My 1987 6.9 N/A is getting cranky in it's old age and won't start first thing in the morning or afternoon unless it's plugged in. I've checked the glow plugs and they are fine, they all check good and the WTS light stays on about 10 or 12 seconds. If I have it plugged it she starts right up as soon as i turn the key so i'm not thinking it's the return lines leaking the fuel back to the tank but other than those 2 issues i'm stumped. When i'm at work and it sits for 8 to 10 hours, she starts right up but when she sits over night it's a no start time. With the temps in the 60's to 70's i don't think it's all that cold even with the glo plugs working. I don't use ether when i need to start her, i do use flammable brake cleaner so she doesn't blow, just does a slow burn.

 

the symptoms you describe sound like bad glow plugs. did you use test light or ohm meter to test? the light method is supposed to be reliable but only touch the tester to the end of the glow plug where the wire connects.

 

I used an ohm meter and checked for continuity. They all checked good as in the meter shows they all have continuity, no shorts or opens.

 

check for voltage going to the glow plugs. if you have voltage at the plugs, they are bad.

 

how much voltage should i see at the glo plugs?

 

around 12 volts.

 

Ok, i checked some of the glo plugs but every one i checked has 12 volts at the wire on the glo plug. Bad plug or plugs?

 

if power is getting to the glow plugs and it still does not start but starts when plugged in, the glow plugs are bad.

 

If you measured during the g.p. cycle, first 15 seconds of Run, you should actually measure 10V, not 12V. Each g.p draws 10A, and the whole draw 80A, which should lower your battery voltage from 12 to 10. If you still measure 12V, that suggests the g.p. are open circuited, ie > 10 ohms. You should measure 0.5 to 1.5 ohms to ground for each disconnected g.p.

Just check with the dash voltmeter.
[____NORMAL____]

^ --- gauge should read here during g.p. cycle, left of the white bar range, corresponding to 10V

............^ = 12V , no current draw, g.p.'s not flowing 80A, not heating up, bad g.p. controller

 

I connected my multimeter to the glo plugs and when i turned the key to on, not start but on, it went to under 12 volts, closer to the 9 or 10 volt but there wasn't a line just open space where i think the "10" would have been then slowly went up to 12 volts. By the Ford voltage gage, it's under the "10 volt" place to start with then slowly goes up.

 

I just ordered a full set, all 8 glo plugs and will pick them up friday or saturday. When i get the old plugs out is there any way to check them to see if they are good or bad?

 

If the ones you ordered aren't motorcraft send them back and get motorcraft.

 

i only get motorcraft.

 

the easiest way to test glo plugs is with a test light. while they are in the truck. clamp the alligator clip to positive batt terminal. touch the tester to the top of the plug where the wire slips on. if it lights up the glo plug is good. you can test them out of the truck with an ohm meter. you have to have one that reads very low ohms. set it to the lowest setting, then touch the two tester terminals one to each end of the glo plug. I dont remember the exact # of ohms but with mine, if I got a reading, the glo plug was good.

 

the only way i have ever found to really test a glow plug is to hook it up to a battery and see if it lights up or not. test lights and ohm meters can tell you the plug is good, but when hooked to power they very well may not light up.