Good morning guys. Having a little cold weather start issue (not too bad, just annoying). Own a 1997 F350 with 235,000 on her. My question is if the the "wait to start" light comes on does that mean the glow plug relay is working? I had read in some posts to change out the relay first before attempting glow plug replacement. My light comes on and stays lit for about 10 seconds or so and then goes off, but I wasn't sure this meant that the relay was working for sure. Figured I would change this first as it seems pretty easy to do. I have heard nightmares about changing glow plugs on high mileage powerstrokes such as glow plugs breaking off etc. which is sort of scaring me from attempting it. dealer wants $600.00 to replace the glow plugs!! But anyway I was curious about the relay being good or bad if the WTS light comes on. Would I be wasting my time and money replacing the relay if the light comes on? Thanks for your help as always. Maxx

 

The wts light is like the seatbelt light. It will come on any time the key is on. A gpr is cheap and you can easily change it out yourself. Just be shure to disconnect the battery first. If you have 250,000 miles, someone has probably changed the plugs before. Also make shure your batteries are good. It takes a lot of juice to fire the plugs in cold weather.

 

Is there a simple way to determine if its a relay problem (pitted etc) vs bad glow plugs?

 

You should be able to hear the relay click on a split second after turning your key on

 

There are 4 terminals on the relay - 2 big ones and 2 small ones. The small ones are the relay control voltages and switch to ground thru the PCM. One of the big ones is hot all the time. The other big one will send juice to the plugs when the relay switches. With the relay off, you should have 12V on one big terminal and nothing on the other. I can't remember if you should see voltage on one or both of the small terminals with the key off. But the important test is when you turn the key. You should hear the relay click and you should have almost no voltage on the small terminals as that side of the relay is now switched to ground. Your voltage needle will swing way over to the left and you should have 12V or close to it on both the big terminals if your batteries are up to par. The big terminal that just went hot is supplying juice to your GPs. Sorry, but w/out any documentation to look at that's the best my rememberer will work today. If the relay clicks and you don't get 12V on both big terminals, your relay is probably bad. Or if it doesn't click at all it also is probably bad. Good luck!!

 

Your plugs will cycle for 120 seconds....if you are trying to start right after your WTS light goes out I bet you don't have any issues. Watch your volt meter instead of the light.....give the plugs a minute or so before you crank

If you get a new relay upgrade to a Stancor 903

You can test the GP's throuh the UVCH....I can't remember what they shoud ohm out to though

 

Oh yeah...very easy to do the GP yourself. Make sure you get ZD-11 GP's. You can find them on ebay for about 60.00.

 

I think they are supposed to ohm out with very little resistance - around 1 or 2 ohms at the most.

 

My truck is in the shop getting the GPs replaced. I'll have her back on Friday.

When I tested the right bank through the UVCH, the back three read infinity and the front read 0.7 Ohms.

Didn't bother testing the right bank. I've heard someone on here say that a resistance in the 20 - 30 Ohm range is okay, too. It's the triple-digit and infinity readings that are bad.