1996 5.7L LX Alpha ICM VS Bravo ICM

[Mjust]

Does anybody know what the difference between the 96 5.7L LX Alpha ICM VS the Bravo ICM is??? I know what the ICM does but what is the difference in setting between the Bravo and Alpha ICM??

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

The Alpha one has wiring and programming for the shift interrupt switch, the Bravo doesn't.
Spark and advance characteristics are the same.

Did you disconnect the shift interrupt switch to test some things like I suggested in your other post?

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Im going to tomorrow, its been raining like crazy here in Texas. So if the RPM's increase after I disconnect this switch does that mean that I need to change to an Alpha ICM??.

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Yep

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Well i do know at least I have a Alpha shift assembly and there is a switch there but since I have the Bravo ICM I wonder what the switch is wired to.

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Don,

I stopped by the boat today to check the switch out and see how it could be wired since I have the Bravo ICM. One wire comes off the switch and is connected to my ignition coil I believe the neg. side. The other wire is a black wire that I cant pin point exactly where it goes but it looks like it goes to the ICM. Make any sense??

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Here is how it is supposed to be hooked up if using an Alpha ICM, but since the Bravo doesn't have one or shouldn't I would guess if you hook it like that it may not run at all.
Of course with the one wire going to the coil, it may kill off your rpm and tach and screw up the rev limiter..... Who knows, That's why they have different ICMs for Alpha and Bravo.

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Yeah everything else is wired exactly like shown in the pic except the interrupt switch. I guess im still confused on what the difference or why is there a difference in an Alpha 5.7L LX and a Bravo 5.7L LX?? There both Chevy 350's producing the same HP and tourqe arnt they??

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Like I said before, the Bravo doesn't have a shift interrupt switch and the Alpha does. So the Alpha ICM is probably exactly the same as the Bravo ICM except it's designed so the shift interrupt system is workable without everything else on the boat going stupid...... Like what is happening to yours at the moment.

Pull that wire off the coil that goes to the shift interrupt and give it a try, like I said to try before. But now that you have looked at the wiring, and it's "Home Made" remove it from the coil. It won't work there for anything.

 

[John_S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Don,

It sounds like they have the switch wired, to ground out the coil, instead of through the ICM. Might explain why he is not getting any clunking on shifts. I'd be concerned that that micro switch wouldn't handle the current. Possible fire hazard???

If I'm reading the Alpha schematics correctly, the switch would normally ground out the distributer sensor output (wht/grn) wire. The other distributer (wht/red) wire looks to be a 12V supply to the distributer sensor, fed from the ICM.

mjust, were you able to check the tach accuracy on this last visit?

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

I'd be concerned that that micro switch wouldn't handle the current. Possible fire hazard

It's only gets used coming out of gear for a split second. Doubt there will be much of a fire hazard.
But it's wired wrong even if it was an alpha ICM so who knows what could happen.
That is why Merc makes different parts for different applications. Just to ****-off the DIYer. And there is no one outside of the engineering department at Merc that could possibly tell someone what all the differences are between the 2 ICM's.
But I will venture to say, if he gets the right parts, it will probably work.

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

OK so I got to test some thing out today. First I used a shop tach and confirmed that my tach is correct and that the Rev Limiter is kicking in a 3950 RPMS when the ICM I have is rated to hit the Rev Limiter at 4950RPMs. I tried to disconnect the shift int interrupt switch and it did not change a thing. I even performed this test under no load just on a hose which I normally wouldn't do but wanted to try to get the most RPMS out of the engine. So after I did the test I went down to the Marina and chated with the Merc guys and they told me that they doubt the ICM is bad. The told me to check two things, One was to verify that at speed I have at least 14V coming off the Alternator, Second the told me to disconnect my Faria Tach from the coil because they have seen Tach's interfere with the pulses that feed the ICM before. haven't had the chance to try these two thing but i wanted to get your guys opinion first.

 

[John_S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Well, regardless of what we may think, both of those checks are easy to perform. After that, be prepared to buy the Alpha ICM and add the alpha wiring.

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Well, regardless of what we may think, both of those checks are easy to perform. After that, be prepared to buy the Alpha ICM and add the alpha wiring.

The boat already has the Alpha wire harness, If you check the Alpha and Bravo harness are the same except for the shift interrupt.

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Look, until you get the proper ICM for an Alpha and hook it up like my pic above, don't expect it to work. PERIOD.
The shift interrupt system isn't on a Bravo ICM, that is why they have a different one. According to your explantion above, your wiring isn't right even if you had the proper ICM.

Post #6 above

One wire comes off the switch and is connected to my ignition coil I believe the neg. side.

Look at my picture I posted. Do you see a wire going from the negative side of the coil going to the shift interrupt switch?.......................... I didn't think so.

If you put things together like they were designed, they will work. Half azz them together and they won't. And all the posts in the world won't change it.

 

[SuperNova]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Remove the wire between the shift interupt switch and the coil from the coil terminal and reattach it to the same post on the distributor that the green and white wire are attached to and then make sure the black wire coming from the other side of the interupt switch goes to a good ground. There that wasn't so hard was it?
--
Stan

 

[Mjust]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Made some progress today! Bought the local Merc mechanic some drinks at the bar on the lake and got him to come out on my boat to check it out for me. First he did confirm that I do have an 97 Bravo 5.7L LX engine or as he called it the merc 350 Mag since it has the high rise intake on it. Anyways he checked the timing and found that it was at 14' instead of 10' at idle so I need to adjust that asap. He also verified that the engine is hitting the rev limiter at 3800 RPM and of course when that happened the timing was all over the place. SO he told me i need to do two things and i'll be all set. 1. is adjust the timing while the purple wire is grounded on the ICM back to 10'. 2. Check over the wire harness to make sure all connections follow the spec and if I dont find anything wrong I need to get rid of the T5 Bravo ICM and change it to the Alpha module.

Also for you guys that think the shift interrupt being wired to the coil is wrong well according to this guy who is a master merc mechanic, there is no difference in grounding the coil through the switch than the distributor since they both cause a momentary ground to reduce spark to make shifting eaiser. He told me that all old merc motors that were bravos or pre T5 or T4 used that setup.

 

[Don S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

Ahhhhhh, another opinion.

Still the engine doesn't run right.

 

[John_S]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

"He told me that all old merc motors that were bravos or pre T5 or T4 used that setup."

Yes. but a different switch and that is what prompted the current carrying load question. But if you follow your mecs advice you will be switching it back to the alpha config, I hope.

You need to do #2 before #1, just incase the purple wire is not connected correctly.

 

[SuperNova]

Re: 1996 5.7L LX Alpha ICM VS Bravo ICM

So....your "master merc mechanic" (aren't they all???) told you to take your bravo icm off your bravo engine?? and put an alpha icm on it??? This is getting more and more interesting. I am going to mail you a quarter so you can buy a clue.--
Stan