Diesel Loses Power When Glow Plugs Engage

When I went to start my van today I was unable to get power. Initially I engaged the glow plugs four times. The glow plugs heat, then the relay chatters. When I turned the key to start there was a pop and the power dropped (eg. Dome lights off, no 12v accessory, battery meter shows no V). Returning the key to accesory did not restore power.

I checked the battery (approx.1yr old) and found 12v across the connectors to the terminals. The connectors were confirmed firmly secured. I then checked fuses, finding only 1 blown fuse for the trailer power which is not connected. All lines from the battery had continuity. I did not detect any parasitic draw. During this time the power came back on.

Now when I engage accessory I recieve power. When attempting to engage the glow plugs I lose power. In accessory the battery voltage no longer reads on the battery meter.

A 2nd car was used for a jump after warming the glow plugs. This caused no change in the symptoms.

Ive uploaded a schematic for the engine electrical for reference. Fuse G is 60a to ignition switch. Fuse U 30a to ignition system l, instrument cluster, pia engine, pcm power relay, abs power relay, 4wabs relay. Fuse 18 is just watning indicators.

The glow plugs are new. Any educated guesses on where I should look for problems? Any ideas are much appreciated.

Edit: Unanswered diagnostic questions
Model: 1993 E350
Engine: 7.3L diesel non turbo idi
Batteries CCA: 810
Weatherwise it was cold

It sounds like a short circuit at the glow plugs possibly a bad glow plug regardless how new.

Is it necessary to repeatedly operate the glow plugs?

12 volts measured across the battery terminals (with everything off) is too low, for a fully charged battery at temps above 40 degrees F. It should measure closer to 12.6 volts. I think you may need a new battery. Suggest you first clean and tighten the connections, and if that doesn’t solve it, have the battery load tested. If the battery is 5 years or older, maybe forget the load test and just buy a new battery.

I had a sort of similar problem w/my Corolla one time where I attempted to start the engine after filling up w/gas. Instead of cranking w/the key in “start”, all the dash lights went dim. The dash lights returned to normal ( brightened up again) after a few minutes with the key in “on” but engine not started. That problem was caused by a loose battery connection at the battery posts in conjunction w/a marginal battery.

I truncated. It was 12.2. I imagine the drop was from the glow plugs, but I will check this. I did not mention checking the terminal comnections in the original post. They were secure. The op has been updated. Thank you for your reply.

I assumed you had 2 batteries on the truck. Is that correct?

We had 2 batteries and then also a 2nd car jumping

Initially the van would start off of one oversize battery. The current primary batyery is <1yr old. The van is an ambulance. The location for the second battery was used for additional electronics for the lighting, and an external voltage regulator installed to the plate which would hold the battery.

It has been necessary to repeatedly engage the glow plugs. Averagely 3 times. The WTS will glow no longer than 12 seconds and then a relay begins to chatter. Reading from the 12v accessory V drops to about 9 under gp load then jumps to 11.8 during chatter. Disengaging will usually show approx 12.2.

When a relay chatters, that’s often an indication of low voltage. Battery voltage is enough the relay’s contacts close, battery voltage drops, which causes the relay’s contacts to open, which raises battery voltage … etc etc etc … and you hear the resulting buzzing noise.

A 2nd vehicle was used to maintain a steady voltage. This was after i could no longer engage the glow plugs, and did not effect the symptoms. The relay chatter has always occured. Is it possible the relay itself may be failing or one of the devices directly conmected to it?

Yes, that’s possible, likewise it could be something that is powered by the relay.

Battery cables have two ends. Check the far ends, especially where the negative cable attaches to the engine block and any body grounds.

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What year is this Ford? What engine is it? How cold is it where you are? How big (CCA) is the single battery? Who removed the second one?

As @NYBo, suggested, check the other ends of the battery cables. If hooking another battery up did nothing, I would think the issue is how the battery is connecting to the van- ground, starter, solonoids, etc.

a bad Glow plug relay won’t stop a diesel from starting, neither will bad glow plugs. They are there to aid in starting, but shouldn’t keep the engine from cranking. I won’t be so quick to rule out a short at the glow plug controller, but not sure that is the place to start either.

You may want to check not only the battery but the charging system. It may even be a mechanical problem with the alternator, like binding up of the alternator shaft putting too much mechanical load on the crankshaft.

Just a thought.

It’s been several years but I recall working on Ford Econoline based ambulances with diesels and they all had 2 batteries wired in parallel to start the engine.

Looking back across this thread it seems that the gist of all posts combined add up to the need to go back to basics. Remove, charge and test the battery(ies) and replace if necessary. Clean all connections and if required install the second battery. Then with an adequate charger connected to the batteries test the glow plugs, timer module, starter, etc can be tested.


After confirming battery and cabling found loose control signal on starter, corrosion on several grounds, and finally a damaged ignition starter solenoid. The IGS is not the solenoid attached to the starter.

Does this mean you are back up and running?

Sounds like you’ve got things under control now. Good for you. Make sure the IGS makes a clean rust-free connection to chassis ground. I had a problem last summer on my truck caused by rust accumulating there. The case of the IGS (at least on my Ford truck) provides its ground connection for the relay selenoid, and must make a good electrical connection to the chassis to work correctly. Rust is a poor conductor.

Yes the original issue is solved. The Ignition solenoids bolt holes were cleaned. There are now other issues, primarily the engine seems to rev high at freeway speeds. Transmission is not slipping however. Thanks for the prior help and suggestions.

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