts but when switched on is only delivering 9 volts to the plugs both at the plug terminal and at the plugs themselves. I have made sure that all of the wires were on correctly and that every wire is clean and burn free. The only wire I have not had a chance to check is the ground wire. Just to make sure I was not crazy, I then wired a manual switch to the ground switch wire and ran the relay that way. the most I ever saw (on the terminal and at the plug boot was 10 volts even when bypassing the controller (also with fresh batteries but bad battery terminals.) I have also tested and all of the plugs are grounded well. Now this truck was free (emphasis on WAS. Lets just say O'Reilly's loves me as a customer.) so if someone has a farm fix for this I would appreciate it.
 
#2 ·
Maybe it's just a junk relay. Lol

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#3 ·
Sounds like you've got a high resistance connection somewhere (you mentioned bad battery terminals).

With your voltmeter, put one probe on the battery post itself and the other on the terminal, then activate your GPR and see how much voltage drop you read across the connection. Do the same at each battery post/terminal, ground connection, between cable terminal and GPR post (both inlet and outlet terminals) and you should find your problem. A good terminal connection should read nearly no voltage drop (definitely less than 1 v). The one that reads the highest should be disconnected and cleaned up. Could also be corrosion inside the cable insulation. The copper will turn to green goo, which doesn't conduct electricity worth anything.
 
#5 ·
I'm now working on changing the battery cables to see if that is the problem. Having problems with finding the ground cables though.
 
#4 ·
If your getting 10 VDC at the GP's that's normal voltage when there heating. It's the amount of time that there cycling to heat the precups for combustion, if the cycle time, say at 40*F is 10-12 seconds, that would be correct.

Sounds to me the engine is not turning over fast enough to create the cylinder temp it needs for combustion. That would be caused by low battery voltage to the starter, starter pulls about 600 to 700 amps just to get the engine to start to turn. Check your voltage when trying to start, I would bet its 10 VDC or below, that indicates weak batteries, corroded connections, internally corroded cables, corroded negative cable connection to engine, any or all.
 
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#9 ·
Is there any way to plug in the plug into the loom and test it like you would a spark plug for spark. Like grounding on the block and then turning on the key to see if they heat up?
 
#7 ·
If none of that fixes your troubles, you might try the starter itself. Don't feel like the lone ranger with the multiple trips to O'rielley's. I had a powerstroke that my loving wife called O' Reilly for that very reason.
 
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#12 ·
Is there any way to plug in the plug into the loom and test it like you would a spark plug for spark. Like grounding on the block and then turning on the key to see if they heat up?
You sure can, pull the plug then reconnect it to the terminal after using a jumper to run from the plug body (the hex area) to a good ground on the truck. Have somebody get in the cab and cycle the glow plugs and the removed plug should get hot. And it's well-known glow plugs can "short out" internally at which time they will light a test light but not get hot. That's why the test light theory is not a true test. An Ohm meter is the preferred method.
 
#14 ·
Thanks man for clearing that up for me. 0:). I will definetly try that when I finish up on the battery cables. I will post what I find out from the test. Thanks again for the info.
 
#16 ·
I made my own. Most "real" auto parts stores will carry heavy cable, ends and the tool to crimp the ends on. Otherwise go to a welding shop and get the cable there.
 
#19 ·
You're welcome, I forgot to say a few guys who had trouble buying battery cables used arc welder cable that can be bought in any length and gauge from any welding outlet store.
 
#22 ·
#23 ·
I went today and got 0 gauge lugs and im gonna try to make them fit on the 4 gauge battery cables. Most likely gonna fold the wire and then solder.
 
#25 ·
Or both.....

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#26 ·
Ok guys I finally got it running. I made the battery cables and then hooked up the batteries. Once I did that the glow plugs began to heat up and start working. The only problem i'm having is they won't turn off until the key is off. To fix it I am just going to run a push button and wire that in instead of the controller. Thanks for all your help and comments. They really helped me find out the problems :grin2::grin2::grin2::yesnod::ford:
 
#27 ·
A push button may help turning the GP's On, but they might still not turn Off, I would suspect the GP relay might be sticking closed, better watch it.
 
#29 ·
The problem was the controller holding them on. The timer has gone bad in it but they are now on a button and working fine.
 
#30 ·
The positive cables I fitted are the factory replacements for the truck. They are the same size as the old ones.
 
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