1997 7.4LX MPI shift cutout switch location? Stalling issue.

[IdahoDoug]

I have been tracking down an intermittent loss of power/stalling issue this summer. This is the non "Cool Fuel" motor that uses the VST vapor component in case it matters. So its the MEF1, not the MEF3 they started in 1997.5 - again if that matters. Bravo 3. I'm about to take it out on the lake with several items tagged with tape, and a multi testor to check a list of things I've gleaned from here (thanks in advance). One item I cannot find is something others have had issues with though not on my specific motor. So I'm wondering if I even have this. It's the shift cutout switch. So many have had issues with this thing so I wanted to have a harness to bypass it while I'm out on the water to see if that's it. I have checked all over the bracketry for the shifter cables on the side of the engine, and either it is simply not there, or Im blind. There are absolutely no electrical wires or anything looking like a plunger sensor anywhere near the shifter cable, and I'm reasonably competent (famous last words).

I have the feeling I'll be starting a new thread, so here's the Reader's Digest if I don't find it today. A few times the last couple summers, the engine will act up and then stall. A typical scenario would be I've just started it up from stone cold and idle through the no wake zone for 5 minutes. Hit the throttle to go up on a plane and it will pull normally for a couple seconds, then dramatically lose power and stall just as we are about to plane out. When I try to restart, it may start right up and do it again, or we may simply drive off as normal. But it's never taken more than 2 minutes to drive off normally and then it may not happen again for days. Another scenario happened last week. At anchor for 4 hours, I start the engine and we idle for about 5 minutes, then up on a plane for 5 minutes or so when I move the throttle to accelerate a bit and instantly the engine is losing power dramatically, then catches itself then does it again several times over a 5 second period and if I throttle slightly back it will smooth out and everything's fine. Then I can barely move the throttle to accelerate and hear the engine ever so slightly lose power - barely perceptively to others on the boat. Move the throttle back where it was and the engine barely perceptively pulls again. As though when I move the throttle there is a flat spot. I'm trying to remember but I think when I gave it full throttle once on encountering the flat spot it simply magnified the power loss/gain cycle. In other words I could not push through this slight hesitation, it just made the stall/recover cycle larger. It definitely seems to happen only when the throttle is actually moving (manifold vaccuum changes, etc).

What I know. Owned since new, fuel separator regularly changed (new this season), good gas. My tach has acted up a couple times randomly over the years, reading a few hundred low or high, but never when this is happening - just mentioning it. I installed a jumper I can disconnect the tach today in case it is grounding which I will do if it acts up (cross your fingers).

So if you know about the shift cutout switch, I'm all ears....

​DougM

 

[alldodge]

I would say if there are no wires coming from the shifter then the neutral safety switch is either not there or has been by passed. A test would be, can you start it in gear?

As for your issue, sounds like a fuel issue and the VST needs to be cleaned every few years, I have a VST on my Formula. Suggest removing the VST and take the top off. Once the top is off the pump will come out and on the bottom of the HP pump there is a screen. I was told "IF your real easy" the screen can be removed without breaking it. I tried but gave up, so I cleaned it without removing it. If the screen is broke you need to buy a new VST or replacement system. The seal kit for the VST is fairly cheap.

If this wasn't the issue, suggest connecting a fuel pressure gauge to your fuel rail to monitor pressure.

Let us know how it goes

 

[IdahoDoug]

To clarify, this is not the neutral switch. Im asking about the shift cutout switch that briefly cuts power when you shift into gear to ease the bang. Nothing has ever been bypassed or changed from factory, so hoping others might have info on this. Im starting to think the research i found was wrong and this model does not have one. We are floating around in a bay right now. Swimming and wishing we had brought some food.... Was able to reproduce the issue. Tach is reading high at idle by apx 1000 rpm. Under way the engine seems to catch up ny 3000 or so. Id heard the tach wire or guage can intermittently ground and test is if you disconnect tach and see if problem goes away. Did not change so not my issue. Was hoping to see gas in the sight tube but did not. Would mean fuel pump is done but no gas in line either under way or stopped. Mech fuel pump on front of raw water pump. Do these pumps fail other ways? Mines making no noise either. On VST, thats interesting. Noted that the wires atop its pump get warm to touch. Will look into that, Dodge - thanks. Did not run into suggestions to maintain that thing anywhere else. Brought stethescope and injectors sound normal, fuel pump quiet, VST box no straining noises. Swimming and thinking....

 

[IdahoDoug]

On fuel pressure, mercruisers engineers appear to have been on strike during this period. They did not provide a schrader valve to check pressure. I have to buy and install an adapter. Grrr

 

[Bt Doctur]

Bravo`s don't use the shift interrupter system, they have cone clutches. The wiring plug should have a jumper in it already

 

[IdahoDoug]

Xlnt thanks. Its getting worse even as we are out here. At 3k or higher I can feel the engine nibbling up and down a few revs and its cutting out and in twice as often. We went to dinner, now back in bay listening to Loons.

 

[IdahoDoug]

Xlnt thanks. Its getting worse even as we are out here. At 3k or higher I can feel the engine nibbling up and down a few revs and its cutting out and in twice as often. We went to dinner, now back in bay listening to Loons.

 

[thumpar]

Bravos don't have a shift interrupt switch. I just went through my VST. The diaphragm at the top was shot. If you dig into it make sure you get the top gasket. The old one won't fit back in the groove. I found that out the hard way. My filter screen was not dirty except for a few bits. I did remove it from the pump and clean it out though. You have to twist it and it comes right off. It kind of scared me putting it back on but it all turned out good. This is a pic of the diaphragm. The picture actually makes it look better than what it really looked like.

 

[thumpar]

IdahoDoug, are you really in Idaho? I am just across the boarder in Spokane if you are close I might be able to lend a hand with the VST.

 

[IdahoDoug]

Thumpar,

Yes, in Coeur d'Alene. So, I will get the gasket and appreciate the tip. Terrible photo, but it is still easy to see the holes!! Heh. Thanks for the offer to lend a hand. I will order the bits and if there is a PM feature here I will send you one with my number so perhaps I can call you if I get stuck on the VST? Did you find a good source for the seal kit? What did cleaning and resealing the VST change on your boat's running condition?

It does feel like a fuel starvation issue. Even tried loosening my fuel filler cap as others have found their tank vents clogged and letting air in the cap made their engines run correctly to reveal the problem. My engine *seemed* to hesitate a lot less when I did this but it was late in the day and my family was getting tired of me zipping around the lake so I was not fully convinced of that. It seemed to improve on its own the last time I fired it up to head home, so still an odd and undiagnosed thing. From the way it behaves, you'd swear I have a lot of water in the fuel, but have not seen evidence of it in the water separator - though I'm not sure I'd see it anyhow since it is a spin on filter. And I only fill up on land and choose national brands - never the corner mini mart gas. Hmmm. Still figuring. I'm down to 1/3 tank. So I'm thinking I will fill it with non-ethanol fuel and pour several cans of HEET in the tank as a nod to the possible fuel issue. Unfortunately, I don't think my boat (or any boats this size) are built with provisions to drain the fuel tank contents to look for contamination. I can't even see my tank..

So, I'm still in the dark.

 

[thumpar]

I was having problems after sitting on a hot day with hard starts and it would also surge. I found fuel in my sight tube from the VST to the flame arrestor. I was able to find the parts at Hagadon Marina but I bought the last one they had a couple weeks ago. I don't know if they ordered another in. With the wife factor I drove there to get the boat backup and running because that is the only place I could fine one. It is easy to take the top off. I used an impact driver so I didn't strip the screws. Once they are out you can pull the top. There is a little circle piece that has 3 screws. That is where the diaphragm is.

 

[IdahoDoug]

Did you find a kit that comes with the top seal and the diaphragm you found trashed? I'm wondering what you bought because the kits I'm finding for about $75 online are just a dozen O rings and a larger O ring for the top seal. But no diaphragm. Hagadone closed at 4 today, so I missed them. Happily I have a screw impact driver - sounds like its needed here.

 

[muc]

You should check fuel pressures --- both high and low pressures. Might also want to check the gear lube that is in the box that drives your mechanical fuel pump, it's something that is frequently missed and can cause the cam that runs the pump to wear flat = low fuel pressure.

 

[IdahoDoug]

So, I have the VST top off, and the filter had a fine layer of dust on it I cleaned off the outside. I am going to pull the diaphragm for a look but want to be clear the diaphragm in your above picture is where I think it is before pulling things apart. This box is $1800 if I screw it up. Would you mind taking a look at the link below and confirming for me that the diaphragm is the part in this diagram labeled #6? I have to remove the float to get to the 3 screws in a metal lid to get to it. Also, if you remember on the filter which way you unscrew it, that would be good to know. I assume normal counter clockwise. It's not indicated, and the plastic assembly feels fragile....and it's hugely expensive as well.

https://www.mercruiserparts.com/Sho...&inbr=2342&bnbr=11&bdesc=VAPOR+SEPARATOR+TANK

 

[thumpar]

Yes it is 5/6 in the diagram. The kit for the new one if needed comes with all the parts pointed to. Mine felt fragile too but was able to get it off and back on. If it doesn't want to go I wouldn't force it and just clean as best you can with it on. I used carb cleaner.

 

[IdahoDoug]

OK, thanks. It's sitting in the garage and I'll pull the float and the diaphragm early tomorrow morning (like 7am - grr) to see if I need to order the diaphragm as well. I used brake cleaner - prolly a little harsh compared to your better call of carb cleaner. I'm not planning to pull the pump off the lid - did you see any need to? My lid O ring is still sitting there in its groove except for an inch of it. I appreciate the help here very much. It's been one of those weeks. The trailer's master cylinder also blew. My classic Audi has a hesitation I have not been able to figure out. And my freshly restored VW Vanagon's ignition switch wiring got so hot today I couldn't touch it. So I have simultaneous wrenching projects to deal with as guests loom and its our anniversary Friday and I wanted us to sneak away in either the boat or the Van for a couple nights. I will make one happen though. I just hope the dang diaphragm is toast because that will mean I've found the fix. If its intact I am still in the dark..

 

[thumpar]

I didn't take the pump off the top. I just removed the one screw for the float and then the three screws for the diaphragm cover. Watch out though. The spring inside will fly.

 

[IdahoDoug]

Couldn't sleep. Went down to the garage and pulled the diaphragm. Dang it - looks perfect. So I am going to stop messing with it at this point and will check off some other more common items, I think. I may be able to put the top back on the O ring. Will put a faint dab of something on the section that's risen up and put the top back on the VST. The above fuel pressure check makes sense. I have been avoiding it because of all the annoying designs there are no fittings on the system to check pressure. I have to buy an adapter, and also a fuel pressure guage since I don't have one. Add these two items up and I'm nearly at the price of a new fuel pump, so that's a consideration - just replace the low pressure lift pump in case the VST tank (feeds the high pressure pump) is running dry at higher RPMs/flow rates due to inadequate flow. So that's on the menu. The engine had a normal tuneup not too long ago but I will also replace the plugs and other tuneup parts it may call for and see if something's amiss. Looking at plugs can sometimes reveal an issue.

Crap. Was hoping the diaphragm would be trashed. Thanks for the heads up on the spring. Tossed a rag over my hands while freeing up the diaphragm housing just in case I fumbled it. The float seemed fine as well - no fuel sloshing in it, and the float valve did not look worn and it worked easily.

DougM

 

[Fun Times]

On fuel pressure, mercruisers engineers appear to have been on strike during this period. They did not provide a schrader valve to check pressure. I have to buy and install an adapter. Grrr

Your fuel pressure schrader valve should be at the front of the fuel rail. The brass cap is hard to find under the plenum. Item numbers 13 and 14.

http://www.mercruiserparts.com/Show...r=10&bdesc=VAPOR+SEPARATOR+TANK+AND+FUEL+RAIL

 

[IdahoDoug]

Well I will look again, rather than maligning the M engineers - heh. I could not see much of anything in there much less the front of the fuel rail. That will be the high pressure test then. Thanks will give it a go.

ON THE VST: Does anybody know if the only filter screen in there is the large one under the elec. pump? When I research other VSTs they all seem to have a hidden extra screen that's small and gets clogged. So only asking before I put the VST back together. The cost of these limits random exploration, you know? Keep the tips coming.