Found a cracked injector seal on a Freightliner at 2am outside Billings. Here's what I learned.

I was doing a roadside call for a guy hauling produce who broke down just east of Billings, Montana. Took me forever to find the issue because it was leaking air, not fuel. The crack was tiny, right where the copper washer seats. Now I always carry spare copper injector seals in my truck. Anyone else run into weird air leaks that turn out to be injector related?

2 comments

2 Comments

the_logan4h ago

Actually copper injector seals aren't really designed to prevent air leaks. They're there for sealing compression, not vacuum leaks. The copper crushes down to seal the high pressure in the cylinder, but air leaks on the return side usually come from the O-rings on the injector body or the banjo bolt washers. I've chased my tail more than once thinking a cracked copper seal was the problem when it was actually just a dried out O-ring letting air sneak past. Those copper washers can look cracked but still hold compression fine. Next time you're in that situation, check the fuel return line fitting first because those banjo bolt washers are way more common for air ingress. The copper seal tricking you into thinking it's the culprit is a classic time waster.

cora5624h ago

Give @the_logan some credit here because he's mostly right about the O-rings being the usual suspects, but I've actually seen a cracked copper seal pull in air on a cold start before. The crack can be so tiny you need a magnifying glass to spot it, and it lets air bubble into the return line once the engine cools down overnight. It's definitely rare, but I still check both the copper seal and the banjo washers just to cover my bases.