99 f-350 80,000m just bought used, previous cummings owner. usually ill plug the truck in at 35 or below just to help out. come out one morning 45 no start. wtsl goes out no start. plug in less than a min start. today at work 38 the truck sits for about 10hrs from 6a-4p. wtsl goes off no start.3 times i do this next time wtsl goes out and peddle to floor starts right up. will the foot in the peddle hurt anything. are my GP's bad or batteries.If the gp are bad would it even matter if you plugged in or not or is this just the block heater.

 

Hard to understand your acronyms but I'd load test the batteries and if they check out ok, Then test the alternator output to make sure your batteries are being charged. Then test the glow plug relay and then the glow plugs. If you have a block heater you can check that too to make sure it works. I plug in if it dips below 30 degrees. Hope this helps.

 

sounds like a bad glow plug system. i would bridge the relay first to rule that out.

 

Tuff you are a bit hard to understand, and I just realized that wtsl means wait to start light, LOL!

Anyway you could have either bad batteries, bad glow plug relay or a few bad plugs. I've just gone through this entire scenario, my problem ended up being two old batteries and a bad glow plug relay.

These 7.3 strokers, unlike the cummins that use a heating plate, use a glow plug relay, much like a starter relay, to run intermittent power to each individual glow plug before you start the truck. These relays, well, after a 100K or so miles tend to get a little fried. It's a little brown (or black) relay that is positioned near your fuel filter on the passengers side just above the valve cover.

Next time you go out to start the truck and she's acting up again, (you might need someone to help you) take a screw driver and bridge the two large terminals on your glow plug relay, and then try to start the truck. If she starts, you have a bad glow plug relay. It's also a good idea to take a look at your batts. If they are original OEM Motorcraft, they probably need replacing.

Edit- If this is a cold start issue, plugging in the truck will definitely make a difference. When they are plugged in they are warm, and don't need the glow plugs, or full power from both batteries, to start normally.

 

my bet is the glow plug relay,take a test light to the glow plug side of relay and cycle key a few times light every time = good no light not so good (the contacter in relay is sopposed to rotate to keep burning one spot can be intermittent start)hope this helps

 

Sorry for the hard to read post I was in a hurry. I checked the batteries 12.6 and goes to 11.6 when cranking. from what ive read it must be the glow plugs\relay.instead of a screwdrver could i use a wire to make contact on the relay if im by myself. thanks for all the info glad i found this site.

 

You will want at least a 10 or 12ga piece of wire, alot of current moving there.