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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11050
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Tan, Hope you are well. Still working on this Mercury 150

Customer Question

Hey Tan, Hope you are well. Still working on this Mercury 150 EFI and need some more assistance, tired of scouring the internet. From our last conservation, have had the ECM rebuilt, bad fuel pump driver and #3 injector driver -cost $595 - back quickly
- Simion Motorsports -***@******.*** - Debbie My fuel pump repair worked and motor is running. I have only run it on the trailer so far, going to put the boat in the water next and run it on the trailer, so I can put it under load. Motor is hard
to start and won't fire off on its own without removing plugs and adding fuel to combustion chamber. Once running she clears up good have run her about 2000 rpm for a bit and bumped the throttle quickly to see response, seems pretty good. However, the last
few times if Iet it idle it will stop after a min - not suddenly - but not real slow either like running out of fuel. Should find another fuel gauge just to verify fuel pressure - my $15.99 one off of ebay - leaks. After she shuts off she won't restart without
the whole fuel thing in the chamber. Does this engine have a choke - primer function? So when you press the key in it gives a squirt of fuel? Looking for good wiring schematic of the engine harness, the dash harness, kill switch and ignition switch. Several
of the safety items on this boat have been bypassed and there are wires just twisted together - it needs attention - and this being a woman's boat I want to make sure items like the neutral safety switch are actually working. Also, need a good source for center
- console, aftermarket throttle/shifting control at a good price. Info on boat: Mercury 150 EFI Saltwater series #OG802569 (power head) Robalo 1920 #WJOB36VAD898 Thanks Michael
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.

Hello Michael.

Have you adjusted the TPS to specification? The TPS can affect start as will the Air temperature sensor.

Here is an explanation of the AIR TEMPERATURE SENSOR
The air temperature sensor transmits manifold absolute
air temperature, through full RPM range, to the
ECM. As air temperature increases “sensor” resistance
decreases causing the ECM to decrease fuel
flow (leaner mixture). Disconnecting the air temp
sensor (open circuit) will increase fuel flow (richen
mixture) by 10%. Bypassing air temp sensor (short in
circuit) will cause fuel flow to decrease 10%.

Air Temperature Sensor Test
Purpose: This test eliminates possibilities of improper
fuel delivery related to air temperature sensor.
1. Disconnect and remove Air Temperature Sensor
from induction manifold.
2. Connect digital meter set at “20K scale” (from EFI
Tester P/N 91-11001A2) to leads of sensor.
3. Place sensor in ice water while monitoring meter

Customer: replied 2 years ago.
Great to hear from you.
Need some direction as to air sensor location..pulled off the 13221A 1 sensor - says its just temperature - doest specify air. (two tan connectors - starboard side - intake plenum)
I do not have access to EFI
Tester P/N 91-11001A2 . Only tool is DVOM Fluke T5..would you please send me links or manuals for the TPS setting procedure and mentioned wire harness schematic
Expert:  Tan replied 2 years ago.

That's the correct sensor. Your meter is fine for doing the test on the air sensor.

Here is a link to the manual.

Go to section 2C. The harness you need is P/N 91-816085.

Post back if you need further assistance. Thank you...Tan

Customer: replied 2 years ago.
Hi Tan,
pulled the sensor back off again. Here are my test results.
this is based off the 200K scale setting on the DVOM.
room temp - 7.9 K ohm
cool water - 115 K ohm
Ice water - 125 K ohm
seems to be working - not sure if the range is correct. What do you think?
Also, do you have a resource to see how the dash is supposed to be wired? Need to find a wiring schematic for where the engine, key switch, kill switch and gauges - harnesses - meet.
Expert:  Tan replied 2 years ago.

What you can do is leave the sensor disconnected and see if the engine will start easier. The sensor disconnected will richen the fuel by 10%.

The sensor seems to be working the exact number aren't critical just that it does change with in those ranges.

Here is dash wiring.

Here is the control wiring with key switch and kill switch. The wiring is the same no matter which control you have.

Customer: replied 2 years ago.
Hey Tan,
Thanks for the links to wiring - Do you also have one of those diagrams as per the key switch wiring ? ( B - red) (M- Black) etc.
Did as you said with the sensor - don't think it made any difference. Still had to add gas to cylinder to get her to kick off and run at about 3000 and clear up prior to lower throttle. Ran the engine at 2200 for a min, the 1800 for a min, then 2800 for a min, then 1250 for a min before putting in gear...ran her up on the trailer to about 2200 for a little while...then she died when returning to idle and didnt want to stat again....add fuel to the chambers (all six) and still would only sputter and when she did catch and clear out...would shut off as if no fuel flow...have great pressure at VST so that not the issue...will order the test harness for TPS..but anything else to check re actually keeping the engine running and restarting without manually adding fuel to combustion chamber?
Expert:  Tan replied 2 years ago.

Here are the letters and colors.

TPS is all it can be. The TPS tells the ECM where the throttle plates are to give the engine more or less fuel.