More 4.3 MPI Water Pressure Issues... Possible to bypass the sensor???

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pilot4net

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Over the last few months I have made several posts about the problems we have been having with our newer 2013 4.3 MPI throwing a false “Low Sea Pump Pressure” code and sending the engine into Guardian mode. We have been back and forth to the shop (under warranty) and it seems that Mercruiser, as well as the mechanic, are at a loss as to what to do next. You can see my last post here:

http://forums.iboats.com/forum/engi...iser-4-3-mpi-with-more-issues?_=1404657073423

On our last outing, the boat ran fine for a couple of hours but then once again we got the dreaded continuous alarm with the accompanying Guardian mode and restricted power. When I brought the boat back to the shop and they plugged in the computer, it once again showed the “Low Sea Pump Pressure” code had thrown but the pressure, as per the ECU, was 35 psi at 4800 rpms and coolant temp of 164 degrees. Per Mercruiser and the shop, this is an abnormally high pressure reading and that is why the alarm went off because the ECU saw the reading as Out-Of-Range high. So, Mercruiser instructed them to change the sensor, again. Firstly, is this possible that the alarm for low water pressure will activate if it sees an abnormally high water pressure? I thought that’s what the “Sea Pump CKT Hi” alarm was for, to indicate that the sensor reading was out-of-range indicating either a sensor failure or wiring trouble. Mercruiser did say that they think that the high reading was not accurate because that would indicate a coolant blockage downstream of the sensor which would cause an overheat situation, which did not happen. What do ya’ll think?

Now, I had read in some older posts that it WAS possible to bypass this pressure sensor. Some members had commented that, “…a trip to Radio Shack and a soldering iron…” could get the sensor bypassed, but did not go into any detail as to how that process would work. I am assuming that we would need to wire in some resistors in the sensor wiring to fool the ECU to think that the water pressure was good but I am not sure as to what resistance that sweet spot is. If anyone knows what resistance to dial this in at to make the ECU happy, please give me some help here. Also, I am assuming the gray wire is the ground so the resistors would have to go in between the other two wires, correct? Even though the boat and engine are under warranty for a few more years, I’m just ready to do this mod and be able to enjoy our boat by bypassing the sensor and installing a mechanical water pressure gauge at the helm to keep an eye on the water pressure.

I hate to have to take these measures and If any of you have any other ideas as to what to have them check, I’m all ears! It just seems as though both Mercuiser and the shop don’t really know what else to do next, and that’s really aggravating with a new boat. Below is a list of the things that have been so far to fix the problem to no avail:
  1. Change water pressure sensor
  2. Change thermostat and check poppit valve
  3. Change Sea Water Pump in lower unit
  4. Reflash ECU with updated software
  5. Check wiring for abrasions, cuts, kinks, or other damage
  6. Change water pressure sensor, AGAIN!
Like I said, any and all information any of you can lend would be great as we are grasping at straws it seems.
Thanks for reading the lengthy post and I look forward to hearing from you all!

Have a great Sunday!!!
 

Fun Times

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Sure you could fool the ECM with installing something like a "potentiometer" that way you can adjust the setting to within specifications seen on the scan tool.

Mercruisers theory is possible that a slight restriction before the sensor could give you a high water pressure reading. I have also seen where if you just wiggle the wires at the sensor, the PSI and volts will change a lot. So be sure the dealer checks that for you as well. Pull the sensor and inspected it. All you need is a deep 1 inch socket. Or pull the water hose at the cooler next to the sensor and look for sand build up, etc. etc. Be sure the threads in the cooler are clear from left over paint as you could have a ground problem due to the paint. Hope this helps, good luck.:)
 

pilot4net

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May 24, 2005
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Thanks for the ideas Fun Times! I will get with them Monday to get them to wiggle the wires at the sensor to see if they see any kind of fluctuation. I had already brought up the idea about paint on the threads of the cooler causing problems with the ground but Mercruiser said that cannot be the problem in this instance as the sensor gets its ground from a dedicated ground wire running to the sensor itselt and is not grounded through the body. Also, they said that it would have to be a blockage AFTER (as in between the engine and the cooler) to show a high pressure like that. This came up because I had read someplace where the hose coming from the outdrive through the transom assembly can sometimes get pinched causing a restricition and they said if it was a restriction between the sensor and outdrive (such as trash at the mouth of the cooler or pinched hose, etc) it would be showing a LOW water pressure reading and that makes since to me. So, I am interested how "...a slight restriction before the sensor could give you a high water pressure reading" as you stated. I am definitely not second guessing your knowledge, just trying to wrap my head around how that would happen to better understand these engines....

Anyway, thanks for the info and hopefully others will chime in as well!

Have a good day!
 

alldodge

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To add a bit, the sensor has three connections. The gray wire is ground, the Blk/Pink is 5 volts and the BK Blue/Wht goes to pin 11 at the ECM at connector B. As I'm seeing readings of Fun times mentioned check the connections, they could be loose or corroded causing a higher then normal resistance
 

pilot4net

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Good morning again guys! Well it looks like Mercruiser is trying to skip out on a warranty claim. We are continuing to have the above listed problems and Mercruiseris saying that the engine package is operating as it should even though there is no other real indication of either high or low water pressure anywhere else in the system. I have requested they try another ECM to rule out a bad parameter setting for the water pressure but they refuse. Tracker is saying that's its not something wrong with the boat so now they are sort of giving up it seems. I fear that going the legal route is just a waste of time so now I am interested in just trying to bypass the sensor and be done with it and actually enjoy my boat. If I go the route of bypassing the sensor with resistors and such to satisfy the ECU, does anyone have any idea where to start as to what resistance the ECU would be looking for? Also, does the ECU look for different values at different RPMS or is it just a static setting built into the logic of the ECU? I have the know how to meaaure, install, and dial in the potentionometer or rsisitors I am just trying to find a starting point so I'm not "fishing in ohm's sea" forever trying to find the magic mark. I know this is not an ideal situation and I don't want to be doing this on a new boat still under warranty but as they are not trying to fix it any further, I am trying to take care of it myself. Thanks for any help you can give!
 

alldodge

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It's my understanding that the ECU has set limits for low/high and only sets a code when these are exceeded. That said need to find the fixed resistance to put it somewhere in the mid range. If you had a scanner you could use a potentiometer and adjust until the reading is where you want it then get a fixed resister. Without that I would suggest taking the sensor and see what values you can read and then adjust in the mid range of them.

The one thing that comes back to my thinking is your getting a high and not a low reading. Things like this leans me to there is a restriction which is causing the pressure to go up. Was anything installed after you bought the boat by the dealer? If not what kinds of stuff does the engine have installed, like hot water heater and such?
 

G1FishnSki

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Not sure if your having the exact same problem as me, but it sounds similar, so I will throw this out there. I looked at your first thread and it sounded a lot like the issues I am having with my 2012 MPI. Especially the part about the temp being stuck low. Mine would show around 165-170 while the key was in the accessory position, but it would drop to 100 within seconds of cranking and pulling in water. Get up to around 3000 rpms and guardian kicks in. Acts like a thermostat stuck open. Talked to my dealer, he had seen in once. He chased codes, (Low seawater, Low temp, Rich fuel, etc...) but stumbled across the real fix by accident. Says its the engine water pump. Specifically, the impeller. It is spinning freely on the shaft. I'm not talking about the one in the lower unit, but the one on the front of the engine. I'm picking mine up tomorrow from the shop. Will test it this weekend. Hopefully it's fixed. The way you can check it to prove if that is the problem is going to the front of the motor, remove the belt, pull the plug in the top of the water pump so you can get a small flat blade down to the impeller and hold it place while you turn the pulley. If the pulley turns and impeller doesn't, shaft is spinning in the hub. He told me they now have a tech bulletin from Merc on it. That there was a bad batch of water pump impellers out there. I also had my lower unit impeller go bad two weeks before this one. Same issue. Split hub. Boat tech that fixed it, said he had never seen one do that. Hope this helps.
 

pilot4net

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Thanks G1! I will get with the tech at the dealership tomorrow and see if they can make that simple check while it's sitting there for them to figure out what to do next. Thanks a lot guys for the ideas so far... Any help is very much appreciated as we work through this. I will keep everyone posted as we work through this!
 

z00m

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Seems a bit strange that Merc can say the 'engine is working as intended' when it sounds an alarm and throws codes. Remind them that they are called 'fault codes' for a reason. That can't be 'as intended'. If you go ahead and do some jiggery to fool the ECM, what happens if the real fault shows up because the guardian doesn't kick in? They'll say it's on you to fix it.

I'm sure it's frustrating but you need to see it through.
 

pilot4net

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I agree Zoom! I am just trying to see what my options are in the future IF Merc backs away from fixing it..... Right now they are still troubleshooting the problem via the dealer so we will see how it goes. They are now going to check the engine mounted water/circulating pump and they have asked the dealer to install sections of clear tubing in the line coming from the sea pump to the engine to check for air bubbles to see which way to head for further diagnostics. I will keep everyone posted as things change. Also, please keep the ideas flowing!!!
 

G1FishnSki

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Hey Pilot,
Haven't put mine in the water yet. Going tomorrow. However, I seen the pump with my own eyes. No doubt it was broke. There is a metal impeller in the water pump that presses on a shaft with no key. The metal plate/impeller was broke in half. My dealer did put it in the water, before and after repairs and confirmed the fault and confirmed the repair. Keep us posted on yours. I am real curious about the water pump. I see some other folk in the forums with the same symptoms. Good luck.
 

achris

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The sensor is a 3 wire sensor, so you need to set up the resistor network to simulate that. It's a simple voltage divider. I'm not at home at the moment so I can't go out and do the measurements from my engine. But, here's what I would be doing. Take the sensor out (or measure in place if you can reach it) and measure the resistance across the power and ground pins of the sensor (and it needs to be unplugged from the rest of the system). That's your starting point. I would then divide that value in half, buy 2 resistors of that value and set them up with one end of each resistor on each of ground and power wires, then joint the resistors together and the third wire (which is the wire the ECU reads) to that centre join point. As I also have the software to see the reading that would create, I would then check that and adjust accordingly. If you do need to adjust the values, you need to keep the total value the same, for example if the reading across the ground and power pins is 10,000 ohms, then use 2x 5000 ohms, or a 4000 and a 6000, or a 3000 and a 7000.... You get the picture.

If you can wait about 3 weeks, I'll be home and can do all the readings on my engine and give you the resistor values...

Chris........
 
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pilot4net

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Thanks for the great insight aChris! I would greatly appreciate and can definitely wait for you to get those values together! I'm still at work for the next 2 weeks so nothing can baleen until at least then. Thanks so much for helping out there...
 

achris

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Just send me a PM around 16th August, to jog the memory... :)
 

achris

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Just send me a PM around 16th August, to jog the memory... :)

Errrr, can you add a week to that? Been asked to stay just a little bit longer... (Reminds me of a song. Jackson Brown if I recall correctly.)
 

pilot4net

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G1, yes they checked the pump like you described late yesterday afternoon and found no resistance turning thr water oump pulley while sticking the screwdriver into the impeller indicating a failed pump. The service manager said that wasn't checked because my engine's serial number was outside the range of serial numbers on that particular service bulletin. He said even though it WAS outside the serial range, he believes Merc will still pay for the repair. I asked him about warranty coverage if not and he said Merc doesn't cover any water pumps, not even the engine amounted pump. I thought they only didn't cover the out drive mounted sea pump since that is a wear and tear frequently replaced item. But, we shall see! Hopefully this is the fix and if it is, I owe you a six pack, lol! Achris, if this doesn't end up being the fix, I will definitely be sending you a reminder.... Thanks guys, I will keep you posted!
 

Sprouser

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G1, yes they checked the pump like you described late yesterday afternoon and found no resistance turning thr water oump pulley while sticking the screwdriver into the impeller indicating a failed pump. The service manager said that wasn't checked because my engine's serial number was outside the range of serial numbers on that particular service bulletin. He said even though it WAS outside the serial range, he believes Merc will still pay for the repair. I asked him about warranty coverage if not and he said Merc doesn't cover any water pumps, not even the engine amounted pump. I thought they only didn't cover the out drive mounted sea pump since that is a wear and tear frequently replaced item. But, we shall see! Hopefully this is the fix and if it is, I owe you a six pack, lol! Achris, if this doesn't end up being the fix, I will definitely be sending you a reminder.... Thanks guys, I will keep you posted!
Did you ever figure out what the problem was? I'm having the same problem with my mercruiser 4.3 liter MPI.
 

achris

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Did you ever figure out what the problem was? I'm having the same problem with my mercruiser 4.3 liter MPI.
7 year old thread (read the forum rules). Start your own thread, and include engine serial number in you post.

Chris.
 
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