Mercruiser/Motorola versus Stand Alone ECM's

[njh1]

Hi all from the uk...new to the forum but would like some help please as you have all been recomended...
I have a Maxum I'm restoring and I have chosen a 5.0 V8 MPi Vortec to fit in it. All fitted fine (Ish!!) but when I test fired it all was bad...ECM doesn't work (Sold as good one but MPR doesnt fire and all that should follow does not) soooo I am thinking about simply fitting Carbs (Inlet Manifolds, Distributor ETC) or getting a sensibly priced Motorola ECM from The US of A or indeed anywhere that has a legit one or a stand alone Like Haltech....
Has Anyone done this (Any Version) or has a link to help. I have a brilliant contact at Wayne Maddox Marine UK but information for us is really hard to find...and he is an official Mercruiser dealer.

Thanks in advance...

 

[isaacs]

Does your engine have a Mercruiser Thunderbolt ignition? Are you sure it's bad? It could just be the sensor in the distributor--cheap and easy to replace.

If the Thunderbolt ECM is bad I hear they are quite expensive. Others have said it's cheaper to buy a whole new up to date ignition. You'll have a new distributor, wires, coil etc.

 

[achris]

Does your engine have a Mercruiser Thunderbolt ignition? Are you sure it's bad? It could just be the sensor in the distributor--cheap and easy to replace.

If the Thunderbolt ECM is bad I hear they are quite expensive. Others have said it's cheaper to buy a whole new up to date ignition. You'll have a new distributor, wires, coil etc.

You're still thinking 'Carb and distributor'. MPI engines run a completely different distributor set up.

OP, how have you determined that the ECU is faulty? And if it is, there are companies in the US who will repair it for a considerable amount less than a new one, or converting (taking a BACKWARDS step) to carb and distributor. If you post the engine serial number we can determine which ECU you have.

Chris......

 

[njh1]

Hi...thanks for replying. It's the ECM control module..On a train currently so wit post details when I get home...

 

[njh1]

Hi.
The ECM does not allow the MPR to fire up which inturn does not allow the fuel relay to operate. It does provide voltage to the coil, coil driver and injectors.
Was just wondering if anyone had found a stand alone ECU that connected simply.
Quite happy to buy replacement but struggling to find one for the 5,0 MPI

Nick .

 

[achris]

Have you tried to force the MPR to pick? (by grounding the Pur/DkGrn line, connector A, pin 22)..

Post the engine serial number and we can isolate exactly which ECM you're looking for.

The only ECUs that will connect will be Mercruiser genuine. When companies like Motorola enter into agreements with companies like Merc, they agree to not supply ECUs outside the OEM supply chain. You will not get an ECU that doesn't comes through Merc.

Chris.......

 

[alldodge]

Agree, need a serial number
If its a MEFI then options are greater

 

[njh1]

Ok...attached engine numbers..
I was told the ECU was working when I purchased the engine. The engine needed a rebuild so only just got to try ECM. I have tried giving the relays their own earth but not tried supplying pin 22 with an earth at key turn...

 

[alldodge]

Those are casing numbers, Merc serial number would be something like 0M123456. If there it would be a plate just above the starter.

Post a pic of the ECM so we know what vintage it is

 

[njh1]

Here you go...
Thanks for your help...

 

[alldodge]

That's a 555 ECM
The MPR is turned ON by the ECM applying a ground

 

[alldodge]

Power that turns ON the ECM is from splice 100 coming from the key switch to pin J1

 

[njh1]

Hi...that's great for two reasons...
1..we aren't going insane and 2, we also confirmed that it wasn't providing an earth so we must all be heading in the same direction.
I will try providing pin 22 with an additional earth by using a relay powered when I turn the key and see if that helps.
Do any of you know where I might source a previously owned 5.0 specific ECM 555?

 

[alldodge]

I would contact Bob at OBD Diagnostics and see what he can advise. Your 865926 is not listed, but if yours is bad he may be able to fix or advise other

https://obd2allinone.com/mercecms.asp

 

[njh1]

Thank you...I shall keep you updated...
Nick.

 

[njh1]

Thank you...I shall keep you updated...
Nick.

He's put me onto someone else...I suspect I'll end up giving up...

 

[alldodge]

Might be something real simple, do those checks and will see

The guy he sent you to, is he/she in the US or UK?

 

[njh1]

Might be something real simple, do those checks and will see

The guy he sent you to, is he/she in the US or UK?

Hi...he is in the USA and seems quite reasonable in terms of price...I plan to get into It on Wedenday.

 

[njh1]

Do you have a suggestion?

 

[alldodge]

Check for 12V on pin 30 and 86 of MPR
Ground pin 85 of MPR to see if things power up
Check for 12V when key is turned to ON, on pin D of DLC connector (purple)