Alpha 1 Gen2 MCM 5.7L dies when shifting

[Skidude17]

I have an MCM 5.7 Alpha engine serial# 0F598365 that was dieing when I would shift from forward to reverse. I adjusted the shift cables, and now it dies when I shift from forward to neutral, and dies when I shift from neutral to reverse. I tested the shift cutout switch using a 1/8” alan wrench, and it seems to be in tolerance. I don’t know what to check next. I did end up having to push the pin on the lower shift cable up quite a bit to get reverse to engage as seen in the pic. What else can I do?

 

[QBhoy]

How is the health of your engine ? It’s not taking in a little water from the risers or exhausts ?
the shift interruption switch as you know will drop 4 of 8 cylinders when it’s activated to drop rpm for a moment...but if you have a weak cylinder or 4 already from anything else...she will stall. Just a thought. Perhaps not relevant but a possibility I’ve seen. Bad fuel would also cause this.

 

[Skidude17]

How is the health of your engine ? It’s not taking in a little water from the risers or exhausts ?
the shift interruption switch as you know will drop 4 of 8 cylinders when it’s activated to drop rpm for a moment...but if you have a weak cylinder or 4 already from anything else...she will stall. Just a thought. Perhaps not relevant but a possibility I’ve seen. Bad fuel would also cause this.

I don’t think it’s either of those. The boat is new to me last year, and it had the problem dieing when shifting into reverse most of the time. Over the winter I changed the engine and drive oil, installed a new impeller and water pump housing, changed the plugs, wires and cap, and recently adjusted the timing. The weather is starting to get nice here in the PNW, so I wanted to get her out. I’m sick of the dieing in reverse issue, especially since it mostly happens at the dock, so I adjusted the shift cables. Now my issue is compounded since I used to be able to get reverse sometimes, and I can’t even shift from forward to neutral.
When I changed the plugs, all of them looked healthy but perhaps one.

 

[Skidude17]

How is the health of your engine ? It’s not taking in a little water from the risers or exhausts ?

...how would I check if water was coming in through the exhausts?

 

[achris]

...how would I check if water was coming in through the exhausts?

Check your spark plugs.

 

[Grub54891]

Replace the lower shift cable. If its getting stiff it will kill the motor. No lube or adjustment will fix it.

 

[Skidude17]

Check your spark plugs.

What am I looking for?

 

[Skidude17]

Replace the lower shift cable. If its getting stiff it will kill the motor. No lube or adjustment will fix it.

I ordered a shift cable kit. I hope this fixes it .

 

[Grub54891]

While you are in there, be sure to check all the bellows, and gimble, along with the trim pucs/wiring. Much easier to do it once rather than twice.

 

[achris]

What am I looking for?

Either wet, or what will look like 'steam cleaned'...

Chris.......

 

[tank1949]

How is the health of your engine ? It’s not taking in a little water from the risers or exhausts ?
the shift interruption switch as you know will drop 4 of 8 cylinders when it’s activated to drop rpm for a moment...but if you have a weak cylinder or 4 already from anything else...she will stall. Just a thought. Perhaps not relevant but a possibility I’ve seen. Bad fuel would also cause this.

I had an 86 Alpha V8, whose shift interrupt caused me grief beyond comprehension. Neither myself or local shop could get it adjusted correctly. Shop also said that switch was OK. However, shop also said that it momentarily killed power to all 8 cylinders, not 4 by directing voltage/current to ground. The 4 out of 8 is news to me. Shop also said that the faster I shifted the better, but that didn't work either. I just lived with it.

 

[Skidude17]

I got it all figured guys. The shift slide at the drive end had a bunch of crud on it that wouldn’t allow it to seat properly. Pulled the drive, removed the shift cable core, cleaned shift slide cavity and slide, reassembled, adjusted shift cables, perfectly in spec now. Thanks everybody!

 

[achris]

.... However, shop also said that it momentarily killed power to all 8 cylinders, not 4 by directing voltage/current to ground. The 4 out of 8 is news to me....

Killing 4 cylinders out of the 8 is for MPIs only. At 1986, you have TB-IV, and you kill spark to all. But 'directing voltage/current to ground' is also wrong...

As per the document I posted on exactly how the system systems (check out the stickies), the switch grounds the pulses from the sensor unit inside the distributor. No pluses, no sparks.. It's really that easy. On a points system it does it by shorting the points to ground, as far as the coil is concerned, it doesn't see a points opening event, so no spark.

I really wish these so called mechanics would take the time to learn how a system actually works before firing off some complete garbage and putting false information out in the community.

Chris.....

 

[tank1949]

Killing 4 cylinders out of the 8 is for MPIs only. At 1986, you have TB-IV, and you kill spark to all. But 'directing voltage/current to ground' is also wrong...

As per the document I posted on exactly how the system systems (check out the stickies), the switch grounds the pulses from the sensor unit inside the distributor. No pluses, no sparks.. It's really that easy. On a points system it does it by shorting the points to ground, as far as the coil is concerned, it doesn't see a points opening event, so no spark.

I really wish these so called mechanics would take the time to learn how a system actually works before firing off some complete garbage and putting false information out in the community.

Chris.....

Thanks, I guess your response may be why the shop could never fix my interrupter. Thanks again!!!

 

[achris]

Thanks, I guess your response may be why the shop could never fix my interrupter. Thanks again!!!

In 1986 I bought a boat with my first stern drive. A 1972 '165' with an MC1 drive. Shortly after I bought it, the drive started shifting hard. I took it to a 'reputable' shop, and after a day they called me and said they had no idea what was wrong, please come and collect the boat. There was no charge, but also, no fix.

I took the boat home, and then bought the Merc service manual. It took me, a completely UNTRAINED person who was only just in the learning stages of my computer repair career, about 20 minutes of reading (the 'troubleshooting' section no less!) to find and work out that it was the shift interrupt that was causing the problem. Took me another 10 minutes to actually fix it...

If I, as an untrained, never seen this machine before, non mechanic (at that stage) could find and understand the system in less than an hour, why are these so called 'factory certified' techncians so incapable of understanding such a bog basic mechanism?

I've since taken it further and actually understood what's happening inside the Thunderbolt modules. (Here's a hint. The pulse that the sensor produces doesn't fire a spark, it sets a timer for the spark for the NEXT cylinder. ) Again, if I can do that, why are so many professional mechanics having trouble? I genuinely don't understand....

Ok, who's next on the soapbox?

Chris......

EDIT: Thinking about it, I may add a 'for the geeks' to the end of the 'Thunderbolt, how it works' document on EXACTLY what's going on inside the module. I'll think about it.

 

[AShipShow]

EDIT: Thinking about it, I may add a 'for the geeks' to the end of the 'Thunderbolt, how it works' document on EXACTLY what's going on inside the module. I'll think about it.

Yes Please!

Side note, are the thunderbolt modules sealed and potted? or are they just circuit boards in a housing that could have components replaced if bad?

 

[tank1949]

In 1986 I bought a boat with my first stern drive. A 1972 '165' with an MC1 drive. Shortly after I bought it, the drive started shifting hard. I took it to a 'reputable' shop, and after a day they called me and said they had no idea what was wrong, please come and collect the boat. There was no charge, but also, no fix.

I took the boat home, and then bought the Merc service manual. It took me, a completely UNTRAINED person who was only just in the learning stages of my computer repair career, about 20 minutes of reading (the 'troubleshooting' section no less!) to find and work out that it was the shift interrupt that was causing the problem. Took me another 10 minutes to actually fix it...

If I, as an untrained, never seen this machine before, non mechanic (at that stage) could find and understand the system in less than an hour, why are these so called 'factory certified' techncians so incapable of understanding such a bog basic mechanism?

I've since taken it further and actually understood what's happening inside the Thunderbolt modules. (Here's a hint. The pulse that the sensor produces doesn't fire a spark, it sets a timer for the spark for the NEXT cylinder. ) Again, if I can do that, why are so many professional mechanics having trouble? I genuinely don't understand....

Ok, who's next on the soapbox?

Chris......

EDIT: Thinking about it, I may add a 'for the geeks' to the end of the 'Thunderbolt, how it works' document on EXACTLY what's going on inside the module. I'll think about it.

My manual back then was a useless as tits on a boar. Manuals, at least for me, have greatly improved. It is also nice to have forums like this to share experiences. THX!!!!!!!!!!!!!!!!!!!!!!

 

[achris]

My manual back then was a useless as tits on a boar. Manuals, at least for me, have greatly improved. It is also nice to have forums like this to share experiences. THX!!!!!!!!!!!!!!!!!!!!!!

It was manual #2, and it hasn't changed. Still the same now as it was in 1986, and as it was in 1977 when it was published..
Chris......

 

[tank1949]

It was manual #2, and it hasn't changed. Still the same now as it was in 1986, and as it was in 1977 when it was published..
Chris......

You probably had MC manual. I had Cliamar (sic) or Chilton POS I bought around 90'ish. The interrupt was happening as it was believed supposed to, but motor would still stay dead. They said cables were free moving as well. Bravos are much stronger and we don't have to put up with that crap.

 

[AShipShow]

That was one of the first things I learned from this forum...Clymer manuals make anchors as good as they make good instructions.

Mercruiser manuals are the only way to go...In fact, this thread convinced me to hop on ebay 20 min ago and buy the actual Merc #17 manual... it will be much nicer having them to be able to have AT the boat instead of having to go into the house to look at the computer...

Plus for some reason, the #17 manual on boatinfo must not have scanned in good quality because the wiring diagrams and other things with small text are impossible to read... the letters are like 2 pixels.