Hi everyone,

I have a 2000 Baja 302 with twin Mercruiser MEFI 3 MCM 7.4L MPI Bravo's. One of the engines cuts off when at low rpm/idle when I shift it into or out of gear. This makes maneuvering very tricky!
I've read about shift interrupter switches, but I've also read that these engines don't have them. I'm looking for a little help on how to troubleshoot and/or find/fix the interrupter switch.

The problem only happens once the engine is hot. ie. after making a long run and trying to enter a marina. It only happens on one of the engines. If I set the rpm's higher with the throttle, I can keep the engine running when I shift, but as you can imagine, this makes shifting pretty violent. Other than when shifting in/out of gear, the engine runs fine. It starts without any problems, idles just fine, but as soon as I put it in gear it dies.

I'm not super mechanically-minded, but from the research I've done, these symptoms appear to line up with a shift interrupt issue. Unfortunately, I can't find anything specific about these motors and where the switch might be and if the engine doesn't have one, what else could be causing the problem?

If it helps, the engine serial number is: 0L836417

Any help would be appreciated.

Thanks to you all in advance,
-Michael

The serial # you provided is for the outdrive I believe. Please no more shifting at high rpm till fixed - hopefully just idle speed valve or something. It’s the fastest way of breaking the outdrive. Surprised you haven’t yet.

Sorry about that. The engine SN is: 0L633801

I've replaced the IAC and MAP sensor with no change in behavior.

Thank you

Btw: Forgot to reply that Bravo drives don’t use a shift interrupter switch. Alpha drives do.

Interesting engine stalls going into neutral too.

Does engine idle fine when started and warmed up ? which is in neutral of course.

The engine stalls when going into gear, not going into neutral. Sorry if I wasn't clear on that.

Engine idles fine all the time... whether cold, warm or at full temp. When the engine dies, I can start it back immediately without issue and it idles just fine. Soon as I put it in gear, it dies.

When the engine stalls, the exhaust smells a little rich. Not bad, but it's like the ignition is being cut while there's still a little fresh fuel in it. It behaves as though there's an ignition interrupt happening. What I mean is that it doesn't spit-and-sputter... it dies instantly.

What rpm is it idling at? Do you have a scanner and can measure iac % at idle?

It idles at around 800... give or take a little. I don't remember the exact numbers. I dont have a scantool right now. The one we've been using is a mercruiser computer. I can't remember if it will do IAC values or not, but it's something I can look at the next time we take it with us. What should the IAC% values at idle be? What should idle rpm be in neutral and what should it idle at in gear? The last time we checked idle rpm's, they were in line with the engine that doesn't have any trouble. Maybe +/- 25 rpm's or so at the most.

I'm going to try to get it on the water tomorrow, weather permitting. I won't have the scan tool with me, but I'll try to get as good a reading as I can from the gauges. Anything else I should try or watch for while I'm out there?

Thank you!

I don’t remember what values that Ecm displays iac in. But you want it to be around 30% so it can open to 100 if needed or close a bit to lower rpm. 7-800 at idle is fine

What get’s me is the engine dying, also, when putting into neutral. Any outdrive experienced people think a drve could cause this ?

Hi SB, sorry for the confusion... it only stalls when going into gear, not when putting into neutral.