Shift Inhibit not functioning on 5.0 MPI

Hellman350

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Jan 12, 2020
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I seem to have an issue with a MCM 5.0L MPI engine (SN 1A082100) in which the shift inhibit does not seem to function.
I have been finding shift form FWD to N is difficult, so went and inspected and adjusted cables, all is in good condition. So I decided to ensure the actual switch was working by manually actuating it whist engine was running, expecting to hear it stumble or die a little. The engine does not falter. I actuated the switch while on the water in FWD at idle, with no stumble. I have tested the switch with a multimeter and am receiving the correct resistance between pins A and C when actuated and not actuated, and have 10K between B and C as per the schematic. Using spoons in behind the wires I can see I have 5VDC supplied to the switch, and a good earth where required. Using spoons again, I have 0VDC at shift inhibit input on connector B pin 19 when switch is not activated, and a steady 5VDC when switch actuated. Wiggle test has no fluctuations of voltage.
Is there any other inputs I can check, at this stage it appears it may be an issue with the controller, however my experience with controllers is that this is unlikely if everything else is functioning properly. Drive system performs flawlessly in every other sense, has only 120hrs on it.
Would love to hear form anyone as to where I go from here, thanks?
 

Hellman350

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Jan 12, 2020
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Hi All. please note, I am speaking of the shift interrupt. Unsure where I came up with inhibit.
 

muc

"Retired" Association of Marine Technicians...
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Hi Hellman350 Welcome to iBOATS

Your serial number has never been registered with MerCruiser. I highly suggest that you get this engine registered in your name. Until that's done, information on recalls and updates are unavailable.

I have some questions.
1. 10 pin or 14 pin wiring harness?
2. DTS or mechanical shift?
3. Do you have Smartcraft gauges?
4. Do you have access to a scan tool?
5. When you talk about a "good earth", where exactly are you connecting that meter lead?

While it is possible that your ECM is faulty. It is more likely the problem is somewhere else.

If you have the proper tools to back probe the ECM. I would suggest the negative lead of your volt meter to ECM connector B pin # 1 and the positive lead to ECM connector B pin # 19. Read voltage with engine running and then voltage when you actuate the interrupt switch.
 

Hellman350

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Jan 12, 2020
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Hi Muc,

Thanks for your time

I have a 14pin round deusch connector but utilizes 9 wires. The harness PN is 84-866058-A02
It is mechanical shift.
No I do not have smart craft gauges fitted, electronic analogue gauges (four winns) type.
At this stage no access to a scan tool, although this was a plan I had, to see if the input is being received in the 555 controller. I would have to find a service center (not local).
I have .2ohms resistance from connector B pin 1 to
the 3 pin connector
pin A at shift interrupt through the black and purple wire. Also measured .2ohm from black and purple wire to engine block, which is where neg lead of the battery is attached.
With engine running between Connector B pin 1 and pin 19 with shift interrupt not actuated I measured 0VDC, and 5.1VDC with switch arm moved (actuated).
All wires from connector B to 3pin switch connector measure under .2ohms.
The engine is not affected by this 5VDC input to pin 19.

I did notice that, whilst testing these items, when I opened the gear indicator switch circuit (unplugged it) the engine stumbled and recovered after maybe 1 sec. Happened every time I opened the circuit, rpm's did not vary once it had recovered. The wire colors on the gear indicator harness do not agree with the colors on the schematic I am using, which I found in #36 engine diagnostic manual. ? Maybe be nothing to do with my issue?

thanks for your help, this has got me beat.
 

muc

"Retired" Association of Marine Technicians...
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Your 14 pin harness should have 12 wires in it.

When you say black with purple wire, I assume you are talking about the black with pink wire? This is the 5 volt reference ground circuit and shouldn't be confused with the engine ground. They are 2 different circuits.

I wouldn't think unplugging the gear indicator should cause the engine to stumble. I've never done it with the engine running, but there is no reason it would on a Alpha ECM. When you unplug that connector all your doing is telling the ECM that you are now in gear. A Bravo or inboard ECM might see a slight RPM increase because some models use this switch as an shift anticipate when bigger props might cause issues when a sudden load is applied to the engine. Does the calibration label on the ECM say Alpha? A Bravo or MIE (inboard) ECM won't work on a Alpha because they use the shift interrupt circuit for start in-gear protection.

The gear indicator circuit should be black/pink to cavity A and yellow/pink to cavity B The wiring diagram in manual #36 might have been valid in 2002 when it was published. But starting in 2007 all wiring diagrams have been moved to a special binder. This was explained in your engine service manual #31 --- which you should be using with #36.

With no scan tool available the next test I would do. Battery disconnected!!!! (Never unplug a ECM with the battery connected -- that's one of the things that can cause these types of failures) -- unplug ECM connector "B" and test for continuity from pin #1 (black/pink wire) to engine ground. Should be infinity on all scales.
 

Hellman350

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Jan 12, 2020
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No continuity from
Connector B pin 1
Black and pink wire to engine ground whilst it is unplugged at connector B.
I Do have continuity to engine ground from this wire when plugged into ECM using multimeter and back probe.
Most definitely see 0VDC between Connector B pin 1 and pin 19 when switch is not actuated, and 5 VDC when switch is actuated. This is with engine running and using back probe spoons in behind wires in plug. Engine does not falter when 5VDC applied to pin 19.

ECM has markings
"5.0 L ALPHA"
MY2007 pAAA_0001_5.0_ALPHA
ECM Burn STW02354

So it is starting to appear like I have an open circuit in the ECM from Pin 19 to circuit board....
I guess I need to get a scan tool and check input? Is there a digital on-off screen in which a user can check the inputs and outputs from the ECM?

again, thanks.
 

muc

"Retired" Association of Marine Technicians...
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I'm not 100% sure if a scan tool will read that parameter on your ECM, but I think it will.

Based on your tests it's looking like you do have a open in the ECM. But that's a high $$$$ part and I think it would be best to get it scanned first.

I can't think of any other tests to run without a scan tool.
 

Hellman350

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Jan 12, 2020
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Thanks Muc,
One last question, if I need to replace the ECM, and can find a 2nd hand unit, will the hour tally form the 2nd hand ECM be transferred to the gauge hour meter, via CAN? Or does the hour meter simply count engine run hours from an active input or the like?
 

muc

"Retired" Association of Marine Technicians...
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The transfer of hours to the dash gauge will depend on what gauges your boat has. I'm not sure, but if my memory is correct in 2007-08 Fourwinns used a gauge package that didn't get the hour readings from the ECM.

When looking for a used ECM.
1. Be careful, Most of the used ECM's have a problem --- that's why they are for sale.
2. You must find one for the exact same ECM you have. This will be a 5.0L MPI ALPHA 1.7R DRAIN between serial numbers 0W650000 to 1A299999 non-DTS, standard cooling
part numbers 866189T04, 866189T005 or 866189T07 are the only ones that will work. New they run about $2000

Having your ECM repaired is a option ---- I recommend this one. https://www.boatunlimited.com/marine-ecm-testing-and-repair/
 

QBhoy

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I think you should try and activate it manually when in neutral and not forward perhaps. Might also just ask and make sure you are operating the correct switch. There are two of them in that area and often mixed up.

not totally sure, but I think there is also a chance that your issue may be elsewhere. What is your ideal rpm in gear and lowest throttle ?

edit...maybe ignore the above. Of course it should operate in gear if manually activated. Haha. Still interested to hear what you’re idle in gear rpm is.
 

Hellman350

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Jan 12, 2020
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Engine plate says idle RPM 600 non - adjustable, but I will check all the same. I am thinking it might change slightly when in in gear, that's why the engine note changes with the gear indicator input.
 

muc

"Retired" Association of Marine Technicians...
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Not only should you check the actual RPM, but more importantly what the ECM thinks the engine speed is. The fact that engine RPM changes when unplugging the gear indicator switch is a big red flag for me.
 

Hellman350

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Jan 12, 2020
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Hi all,
I have an update and eventual rectification for the inhibit issue.
Long story, but the previous owner had a 5.7 long block fitted and during this, must have had the ECU reflashed for the larger engine.
Whatever it was reflashed to did not have the alpha leg inhibit function.
So a reflash of the ECU to a 5.7L alpha drive and it now functions as intended.
Of note, a Mercruiser MPI engine when the shift interrupt switch is activated whilst its idling, will drop RPM to 400rpm or so, but does not stall. Definitely changes the engine note and speed, for anyone looking to test it.

Thanks for everyones help.
 

muc

"Retired" Association of Marine Technicians...
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Glad you got it.
Could you share who reflashed for you and if your happy with them?
 
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