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7.3L Powerstroke Glow Plug Failure: Symptoms and Solutions

Updated: Jan 28

If you own a 7.3L Powerstroke diesel engine, you know that it's a reliable and powerful machine. However, like all engines, it can experience problems, and one issue you may encounter is glow plug failure. Glow plugs play a crucial role in the combustion process especially when it’s cold out, and if they're not functioning properly, it can lead to several problems with your engine. In this blog, we'll cover the symptoms of glow plug failure in a 7.3L Powerstroke and what you can do to fix the problem.

Symptoms of Glow Plug Failure

  1. Engine won't start: If the glow plugs are failing, the engine may not start, especially in cold weather.

  2. Engine misfires: Glow plugs play a crucial role in the combustion process until the Engine is warmed up, and if they're failing, it can cause the engine to misfire and run rough.

  3. Engine stalls: If the glow plugs are failing, the engine may stall when starting, especially in cold weather.

  4. Check engine light (CEL): A malfunctioning glow plug system can trigger a check engine light to come on.

  5. White Smoke: If you have white smoke coming out of your tailpipe, especially while cranking and continuing until the engine warms up, you may have one or more glow plugs that are inoperative.

Solutions for Glow Plug Failure

If you're experiencing any of these symptoms, it's important to have your glow plugs inspected and replaced if necessary. In the 7.3L Powerstroke, bad glow plugs typically show themselves as white smoke coming out of the tailpipe. The white smoke is unburned fuel due to incomplete combustion, due to the cylinder temperatures being to low. If you can get the truck started, it will usually continue to white smoke until the truck gets up to operating temperature. If you have several glow plugs that are bad, you may also experience a “dead pedal” until the engine warms up.

A professional mechanic can diagnose the problem and determine if the glow plugs need to be replaced. If left unaddressed, a failing glow plug system can lead to more serious engine problems, so it's important to address the issue as soon as possible.

In conclusion, glow plug failure in a 7.3L Powerstroke engine can lead to several issues with the engine not running correctly, or not starting. With proper maintenance and timely repairs, you can keep your engine running smoothly. If you're experiencing any of the symptoms of glow plug failure, don't hesitate to have your truck inspected by a professional. If you are a DIY person, continue reading below.

Quick Diagnostic Tips:

If you’re a DIY kind of person, here are some quick tips that can help you diagnose your glow plug system. Let’s assume it’s cold out. Please note that if you are unsure about anything, consult a professional.

  1. Truck white smoking while cranking, and will start after several key cycles, possible dead pedal: most likely several glow plugs are out, or you have a bad UVC harness on one side. It is recommended to replace all 8 and the under valve cover harnesses at the same time.

  2. Truck white smoking while cranking, but never starts: glow plug relay and UVC Harnesses are the most likely suspects here, or you have 4+ glow plugs out. You can turn the key on, and listen for a loud click coming from the relay. If you don’t hear a click, the relay may your problem. Remove the harness connector from the UVCH, and inspect it. If the outside pins look burnt, you will need to replace the UVCH and the pigtail. Typically over time, the engine vibrations cause the pins to work themselves loose, which increases resistance at the connection. Over time the increased resistance will create excessive heat which leads to the connectors melting. If this continues unchecked, the pins will eventually short out, and cause the relay to fail. The short will cause to much amperage to be drawn from the batteries, create excessive heat, and melt the relay.

  3. Truck starts, but white smokes until engine warms up: Most likely you have just one or two glow plugs out. You can use a multimeter or a test light to inspect further. A quick test is to use a test light. Disconnect the harness connectors and inspect. If they do not look burnt, then take your test light and connect the alligator clip of the test light to the positive side of the battery. Looking directly at the harness under the valve cover,(not the connector that is a part of the engine harness) the two furtherest pins on the left and right side are your glow plug pins. Touch the test light to each of these pins, one at a time. If the test light illuminates, you most likely have a good glow plug. If it does not illuminate, you have a harness issue or a glow plug issue and you will need to remove the valve covers to inspect further. You can remove the UVCH and touch the tips of the glow plugs directly. If the test light illuminates, the glow plug is good, and your harness is the most likely issue.

Just remember that these are just words on a blog, and is not a definitive guide to diagnosing your truck. Diagnosing your truck requires some mechanical knowledge and skills. If you do not possess the knowledge or skills, do not attempt. If you have any questions, please consult a professional.

If you are having any of these issues, we recommend saving your self the headache and replacing the complete glow plug system. We have glow plugs, under valve cover harnesses and glow plug relays in stock. Feel free to purchase from our store. Links down below.


7.3L Powerstroke UVCH Connector that has melted due to a bad connection on the glow plug terminals.
UVCH Connector that has melted due to a bad connection on the glow plug terminals.

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