My '97 powerstroke normally draws over 400A for the glow plugs. Intermittently it will only draw about 200A, and fails to start. Usually trying again one or two times clears the problem: I see the 400A draw, and it starts right up.

The glow plugs are Motorcraft, new in October. Last month, I stuck in a new glow plug relay, and opened up the old one. No sign of arcing inside, as it might have if it had been sticking rather than closing fully. The problem persists with the new relay, of course.

Any thoughts on what might cause this? Could some of the glowplugs have an intermittent fault?

 

Since it's about half, I'd be tempted to say it's one bank that's not energizing. If you look at the large terminals on the relay, the terminal goes to the GPs actually has two wires on it. One goes to each bank. I'd be willing to bet there's an intermittent break in one of those two wires. Only way to tell for sure is to check for voltage at each UVCH terminal at the moment you're getting the 200A draw instead of the 400.

Is this a California truck, by any chance?

 

Thanks, that makes sense. This truck has loads of wiring problems, and it's all-electric. Not sure if it's California.

 

Voltage/resistance=current

12 volts / 1 ohm = 12 amps X 8 cylinders = 96 amps. There will be an initial current spike when the glow plugs are cold but will drop off as they warm up. I'm seeing around 140 amps with new glow plugs and new UVCH. It sounds like you have some wiring issues as previously stated. At 400 amps I think you'd melt the GP wiring. Just my two cents.

 

I think my Bluepoint MT109 is probably not well calibrated, and it may well be less than 400A in reality.