7.3 Engine Knock on 87 Octane
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Cross-Country
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7.3 Engine Knock on 87 Octane
My '25 7.3, with a little over 2K miles, knocks on 87 octane gas. I've recently confirmed this by switching between 87 and 91. The knocking went away with 91.
I've ran the 7.3 on 87 octane since day 1 and have procured gas from many different stations throughout Texas, Oklahoma, and Arkansas. I ran 1 full tank of 91 on a previous fill-up...and the knock completely stopped. I switched back to 87...and the knock returned. When I run on 87 my engine knocks lightly about 2 times per second, which is mostly noticeable when the engine is lugged. My valvetrain/lifter noise has stayed the same regardless of fuel octane level.
I tried a 1:1 mix of 87 and 91 and the knock frequency is greatly reduced to about an average of 1 knock every 1 or 2 seconds.
Maybe Ford updated the ECM firmware/software on my '25 (build date of 7/25) so that timing is closer to the knock threshold...dunno. I'd like to see if I can log the knock sensor data using Forscan when running 87 then again at 91 but am unsure if this is even possible. I'd also like to hear any suggestions from folks on troubleshooting this.
I've ran the 7.3 on 87 octane since day 1 and have procured gas from many different stations throughout Texas, Oklahoma, and Arkansas. I ran 1 full tank of 91 on a previous fill-up...and the knock completely stopped. I switched back to 87...and the knock returned. When I run on 87 my engine knocks lightly about 2 times per second, which is mostly noticeable when the engine is lugged. My valvetrain/lifter noise has stayed the same regardless of fuel octane level.
I tried a 1:1 mix of 87 and 91 and the knock frequency is greatly reduced to about an average of 1 knock every 1 or 2 seconds.
Maybe Ford updated the ECM firmware/software on my '25 (build date of 7/25) so that timing is closer to the knock threshold...dunno. I'd like to see if I can log the knock sensor data using Forscan when running 87 then again at 91 but am unsure if this is even possible. I'd also like to hear any suggestions from folks on troubleshooting this.
Cross-Country
Joined: Jul 2021
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I don't see nothing to trouble shoot. I bought a 2025 7.3 Tremor last spring, have 5000 miles on it. I have run premium since I bought it. Since I drive in a higher elevation & pull a 10,000 lb RV. And I have heard no knocking on 91 octane gas. As there shouldn't be. This engine has a lot of power & torque. And to get the best out of it you run the 91 octane. Says so in the owners manual. If not & you run middle grade you will have a slight knock. The way I see it if you can afford the truck, what's a little more per gallon for premium so the engine puts out top performance.
Cheers,
Russ
Cheers,
Russ
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Cross-Country
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My concern is that I've searched thru the web and I have not read of anyone with a 7.3 actually stating that they have a knock when running 87. Here's an example of a long thread, with many folks stating that they run 87 and have no issue/knock. --> https://www.fordtremor.com/threads/what-octane-of-fuel-do-you-run-with-the-7-3l.260/. This, in my opinion, is cause for concern, especially when I'm experience a consistent knock when putting around in the truck unloaded. My truck consistently knocks lightly, not "sometimes knocks lightly". I would expect to see a light knock but only when operating the truck under high load low RPM conditions and not when unloaded and putting around.
You state that you have not experienced knocking running 91 and this is also my experience. But have you tried running on 87? Would be interesting to see if you experience knocking on 87 like me.
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Cross-Country
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We've got an abundance of E0 here in Oklahoma and I've ran a full tank of E0 many times. I still get the same knocking with E0/87 that I do with E10/87.
Cross-Country
Joined: Jul 2021
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No, I have not tried running on 87 octane. Because I do believe I would get the occasional knocking sound. As stated, I live at higher altitudes & steep mountain roads & what not in the 4 corners area. Plus pulling my RV up steep forest service roads it just makes since to run 91 octane for my usage. Actually this motor puts out a little over 500 horse power & a little over 600 foot pounds of torque on the independent dyno machine. With that kind of power you can see why premium makes that kind of difference. If you want to de-rate the motor on 87 octane & listen to the ping Ford says its okay. But that's not the way that I do things. I love my pull dog.
Cheers,
Russ
Cheers,
Russ
Fleet Mechanic
Joined: Jan 2015
Posts: 1,377
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From: SE Michigan
Just because you CAN run on 87 doesn't mean you SHOULD, especially if the owner's manual is already noting that it could be an issue.
As was shared, operating the same vehicle in a different environment under different conditions in a different manner using different fuel products (your area) could be the difference between regular knocking and 'sometimes knocks lightly'.
Personally, I would rather run the 91 and not worry versus run 87, save a few nickels, and potentially have to deal with catastrophic engine damage.
As was shared, operating the same vehicle in a different environment under different conditions in a different manner using different fuel products (your area) could be the difference between regular knocking and 'sometimes knocks lightly'.
Personally, I would rather run the 91 and not worry versus run 87, save a few nickels, and potentially have to deal with catastrophic engine damage.
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Mountain Pass
Joined: Jan 2024
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I run my 7.3 on 87 octane all the time, I live at about 4,500 feet above MSL and haven't noticed any knocking. I pull an 8,500 pound trailer occasionally, and have had no problems pulling steep grades. I don't lug the engine, and just let the 10 speed do it's thing....
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Cross-Country
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In all seriousness, I think you might be reading the owners manual a bit differently than me. I'm reading that Ford has designed the 7.3 to run on 87, and in some use cases or set of parameters that they have not identified in the manual, we may experience a "sometimes knocks lightly" event. I'm concerned that I am, seemingly, the only person experiencing this knock on 87. This, to me, is cause for concern for a possible issue.
I'd be really interested in hearing from others that regularly (no pun intended) run on 87 gas. I'm also interested in some input/recommendations on gathering data to help with identifying and determining if this is an issue. Please let me know what you think.
Fleet Mechanic
Joined: Jan 2015
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From: SE Michigan
I appreciate your experience and feedback on this. Our local price difference between 87 and the next highest octane is at least $0.25/gal...which equates to about $8.00 per tank. I'll send you my paypal link if you'd like to donate to my gas fund each fill-up. I'll also accept a $2,000 one-time payment to cover the first 100k miles. ;-)
I also installed relocated front fuel filter and rear fuel/water separator (to make them easier to change) and use fuel additive (Archoil 6300 and 6500) at ever fill up. I'd rather spend a few dollars more filling up the tank than replacing fuel systems and engines.An ounce of prevention is worth a pound of cure, momma always used to say. If $8 per tank isn't worth it to prevent your engine from potentially experiencing a catastrophic failure (which knocking can/will lead to), then you better be saving that $8 per tank under your mattress for when you need your engine rebuilt.
Laughing Gas
Joined: Feb 2020
Posts: 891
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From: End of the Rockies
I run the truck in the same areas that you are in. My 2020 7.3 and my 2025 6.8 both have no problems running the lower octane.
I only have a 3,000 pound truck camper that does not put much stress on the engine. I never had any knocking.
You could take it to the dealer for them to note the problem in case something happens to the engine. I would be sure not to run the 86 octane in the area.
Does it knock at higher RPMs or only when you are lugging it?
I only have a 3,000 pound truck camper that does not put much stress on the engine. I never had any knocking.
You could take it to the dealer for them to note the problem in case something happens to the engine. I would be sure not to run the 86 octane in the area.
Does it knock at higher RPMs or only when you are lugging it?
Fleet Mechanic
Joined: Jan 2015
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From: SE Michigan
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Cross-Country
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I'm noticing the knock when lugging. By 'lugging', I'm meaning: 10 gear @ 50 mph and very slight hill/grade, which is the most notable case. I'm not sure if it's pinging at higher rpm but this is one of the reasons I'd like to log the knock sensor data.