Plastic return line cap melted? How to prevent in the future.

Hey y'all, I was bringing my truck into work this morning when I noticed a distinct burning smell. I was hoping it was the guy in front of me, but the smoke coming under my dash quelled that suspicion. I get her off the road, pop the hood, and fuel is gushing out of the driver side cylinder one. Thankfully, I managed to make it home.

Upon closer inspection, the fuel was leaking out directly under the plastic return line cap; which had managed to melt! I went to crack the 5/8 fuel line loose to pull the cap often look at it; and the whole injector spun with it. My guess would be that the heat from the combustion chamber managed to get up past the injector with it being so loose.

Has anybody ever had something like this happen before, and is there a good way to prevent it in the future? Or am I just an idiot who's going to become a learning experience for other people on the forum (haha!)?

Looks like your injector is allowing exhaust back up to the inlet.

gnathv said:

Looks like your injector is allowing exhaust back up to the inlet.

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Interesting idea. Upon first look I didn't even think about that. Good hypothesis.

Did you notice an abnormal amount of carbon around that injector?

I'm glad the fuel didn't ignite... Luckily its diesel...

Once you have fixed your injector issue (torque it down), you could kill 2 birds with one stone by installing R&D IDI fuel return rails. They are billet aluminum (not gonna melt) and once properly installed they minimize air intrusion.
I got some for free with a couple parts IDIs and I like em'. Haven't used them on a DD yet though.

Happy Tinkering!
-CalIDI

CalIDI said:

Interesting idea. Upon first look I didn't even think about that. Good hypothesis.

Did you notice an abnormal amount of carbon around that injector?

I'm glad the fuel didn't ignite... Luckily its diesel...

Once you have fixed your injector issue, you could kill 2 birds with one stone by installing R&D IDI fuel return rails. They are billet aluminum (not gonna melt) and once properly installed they minimize air intrusion.

Billet Injector Fuel Return Rails | R&D IDI PERFORMANCE

Replaces the leak prone factory hose based return system with solid rails and includes Viton O-rings.

idiperformance.com

I got some for free with a couple parts IDIs and I like em'. Haven't used them on a DD yet though.

Happy Tinkering!
-CalIDI

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There honestly wasn't any carbon buildup on the injector itself, which seemed to be a good sign.

I actually run WMO, which has a higher flash point; but yeah it's a really good thing it didn't ignite.

I'll look into the rails. I do have a turbo, so would the heat be a concern with aluminum? I don't think so, but it's worth asking.

Thanks for the response!

I've been interested in those rails also. Seems like they would eliminate some problems but I wonder if they would also hide some problems?
How would you know if o-rings are leaking? Or if, like the OP, you had a loose injector spewing heat out?

If your copper washer was leaking you would have carbon on the injector threads. You’ve got heat traveling up the fuel feed of your injector. Aluminum rails may not melt like plastic caps but you’re not fixing the problem. It’s only one cap melting? There’s a problem with that injector.

I haven't heard of issues with rails and a turbo. Then again, anything is possible. This thread has some info on aftermarket fuel return setups... Might be a worthwhile read:
Seems like people run turbos and rails without issues.

My only concern would be running the rear rubber line under the turbo with all the heat. Those rails can be set up to have the rear hose connecting the two rails rout through the middle next to the intake if you are worried...

Are all of your injectors the same age and model code?
Id probably replace all of them unless you had a source of used ones cheap to throw in for a few miles.

Happy Tinkering!
-CalIDI

I have been on this board for awhile, and this problem is not common. I would not spend big money on something you do not need to cure the problem. Good stock parts should fix it.

franklin2 said:

I would not spend big money on something you do not need to cure the problem. Good stock parts should fix it.

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Good advice. Then again, if you are like me you'll wanna fix it even if it aint broke yet.

CalIDI said:

Good advice. Then again, if you are like me you'll wanna fix it even if it aint broke yet.

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You'll never regret preventive maintenance.

The injectors are cooled by the return fuel flow, so I wonder if your return line clogged or something and kept that injector from being able to cool itself.

franklin2 said:

I have been on this board for awhile, and this problem is not common. I would not spend big money on something you do not need to cure the problem. Good stock parts should fix it.

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I've got a local U-pull yard with a good selection of complete 7.3 IDI's. Will the 7.3 injectors can caps work with the 6.9? If so, I'll pick one up this weekend.

ROCK HARVEY said:

The injectors are cooled by the return fuel flow, so I wonder if your return line clogged or something and kept that injector from being able to cool itself.

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Any good way to check it? By ear it didn't sound like the engine was missing or sputtering.

gnathv said:

If your copper washer was leaking you would have carbon on the injector threads. You’ve got heat traveling up the fuel feed of your injector.

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I was looking for carbon on the tip, didn't see much if any. There was a little bit on the threads, but I reckon the heat would have burned some of that off. I did see blow by coming out from the injector hole with the injector still in the engine, so I think my heat was coming up the side, not internally.

Just to be on the safer side of things, is there a good way to check and make sure?

Injectors and caps are the same.