Is It Worth Replacing High-Mileage Injectors?

Wondering what the consensus is here on the forum about fuel injectors needing replacing, cleaning, or rebuilding after putting lots of miles on them.

I have 375k miles on my truck and I'm not sure whether the injectors are original or have been replaced at some point. I did a 6.0L swap into this truck a couple years back and left the 5.3L injectors in it. It was the 5.3L flex VIN so the lb/hr is sufficient for the 6.0L.

I have off and on felt like this truck has some fueling issues as sometimes the power will go in and out as I am coasting in a low-load situation, and sometimes it will lightly bog in near-idle situations. Not sure if this can be attributed to a tune-related issue or a fueling issue, but I just had it occur to me that a fueling issue could also be (at least partially) to blame. I know I need to replace the fuel filter so I picked one up and plan to do that at some point.

In my research I found several injector shops that claim that rebuilding or cleaning injectors can boost mileage by as much as 15%. Does anyone think that holds any water? Makes sense on some level of the injectors aren't atomizing as efficiently (or whatever) that there would be less efficient combustion, but was looking for anecdotal evidence to that end, if anyone had any.

Probably wouldn't hurt to get them cleaned. I don't know about boosting mileage by 15%. That's probably assuming the injectors are not running at optimum to begin with, if I had to guess.

OTC sells a gadget to clean injectors, if you aren't aware of that. Maybe someone here has used that? I believe it's like $250-ish?

But the advantage of the folks that clean them is they can also flowrate-match them. I'm not sure how they do that tho.

squeeler642 said:

Wondering what the consensus is here on the forum about fuel injectors needing replacing, cleaning, or rebuilding after putting lots of miles on them.

I have 375k miles on my truck and I'm not sure whether the injectors are original or have been replaced at some point. I did a 6.0L swap into this truck a couple years back and left the 5.3L injectors in it. It was the 5.3L flex VIN so the lb/hr is sufficient for the 6.0L.

I have off and on felt like this truck has some fueling issues as sometimes the power will go in and out as I am coasting in a low-load situation, and sometimes it will lightly bog in near-idle situations. Not sure if this can be attributed to a tune-related issue or a fueling issue, but I just had it occur to me that a fueling issue could also be (at least partially) to blame. I know I need to replace the fuel filter so I picked one up and plan to do that at some point.

In my research I found several injector shops that claim that rebuilding or cleaning injectors can boost mileage by as much as 15%. Does anyone think that holds any water? Makes sense on some level of the injectors aren't atomizing as efficiently (or whatever) that there would be less efficient combustion, but was looking for anecdotal evidence to that end, if anyone had any.

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If you're having fluctuations in running smoothness, validate you have a consistent, adequate fuel pressure. 375k is a lot of miles, and I can't speak to that. I can say that I've had great results cleaning injectors with an ultrasonic cleaner.

Wow thats alot of miles on injectors. My logic is, if you got the money spare buy a new/rebuilt set of OEM injectors. If you dont have the money to spare then have yours atleast cleaned. Shop around of course. Injectors when working correctly they spray conical shaped atomized (Mist) of fuel and air mixture downward into the combustion chamber. When injectors get alot of miles on them they tend to get deposits from fuel additives which affects their ability to keep that atomized fuel in a conical shape and end up with droplets and funky patterns of spray. Then there also becomes a problem with the injectors being able to be fully closed when they arent turned on because of the deposits. Very similar to a non sealing intake/exhaust valve. Only with a leaking injector it is adding fuel to your cylinder when it isnt suppose to be when engine is running AND even when the engine is off and that fuel will find its way past your piston rings and down into your oil. Now you have gasoline and oil in your engine for lubrication of bearings, pistons, cam, etc. Gasoline will wash oily film off of components in the routes that oil takes to lube your engine and this is not good because all the metal parts in your engine that are lubed rely on that oily film to remain there constantly to protect against friction and heat as well. Think of oil as an internal coolant also. It draws heat away and dissipates it in the oil pan and oil coiler if equipped.

squeeler642 said:

Wondering what the consensus is here on the forum about fuel injectors needing replacing, cleaning, or rebuilding after putting lots of miles on them.

I have 375k miles on my truck and I'm not sure whether the injectors are original or have been replaced at some point. I did a 6.0L swap into this truck a couple years back and left the 5.3L injectors in it. It was the 5.3L flex VIN so the lb/hr is sufficient for the 6.0L.

I have off and on felt like this truck has some fueling issues as sometimes the power will go in and out as I am coasting in a low-load situation, and sometimes it will lightly bog in near-idle situations. Not sure if this can be attributed to a tune-related issue or a fueling issue, but I just had it occur to me that a fueling issue could also be (at least partially) to blame. I know I need to replace the fuel filter so I picked one up and plan to do that at some point.

In my research I found several injector shops that claim that rebuilding or cleaning injectors can boost mileage by as much as 15%. Does anyone think that holds any water? Makes sense on some level of the injectors aren't atomizing as efficiently (or whatever) that there would be less efficient combustion, but was looking for anecdotal evidence to that end, if anyone had any.

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Simple answer is yes, new injectors.
I use for my example my '97 Moto Guzzi 1100 Sport. It had about 22k miles when I bought it. I tuned it up using an aftermarket ECU so I have full access to fuel and timing. I took a 10k mile trip, micro-tuning it all the way- having started with a map that was pretty close anyway.
Over the course of a few more years, and a leaky gas cap that got water in the fuel 3 times the tune went off a bit. Still ran ok, but I could tell it just wasn't sharp and I couldn't bring it back. I sent the injectors out for cleaning and inspection (low miles, so no replacement necessary) to InjectorRX and they came back perfect as new; the point to this novel is that one side was down 4% and the other side was down 9%. After installing the renewed injectors, I had to retune the entire map, and my average mileage went from 37 to 45.
The mileage, in a nutshell, comes from balance; your O2 sensor sees an average of all the cylinders that pour into it. In my case, micro-tune only made one cylinder a little lean and the other cylinder a little rich so neither was optimized. Multiply that by 8, then factor in your mileage and expected wear on the injectors it's easy to see the wisdom in replacement.

Well the big thing I see is did you get a tune for the 6.0 to run the flex injectors? The 6.0 injectors are 24ish lb/hr flow vs the flex 33lb/hr. So if you didn't get a tune to offset the extra flow, you are completely relying on the ecm to adjust by reading the O2 sensors. I'm fairly surprised you haven't killed a cat converter already.

Almost 400k on injectors is a lot. Unless every single aspect of the motor and fuel system has been perfectly maintained, it’s probable that the injectors probably have at least some build up constricting flow or preventing that precise conical spray pattern.

A good clean would probably do you some justice. I agree with @rockola1971, (whose post should be noted as highly informative) about replacing them if you have some extra cash laying around, and if you go that route, replace them with OEM. If that’s not a viable option, then give them a good cleaning.

A couple notes/responses to some points here. Appreciate the dialog happening here for sure!!

Pressureangle said:

The mileage, in a nutshell, comes from balance; your O2 sensor sees an average of all the cylinders that pour into it. In my case, micro-tune only made one cylinder a little lean and the other cylinder a little rich so neither was optimized. Multiply that by 8, then factor in your mileage and expected wear on the injectors it's easy to see the wisdom in replacement.

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Completely my logic in wanting to get them cleaned/replaced. Not sure how out of balance they are but I can't imagine I wouldn't see at least a marginal difference (1-2mpg) before/after.

Mudsport96 said:

Well the big thing I see is did you get a tune for the 6.0 to run the flex injectors? The 6.0 injectors are 24ish lb/hr flow vs the flex 33lb/hr ... I'm fairly surprised you haven't killed a cat converter already.

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Truck came equipped with the flex 5.3L, so I already had the 33lb/hr injectors. Got the truck dyno tuned after the swap and have a wideband O2 monitoring bank 1 exhaust flow. Not ideal in my mind to have WB data for only half of the motor, but I figured it's good enough for what I'm doing, making my daily driver a little more fun. Also did long tubes with the new motor, so I haven't given cats much thought.

PPV_2018 said:

Almost 400k on injectors is a lot. Unless every single aspect of the motor and fuel system has been perfectly maintained, it’s probable that the injectors probably have at least some build up constricting flow or preventing that precise conical spray pattern.

A good clean would probably do you some justice. I agree with @rockola1971, (whose post should be noted as highly informative) about replacing them if you have some extra cash laying around, and if you go that route, replace them with OEM. If that’s not a viable option, then give them a good cleaning.

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There have definitely been some years of less than ideal maintenance. The truck has been in the family since the dealership, but some folks were better than others about maintenance. But the oil changes (miraculously!) we're always regular, allowing me to get 350k out of the original motor. It was pissing oil out of every orifice by the time I swapped the 6.0 in there.

I go back and forth on the OEM vs clean route. I really want to know how these would flow test before/after cleaning because that would give me an idea of how matched (or likely not) they are at this age/mileage. I am thinking of going this route, but would be open to replacing them as a set if one or two of them don't clean up well.

squeeler642 said:

Truck came equipped with the flex 5.3L, so I already had the 33lb/hr injectors. Got the truck dyno tuned after the swap and have a wideband O2 monitoring bank 1 exhaust flow. Not ideal in my mind to have WB data for only half of the motor, but I figured it's good enough for what I'm doing, making my daily driver a little more fun. Also did long tubes with the new motor, so I haven't given cats much thought.

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Well a good tuner would have changed the injector data I would hope. Otherwise, even with a dyno tune for power, daily driving will be off if the flow rate is being calculated incorrectly. Which can cause surging. Where is your wide band when cruising in closed loop?

Mudsport96 said:

Well a good tuner would have changed the injector data I would hope. Otherwise, even with a dyno tune for power, daily driving will be off if the flow rate is being calculated incorrectly. Which can cause surging. Where is your wide band when cruising in closed loop?

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O2 cycles roughly between 0.95 and 1.05 while driving. What do you mean by surging? As a reminder this is the same ECU/injectors that were originally on the truck before the 6.0L was swapped in.