Hollow knock, few seconds on startup

[osufireman]

I've been noticing the last month or so that I get a hollow knock that happens for about 5 seconds or so when cold start-up in the mornings after the truck has sat over night. I've read some posts while searching the forum. No puff-puff sound that I can notice from the exhaust or intake, well not more than I can tell that the diesel should have during normal operating. slight faint ticking when the engine is heated up, but softened by far after using Power Service fuel additive.

Perhaps fuel injectors are due for change? I bought the truck with 209K miles and no info on previous servicing. If injectors are possibly the problem, what brands are good ones to get on a budget?

Thanks,
Brandon

[bigblackstroker]

The diesel fuel lubicrates the upper portion of the cylinder and lack of it in one or more cylinders could cause this. Checking the fuel lines would be where I'd start, if air seeping into the lines overnight could be your problem.

[cdnsarguy]

One indication of OEM installed injectors and return lines is they are grey painted. A bad injector can cause a bottom end knock that sounds like a rod bearing anytime.

return line kits Oregon area

Oregon Fuel Injection, diesel injector pump, injector, Powerstroke injectors, turbo and turbo parts for Ford Diesel pickups 6.9 l, 7.3 L, 6.0 L & 6.4 L

[osufireman]

Thanks for the info. I'll check out the fuel lines soon.

Also, another random question but I'd like to not have to start another post. Are the heads on 7.3L IDI and 6.9L IDI interchangeable? My brother has an extra 6.9L at his house that I want to take off his hands and see if there is anything salvageable. Heads might be good, I'd like to rebuild em and have them as spares for if mine go, also it has the IP on it too.

[rsr911]

I believe the IP can be rebuilt to your model year specs. Don't know about the heads. I'd like to know as well because I found a core locally for scrap price and planned to pick it up.

[cdnsarguy]

7.3 and 6.9 engines are different, heads are not interchangeable....

The core on a rebuild is usually required to be same model.... but check with a rebuilder.