LM4 5.3L engine: specs, donor vehicles & swap notes
The LM4 is a 5.3 L aluminum-block Generation III engine built 2003–2005, rated 290 hp. It came in 6 vehicle applications, including Isuzu Ascender, GMC Envoy XL.
| Spec | Value |
|---|---|
| RPO | LM4 |
| Family | Generation III |
| Years | 2003–2005 |
| Displacement | 5.3 L / 325 ci |
| Horsepower | 290 hp |
| Torque | 325 lb-ft |
| Bore × stroke | 3.78 × 3.622 in |
| Compression | 9.50:1 |
| Block | aluminum |
| AFM/DOD | No |
| VIN 8th digit | P |
| Reluctor | 24x |
| Throttle | Drive-by-wire |
| Stock cam | Duration 191°/190° @.050 in. int./exh.; valve lift 0.457"/0.466" int./exh.; 114° LSA; 3-bolt cam gear. |
| Firing order | 1-8-7-2-6-5-4-3 |
- Knock sensor corrosion (water intrusion under intake). Fix: Replace sensors and harness; seal valley; new intake gaskets.
- Oil consumption (rings / PCV). Fix: Monitor level; check PCV and valve seals; rings if excessive.
Aluminum
The LM4 specs above are not yet confirmed against GM documents; GM ratings varied by year and vehicle.
How the LM4 differs from the other 5.3 L Gen III engines
The LM4 is one of the four 5.3 L Gen III engines we list: L33, L59, LM4, LM7. From our engine table:
- Aluminum block. Among the 5.3 L Gen III engines, the LM4 shares it with the L33; the L59, LM7 are iron.
- Compression 9.50:1, within the group's 9.49–10:1 spread.
- Up to 290 hp from the factory (4th of the four 5.3 L Gen III engines we list; the group tops out at 310 hp).
- Built 2003–2005.
Swapping the LM4: what to plan for
- Computer: 24x crank, so the LM4 matches a Gen III computer (0411/P01 or P59); an E38 or E67 only reads 58x. Throttle and wiring have to suit the computer too. More: how to wire your LS (the full checklist for your engine and computer).
- Drive-by-wire throttle. Plan on the pedal and throttle body that match the LM4, and a computer that runs drive by wire; the base Holley Terminator X is cable-only (the X Max does drive-by-wire). More: drive-by-wire pinout.
- From a midsize SUV (Buick Rainier, Chevrolet TrailBlazer EXT, GMC Envoy XL, GMC Envoy XUV and 1 more): measure the accessory drive spacing before you buy brackets; we haven't confirmed which spacing these use (not confirmed in our data). More: how to measure accessory spacing.
Refresh parts for the LM4
From our Gen III refresh list, the parts that are specific to the LM4. Seals, gaskets and the upgrades worth doing on any Gen III with the engine out are in the full refresh list, next to every torque spec.
We may earn a commission when you buy through links on this page.
| Part | GM part # | Why for this engine |
|---|---|---|
| Chevrolet Performance 4.8L & 5.3L truck head gasket | 12575329 | Listed for the LM4; a new gasket goes on any time the heads come off. |
| Stock cylinder head bolt set, 1997-2003 LS (unequal-length design) | 12498545 | LM4 engines built through 2003 use the first-design, unequal-length bolts. Single use. Engines built from 2004 take the second-design, equal-length set (in the Gen IV list). |
| Chevrolet Performance Gen III LS knock sensor 12589867 (each) | 12589867 | The LM4 has its knock sensors in the valley, under the intake, where water collects. |
| Chevrolet Performance LS Gen III camshaft position sensor 19420911 | 19420911 | 24x engines like the LM4 read the cam at the rear of the block. |
From real tunes: 5.3 L on a Gen III computer
What these settings look like in the 472 naturally aspirated pump-gas tunes for 5.3 L engines on Gen III computers (0411/P01, P59) in our tune library (as of 2026-10-15). Every RPO of this size is pooled, not only the LM4, and so are all cams, heads and builds: that is why the ranges are wide. Use them to spot a value that is far outside what works, not as your numbers.
| Setting | Range | Median | Tunes |
|---|---|---|---|
| Hot idle target | 525 rpm to 900 rpm | 698 rpm | 472 (middle 80%) |
| Warm idle airflow, in gear | 5.6 g/s to 12.7 g/s | 6.8 g/s | 471 (middle 80%) |
| Idle spark (around 800 rpm) | 18° to 25° | 18° | 472 (middle 80%) |
| Power enrichment (PE) lambda | 0.78 to 0.87 | 0.80 | 464 (middle 80%) |
| WOT spark at 5,000 rpm, about 0.9 g/cyl | 11.0° to 26.0° | 15.6° | 472 (middle 80%) |
For starting values matched to your LM4's cam, injectors and fuel, use the turn-on tune builder. Always finish on a dyno, and read our safe tuning limits before any wide-open pass.
Donor vehicles with the LM4
Where to find an LM4 at the junkyard: 6 vehicle applications below. Confirm it from the RPO sticker in the glovebox or the 8th VIN digit (for the LM4: P).
| Vehicle | Years |
|---|---|
| Buick Rainier | 2004 |
| Chevrolet SSR | 2003–2004 |
| Chevrolet TrailBlazer EXT | 2003–2005 |
| GMC Envoy XL | 2003–2004 |
| GMC Envoy XUV | 2004 |
| Isuzu Ascender | 2003–2004 |
Buying a used LM4
A used LM4 has no single part number, so this page does not link a search. Confirm the engine from the RPO sticker or the 8th VIN digit (for the LM4: P) before you buy.