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MAP Sensor 864856A1 – Fits MerCruiser 350/377/454/502 EFI
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How to Match This Part
This aftermarket manifold absolute pressure (MAP) sensor replaces MerCruiser / Mercury 864856A1 and the earlier number 805217A1. The ECM uses manifold absolute pressure to meter fuel on GM-based MerCruiser EFI engines.
Match this part in this order:
1. OEM number on the sensor or in your parts list — 864856A1 or 805217A1 (also Sierra 18-7684 / Mallory 9-33601)
2. Engine serial number on the MerCruiser identification plate (block, flame-arrestor cover, or near the ignition coil bracket)
3. Engine family against the Compatible Engine Models table below
Compare the product images to your original sensor before ordering. Later MerCruiser MPI applications (for example many MX 6.2L MPI / 7.4L MPI from 1998) often use a different MAP family such as 861249A1 — do not force-fit this listing if your OEM number does not match.
Part Number Cross-Reference
Use this table to confirm equivalent OEM and aftermarket numbers for the same MAP sensor application.
| Type | Brand | Part Number | Notes |
|---|---|---|---|
| OEM | Mercury / MerCruiser | 864856A1 | Primary listing number (SENSOR-MAP) |
| OEM | Mercury / MerCruiser | 805217A1 | Former number; superseded by 864856A1 |
| OEM | Volvo Penta / OMC | 3850396 | Equivalent OEM on matching GM-based EFI applications |
| OEM | Crusader | 48004 | Equivalent OEM MAP sensor cross |
| Aftermarket | Sierra | 18-7684 | Aftermarket replacement for 864856A1 |
| Aftermarket | Mallory | 9-33601 | Aftermarket replacement for 864856A1 |
This is an aftermarket part manufactured by JLM Marine and is not sold as a genuine Mercury Marine or MerCruiser component.
Compatible Engine Models
This MAP sensor is intended for MerCruiser MCM/MIE GM V-6 & V-8 (350, 377, 454 & 502 cid) EFI engines that call for 864856A1. Always confirm with the OEM number on your sensor and your engine serial plate. For MerCruiser owners: Mercury / MerCruiser Serial Number Guide and Mercury Parts Diagrams.
| Engine Family | CID / Liters | Notes |
|---|---|---|
| MerCruiser MCM / MIE GM V-6 EFI | V-6 (GM) | When parts list calls for 864856A1 / 805217A1 |
| MerCruiser MCM / MIE 350 / 5.7L EFI (incl. 377 where catalogued) | 350 / 377 cid | TBI / EFI applications using this MAP |
| MerCruiser MCM / MIE 454 / 7.4L EFI | 454 cid | Including early Mag MPI years that list 864856A1 |
| MerCruiser MCM / MIE 502 / 8.2L EFI | 502 cid | Including early Mag MPI years that list 864856A1 |
Not every MerCruiser MPI uses this sensor. If your parts list shows 861249A1 (or later supersessions in that chain), order that MAP instead.
Technical Specifications
| Specification | Value |
|---|---|
| Part type | Manifold absolute pressure (MAP) sensor |
| Primary OEM number | 864856A1 |
| Supersedes | 805217A1 |
| Function | Measures intake manifold absolute pressure for EFI fuel control |
| Approx. shipping size | 3.25 in L × 2.00 in W × 1.25 in H |
| Approx. weight | 0.14 lb |
Installation Guide
1
Stop the engine, disconnect the battery, and relieve fuel-system pressure per the MerCruiser service procedure for your model.
2
Locate the MAP sensor on the intake / plenum. Unplug the harness connector and note vacuum-hose and wire routing.
3
Remove the mounting fasteners and the old sensor. Inspect the vacuum port, seals, and connector for cracks or corrosion.
4
Install the new sensor, reconnect the vacuum line and harness, restore power, and clear any related diagnostic codes after confirming a vacuum-tight install.
Warning: Work with the ignition off and fuel system depressurized. A vacuum leak at the MAP port can cause rich/lean running or driveability faults — verify hose condition before restart.
Troubleshooting & FAQ
Will this fix hesitation or a MAP-related check-engine light?
Only if the sensor itself failed. Check vacuum hoses, connector terminals, and fuel pressure before replacing. Match the OEM number on your old sensor first.
Is 861249A1 the same part?
No. 861249A1 is a different MerCruiser MAP family used on many later MPI engines (including MX 6.2L MPI and 7.4L MPI applications). This listing is for 864856A1 / 805217A1.
Does Sierra 18-7684 cross to this sensor?
Yes. Sierra 18-7684 and Mallory 9-33601 are verified aftermarket replacements for MerCruiser 864856A1.
Why Choose JLM MARINE?
- Precision Fit: MAP sensor matched to MerCruiser 864856A1 / 805217A1 applications listed above.
- Quality Control: Each batch is inspected for dimensional consistency and workmanship.
- Direct from Manufacturer: New-production aftermarket marine sensors engineered for GM-based MerCruiser EFI fuel control.
We can ship to virtually any address in the world with free shipping available for most regions.
For our typical US and Canadian customers , our shipping timeframes are as follows:
- Amazon FBA: orders will be delivered within 1-5 business days after placing the order (during certain special periods such as major promotions, Christmas, etc., the delivery time of Amazon FBA may be affected).
- US warehouse shipment: orders will be delivered within 5 days after placing the order.
- China warehouse shipment: orders will be delivered about 12 days after placing the order.
When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.
Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.
Founded in 2002, JLM Marine has established itself as a dedicated manufacturer of high-quality marine parts, based in China. Our commitment to excellence in manufacturing has earned us the trust of top marine brands globally.
As a direct supplier, we bypass intermediaries, which allows us to offer competitive prices without compromising on quality. This approach not only supports cost-efficiency but also ensures that our customers receive the best value directly from the source.
We are excited to expand our reach through retail channels, bringing our expertise and commitment to quality directly to boat owners and enthusiasts worldwide.
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