What is the difference between P0284 and the cylinder 8 injector circuit codes?

P0282 and P0283 are electrical statements about the injector's control wire — low voltage where high was expected, or high where low was expected. P0284 says nothing about wiring at all; it says the cylinder produced less power than its neighbors, measured at the crankshaft. That distinction decides your first move. If a circuit code is stored alongside P0284, fix the electrical fault and the balance fault usually clears with it. If P0284 is on its own, the wiring is fine and the cause is fuel delivery, ignition, or compression.

Should I do a compression test before replacing the injector?

Yes, and on cylinder 8 more than anywhere. A worn ring pack or a burnt valve produces exactly the same weak-contribution reading as a tired injector, and no new injector restores compression. Cylinder 8 is the rearmost injector on virtually every V8, which usually means removing the upper intake plenum to reach it — so a wrong guess costs you the teardown, the gaskets, and the part. A compression and leak-down test either clears the mechanical path or saves you the entire job.

Which cylinder is number 8 on my engine?

It depends on the manufacturer, and this is the sharpest split in the whole block. GM V8s number the passenger bank 2-4-6-8, which puts cylinder 8 at the very back on the passenger side. Ford modular V8s number the driver's bank 5-6-7-8, which puts cylinder 8 at the very back on the driver's side. Same code number, opposite sides of the engine. Do not use the firing order to work it out — the firing order tells you when a cylinder fires, not where it sits.

Can I drive with P0284?

Short trips to a shop are generally fine, because the engine still runs. It should not be left alone, though. A cylinder burning its fuel incompletely sends unburned fuel into the exhaust, which can overheat the catalytic converter on that bank over time, and on a V8 that converter is not a cheap part. If the check engine light starts flashing, stop driving and have the vehicle towed.

OBD-II trouble code

P0284: Cylinder 8 Contribution/Balance Fault

Cylinder 8 is producing less power than the rest, measured through crankshaft acceleration. Fuel, ignition and compression all look identical here — the whole job is testing them in the right order, cheapest and most definitive first.

Medium severityPowertrainFuel InjectorsDrivable short-term

Quick facts

System: Powertrain
Category: Fuel Injectors
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $100 – $3,500
DIY difficulty: Intermediate DIY

What does P0284 mean?

P0284 reports an outcome rather than a wiring condition. The engine control module (ECM) reads crankshaft rotational speed at high resolution through the crankshaft position sensor. Every power stroke gives the crankshaft a brief acceleration whose magnitude reflects how much work that cylinder produced, and the ECM compares all cylinders against one another. When cylinder 8 falls outside the allowed spread, P0284 sets.

P0284 is the last code in the per-cylinder injector block that runs from P0261 to P0284, and it is a good place to explain how the three code types in that block relate — because people routinely confuse them and chase the wrong repair.

A circuit LOW code (P0282 for this cylinder) means the ECM measured voltage on the injector control wire that was lower than it should have been. That is an electrical statement about a wire: a short to ground, a shorted injector coil, or a driver stuck on. A circuit HIGH code (P0283) is the opposite electrical statement: an open circuit or a short to power. Neither of them says anything about how well the cylinder is burning fuel. A contribution or balance code — P0284 — says nothing about the wiring at all. It says the cylinder produced less power than its neighbors, and the wiring may be in perfect condition. That is why the first diagnostic step is always to read every stored code: if P0208, P0282, or P0283 is present alongside P0284, the electrical fault is the cause and repairing it normally clears the balance fault with it. If P0284 stands alone, the wiring is fine and something else is limiting that cylinder.

That something else falls into exactly three buckets, and the crankshaft sensor cannot distinguish between them. Fuel: a restricted, worn, or slow-opening injector delivers less than commanded. Ignition: on a gasoline engine, a worn plug or a coil breaking down under load leaves combustion incomplete. Compression: worn rings, a burnt or leaking valve, or a head gasket leak means the cylinder cannot turn combustion into pressure on the piston. Because all three read the same, the entire value of this diagnosis is the ORDER. Inspect the plug and swap the coil first, since that costs minutes and nothing. Compression- and leak-down-test the cylinder second, since it is cheap and definitive. Buy the injector last. Fitting a new injector to a cylinder that has lost compression is the most expensive mistake on this whole family of codes, and on cylinder 8 — the rearmost injector on nearly every V8, frequently under the upper intake plenum — the teardown costs as much as the part.

Cylinder 8 exists only on V8 and larger engines, and the numbering conventions disagree about where it sits: GM V8s number the passenger bank 2-4-6-8, while Ford modular V8s number the driver's bank 5-6-7-8. Confirm your engine's diagram first.

On diesel V8s — the 6.0, 6.4 and 6.7 Power Stroke and the Duramax families generate most of the real-world traffic on this code — the analysis narrows to fuel and compression only, since there is no ignition system to rule out. Factory tools expose a per-cylinder balance rate, which is the size of the fuel correction the ECM is applying to keep the engine smooth. A large, steady positive correction on cylinder 8 with healthy compression points at that injector. Diesel injectors degrade slowly rather than failing outright, which is precisely the decline a balance monitor is built to catch.

Common causes

Restricted, dirty, or internally worn cylinder 8 fuel injector
Injector opening late or producing a degraded spray pattern under load
Worn spark plug or a failing ignition coil on cylinder 8 (gasoline engines)
Low compression on cylinder 8 from worn rings, a burnt valve, or a valvetrain fault
Head gasket leaking between cylinder 8 and a neighbor or into the coolant jacket
Intake plenum or runner gasket leak on the bank cylinder 8 sits on
Low fuel rail pressure, a restricted fuel filter, or contaminated fuel
Weak high-pressure fuel pump on a direct-injection or common-rail diesel engine
High-resistance wiring or a corroded connector at the cylinder 8 injector

Symptoms

Check engine light on
Rough idle and a shake most noticeable at low RPM
Reduced power and hesitation under load
Companion misfire codes such as P0308 or P0300
Poor fuel economy
Hard starting or extended cranking, particularly on diesels
Excessive or black exhaust smoke on diesel applications

Diagnostic steps

1.Read every stored code first. P0208, P0282, or P0283 present alongside P0284 means the injector circuit is electrically faulty — repair that and the balance fault normally resolves with it.
2.Note which other contribution codes are stored and map them to banks. One bank weak points at something that bank shares; both banks weak points at the whole fuel supply.
3.Confirm which physical cylinder your engine calls number 8. GM V8s put it at the rear of the passenger bank; Ford modular V8s put it at the rear of the driver's bank.
4.Run the scan tool's cylinder balance, injector contribution, or diesel balance-rate test and record how far cylinder 8 sits from the others. A large, repeatable deviation is meaningful; a small wandering one usually is not.
5.On a gasoline engine, remove the cylinder 8 spark plug and compare it against the others. Heavy wear, fouling, or oil on the electrode can account for the weak contribution by itself.
6.Swap the cylinder 8 ignition coil with a neighboring cylinder, clear the codes, and drive. If the fault follows the coil, stop there.
7.Compression- and leak-down-test cylinder 8 before buying any fuel component. On the rearmost cylinder of a V8 this step is worth more than anywhere else on the engine, because a wrong guess costs the teardown as well as the part.
8.Check fuel rail pressure under load, on the affected bank specifically if the engine has separate rails or a crossover, and inspect the fuel filter at the same time.
9.Smoke-test the intake for a plenum or runner gasket leak on that bank.
10.If fuel supply, ignition, and compression all check out, swap the cylinder 8 injector with one from a healthy cylinder and see whether the fault follows the injector.

Repair cost

$100 – $3,500

A spark plug or ignition coil on the weak cylinder is typically $100-$350 installed. A gasoline fuel injector runs $60-$400 in parts plus 0.5-3 hours of labor, and cylinder 8 sits at the top of that labor range on nearly every V8 because it is the rearmost injector, often under the upper intake plenum, which adds gaskets. Diesel injectors commonly reach $400-$900 each installed, and a full set on a high-mileage Power Stroke or Duramax runs $2,000-$3,500. Fuel filter or fuel pressure repairs generally land at $150-$800, and a high-pressure fuel pump is $600-$1,600. Mechanical causes — rings, a burnt valve, or a head gasket — start near $1,200 and can exceed $3,000. Diagnosis alone is usually $100-$200, because the code calls for a sequence of tests rather than one measurement.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.