The Mercedes-AMG M177 and M178 4.0 litre twin-turbo V8s respond well to tuning, but the factory fuel system becomes the limit once you add power or switch to ethanol. The usual upgrade path is: an ethanol analyzer if you plan to run E85 blends, a Stage 3 low-pressure fuel pump to keep the high-pressure side fed, and then upgraded high-pressure fuel pumps (Spool FX-200 or FX-350). Each part is made for a specific model, so the right kit depends on whether you have a C63, E63, GT63, G63, GLE63 or AMG GT.
This guide explains where the stock system runs out, what each upgrade does and which parts fit which car.
Where the Stock M177 Fuel System Runs Out
Like other direct-injection engines, the M177 has a low-pressure side (an electric pump in the tank) and a high-pressure side (engine-driven pumps that feed the injectors). The M177 uses two high-pressure pumps; the Spool kits for it include two FX pumps. The Spool listings describe the stock high-pressure pump as severely limited once you try to raise output, and say it runs out of capacity fast once you start tuning. They describe the factory low-pressure pump as a bottleneck when chasing high horsepower, "especially on E85".
The signs are the same as on any DI engine: fuel pressure falling under load in data logs, the tune pulling power at high rpm, and fuel pressure faults after a tune or a move to ethanol. Our HPFP vs LPFP guide explains how to tell which side is struggling.
Step 1: Ethanol Analyzer
If you plan to run E85 or a mix, start here. The Spool C63 kit listing notes that fuel sold as E85 can contain anywhere from 51% to 85% ethanol, and that running a lower blend than the tune is built for can damage the engine. The analyzer shows live ethanol content and fuel temperature on your phone. Several Spool HPFP kits let you add the analyzer at checkout, so check before ordering it separately. See our ethanol analyzer guide for more.
Step 2: Low-Pressure Fuel Pump (Stage 3)
The Spool Stage 3 LPFP kit for the M177 uses a twin-pump design. One pump runs normally and the second switches on at boost onset, providing almost double the flow of a stock pump, according to the listing. Upgrading the low side first makes sure any high-pressure pump upgrade is properly fed.
Step 3: High-Pressure Fuel Pumps (FX-200 or FX-350)
Spool offers two designs:
- FX-200: the C63 listing describes a bigger bore than stock for more flow, full E85 compatibility and plug-and-play fitment with no cutting or splicing. The kit includes two pumps, a 10-micron filter and upgraded lines.
- FX-350: runs at 35 MPa (350 bar) versus 25 MPa on the FX-200, according to the E63 and G63 listings. Higher pressure lets the injectors flow more fuel before they reach the limit of the injection window, and improves atomization. Kits include two pumps, a Bosch-spec 10-micron high-flow filter, upgraded lines and hardware, with the analyzer optional.
Choose based on your power goal and fuel. Your tuner can tell you which pump their calibration is built around.
Model-by-Model Part Table
| Model | Engine | HPFP kits | LPFP | Analyzer |
|---|---|---|---|---|
| C63 / C63 S | M177 | FX-200, FX-350 | Stage 3 | Yes |
| E63 / E63 S | M177 | FX-200, FX-350 | Stage 3 | Yes |
| GT63 (4-door) | M177 | FX-200, FX-350 | Stage 3 | Yes |
| G63 and G550 | M177 | FX-200, FX-350 | Stage 3 | Yes |
| GLE63 | M177 | FX-200, FX-350 | Stage 3 | Yes |
| GLC63 | M177 | FX-200, FX-350 | Stage 3 | Yes |
| S63 and SL63 | see listing | FX-200, FX-350 | Stage 3 | S63 yes |
| AMG GT, GT S, GT C, GT R | M178 | FX-200, FX-350 | Stage 3 | Yes |
The table shows which kit types we stock for each model. Engine versions changed across generations of some models, so confirm the engine and fitment on the listing for your car's year.
Exhaust Side: Downpipes
Fuel upgrades usually go with more airflow. The M177 and M178 downpipes in stock include Spool race downpipes for the C63, the E63 and GT63, and the AMG GT, plus IRL MaxFlow downpipes for the AMG GT and STRATEC 300-cell catted options for the E63, AMG GT and GT63. Catless and high-flow downpipes and other emissions-related parts are intended for off-road and competition use and may not be legal for road use where you live. Check your local laws and inspection rules. See our catless vs catted guide.
Parts and Tools
- Spool Mercedes-AMG C63 Wireless Ethanol Analyzer Kit
- Spool Stage 3 LPFP, AMG C63 (M177)
- Spool FX-200 HPFP System, AMG C63 (M177)
- Spool FX-350 HPFP Kit, AMG E63
- Spool Stage 3 LPFP, AMG E63 (M177)
- Spool FX-350 HPFP Kit, G63 & G550
- Spool FX-350 HPFP Kit, GLE63
- Spool FX-350 HPFP Kit, AMG GT (M178)
- Spool AMG M177 C63 Race Downpipes
- 22-Piece Quick Disconnect Tool Kit — for fuel line connectors
See the full range in Mercedes-Benz Performance Parts and Fuel System Upgrades, or shop by model in Mercedes-AMG GT.
Shop: Mercedes-AMG M177 / M178 Fuel System Upgrades.
Install Notes
- Tune: plan the calibration before the parts go in. Upgraded pumps are meant to be paired with a tune that uses them.
- Relieve fuel pressure before opening any line. High-pressure lines can hold pressure after shutdown.
- Work safely: ventilated space, no sparks or flames nearby, fire extinguisher at hand, eye protection on.
- Keep it clean: cap open lines and pumps so no dirt reaches the injectors.
- Get help if unsure: high-pressure fuel work on these engines is a job many owners leave to a shop.
Frequently Asked Questions
Should I upgrade the LPFP or HPFP first on an M177?
Log fuel pressure to find the limit. On ethanol builds both usually need upgrading, and the low side should be able to feed the high-pressure pumps you choose.
How many high-pressure pumps does the M177 use?
Two. The Spool FX-200 and FX-350 kits for M177 models include two pumps.
Is the FX-200 E85 compatible?
Yes. The C63 listing describes it as completely E85 compatible.
Does the AMG GT use the same kits as the C63?
No. The AMG GT uses the M178 and has its own kits. Always order by model.