I am having a hard time starting 7.3 diesel 1999 engine in temp below 40 degrees. I talked to the dealer and they said just plug in the engine warmer, but they said it is most likely the relay for the glow plugs and the manifold pre heater (they stock 4 of them). When I asked how to check it they said there is none. I really don't want to spend $90. dollars on a relay if the glow plugs or bad. It cranks for 10 seconds and I turn it off and go back to restart in 30 seconds. When it finely does start in the 4th or 6th try it looks like I have a white smoke signal that drifts for 30 or so feet. What do I check for the problem?

 

Sounds like it is most likely the glow plug relay. $90 for a glow plug relay is cheaper in the long run than a starter going out from having to cycle it repeatedly. Also, it would probably start if you plug it in, but what happens if you get caught somewhere and have shut it off and it is cold and not way to plug in the heatere. My 2001, had the same problem the first Fall after I bought it used. The relay was replaced and took care of the problem. Batteries are getting weak now and may have to finally replace them this winter if they give me any problems.

 

With key off you should have battery voltage to one large terminal and nothing to the other large or either of the small terminals.

With key on for the first two minutes or so you should have battery voltage to both large and one small terminal. The other small terminal should show ground. This shows the relay active.

With the key on and after the glow plug cycle has finished you should have battery voltage to one large and both small terminals. The computer activates the relay by grounding the second small terminal thus activating the relay.

It is possible to have battery voltage to both large terminals when the relay is active and still have a bad relay. If the contacts inside are pitted or corroded you may have low amp voltage passing through it but not enough power to actually run the glow plugs.

The information linked here is for 94-97 trucks but the principles are the same o n99 and up. There are a couple differences (one plug per valve cover gasket instead of two so the pin locations will not apply, two relays {one for glow plugs, one for intake heater} and so on) in the newer trucks.

CLICK HERE to go to an excellent how to article for the glow plug system by Carpentractor.

Hope these help out - Carpentractor's article helped me a lot.

I have both saved in MS Word if you would like them in that format. If you would like a copy, click on my user name and send me an eMail (private message will NOT work) with GLOW PLUG RELAY in the subject line and let me know what eMail address you would like it sent to and I will reply with the attachments.


Dave / Believer45

 

thanks Husker and Believer45 for the info, I am glad you folks didn't tell me to start with changing out the glow plugs. I printed out the link and will try to run the curcuit tests this week and get a relay if that is the answer, I know the local dealer has four in stock for a reason.