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I have not seen any additives (such as those used in automobiles) to clean and maintain fuel injectors in aviation engines. Is there a reason for that such as the use of lead in 100LL or something else? The fuel injectors will eventually constrict or clog as the avgas leaves residual deposits.

Is there some technical reason or is it just that no one has gone through the certification process or at least (like AVBlend or CamGuard) received the "will do no harm" approval from the FAA?

Removing, cleaning, reinstalling fuel injectors is not only expensive but you also risk damaging them and if you have the GAMI injectors you can have quite a bill coming at you.

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Fuel injectors in GA piston engines are actually fixed nozzles, so short of fuel contamination, are not so easy to clog,since the only thing that can be deposited with clean fuel is the blue dye in the avgas.

In 8 years maintaining a fleet of 6 to 8 injected Continental engines, running 200-700 hours / year, I did not see a fuel-deposit blocked nozzle. Deposits did change the flow rate enough for us to routinely clean them ultrasonically (our pilots were cruising lean of peak, and would start complaining), but removing, cleaning and reinstalling the injector nozzles was a routine, straightforward and scheduled event in my experience.

With position tuned nozzles, as current Continental ones are, you need to be careful to get them back to their correct position, just like GAMI ones, but it's not rocket engineering. The torques for installation are in the manuals, and they are not the most challenging item to work on (one b-nut and one pipe thread per nozzle) on the average GA engine. There's no need for special additives.

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  • $\begingroup$ While this is a great answer to a slightly different question, it does not answer this question. $\endgroup$ – CGCampbell Apr 21 '15 at 14:46
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I'm not aware of any FAA-approved (or FAA-accepted) products for on-engine fuel injector cleaning. If your injectors are blocking due to lead deposits a tricresyl phosphate additive may help improve lead scavenging and prevent the problem, but it's probably not going to clean a clogged injector. (TCP is also pretty nasty stuff – leaning your engine more aggressively can often accomplish the same thing without the chemicals.)

Frankly 100LL is a pretty darn good solvent: it even dissolves that blue dye they put in it which nothing else ever seems to budge. If your injectors are blocked due to contamination that 100LL won't dissolve having your mechanic take them off and bench-clean them is probably a good idea (as Thomas pointed out this isn't rocket surgery - any competent mechanic should be able to do it without damaging anything).

As far as other "pour it into the gas" cleaning additive, as with many things There's an Advisory Circular that covers this (AC 20-24D) - at least to some extent: That Advisory Circular deals with fuel specifications for type certification of aircraft/engines/APUs, but it contains this interesting nugget:

(1) Fuel additives that are incorporated into ASTM, governmental or military specification, or other industry-based consensus organization specification, are considered to be identified in sufficient detail to be accepted by the FAA under existing operating limitations on TCs, amended TCs, STCs, or ASTCs, provided there are no changes to those operating limitations.

So if you can show that the injector-cleaner chemical you want to use is an approved additive according to ASTM D910 (the standard that governs 100LL avgas), your use of the additive is in accordance with the specification ("not more than X% or Yppm"), and the additive is not contraindicated by the manufacturer (of the engine, airframe, or any components) you should theoretically be OK to use it.

Navigating that legal morass is something you probably don't want to do though: The risks of getting it wrong are not just paperwork-related: some additives can damage your fuel system, or even lead to an engine failure.
A bench cleaning of your injectors is probably the easier and safer option.

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    $\begingroup$ I believe that is the circular, which you quoted, that allowed AVBlend and CamGuard to sell their oil additives. My question was not to the extent to clean a clogged injector but as a preventative measure to avoid future clogging and a possible scrub of a mission to have the injectors serviced. Thanks. $\endgroup$ – TB Flyer Apr 22 '15 at 2:19
  • $\begingroup$ @TBFlyer I'm not sure if that AC was the totality of the justification for AvBlend & CamGuard - I believe they went through some additional processes - but I'd bet money they referenced it :) Re: preventing injector clogs, if that's your goal I personally think aggressive leaning is your best bet to avoid lead deposit clogs, and following that using fuel additives containing TCP. I'd only consider the latter if you have a repeat problem you can trace to lead deposits on the injector though. $\endgroup$ – voretaq7 Apr 22 '15 at 7:37
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Keep fuel injector clean by using fuel injector cleaners isn't a bad choice at all. I have been using them for years. Try Chevron, Lucas or BK44 to see different between before and after.

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