Going to the next larger inside diameter (ID) fuel lines and fittings can help lower the vacuum also. This larger diameter ID can
also help correct vapor locking conditions. An example is shown below.
8 mm (5/16 in.) fuel line ID 17.8 kPa (5.5 in. Hg) Too high
9.5 mm (3/8 in.) fuel line ID 8.2 kPa (2.5 in. Hg) Too high
12.5 mm (1/2 in.) fuel line ID 2.7 kPa (0.8 in. Hg) Good
See MerCruiser Service Bulletin 99‑7 (Rev. 1/01) for information on gasoline engine vapor locking.
Equipment Used to Test Fuel RVP, Fuel Temperature, or Fuel System Vacuum
The following information is contained in Mercury MerCruiser Service Bulletin 99‑7 (Revised October 2000).
Testing fuel RVP:
SPX OTC sells a test kit, Gasoline Quality Testing Kit ‑ P/N 7670.
Testing fuel temperature or vacuum:
Fittings required to make connections between engine fuel inlet and the boat fuel line and fitting.
(1) Pipe fitting ‑ 1/4 in. pipe thread at both ends, 38 mm (1‑1/2 in.) long
(1) T‑ fitting ‑1/4 in. female pipe thread
(1) Schrader valve ‑ P/N 22‑805408
(1) Cap, Schrader valve ‑ P/N 22‑805515
Tools required to measure fuel vacuum at fuel inlet of the engine.
(1) Digital compound gauge (–101 kPa to 689 kPa [–30 in. Hg to 99.9 psi]), that has an accuracy of within 2% of the reading.
Cole‑Parmer ‑ P/N P‑68950‑00. (Note 1)
(1) Gauge guard (–101 kPa to 103 kPa [–30 in. Hg to 15 psi]). Cole‑Parmer P/N U‑07359‑02. (Note 1)
(1) Gauge guard liquid 118 cc (4 fl oz). Cole‑Parmer P/N U‑07359‑50. (Note 2)
(1) Hose connected to digital gauge with adapter to connect to the Schrader valve. Can use hose and Schrader valve
connector from Fuel Pressure Kit, P/N 91‑88183303.
Tools required to measure fuel temperature at fuel inlet of the engine.
(1) DMT 2000 meter ‑ P/N 91‑854009A3, or DMT 2004 Meter ‑ P/N 91‑892647A01.
(1) Reducer bushing ‑ 1/4 in. male to 1/8 in. female pipe thread ‑ P/N 22‑48556.
(1) Temp probe compression fitting ‑ 1/8 in. pipe thread. Cole‑Parmer ‑ P/N H‑08539‑04.
(1) Temp probe ‑ 4 in. long with K connector. Cole‑Parmer ‑ P/N P‑08117‑45.
(1) Temp probe extension cable ‑ 10 ft long with K connector. Cole‑Parmer ‑ P/N H‑08516‑30.
Cole‑Parmer Instrument Company
Phone: 847‑549‑7600 or 800‑323‑4340.
Fax: 847‑247‑2929
International Fax: 847‑549‑1700.
NOTE: 1 The gauge guard has to be used with the gauge listed to protect it from liquid gasoline or vapors. Failure to use the
gauge guard will damage the gauge. When using the guard, the maximum range that can be applied to this guard installed on
the gauge is –101 kPa to 103 kPa (–30 in. Hg to 15 psi).
MPI ECT Fuel System
Page 5A-32 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015
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