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 Mercruiser ECT Sensor Question -- Issue Solved
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Author Previous Topic: Diesel tank access plate. Topic Next Topic: Mercruiser 7.4 Bravo3 Alarm  -- Issued Solved  

CharlieD

RO# 11530

Posted - Jun 08 2010 :  09:00:29  Show Profile  Reply with Quote
The constant alarm was caused by a fourth alarm signal input to the MEFI-3 ECM. This input was the transmission overtemperature signal. Bravo3 has an optional transmission sensor which was not installed in this boat. However, the mechanic who replaced the bellows and trim sensors incorrectly connected the trim sending sensor to the OT wire in the three wire cable -- two wires for the trim sensor and one wire for the optional OT sensor. This boat does not have a trim indicator; thus, this lost function was not noticed. The misconnection caused the OT fault to the ECM. Thanks to all who responded with comments.

Edited by - CharlieD on Jun 16 2010 13:40:35

Homeport: New York

Sandy

RO# 1159

Posted - Jun 08 2010 :  10:30:16  Show Profile  Reply with Quote
CharlieD- No pro at this , just a lowly Crusader 5.7 L owner with a MEFI-4 ignition diagnostic manual and handy Rinda scanning devices, but I believe the ECM monitors the signal voltage from the ECT for both engine control and presumably ECM alarm output. Codes and /or alarms would be activated by both high and low temps which you have simulated by opening & possibly when closing the circuit. Closest to "room temp" in the table I have shows 59*F = 4450 ohms and 77*F = 2796 ohms .

My manual says ,
"The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies 5 volts on CKT 410 (circuit) to the sensor. When the engine is cold, the sensor (thermistor) resistance is high. As the engine coolant warms up,the sensor resistance becomes less. At normal operating temperature (185-203*F), the voltage will measure about 1.5-2.0 volts. "

If you'd like the 4 pages that deal with ECT high and low temp indications , email me a fax # and I'll send them out . But probably not until tonight when I get back from fishing.


Sandy

Edited by - Sandy on Jun 08 2010 18:50:48

Homeport: The Vineyard Go to Top of Page

CharlieD

RO# 11530

Posted - Jun 08 2010 :  18:40:44  Show Profile  Reply with Quote
Sandy, thanks. Your reply helps. I am doing this diagnostic activity for a friend and will apply your advice tomorrow PM.


Homeport: New York Go to Top of Page

CharlieD

RO# 11530

Posted - Jun 09 2010 :  18:39:11  Show Profile  Reply with Quote
Measured the resistance of the ECT sensor from the ECM connector at 3200 ohms/72Deg F. Judged sensor to be OK. Oil pressure switch sensor measured at 30 ohms with engine off. This measurement effectively should be 0 ohms at engine off and open with engine running. Any comments on whether 30 ohm resistance at no pressure should be suspected?


Homeport: New York Go to Top of Page

Billylll

RO# 24494



Posted - Jun 09 2010 :  20:27:24  Show Profile  Reply with Quote
This maybe way off base Charlie but I had a high temp alarm on one of my 2007 8.1L HO's early this season. However looking at the System View 5000 monitors both the RW and internal closed cooling temperatures were identical and in normal ranges. My issue turned out to be an unplugged/dislodged ambient air temperature sensor up in the bridge.
Bill


WIRELESS ONE,
36 Gulfstar
Trawler
Little Egg, N.J.

Edited by - Billylll on Jun 09 2010 20:34:15

Homeport: Tuckerton, N.J. Go to Top of Page

Sandy

RO# 1159

Posted - Jun 09 2010 :  23:14:17  Show Profile  Reply with Quote
Charlie- Sorry, I have never tested the resistance of an o.p. switch . The concept that there is usually a temporary overide function somehow built in to the system to not sound the alarm or shut down the engine while engine has started but not quite yet reached min. allowable oil pressure may come into play with non-running resistance readings, dunno. "If" that is the case , it may not be just infinity OR zero resistance. Also ,I imagine you did this, but was that reading at the switch with wire disconnected, and from clean switch wire terminal to the threaded base for accurate reading? The last rationalizing thought is they may have them designed with spec resistance even with engine off to make it easier to tell if it is really faulty/shorted out. OK, it's a stretch.

It may well be stuck/faulty, not completely releasing-contact "open" when at normal running pressure & not good clean closed contact (o ohms) when off . You might check one on a boat near your friend's, or on the other engine if he has twins.

Did you try starting the engine and running it with the switch wire removed and insulated to see if the alarm is absent? You might check the transmission alarm switch also, since water temp sw, oil pressure sw and trans. temp sw all usually go to the alarm.

Billy III- I'm ...pretty... sure my blue 5.7L MPI's don't have any kind of remote ambient air temp sensor (though I believe the ECM does get that input), but if CharlieD's friend's boat has that it would be good to check it.


Sandy

Edited by - Sandy on Jun 09 2010 23:15:31

Homeport: The Vineyard Go to Top of Page

CharlieD

RO# 11530

Posted - Jun 10 2010 :  17:28:19  Show Profile  Reply with Quote
I eliminated the oil pressure switch by shorting its harness lead to ground at engine start and opening the lead a few seconds later. Alarm still sounds 10 seconds after start. I noticed that the MEFI-3 ECM has a transmission temp input. Anyone know if Bravo3 has a temp sensor. A marine mechanic has addressed this alarm issue as well; his final recommendation was to replace the ECM for $1200.

Off topic comment to Sandy: B&G network engine analyzer would help with this problem. I have one installed on my twin 350 Horizon setup. Thanks for your input.



Homeport: New York Go to Top of Page

Sandy

RO# 1159

Posted - Jun 11 2010 :  00:39:23  Show Profile  Reply with Quote
Charlie- Is your friend's 7.4l boat a single or twin? It would be handy to be able to be able to swap out ECMs before saying bye to $1.2 Boat Units (which sounds kind of high). I believe that would only work if twins were same rotation as on I/O's and some I/B's with full reversing gears. My I/B engines are not, and even though I carry a spare new ECM, it's a 50-50 shot that in the very remote case of ECM failure it would be on the matching rotation engine. Murphy might say much lower odds.

Sorry, I don't know whether the drive would have a temp sender or overtemo alarm sw.

Not sure how much help the B & G Net engine would be for this, as handy as it is. It might show Check Engine or possibly even a code, but it will not display anywhere nearly the same number of ECM data parameters the true diagnostic scanners can.
I've mentioned this often , in my very unprofessional opinion, if a boater has an MEFI MPI engine (or even some EFI's ) and hopes to do at least some trouble shooting him/herself or even wishes to understand better what the mechanic has found , obtaining the diagnostic scanner or software plus cable adapter, plus ignition diagnostic manual, can save a lot head scratching . But there is a bit of a learning curve that is still wrapping around my head. That's OK because I learn a lot more about these systems anytime I persue a particular new MEFI related problem, mine or other's. Definitely worth the considerable outlay IMO, especially since the nearest Crusader dealer/authorized service to here is about 25+nm away , and a lot farther by car and ferry. Charlie , it sounds like you were able to observe the mechanics diagnostic device.

The Rinda Technologies Marine Diacom SW includes a CD with the excellent manuals that download to your notebook for reference anytime. I have that for best diaqgnostic access, display & recording , but also got very lucky and was able to purchase the TechMate handheld scanner full kit in new condition for less than 1/2 price from a boating forum classified. I keep the latter onboard in case trouble rears it's ugly head at sea. It accesses the same data and performs power balance tests . Just less on the display at one time and no graphing or recording. Honest ,I have no connection to Rinda other than as a 1 1/2 time purchaser.

For those who have seen my posts about this too many times I apologize, but these "tools" can be really helpful when dealing with these usually terrific MEFI engines, even if they only end up helping rule out parts on the Usual Suspect list much faster. Few owners seem to have the opportunity to try them to see what they reveal. In the case of my MPI engines, it's essentially the ONLY way the necessary Cam Retard can be checked or set to their spec 45*.


Sandy

Homeport: The Vineyard Go to Top of Page

Billylll

RO# 24494



Posted - Jun 11 2010 :  05:51:58  Show Profile  Reply with Quote
The ambient air sensor is needed to properly control the fuel to air ratio on my motors. Call Mercruiser directly but I wouldn't spend $1200 on a "WAG". I will ask our marina's top mechanic today about the motors you are asking about Charlie.
I will report back what he tells me.
Bill


WIRELESS ONE,
36 Gulfstar
Trawler
Little Egg, N.J.

Homeport: Tuckerton, N.J. Go to Top of Page

CharlieD

RO# 11530

Posted - Jun 11 2010 :  07:01:10  Show Profile  Reply with Quote
Thanks again for the replies. Any further input will be appreciated. The engine setup is single engine, thus no swap and no similar power setup at our club. Also, the mechanic did scan for fault codes with no success. On Monday I will try one last test which I should have thought of earlier. I plan to measure the resistance to ground at J2-8 of the ECM cable harness, assuming a wire at this location. This pin is the transmission overtemperature input to the ECM. If this lead is not open, then there is an OT sensor somewhere or some unknown sensor/fault. Thanks again.


Homeport: New York Go to Top of Page

Sandy

RO# 1159

Posted - Jun 11 2010 :  15:08:54  Show Profile  Reply with Quote
Charlie, I just found this helpful list on the Chaparralboats website in response to an internet search of "Mercruiser MPI constant alarm" .

The "constant alarm section" is interesting , particularly the #5 "Sea Pump PSI Low" item . That might be worth looking into as well. :


From Chaparralboats:
"The 2 beeps per minute can be generated by quite a few things. Some of the error conditions will limit the available power the engine produces. The 2 beeps/minute can be generated by: cam sensor open or shorted, engine cooling temperature circuit open or shorted, coil harness wire (EST) open or shorted, fuel injector open or shorted, IAC output, knock sensor, MAP sensor, MAT sensor, oil pressure circuit open or shorted, port/starboard exhaust manifold cooling temperature circuit open or shorted, sea pump circuit open or shorted, fuel pump relay, throttle position sensor circuit open or shorted, low 5 volt power supply as well as other errors.
Best suggestion for the 2 beeps per minute is to have the dealer/shop read out the error log to see what is generating the error condition.

This table is a guick guide, showing what warning output will accompany a fault for the Mercruiser Sterndrive engines. (MCM)

Warning system Faults, SC1000 Yes/No, Audio Alarm, Available Power %, Description.

(1) Cam Sensor Yes 2 Bp/min 90% Open or short, engine must be cranking to set this fault code.
(2) ECT CKT HI Yes 2 Bp/min 90% Open
(3) ECT CKT LO Yes 2 Bp/min 90% Short
(4) ECT Coolant Overheat Yes Constant 6-100 % Engine guardian overheat condition
(5) EST 1-8 Open Yes 2 Bp/min NA Coil harness wire open
(6) EST 1-8 Short Yes 2 Bp/min NA Coil harness wire short
(7) Fuel Injector 1-8 Open Yes 2 Bp/min NA Fuel injector wire open.
(8) Fuel Injector 1-8 Short Yes 2 Bp/min NA Fuel injector wire short
(9) IAC Output Yes 2 Bp/min 90% Only with rpm
(10) Knock Sensor 1 Yes 2 Bp/min 90% Alarm sounds for 20 seconds in NEUTRAL and indefinitely in gear.
(11) Knock Sensor 2 Yes 2 Bp/min 90% Alarm sounds for 20 seconds in NEUTRAL and indefinitely in gear.
(12) Low Drive Lube Strategy Yes Steady Bp 0-100% Low oil in sterndrive.
(13) Low Oil Pressure Strategy Yes Constant 0-100% Low oil pressure strategy.
(14) MAP Sensor 1 Input High No 2 Bp/min 90% Short, no visual on SC1000.
(15) MAP Sensor 1 Input Low No 2 Bp/min 90% Open, no visual on SC1000.
(16) MAT Sensor Yes 2 Bp/min 90% Open or short in MAT circuit.
(17) Oil PSI CKT Hi Yes 2 Bp/min 90% Short, defaults to 51.7 psi.
(18) Oil PSI CKT Lo Yes 2 Bp/min 90% Open, zero oil pressure.
(19) Overspeed Yes Constant RPM Limit Engine over rpm limit
(20) Port EMCT CKT Hi Yes 2 Bp/min 90% Open, defaults to 32 degrees F.
(21) Port EMCT CKT Lo Yes 2 Bp/min 90% Short, defaults to 32 degrees F.
(22) Port EMCT CKT Overheat Yes Constant 6-100% Overheat condition, 212
degreesF(100 degrees C) limit.
(23) Sea Pump PSI Lo Yes Constant 6-100% Low water pressure strategy, defaults to 43.4 psi.
(24) Sea Pump CKT Hi Yes 2 Bp/min 90% Open.
(25)Sea Pump CKT Lo Yes 2 Bp/min 90% Short.
(26) STB EMCT CKT Hi Yes 2 Bp/min 90% Open, defaults to 32 degrees F.
(27) STB EMCT CKT Lo Yes 2 Bp/min 90% Short, defaults to 32 degrees F.
(28) STB EMCT CKT Overheat Yes Constant 6-100% Overheat condition, 212 degrees (100 degrees C) limit.
(29) Steer CKT Hi Yes No No Open and short.
(30) TPS1 CKT Hi Yes 2 Bp/min 90% Short, signal to 5v+, engine will not start. Refer to data monitor screen.
(31) TPS1 CKT Lo Yes 2 Bp/min 90% Open.
(32) TPS 1 Range Hi Yes 2 Bp/min 90% Above 4.8v, 994 counts.
(33) TPS 1 Range Lo Yes 2 Bp/min 90% Below 0.5v, 35 counts.
(34) Trim CKT Hi Yes No No Short, high range, visual warning on SC1000 only.
(35) Trim CKT Lo Yes No No Open, low range, visual warning on SC1000 only.
(36) 5 VDC PWR Low Yes 2 Bp/min varies Short any 5v+ to ground.


Here's some other information that what will sound the alarm on a mercruiser Engine.
Constant tone alarms are for:
1.) engine coolant temp overheat,
2.) low engine oil pressure,
3.) engine overspeed,
4.) exhaust manifold cooling temp overheat
5.) sea pump PSI low.
Note #5 is known to be a common problem, It's been said that this fault might not show up in the fault history section of the scan tool.
If that is the case then the only other way to know if this is your problem, is to watch this sensor live as it happens out on the water with the scan tool hooked up to the engine.
Also make sure all the Battery cables are clean & tight plus a fully charged Battery is very important.
Check the water pressure sensor threads for any paint, Also check the sensor to see if it has come loose or Has a blockage of some kind.
If any sensor loses it's ground it could sound the alarm. As an additional test, try adding a ground wire to the sensor threads to stop the horn.
Or there is a chance you could have picked up or created some air bubble for a short time, until the boat slowed down, possibly due to the brass water pump impeller Housing could be failing do to deep grooves inside housing creating a disturbance with the water flow.

Constant beep alarms are for:
1.) low outdrive lube level.

Two Alarm beeps every 60 seconds are for:
1.) Faulty cam,
2.) IAC,
3.) MAP,
4.) MAT,
5.) knock sensors.
6.) open/short in the engine cooling temp circuit
7.) open/short in fuel injector wiring circuit,
8.) open/short in oil PSI circuit,
9.) open/short in exhaust manifold cooling temp circuit,
10.) open/short in sea pump circuit,
11.) open/short in throttle position circuit "


Sandy

Edited by - Sandy on Jun 11 2010 15:10:28

Homeport: The Vineyard Go to Top of Page

CharlieD

RO# 11530

Posted - Jun 14 2010 :  16:54:55  Show Profile  Reply with Quote
As a follow-up to my previous post, I measured a short from the J2-8 wire position of the ECM to ground. I expected an open circuit given that this ECM input is defined for "transmission overtemperature". My question: Is there a sensor connected to this wire position for a 2000 Bayliner 7.4MPI Bravo3? If so, where is it located? Thanks,


Homeport: New York Go to Top of Page

Sandy

RO# 1159

Posted - Jun 16 2010 :  15:03:42  Show Profile  Reply with Quote
Congratulations on the find. Good sleuthing, CharlieD.

Sandy

Homeport: The Vineyard Go to Top of Page
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