fuel injector seal
fuel injector seal
(OP)
One of the fuel injectors in my car developed a leak on the inside valve. This got me thinking - why is the needle seal metal-to-metal? With the different types of fuel resistant polymers and elastomers out there today (ex. PTFE, PFA, Delrin, Viton rubber) , wouldn't it be more reliable and less costly to make the needle seat on something softer?





RE: fuel injector seal
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RE: fuel injector seal
Regards
Pat
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RE: fuel injector seal
The only reason I can think of is that a fuel injector will see something like 1E9 cycles over a decade and using a polymer or elastomer seal there would be issues with creep and compression set. This would probably affect the flow rate of the injector because I'm guessing the ball valve lift is only a few thous.
RE: fuel injector seal
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: fuel injector seal
RE: fuel injector seal
Some injectors are VERY expensive, even from the OEM. The already mentioned Bosch NG injectors are a good example. But even those are relatively cheap if you buy thousands of them. For most parts though, it is all about the markup between the injector manufacturer, and the OEM, their dealer, etc. It is more on the order of $10 from the manufacturer, in high enough volumes.
RE: fuel injector seal
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: fuel injector seal
I've seen some OEM injectors sold at retail for only about 1.5X the OEM cost...but buying just one of them would cost as much as replacing 25 of yours.
RE: fuel injector seal
RE: fuel injector seal
There is no shut off valve, the rail is supposed to maintain pressure when the engine shuts down. As a rule, leaky fuel injectors are quite rare these days, the primary failure mode is contamination. A soft seal may or may not be less susceptible to failure from contamination. Hard contamination may damage a soft seal but eventually work it's way out of a hard seal.
From my experience at least 75% of the automotive fuel injectors that are replaced have no failure at all. Some of these may have been replaced because one was bad and the labor charge is basically the same to replace them all. Others are replaced because the mechanic (parts changer) has no idea what is wrong and is just changing one thing after another. A lot are replaced because someone is trying to make a boat payment.
I'm curious, what was the problem that was supposedly caused by your leaky injector and how did they diagnose it?
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: fuel injector seal
RE: fuel injector seal
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: fuel injector seal
RE: fuel injector seal
RE: fuel injector seal
I know of no cars with the tank above the engine.
The amount of leak we are talking about here is miniscule. Typically for a port injected engine the spec is less than 1 sccm nitrogen with 4 bar differential pressure. Obviously it will be a lot less on gasoline. So much less it gets really hard to measure which is why all the testing is done on nitrogen.
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: fuel injector seal
http://www.allstates.com/fuel%20injector%20asnu%20...
I have some Bosch LH FI info that says some modest amount of injector leakage is still OK. Maybe a few drops per minute.
If left long enough the residual pressure would drop, and the pump would have to run a few seconds to fill and pressurize the system again, resulting in slightly delayed starting. The Fuel pressure regulator and residual pressure valve near the pump can leak, and create similar symptom.
RE: fuel injector seal
Before 1920 most cars had the tank higher than the engine, however I don't recall any being injected.
If you think about the volume of fuel under pressure, the potential size of the leaks and the volume of the cylinder and the potential leaks from the cylinder it really becomes very obvious that this is a non issue.
Regards
Pat
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