5.0 MPI Intermittent Continuous beep, no Smartcraft output

Hey Lazy Daze, thank you for your input

I always flush the engine after use and the boat is trailered, however I am not the original owner. We bought the boat with 133 hours and the original owners kept the boat on a lift. I believe that it was always flushed.

As far as the old impeller, it was in nearly as good shape as the one I replace it with. The impeller must have been changed right before we purchased the boat.

I just stopped by the boat on my way home and checked the tension. It doesn't seem that loose, however Between the top two pulleys I can displace the belt about a half inch to an inch. I just did a quick search online and it looks like I should only be able to move the belt about a quarter inch.

I didn't have the right size wrench on me (good to know, I'll pickup a set for the boat), but I'll tighten it before testing the boat out again.

I'm hoping that this is the root of the issue, but I'm a bit skeptical as there are no other issues and no belt squeal.

OK, so we can likely (hopefully!) eliminate "Bravo-itis", or a closing/constricting of the water passage that comes through the drive.

If you can only move the belt that far, I'm a bit skeptical, as well, that that little bit of extra play would cause this. BUT, weirder things can happen.

There's a test that can be done to check for proper output/flow of the impeller, but Merc only lists specs for 1,000RPM. You could try it, but I'm not sure it would help in this case. A better way might be to temporarily install a piece of clear vinyl tube between the intake hose and the t-stat housing. Then, observe the flow at idle, elevated idle at various higher RPMS... then again at slow speed and various planing speeds. This may or may not be a definitive test, but if there's a noticeable difference in flow as you go faster then we have at least narrowed down the search to a physical problem, not electrical. At that point, we can backtrack - but it may require removing the drive. If you don't know when the drive has last been off, it's probably due for an alignment check, anyways (bellows, too?).

I didn't mention it above, but in the back of my head, I keep coming back to some type of restriction in the drive's intake or more specifically, a disruption in the water flow across/into the intake grill. At low RPM, the water pressure/flow across the intake can be forced/sucked into the intake. But if something was disrupting the flow, then at higher speeds the flow of water would not be smooth/laminar across the drive and would instead be turbulent - in essence, less water would enter the system. If you haven't already, take a REAL good look at/into those intake holes.

Let's hope for the serp belt possibility!

So if your temp gauge is not showing an increase at high speed running, that's telling you that there is adequate volume being produced from the pump to maintain a normal temp.

The water pressure gauge jumping around, as you mention, may indicate a conductivity issue. There is no need to do any splicing of wires at this point. To eliminate the grounding issue as a possibility just rig a jumper wire from a ground source to the sensor body.

Could a grooved impeller housing cause the high-speed loss of pressure? That doesn't seem to make sense based on normal temps. Also I only have experience with a B3 so I'm not sure if the pump set up is the same on a B1 and I may be off in left field...

LazyDaze has a good troubleshooting plan but before I did that I would pull the t'stat housing and inspect / test the t'stat itself. Other than an anomaly it is the only "flow restriction" not reportedly looked at.

To be clear how this system works, any restriction down stream of the pressure sensor would show as high pressure on the gauge. The sensor is first in line after the raw water pump, a low reading would indicate inadequate water pressure from the pump, but since the OP's motor doesn't overheat then he's getting adequate flow.

DaleM said:

I'm not sure if the pump set up is the same on a B1 and I may be off in left field...

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Dale, all Bravo pumps (B1, B2, B3) and inboard Merc pumps are the same. While the styling has changed a little bit over the years (for example, to drain the older styles you have pull the hoses off - no blue plugs or air actuated system), they are all the same setup.

Dale, all Bravo pumps (B1, B2, B3) and inboard Merc pumps are the same. While the styling has changed a little bit over the years (for example, to drain the older styles you have pull the hoses off - no blue plugs or air actuated system), they are all the same setup.

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cool - thanks for that. I like learnin' stuff

First of all I just wanted to thank everyone for taking the time to help me with this issue. I really appreciate everyone's willingness to jump in and help out, really nice to not feel alone in this!

Lazy Daze said:

There's a test that can be done to check for proper output/flow of the impeller, but Merc only lists specs for 1,000RPM. You could try it, but I'm not sure it would help in this case. A better way might be to temporarily install a piece of clear vinyl tube between the intake hose and the t-stat housing. Then, observe the flow at idle, elevated idle at various higher RPMS... then again at slow speed and various planing speeds. This may or may not be a definitive test, but if there's a noticeable difference in flow as you go faster then we have at least narrowed down the search to a physical problem, not electrical. At that point, we can backtrack - but it may require removing the drive. If you don't know when the drive has last been off, it's probably due for an alignment check, anyways (bellows, too?).

I didn't mention it above, but in the back of my head, I keep coming back to some type of restriction in the drive's intake or more specifically, a disruption in the water flow across/into the intake grill. At low RPM, the water pressure/flow across the intake can be forced/sucked into the intake. But if something was disrupting the flow, then at higher speeds the flow of water would not be smooth/laminar across the drive and would instead be turbulent - in essence, less water would enter the system. If you haven't already, take a REAL good look at/into those intake holes.

Let's hope for the serp belt possibility!

Click to expand...

I actually like the idea of removing the drive. It's been on my to-do list but I have been putting it off because I'm a bit intimidated, this might be a good opportunity. As far as checking the flow with a clear tube, that's another great idea. Is there a way to disconnect the transmission cable temporarily so that I can run the engine at higher RPMs in the driveway? When I remove the outdrive, is there anywhere I should specifically look for obstructions?

The obstruction idea actually makes sense. At lower RPMs the pump may have enough water intake to keep the PSI high, however I can see how at higher RPMs an obstruction might not let the pump suck in enough water, resulting in the PSI drop.

scoflaw said:

So if your temp gauge is not showing an increase at high speed running, that's telling you that there is adequate volume being produced from the pump to maintain a normal temp.

The water pressure gauge jumping around, as you mention, may indicate a conductivity issue. There is no need to do any splicing of wires at this point. To eliminate the grounding issue as a possibility just rig a jumper wire from a ground source to the sensor body.

Click to expand...

Hey Scoflaw, I like the idea of rigging the ground wire to the body of the sensor, that makes more sense than splicing into the harness. I think I may have miscommunicated how much the PSI is jumping around. The PSI is jumping around in a range that makes sense and typically drops gradually. When I go on plane, the PSI will go to about 8 PSI and then drop gradually to 5 or lower. At no point is it reading something too high or low that don't make sense. I would think if the problem was electrical it would read way out of range.

Gary Hill said:

LazyDaze has a good troubleshooting plan but before I did that I would pull the t'stat housing and inspect / test the t'stat itself. Other than an anomaly it is the only "flow restriction" not reportedly looked at.

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Hey Gary, I left it out of the original post because I didn't think it was relevant, however I changed the thermostat at the same time as the impeller. In fact, I changed the thermostat and impeller because the old thermostat was stuck and caused the engine to start running hot.

scoflaw said:

To be clear how this system works, any restriction down stream of the pressure sensor would show as high pressure on the gauge. The sensor is first in line after the raw water pump, a low reading would indicate inadequate water pressure from the pump, but since the OP's motor doesn't overheat then he's getting adequate flow.

Click to expand...

Good information! I was wondering about where in the water flow the sensor was, it makes complete sense that depending on where the obstruction is that it would affect the PSI in different ways.

What water temp are you seeing ? Sounds like you can't run on plane, so if that's the case, maybe it would overheat at a high rpm, which brings you back to the pump. Those brass pumps score easily. how scored was yours ? Sometimes putting a new impeller in a worn housing makes things worst.

David, I hate to say this... I think you need to look at "bravoitis" as a possibility like Dennis had mentioned. I had a very similar experience as you starting at the end of the 2014 season. In the spring of last year, I connected my water pump inlet to the air conditioner through hull (and plugged the hose coming from the transom) as a work around. My mechanic is fixing it this week. I also need the swivel shaft and seal replaced, so we're basically doing a complete transom assembly overhaul. New trim senders, water line, bellows, shift cable, etc..

"4. There is a clog somewhere in the raw water system. I don't think this makes sense as the clog wouldn't cause the drop in PSI at higher RPMs, right?"

The inlet tube gradually gets crushed over time and the inside diameter gets smaller and smaller. You are still in the earlier stages. Basically, the tube diameter is only large enough to pass sufficient water to the water pump up until a certain RPM. After that point, the water pump tries to draw more water than the current diameter of the inlet tube can supply and the pump impeller starts to cavitate. This causes bubbles to appear in the pump output (which causes erratic PSI readings) followed by the pressure dropping.

It is not too difficult to check to see if this is your problem. You only need to have a new gasket in hand before you start. Pull the water inlet housing from the inside transom assembly and take a look at the water inlet hose underneath of it where it comes through the transom. I had to pull the power steering actuator to get to mine. It has two 7/16" bolts that hold it on. If you do this, be very careful of the plastic quick disconnect for the gear lube that connects to the fitting below and to the left of the inlet housing. I broke mine, and the whole lube reservoir full of brand new oil emptied into my bilge. Disconnect the lube line by squeezing the little grey plastic button on the connector and pulling it straight off of the transom fitting. Wire tie it to something so that the quick connect is above the height of the reservoir to prevent siphoning all of the gear lube out. I couldn't actually see the end of my inlet hose, but I used an allen wrench to poke around and I could feel that it was nearly completely crushed closed. I had to push fairly hard to get the allen wrench to go into the hose. I also had some corrosion around the inlet housing gasket, which was very brittle and had some pieces missing. I was shocked to see the condition of that gasket. Clearly, it was not sealing anything.

I hope it is not your issue, but it is easy enough to check before knocking yourself out chasing other answers. Scoflaw has a point, though. Be sure to double check the condition of the surfaces that the impeller rides on inside of the pump. If there is scoring on either surface, correct that before moving on to the inlet tube.

scoflaw said:

What water temp are you seeing ? Sounds like you can't run on plane, so if that's the case, maybe it would overheat at a high rpm, which brings you back to the pump. Those brass pumps score easily. how scored was yours ? Sometimes putting a new impeller in a worn housing makes things worst.

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Good question Scoflaw, the temperatures actually look really good. Stays right about 154 degrees F, however I have to admit that I've been paying much more attention to the Water PSI. I don't really have an issue running on plane, however once the PSI triggers the alarm the Guardian motor reduces the max RPM to about 3500. Even if I keep it on plane at that limited RPM for a bit, I haven't seen it overheat. It isn't until I go back to idle, though, that the PSI returns to a value that stops the alarm.

Also, there have been times when I've been able to be on plane for several miles before the low PSI would trigger the alarm, throughout which it never overheated.

Of course, this isn't to say that it wouldn't eventually overheat, it is very possible that the PSI alarm is preventing me from pushing the engine far enough to overheat.

As far as the pump, I wish I had taken a picture when I replaced the impeller. I took a picture of the impeller side of the pump, to make sure I push the impeller back in properly, but not of the backing plate. I did inspect the backing plate and noticed light scoring, however nothing that I would consider excessive.

skibum said:

David, I hate to say this... I think you need to look at "bravoitis" as a possibility like Dennis had mentioned.

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Skibum, I'm sorry that you've been going through the same thing but really appreciate you detailing bravo-itis further, I have to admit that I really wasn't sure what this was. A restriction at that point in the system certainly seems like it would cause an issue like what I'm experiencing. However, It looks like the majority of people online with this problem found this out because of an overheating issue, hopefully this is evidence that I don't have the same problem.

I did a quick search online of picture of the fitting you are referring to, and agree that it looks like an easy thing to check for. I found the gasket online for a couple bucks, so this is something I'll be looking into this weekend. I'll probably check this and pull the out-drive for inspection around the same time.

So far, this is the plan:

1. Tighten the drive belt, check to see if the problem still persists (celebrate if this resolves the issue)
2. Install clear tube to thermostat housing input, visually check for good water flow
3. Check for bravo-itis, pull outdrive and inspect (I don't consider this a waste of time, because it has been on my to-do list)
4. If everything else seems good up to this point, pull the raw water pump and reinspect

What I'm still curious about is whether or not there is a way to disengage the transmission from the throttle, so that I can test the engine at higher RPMs without having to be in the water. This will be a much faster process if I can test the engine in the driveway.

Thanks again to everyone, this really is one of the best forums around!

Running it in the driveway will determine nothing. What can be done for a few bucks is to bypass the water pressure sensor. A couple of radio shack resistors and a soldering gun. BT Doctur has the specs on the resistors your looking for. WPS issues have been well documented, not uncommon at all.

You run it in the driveway to look at water flow, but the real test is in the water. Largely because you won't pull as much water in from a hose as you will in the water. BUT, I think it's still worthwhile to do this to get a basis for comparison.

To disengage the tranny... This is pretty much the same for all Mercruiser's for many, many years - and some other manufacturer's as well. All you need to do is push the "throttle only button" and then push the stick (throttle/gear shift lever) into gear. BUT, it won't go into gear - you will actually still be in neutral and can rev the engine. Just don't do it for long periods of time when on the hose. The amount of time you'll need to do it for in this case is just fine, though.

Look at the stick - look at where it "pivots". That pivot area is actually a button. Push it in, while the stick is in neutral. Hold the button in and shift the stick forward or reverse. Once you get the stick past the "detent", you can let go of the button. You are now in neutral and can rev up. Carb'd engines would use to "pump the throttle" or for warm-up. Once you pull the stick back into the straight-up-n-down orientation, the button will pop back to normal. It's actually easier and takes less time to do than the time it took me to write this or you to read it. :smt001

davidh82 said:

At idle I get around 3 - 5 psi, then at around 1,500 it just to around 10 psi, at these speeds the PSI is steady. Increasing the throttle causes the PSI to grow at this low range.

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pressures and readings might be different since you have a 5.0 mpi bravo one and i have a 5.0mpi bravo three but your numbers sound odd after i closely recorded my waterpressure readings on the smartcraft :

at pure idle about 0.15 bar so rougly 2 psi.

at 2500 rpm or above about 0.28-0.35 bar so 4-5 psi.

i have no alarm or overheating with this numbers , i even crosschecked on a friends maxum with 5.0mpi b3 - he has roughly the same pressures.

so not that sure if you are chasing the right problem. are you really sure the alarm relates to water pressure ?

can you exclude the scenario you overfilled engine oil so the crankshaft in some conditions starts to punch it up and this results in engine oil pressure fluctuarions and an alarm ?

i would look at your oil pressure when the alarm happens.

Before you do the test in the driveway, let me add a little more information for you. As I mentioned above, the problem with running the engine on a hose is that it usually does not supply the same amount of water as does being actually in the water. While you won't damage the impeller in the short period of time you'd be doing this, you could end up invalidating the test because of lack of water flow. At the clear hose, it would look like there's a problem with your engine/pump, but it would really be due to not having enough supply water.

A "good" Bravo impeller will pump about 7-9 gpm at 1,000RPM. About twice that of an Alpha. Let's measure your water flow coming out of the hose, first. This can easily be done by making measured/graduated marks on a 5-gallon pail and then filling the pail for 15 or 30 seconds, then converting the measured amount to what it would be in a minute. Do that a few times, just to be sure. If you're getting at least the "spec" amount, do the same test on the engine (at 1,000RPM) by removing the intake hose from the t-stat housing and directing it into the bucket. If you're not getting at least the "Spec" from your hose, skip doing this at home. If you are getting more than the spec from your hose, then you can elevate your RPM even higher - but stop just before no more water escapes around the edges of the muffs. If you're getting less from the intake hose than from your garden hose, that's pointing to a blockage or worn impeller/housing. But we may not see an issue till you do elevated RPM testing.

scoflaw said:

What can be done for a few bucks is to bypass the water pressure sensor. A couple of radio shack resistors and a soldering gun. BT Doctur has the specs on the resistors your looking for.

Click to expand...

I actually think this is a really good idea. Since I haven't had any problem with overheating what I'd like to do is fabricate something that I can plug into the harness to bypass the sensor temporarily. This will allow me to use the boat while also troubleshooting this issue. Of course, I'll need to keep a close eye on the engine temperature. I'll try to look for posts from BT Doctur regarding the resistors.

Lazy Daze said:

To disengage the tranny... This is pretty much the same for all Mercruiser's for many, many years - and some other manufacturer's as well. All you need to do is push the "throttle only button" and then push the stick (throttle/gear shift lever) into gear. BUT, it won't go into gear - you will actually still be in neutral and can rev the engine. Just don't do it for long periods of time when on the hose. The amount of time you'll need to do it for in this case is just fine, though.

Look at the stick - look at where it "pivots". That pivot area is actually a button. Push it in, while the stick is in neutral. Hold the button in and shift the stick forward or reverse. Once you get the stick past the "detent", you can let go of the button. You are now in neutral and can rev up. Carb'd engines would use to "pump the throttle" or for warm-up. Once you pull the stick back into the straight-up-n-down orientation, the button will pop back to normal. It's actually easier and takes less time to do than the time it took me to write this or you to read it. :smt001

Click to expand...

Hey Dennis, thank you so much for this information! I've noticed that circle at the pivot-point, but never thought that it could be a button. I was thinking I would have to disconnect some linkage at the engine, this is much easier!!

aerobat77 said:

pressures and readings might be different since you have a 5.0 mpi bravo one and i have a 5.0mpi bravo three but your numbers sound odd after i closely recorded my waterpressure readings on the smartcraft :

at pure idle about 0.15 bar so rougly 2 psi.

at 2500 rpm or above about 0.28-0.35 bar so 4-5 psi.

i have no alarm or overheating with this numbers , i even crosschecked on a friends maxum with 5.0mpi b3 - he has roughly the same pressures.

so not that sure if you are chasing the right problem. are you really sure the alarm relates to water pressure ?

can you exclude the scenario you overfilled engine oil so the crankshaft in some conditions starts to punch it up and this results in engine oil pressure fluctuarions and an alarm ?

i would look at your oil pressure when the alarm happens.

Click to expand...

Hey Aerobat, thanks for your input! I went through the same thought process in regards to the oil pressure, however I'm pretty sure that it has been eliminated. When the engine alarm comes on, the 'OK' in the PSI section (in the SmartCraft screen that lists the three 'OKs') becomes an exclamation mark. Also, the message that is displayed specifically calls out low pressure, if the problem was with too much oil in the system I would expect high pressure, right?

That being said, I definitely plan on checking the oil level again and siphoning out the half quart or so that I am over. The resistor trick above to "fake out" the system will be another way to verify that the problem is in fact the water psi.

As far as the discrepancy between your psi and mine, I wonder if that has to do with the difference in years. My engine is a 2010 and has the added emissions control features. I did some research online, and I don't remember exactly where I saw it but the computer expects to see about 1-5 psi at idle, and 7-17 at WOT. Actually, come to think of it, when I had the boat out last weekend the alarm didn't present itself until I tried to push the engine a bit harder. I was able to run on plane for a couple minutes with no problem, then decided to raise the RPMs a bit (to about 4k) when the alarm came on. Does anybody know what this engine would consider WOT?

Lazy Daze said:

Before you do the test in the driveway, let me add a little more information for you. As I mentioned above, the problem with running the engine on a hose is that it usually does not supply the same amount of water as does being actually in the water. While you won't damage the impeller in the short period of time you'd be doing this, you could end up invalidating the test because of lack of water flow. At the clear hose, it would look like there's a problem with your engine/pump, but it would really be due to not having enough supply water.

A "good" Bravo impeller will pump about 7-9 gpm at 1,000RPM. About twice that of an Alpha. Let's measure your water flow coming out of the hose, first. This can easily be done by making measured/graduated marks on a 5-gallon pail and then filling the pail for 15 or 30 seconds, then converting the measured amount to what it would be in a minute. Do that a few times, just to be sure. If you're getting at least the "spec" amount, do the same test on the engine (at 1,000RPM) by removing the intake hose from the t-stat housing and directing it into the bucket. If you're not getting at least the "Spec" from your hose, skip doing this at home. If you are getting more than the spec from your hose, then you can elevate your RPM even higher - but stop just before no more water escapes around the edges of the muffs. If you're getting less from the intake hose than from your garden hose, that's pointing to a blockage or worn impeller/housing. But we may not see an issue till you do elevated RPM testing.

Click to expand...

All great information, I'll definitely check the rate of flow from the hose before checking in the driveway.

Thanks Dennis!

davidh82 said:

Skibum, I'm sorry that you've been going through the same thing but really appreciate you detailing bravo-itis further, I have to admit that I really wasn't sure what this was. A restriction at that point in the system certainly seems like it would cause an issue like what I'm experiencing. However, It looks like the majority of people online with this problem found this out because of an overheating issue, hopefully this is evidence that I don't have the same problem.

Click to expand...

Guardian mode prevents our boats from getting to the point of overheating. People without Smartcraft find out about the issue when they overheat.

Best of luck to you!

Wait a minute... David, can you double check something? I believe that that first screen (the three "OK's") shows Engine temp, Battery Voltage and OIL PSI, not Water PSI. Could you be getting the two PSI's confused? It might be easiest if you had the compuker read by a technician to see exactly what fault is sending it into guardian mode.

Too much oil will not cause high PSI. But, it could cause low oil PSI as the oil coudl get aerated.