7.3 Dsl Fuel Knock or mechanical?

Mervin Owner/Technician Indiana Posted   Latest   Edited  
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1997 Ford F-250 HD XL 7.3L (F) 4-spd (E4OD)

Hello to all.

We Have a 1997 7.3 dsl in the shop, it was at a dealership approx 3-4 months ago and had all new injectors and glowplugs installed, after that it does not run very even or smoothly and has a slightly non consistent knock noise. we narrowed it down to num 7 cylinder by removing the valve cover when the knock was present, upon disconnecting the injector connector for Num 7 , the knock stopped at the same time, this was very consistent….. thus we said we would do a new injector, installed it and now is has a much more pronounced knock that is very consistent and there all the time and when unhooking the 7 injector connector the knock stops…. ….. questions we have is this a mechanical issue or a bad NEW injector ?? Is the old injector not flowing enough so that the mechanical knock is masked? Then the new one flows as is should , thus exposing the mechanical knock issue??????? At this point we put the old one back in, truck runs as it did when we first started on it this morning. Is this a fuel knock or a rod knock issue?????

Thanks in advance!

Mervin

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Daniel Owner/Technician
New York
Daniel
 

Some of these had a number 8 injector that is a different part number than the rest to “ even out“ how it ran. ” fuel balance “ I believe. Might wanna check into that first. If not then probably just a bad injector if the knock goes away when disabling that injector. Just fuel knock

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Marvin Mechanic
Mississippi
Marvin
 

That was for a sound they called cackle….chicken sound lol that injector on #8 will always fail cylinder balance test

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Cmore Mechanic
Connecticut
Cmore
 

Not a big diesel guy but couldn't you swap injector with another cylinder for testing?

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Rusty Owner/Technician
Massachusetts
Rusty
 

Do you realize that #7 is the rear cylinder on the passengers side? #8 should be a “long lead” injector, different than the others

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Marvin Mechanic
Mississippi
Marvin
 

1997 f250 should have a aa code injector they didnt start the different injector until the ad injector in 1999 with electric fuel pump and it used a ae ll injector

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Jake Technician
Vermont
Jake
 

Indeed make sure, as has been mentioned, that you are on the correct cylinder. If you have the correct (different) injector in the number eight hole, and you have questions about quality of new parts on these engines, I used to have a brand I could recommend, and I hate to say it, but these days, on that engine- The best test is to use an injector that you've already tested INSIDE the engine. In…

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Rex Technical Support Specialist
Ohio
Rex
 

Jake, is Alliant the brand you are thinking of? I have used only their remans for decades with few if any issues. Mostly DT's but some 7.3's. Put a set in a DT last week. I hope they are still good. FWIW their G2, G5 injectors for the 04 and up NAV's are excellent. They are done by Pure Power, the OE and sold under the Alliant brand. That makes the second time Navistar has missed a market. First…

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Jake Technician
Vermont
Jake
 

Yeah, that's the brand I'm thinking of. If I needed a set of injectors that they carried for a job tomorrow, I'd still probably use them, but we're fresh out of engines that use what they provide. My understanding (and again, it's an “understanding”, no more…) is that there are other brands that do a good job with these, which was not always the case. When we got the first 7.3 and T444E engines…

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Ryan Owner/Technician
British Columbia
Ryan
 

When we got the first 7.3 and T444E engines, Alliant was the gold standard, you could take that stuff to the bank. At some point that changed. I never had problems with the durability of their stuff, it was more dead or sick right out of the box issues. Solenoid codes (low resistance) and leaking nozzles on the DT and 7.3 injectors. That's interesting, I have had a zero percent warranty rate…

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Glenn Owner/Technician
Texas
Glenn
 

Hi Mervin, When you swapped injectors, did you give it plenty of run time to purge out trapped air in the oil galley and injector? Knock goes away when you unplug the injector? A compression test is the next thing to perform. Do this through the glow plug hole. If someone allowed too much oil get into the cylinder when switching the injectors and did not purge it, it will buckle a rod. I've…

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John Diagnostician
Colorado
John
 

Did you do a compression test? 350 to 400 is good, 325 to 350 is okay, less than 325 is bad.

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Marvin Mechanic
Mississippi
Marvin
 

And john unplug the injector or ficm so injector is not supplying any fuel…also dont hook guage till engine has cleared the fuel or any oil that run back in glow plug hole when it is renoved,,,,

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Marvin Mechanic
Mississippi
Marvin
 

Make sure all on that side same injectors too that model could use aa or ab ab injectors were called a split shot INJECTOR​.​THE plunger had an extra cut whre it injected a small amout of fuel to start the fire then as plunger went down further it gave more fuel ,,this gave a quiter running engine….maybe they are some of both in this engine…

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Walker Mechanic
South Carolina
Walker
 

Sounds like a mechanical knock. Check the oil filter for pieces and parts.

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Steven Mechanic
Connecticut
Steven
 

Did the old copper washer stay in bore two washers can do strange things

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Clement Technician
Missouri
Clement
 

Fuel knock typically comes from over fueling condition. Which would create excessive white smoke out the tailpipe. Can you see a difference in smoke when you disable injector? Mechanical knock it would tend not to have white smoke unless you have a compression problem.

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Ryan Owner/Technician
British Columbia
Ryan
 

Hello Mervin, As Clement suggested, does this engine smoke when the knock is present? If no, then I would be looking into more of a mechanical issue. This year of 7.3L should have AA code injectors but a California truck may have AB injectors in 1997. I see this in the listing but I don't personally see many California trucks this far north. I have never been a fan of a cut-out test. In some…

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