Got a dead knock in my 7.3, seems to be coming from the top passenger side by the IP. Truck runs great other than the knocking, I checked the valve train and everything looks good. I have good oil pressure (about 48psi at idle), I also cracked the injectors to see if it would change but it doesn't really make a difference. when I crack #5 fuel sprays out, and on all the others the fuel just trickles no matter how much I loosen the nut. Thoughts?

 

I installed a spare set of fuel injectors from my 7.3l IDIT in my Bullnose truck. One of them created a pretty horrendous knock. I quickly went back to the original injectors I had been using. Eventually, I got a set of new injectors from the auto parts store. They run ok, but the drivability of my truck was improved more by setting the injection pump timing.

 

Yeah I did mess with the pump timing but it didn't change anything, do you think it could be a bad IP, if so will turning it up a couple flats possibly resolve the knock

 

I think the injectors I used that were knocking were hanging open.

I wouldn't change the fuel delivery screw until you fix the knock, be it an injector or IP. Do you have any spare injectors? If you don't want to spend money at the auto parts store you could always try to find used injectors in the salvage yard. Use this search engine to find an IDI in a local salvage yard.

http://www.car-part.com/

 

10-4, the injectors haven't been replaced in almost 20 years although there's only about 100,000mi on them. they're probably the whole issue so I'll throw some in and see what happens.

 

I dealt with an injector knock a few months ago. I just replaced all the injectors since they were about 19 years old but low mileage. If I had it to do over I probably would have just replaced the one injector and then seen how the engine sounded. My reasoning is that it's better to know that you fixed the problem before installing the other injectors since it's very possible to have a bad injector out of the box and that will just add symptoms to the situation.

 

wanting to follow this thread since I removed my valve covers thinking a valve was sticking slightly open, causing a knock sound to come through the intake. If it is injectors, what’s the best way to pinpoint which cylinder is the issue? I’ve got an 89 with only 49k miles, so from what I’m seeing it is entirely possible to have a bad injector solely based on age.

 

You can ID a bad injector by loosening the fuel line nut at each injector with the truck running. If there's no change in the idle you know that the injector is suspect.

You could also buy a NEW injector (not rebuilt) from the auto parts store and replace the injectors in your truck one at a time until you find the bad one.

If you get injectors from the salvage yard I'd just take the entire set. It's always good to have spares.

 

then maybe I don’t have a bad injector, since I’ve done this already and each cylinder changed rpm when you loosen the fuel line. What else could cause a thumping noise to come through the intake?

 

A sticking injector that causes a knock, will also be hot to the touch. If you feel one much hotter than the others, you can find it that way too. Another way is to use a screw driver with a long handle. Place the working end on the injector body and place your hear on the handle. A good injector has a nice, clean, distinctive click to it. A bad one will sound more like a soft thud.

 

Using either the screwdriver method or a mechanic's stethoscope you should be able to at least isolate the noise to the driver or passenger side. I bought a cheap stethoscope and it was worth the $10. The driver side sounded good but the passenger side clearly had a knock. Swap the injectors and the knock is gone but I still have a light tick and an odd exhaust sound. From time to time the tick goes away and everything sounds normal but then it returns. I've done an engine flush with Kreen that seemed to help and have switched over to full synthetic to help clean out the engine internals.

 

I’ve just used a stethoscope on my injectors, and I didn’t hear anything off right now. At least nothing seemed to stand out. Would it be worth throwing a set of injectors at it without knowing? My mind keeps veering to that idea but I’d hate to spend $300+ on a set of injectors and the noise still be there. The whole reason I’m chasing this is because the noise I’m hearing is most noticeable through the intake when idling. Can’t really tell if it’s still there when above idle. Will leaving these injectors like this for too long (if one is bad) lead to any major failures? This is my first diesel so I want to make sure I do it right the first time.

 

If they are the original injectors from 1989, they're 36 years old. It's not going to be a bad idea to replace them, whether they cure a ticking sound or not. If you want to know their condition for sure, you'll have to pull them and pay a shop to pop test them for you, where they'll check the pop pressure, spray pattern and check for any leakers.

I changed the injectors in my F450 back when I first got it in '13. I replaced them recently with I dunno, just 20k miles or so I think without checking my records, and I clearly had at least one bad one and I knew it was bad. I couldn't really narrow it down, but just because the truck has many hours of idling too, using the crane on the truck, I just figured a set of injectors treated me more than well for a decade so I just changed them all. I did keep them, but I doubt I'll mess with them again. Probably should have just returned them for the core $. I didn't have a known good spare set and I think it's good to have a few on hand just in case, for peace of mind, so I guess they're worth more to me than core $.
Anyway, one of them was gummed right up in what looked like sticky varnish. The rest looked great. I don't know if your tick will go away, but I'd think about freshening up a set of almost 4 decade old sticks if I were you anyway or at least have them tested.

As a general rule the injectors are good for about 100k, the IP 100-150k but idle time and age needs to be taken into consideration too. Once you hit a decade on stuff, you're getting up there. Most people don't even keep their vehicles for a decade. A diesel tune up isn't asking too much every 100k or 10 years, whichever comes first really. Modern diesel owners would love to have things so cheap and reliable haha. $300 isn't even half a months average truck payment. In fact, the average monthly truck payment in the US is over $900. Every 10 years, $300 is pennies. Never feel bad about keeping an old IDI tuned up and fresh. We have it good. Very, very good.

 

that’s a great way to look at it lol. And also with the paperwork I have, the injectors appear to be original. Though the truck did sit around not running for probably at least 10 years, if not longer. It only has 49k miles at this point, and the guy I bought it from said that it was making the same noise the whole time he had it as well, which was from December 2019-may 2025. My old work has a pop tester (which I completely forgot about). I’ll go ahead and replace them with a fresh set and then see which injector was causing an issue, if any

 

If you have access to a pop tester, you may not need to replace them. Especially if you are confident about the low mileage. Pull them out, test them and see what you get. Taking them apart and thoroughly cleaning them may also help if a few are sticky. Just make sure you keep the parts together as the pop pressure is adjusted by the shims.
The odometer from an 89 doesn't show the 6th digit... so if it shows 49K, it could also be 149K, or 249K... so keep that in mind. However other things like the pedal pads, seat wear, etc can help you figure out the actual mileage if its not documented other ways.