'91 7.3 Glow Plug Relay

[PSDfreak]

On a friends of mines '91 7.3 the glow plug realy clicks on and off, on and off when you start the truck...as opposed to my PSD which when the truck is cold and started the relay closes, leaves the plugs on for approx 90 seconds then open and turns the plugs off....

Should the relay in the '91 be clicking on and off like that or should it stay on solid until the plugs are ready to turn off??? Sounds like a bad relay to me but just wanted to be sure before replacing it.

Thanks,
Casey

 

[tractorman86]

no no no that is what they are suposed to do, should stay on for a few(5-10) seconds then cycle as mentioned.

 

[PSDfreak]

oh ok...Well then I am glad I checked...I wouldnt say its even 5-10 seconds though, maybe every 3 seconds it cycles....This goes on for approx a minute or so till its shuts off completely...You can hear it and watch the volt gauge move as it clicks...Sounds normal though?

 

[tractorman86]

yea what is the wheather like up there, pretty mild isn't it? sounds ok to me. if you have a multimeter handy ohlm out each glow plug he might have one or two out but you're probably alright

 

[LCAM-01XA]

Something ain't right with his GPs, probably some burned out - normally the relay comes on and stays on for a duration based on the engine temperature (may be pretty short with a cold engine in hot weather, or near 20 seconds with a cold engine in very cold weather), but it should not cycle on and off - cycling is a classic symptom of dead GPs, so have your buddy test them for resistance, should be less than 0.5A between the bullet connector and the base (you need to unplug the harness from the GP prior to measuring).

 

[bigbaddiesel37]

if i'm not mistanken the glow plug operation on a 91 7.3l na works the way it was first said, should come on as should the wait to start light then when the light goes out and you crank the glow plug relay will pulse on off on off. ford changed this from the system used on the 6.9l trucks which would heat for 5-10 sec then off for 20 sec or so then heat 5-10 sec then off. the hayes manual even states this. i dont really like this system cause my 84 6.9l starts easier than my 91 7.3l, but that is the correct way it should work.

 

[LCAM-01XA]

Some do the afterglow, some don't, the only way to know for sure is to have the WTS light rewired so it blinks when the afterglow happens - mine don't afterglow, never did, yet with the new glowplugs it starts up right away every time.

 

[LA350]

My 92 does this too. First flip of the switch the clicks cycle every few seconds, and the ampmeter dips w/ each click. This happens for 15-20 seconds.

 

[tractorman86]

every 7.3 i've been in cycles like that. like you said he might have a couple burnt out causing the wts light to have a short cycle but otherwise sounds good