5.7 Hemi Fuel Injectors Buying Guide

TL;DR: The 5.7 Hemi uses port fuel injection — the injectors sit in the intake manifold and spray at the back of the intake valves, not into the cylinder. That makes them serviceable without pulling heads or dealing with high-pressure fuel hardware, and it makes cleaning a real option rather than a last resort. The two things that ruin a Hemi injector purchase are buying on engine displacement alone instead of confirming fitment against your specific application, and replacing injectors for a misfire that was actually a coil, a plug or a wiring fault. Confirm the current part number against the manufacturer catalogue for your year and application, replace the O-rings and any retaining hardware as a matter of course, and buy a flow-matched set rather than mixing new and old.

What a 5.7 Hemi injector actually has to do

The 5.7 is a pushrod, two-valve-per-cylinder V8 with two spark plugs per cylinder — sixteen plugs, eight coils. That plug and coil count matters here because it is the single biggest reason people misdiagnose an injector. Half the ignition events on a Hemi come from the second plug in each chamber, and a partial ignition fault produces a soft, load-dependent stumble that reads a lot like a lazy injector.

The fuel side is conventional port injection: a fuel rail feeds eight injectors, each seated in the intake manifold with O-rings top and bottom, firing sequentially. Fuel pressure is regulated at the tank on these applications rather than by a rail-mounted regulator with a return line, which means a pressure problem is usually a pump, filter or sock issue rather than something you fix at the rail.

Practically, that gives you a clean division of labour when you diagnose:

• Fuel delivery to the rail — pump, filter, in-tank regulator, wiring.
• The injector itself — coil winding, pintle or ball seat, spray pattern, internal screen.
• The command — PCM driver, harness, connector corrosion.

Injectors get blamed for all three. They are only responsible for the middle one.

Symptoms that actually point at injectors

An injector fault on a 5.7 tends to be cylinder-specific and repeatable. The tells:

A misfire that follows the injector, not the coil. Swap the suspect injector with a known-good one from another cylinder and see whether the misfire moves. This is the single most valuable test on this engine and it costs nothing but O-rings and time. If the misfire stays put after the swap, you have a coil, plug, wiring or mechanical problem — go look at ignition components instead.

A dead-cold start complaint that clears once warm. A leaking injector floods its cylinder overnight and produces a rough start with a fuel smell that cleans up in thirty seconds. Note this pattern precisely; it is very different from an injector that flows too little.

Long-term fuel trim skewed on one bank. A restricted injector on one bank shows up as positive trim on that bank while the other stays near zero. That is a strong signal, but confirm it against intake leaks and a lazy oxygen sensor before you spend — the engine sensor side produces the same trim pattern often enough to be worth ruling out.

Injector circuit codes. A driver or circuit code names a specific cylinder and gives you a wiring test to run. Do the wiring test. A corroded connector pin is common on high-mileage trucks and no new injector fixes it.

A dead cylinder with good spark and good compression. Once ignition and mechanical are cleared, the injector is what is left.

What does not point at injectors: a general lack of power with no misfire, an overall lean condition on both banks, a rough idle that changes when you touch a vacuum line, or a fuel pressure problem. Those are all upstream or elsewhere.

Clean, remanufacture, or replace

Because these are port injectors, all three routes are legitimate — which is not true on the direct-injection engines.

Two things are true regardless of route. First, buy or service all eight together. A single new injector alongside seven worn ones puts one cylinder out of step with the others and gives the PCM a trim target it cannot satisfy cleanly. Second, insist on flow matching within a stated tolerance across the set, and keep the sheet. When a Hemi comes back with a complaint a year later, that sheet is how you clear the fuel side in five minutes.

Cleaning has a hard limit worth naming: it fixes flow restriction and spray pattern. It does not fix a shorted or open winding, a cracked body, or a damaged pintle. A flow test that comes back with one injector electrically out of spec means that injector is finished.

Getting fitment right the first time

This is where most returns come from. "5.7 Hemi" is not a fitment. The engine ran across a long production span in a lot of vehicles, and it changed along the way — intake manifold and cylinder head revisions, applications with cylinder deactivation and applications without, and calibration differences between truck and car platforms. Injector length, connector style, O-ring sizes and flow rating do not all carry across every one of those.

Work through this before ordering from the fuel injector selection:

1. Confirm the current part number against the manufacturer catalogue using your year, platform and build date rather than displacement alone. Build date matters more than model year on this engine family.
2. Pull one injector and physically compare it to the listing photo — overall length, the shape of the fuel rail cup end, the connector body, and the O-ring seats. A physical comparison is worth more than any listing description.
3. Match the electrical connector exactly. Adapters exist, but a harness adapter on a fuel injector is one more connection sitting on a hot intake for the life of the engine. Buy the right connector.
4. Match the flow rating to the calibration, not to an ambition. A stock, unmodified 5.7 wants the flow the factory calibration expects. Larger injectors without a matching tune produce a rich condition, fouled plugs and a check engine light, not power.
5. Confirm what the kit includes. Some sets ship with new upper and lower O-rings and clips; some ship bare. Never reuse old O-rings.

If the engine has been modified — a cam, a supercharger, or anything that meaningfully changes airflow — the injector decision belongs to whoever is writing the calibration. Get the injector data from the tuner first, then buy. The rest of the 5.7 Hemi parts catalogue is organised the same way, by application rather than by displacement alone, for exactly this reason.

Installing them without creating a new problem

The job is mostly intake work. Budget the shop labour accordingly — on most applications this is a low single-digit labour-hour job for an experienced tech, more on a tightly packed engine bay or if the intake gaskets are being replaced at the same time.

• Depressurise the fuel system and disconnect the battery before anything comes apart. There is fuel in the rail and it stays there.
• Keep the intake clean. Anything that falls into an open port is going into a cylinder. Plug the ports the moment the rail is off.
• Replace every O-ring, and lubricate them with clean engine oil — not silicone grease, not assembly lube — before seating. A dry O-ring rolls and tears going in and you will not know until it leaks.
• Seat each injector fully and verify the retaining clip is engaged before the rail goes down. A partially seated injector will push out under pressure.
• Torque the rail and intake fasteners in the factory sequence to the value in the service manual. Do not guess at these, and do not reuse fasteners the service information calls single-use. Fresh gaskets and seals on anything disturbed is cheap insurance against a vacuum leak that ruins the whole job.
• Prime and leak-check with the engine off — key on, listen for the pump, look and smell around every injector before you crank.
• Clear codes and let the fuel trims relearn before you judge the result. Trims take a drive cycle to settle.

While the intake is off, look at the fuel filter service history and at the condition of the plugs in each cylinder. Plug colour per cylinder is free evidence about which injectors were actually misbehaving, and it is the last chance to read it.

Frequently Asked Questions

How do I know if a 5.7 Hemi injector is bad or if it is the coil? Swap the suspect injector with one from a known-good cylinder and re-run the engine. If the misfire moves cylinders, the injector is at fault. If it stays, the problem is ignition, wiring or mechanical. Doing the same swap test with the coil separates the two in a few minutes without buying anything.

Do I have to replace all eight injectors at once? On any engine with real mileage, yes. Worn injectors drift in flow as a group, and a single fresh injector among seven tired ones creates a cylinder-to-cylinder imbalance the fuel trims cannot correct cleanly. A one-off replacement is only reasonable on a low-mileage engine with a single confirmed electrical failure.

Are remanufactured Hemi injectors worth it? For a high-mileage daily-driven engine, a properly remanufactured, flow-matched set is usually the best value — you get new seals and internal wear items, matched flow and a warranty. Ask for the flow data and the tolerance the set was matched to. If the seller cannot produce it, that is not a remanufactured set.

Can I put larger injectors in a stock 5.7 Hemi for more power? No. The factory calibration meters fuel based on the flow rate it expects. Larger injectors without a matching tune deliver too much fuel, which costs you power, fouls plugs and sets codes. Larger injectors are a supporting part for a modified engine and a new calibration, never a standalone upgrade.

How long do 5.7 Hemi fuel injectors last? There is no fixed interval — they are not a scheduled service item. Service life depends heavily on fuel quality and filter maintenance, and problems tend to appear as cylinder-specific misfires or trim drift rather than at a set mileage. Consult the maintenance schedule in the service manual for your application for filter intervals, which are what actually protect the injectors.

Do I need to replace the O-rings if the injectors are new? Yes, and new injectors normally ship with them. Never reuse an old O-ring, even one that looks intact — it has taken a compression set in its groove and will not seal reliably in a new position. Lubricate new O-rings with clean engine oil before seating.

Sources

Written from the Core Powertrain Parts technical team's shop experience on Gen III Hemi engines, our internal fitment and cross-reference notes, and the general service practice for returnless port-injection fuel systems. Year-, platform- and build-date-specific part numbers, torque values and tightening sequences were deliberately not stated here — confirm them against the manufacturer catalogue and the factory service information for your exact application before ordering or assembling.

Questions on fitment for your specific truck or car? Email sales@coretransmissionparts.com with the year, platform and build date and we will confirm the correct set before you buy. Free shipping on orders over $70.