5 Most Common 7.3 Bad Glow Plug Relay Symptoms (With Fixes)

7.3 Powerstroke glowplugs are quite nippy at their job no matter how nippy the weather is. It doesn’t take much time to heat the engine and start it. That said, despite the performance, the device can deteriorate slowly or suddenly.

7.3 Bad Glow Plug Relay Symptoms includes:

Black smoke emissions
Followed by rough start
Misfires & Faulty Control Modules
Illuminated warning indicators
And power loss

I’ll discuss them here along with problems and steps to take.

Table of Contents

7.3 Bad Glow Plug Relay Symptoms

Whenever glow plugs in 7.3 Powerstroke experience problems, it results in a variety of visible warnings.

Let me show you what happens when a glow plug relay fails.

#1- Dark Smoke

Emission of black smoke can be the earliest symptom of bad 7.3 glow plug relay.

The combustion system uses a definite air-fuel ratio to work. But when there’s a problem with heating device, it fails to set the mixing correctly. If it has more fuel with little air, then there might be some very dark smoke. While the combustion is disturbed, fuel can leak into the exhaust and emit partially burnt carbon.

However, glowplugs can be at fault particularly if there’s a rough start accompanied by dark smoke.

#2- Start Issues

This is a prime sign of 7.3 glow plug relay failure. Diesel engines depend on this heating device along with chamber pressure for the ignition.

If it malfunctions, timer relay fails to properly communicate with glow plugs to power the engine. Because of this, the combustion chamber doesn’t reach the right temperature in cold weather and ignite fuel. Consequently, you experience different kinds of start issues.

The 7.3 Powerstroke may start roughly, slowly, or even may not start. It depends on the number of bad plugs.

Let’s say you have a 4-cylinder engine. One going bad may trigger slightly hard or slow start and a miss. Two may cause difficult and rough starts. Three or four bad plugs and it won’t even start the vehicle.

#3- Misfires

Faulty glow plug relays in 7.3 Powerstroke affect the supply of heat that may trigger engine misfires. Not just that, it can lead to other problems like deceleration and decreased fuel efficiency.

Combustion process works with a combination of compression ratio as high as 17.5:1, accurate quantities of fuel, right timing, and right temperature. To ignite the fuel, it needs to reach at least 410 to 450°F. This is ensured by glowplugs along with compression pressure. The heating element provides constant flow of heat and keeps the engine running.

However, when glow plug relay fails, 7.3 engine goes through a loss of heat. It causes brief pauses in the combustion and the whole process gets affected. As a result, the vehicle experiences misfires.

#4- Power Loss

Physical damage in the 7.3 glow plug relay can prompt cylinder leak leading to power loss.

The heating device is mainly attached to each cylinder head so that it keeps pressure from leaking out. If the sealing breaks due to damaged parts of glowplug, it can cause air to escape from cylinder during compression strokes. Plus, the same can cause high temp combustion gases to break out during power stroke. This leak will result in power loss.

In case it’s the parts of glow plug relay that broke, then the device is the sole culprit. If there’s a crack around cylinder head, then both device and cylinder or only the latter can be the one to blame.

#5- Warning Lights

A failing 7.3 glow plug relay can illuminate Check Engine Light (CEL) on screen. You’ll need an OBDII scanner to analyze the diagnostic trouble codes (DTC). Besides CEL, the indicator warning light of glow plug will also illuminate.

Here are 2 common glow plug trouble codes:

P0380 i.e. “Glow Plug / Heater Circuit ‘A’ Malfunction”.
P0670 i.e. “Glow Plug Control Module Circuit/Open”.

Some other DTCs related to glow plug issues are: P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679, P0680, P0681, P0682, P0683, P0684, P0381, P0382, P0383, and P0384. These will help you know about specific issues with the device in 7.3 Powerstroke.

Why Does 7.3 Powerstroke Glow Plug Relay Fail?

Physical damage, debris/sediments, and system failures are three major 7.3 Glow plug relay problems. The only solution to the severe damage is replacement. However, sometimes these issues can lead to other issues or vice-versa.

Overheating

In case glowplug coil in 7.3 Powerstroke gets too hot, it will melt. This mostly happens due to exposure to extreme temperatures. The heating device may not be able to handle the combination of functions required to run an engine which can lead to overheating.

So, it’s important to keep the internal temperature steady before the coil gets damaged. One way to cool it down is to keep the engine cool. A very effective trick would be turning A/C off and turning heater On to Full Blast Mode. If it gets damaged, then you have to replace the glow plug.

Excessive Voltage

Putting out too high of a voltage can explode the glow plug tip. Usually, the heating device requires right temp and voltage to work. Here, the controller works to switch electric currents to 7.3 glowplugs for a particular period to ensure proper heating. In case the controller fails, it results in current being applied for a longer time. This is followed by the overheating of glow plug that exceeds the threshold of 2012°F and damage.

To prevent it, ensure the voltage flowing through the heating element is correct. Use a multimeter to check it. You can also keep the voltage regulated with a device like Zener diode. I’d suggest you take expert’s help for the job if you aren’t one.

Misfiring Injectors

During injection, the spray pattern of fuel injector strikes the hot tip of glowplugs directly. However, if the pattern is incorrect, it can burn the tips. Such irregularities happen mostly due to dirty fuel or faulty injectors.

To fix them, you may either need to add a good cleaning fuel additives to the tank or get an injector replacement.

Faulty Control Module

Depending on engine’s temp, Powertrain control module (PCM) works with Glowplug control module (GPCM). When sensors send cold engine signals to PCM, the latter instructs GPCM to activate the heating element.

However, various factors like solenoid failures or corroded wires can damage the modules and affect the connection. Doesn’t matter whether it’s PCM or GPCM that fails, it wouldn’t establish proper communication or send right signals. And these errors can damage glow plugs.

In this case, you have to check the severity of the PCM or GPCM damage and take proper steps. If it’s intense, you have to replace the control unit.

Excess Carbon Buildup

Sometimes carbons are accumulated around the chambers due to incomplete fuel combustion. This leads to overheating of the 7.3 glow plug which makes its tip burn out.

To get rid of it, I suggest you use combustion chamber cleaner. You can also opt for solvents or other carbon cleaners. But before that, make to ask experts about it for safety.

Frequently Asked Questions (FAQs)

1. Will One Bad Glow Plugs Cause No Start?

Yes, you can start the engine and drive with one bad glow plug on 7.3 Powerstroke.

It’s safe to continue driving if one of them is bad and this shouldn’t affect the speed or engine performance. However, the engine wouldn’t start if three or more glow plugs fail.

2. How Do You Test A 7.3 Glow Plug Relay?

For the 7.3 glow plug relay test, you need an advanced glow plug tester device.

First, disconnect the glow plugs from wiring harness. Connect 12V test light to the two positive battery terminals. Then, touch the probe to the glowplug terminal (not the wiring harness). If the light doesn’t illuminate, the device is bad and requires a replacement.

3. When Should I Replace Glow Plug Relay?

Replace glow plug relay in 7.3 when two or more malfunction.

Typically, the device may last from 100,000 to 200,000 miles and deteriorate over time. Consider opting for 7.3 glow plug relay upgrade whenever it shows major symptoms like hard or no start.

Conclusion

To recap, here are the 5 most common 7.3 Bad Glow Plug Relay Symptoms includes::

Black smoke emissions
Followed by rough start
Misfires & Faulty Control Modules
Illuminated warning indicators
And power loss

Glow plugs in 7.3 diesel can last over half a decade in case you take care of it properly. And it’s more effective when you’re aware of the warnings and problems.

However, you may notice that the signs of failing 7.3 glow plug relay are pretty general. They can indicate other problems. So, I advise you to check and test the device for damage.

Video References

thomas brian

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Iyul Nasruddin

Nasruddin is a passionate car enthusiast with a love for troubleshooting and diagnosing all sorts of vehicle problems. With years of experience in OBD diagnostics, Nasruddin, has become an expert in identifying and solving complex automotive issues.

5 most common 7.3 Bad Glow Plug Relay Symptoms (with fixes)