Logo
FULL SITE MENU

Engine acts like it is in limp mode.

S

Superdaveusa

New member
Started with a left hand turn while out running the boat. Will start right up and idle perfectly. When applying throttle, engine will not take full throttle. It will lope like in limp mode. All filters have been changed. TPS was changed, no effect. Could it be a tilt sensor? Where should i look next? Could it be a wire short?
 
You might want to indicate which model and year of the engine, as well as the serial number (all info from Merc requires serial number for accuracy).
 
Is this engine fuel injected? Check the temperature sensor with two wires at room temperature- if it has two (likely does), that one sends info to the ECM. Remove the two wire plug and measure the resistance with a multimeter while it's not running correctly If the resistance is far lower than 200 Ohms, make sure the engine isn't actually overheating. If it reads low at room temperature, it needs to be replaced.

Has the raw water pump impeller been replaced in recent memory? If not, it may be overheating.

When was the fuel/water separator checked last?

 
2016 3.0 Mercrusier Alpha one Drive

Fuel water separator filter just changed.

Not sure it could be overheating, no alarms and it happens when you start it.

Fuel injected
 
What's the model of the engine? Can you post a photo?

Neutral safety only interrupts the voltage from the switch to the ignition circuit, whether it's a simple coil/distributor or Ignition Control Module in an injected engine.

If your engine is the Multi-Port version, you'll see a valve on the lower edge of the fuel rail (shown in the diagram)- attach a fuel pressure gauge and check the pressure at KEOE (Key On/engine off, Idle, 2000 RPM and WOT (Wide Open Throttle). This was the procedure we were taught when I went to MasterCraft training and it's a good way to verify proper pressure. Use a gauge that has a bleeder valve, to purge any air and while you're at it, use that gauge to take a fuel sample- I use a clean/dry water or soda bottle that's clear. Let the gas sit for awhile and look for cloudiness, water droplets, other stuff.

Download the manual if you don't have one and check the troubleshooting section (starts at pg 98) for info about various conditions.

www.manualslib.com

MERCRUISER 3.0 MPI OWNER'S MANUAL Pdf Download

View and Download MerCruiser 3.0 MPI owner's manual online. 3.0 MPI engine pdf manual download.
www.manualslib.com www.manualslib.com
 
It is a 2013 3.0MPI with 175 hours on it SN2A047033. I have the manual, but can't figure what is wrong. No codes, starts right up, but wont increase withput going into some sort of g
 
It is a 2013 3.0MPI with 175 hours on it SN2A047033. I have the manual, but can't figure what is wrong. No codes, starts right up, but wont increase throttle without going into some sort of guardian mode. So if i hook up the pressure gauges, I won't be able to do WOT and not sure i can do 2000rpm. Where is the valve located to hook up pressure gauge? Wont let me attach a pic
 
1719073348095.jpeg
 
Superdaveusa said:
It is a 2013 3.0MPI with 175 hours on it SN2A047033. I have the manual, but can't figure what is wrong. No codes, starts right up, but wont increase withput going into some sort of g
Click to expand...
Forget about codes- they're just for making diagnostics faster in the event that a sensor fails or is getting bad voltage. We were taught that if an engine has performance problems, it's highly likely that the fuel system is at fault. Indmar's message when people were on hold included "Did you know that 85% of performance issues are caused by fuel delivery problems?". If you don't have proper fuel pressure, the fuel won't atomize properly and large droplets or stream doesn't burn efficiently. Have you ever seen how well a fine mist ignites far better than dumping liquid on an ignition source? That leaves fuel flow rate and purity- if the gas has water in it, it's not going to burn well and taking a sample is the first step because that's coming from what goes to the engine, regardless of having installed a new separator. I would also take a sample directly from the tank- While the separator does remove water, it will still push through the filter if the tank has a lot of water.

Open the first pdf to read the description of the work I had to do on the boat that had the separator in the photo.

The second pdf shows the whole fuel rail and intake- part 6 is the cap, part 5 is the Shrader valve used for testing (same as a tire valve).

Don't replace any parts until and unless you know something is bad.
 

Attachments

  • Water in gas.jpg
    Water in gas.jpg
    113.2 KB · Views: 111
  • Fuel Water separator service.pdf
    16 KB · Views: 133
  • Fuel Rail and Drain System Bracket.pdf
    114.9 KB · Views: 94
The fuel when separator removed was pristine. So i will try to check the pressure at off and idle and as high an RPM as motor will let me. Report back when complete
 
Superdaveusa said:
The fuel when separator removed was pristine. So i will try to check the pressure at off and idle and as high an RPM as motor will let me. Report back when complete
Click to expand...
If you remove the throttle cable linkage, you should be able to see if it's being restricted- you can do this while the engine is off but if it's lumpy when it runs, I would check the Engine Coolant Temperature sensor- if the resistance is far too low, it will run like crap, if at all.

Is your oil pressure gauge flaky, reads low or jumps around?
 
Ok, ran this am. With key off 0 pressure on fuel rail. Key on 35 idle 35-38 tried to get to 2000 rpm before lope it was 40-42 then went to limp mode. Only ran about 5 mins and temp gauge was at 180+ so i turned it off. Seems like water pump is not right, shouldnt get that high in 5 mins on hose idling. But would that make it go into guardian mode but no horns?
 
Superdaveusa said:
Ok, ran this am. With key off 0 pressure on fuel rail. Key on 35 idle 35-38 tried to get to 2000 rpm before lope it was 40-42 then went to limp mode. Only ran about 5 mins and temp gauge was at 180+ so i turned it off. Seems like water pump is not right, shouldnt get that high in 5 mins on hose idling. But would that make it go into guardian mode but no horns?
Click to expand...
I wouldn't want to say it can't trigger guardian mode- when was the most recent impeller change? I have read comments from people who say it should last for years, but I have changed literally hundreds and would never recommend that a rubber impeller be left in for more than a couple of years, especially in brackish, salt or sandy water.

How long is your hose between the valve and the boat? Typical garden hoses that are 1/2" or 5/8" diameter can't move enough volume to cool an engine, especially if the RPM is high, which shouldn't be done on the hose. I don't know the Mercruiser spec for fuel pressure, but if it's consistent, I think that could be ruled out since the pressure at higher RPM is higher than at lower RPM.

Does your warning horn make noise at any other time? I would test it by disconnecting the oil pressure switch and if the horn doesn't sound, test it and the wire feeding it.
 
Superdaveusa said:
Horn test comes on with key on , then goes off. I have ordered a impeller kit and will get that done.
Click to expand...

When you run the engine on a hose, do you see water coming from the transom soon after starting?

Does your engine have the closed cooling system?
 
Ok Changed impeller and ran in a large tub. Did get return water from exhaust. Again idled fine, when throttle increased it lopes like guardian mode. Also heated up quickly according to temp gauge got to 175 and I shut it down, but the exhaust manifold could still be touched, was very warm, but touchable. Not sure where to go from here.
 
Superdaveusa said:
Ok Changed impeller and ran in a large tub. Did get return water from exhaust. Again idled fine, when throttle increased it lopes like guardian mode. Also heated up quickly according to temp gauge got to 175 and I shut it down, but the exhaust manifold could still be touched, was very warm, but touchable. Not sure where to go from here.
Click to expand...
If you ever changed the impeller and saw that part(s) of one or more vanes had broken off (like in my boat), it's possible that the rubber was sent into the water passage and is lodged in the copper pipe where the short hose from the outdrive and engine connect at the transom.

When I was replacing hoses and other parts on my engine, I used a flexible camera scope to see into the exhaust passages behind the manifold and the output from the manifold because ALL of the vanes on the old impeller had broken off. I then chased the long water supply hose from the transom to the thermostat housing cover and the copper tube where the two hoses connect. These cameras are sold as 'endoscope' and sold on Amazon for about $25, made for Andriod and iPhone (with an adapter).

I think it would be a good idea to verify the operation of the thermostat, too- they don't always work properly, even when new. I used to see impeller pieces stuck in a hole in thermostat housing on ski boats, but those had the water pump on the front of the engine and nothing in the way to stop these pieces moving.
 
Superdaveusa said:
Ok Changed impeller and ran in a large tub. Did get return water from exhaust. Again idled fine, when throttle increased it lopes like guardian mode. Also heated up quickly according to temp gauge got to 175 and I shut it down, but the exhaust manifold could still be touched, was very warm, but touchable. Not sure where to go from here.
Click to expand...
Try your oil pressure switch, it will nerf power to the fuel pump after 1900 rpm, if it detects low oil pressure.

Check actual pressure with a mechanical gauge, and test the oil pressure switch itself.

Do you run rec fuel or auto fuel? You may want to try changing your fuel filter as well.

Does the engine act the same way in neutral, and under a load? Checked timing? How do the plugs look?
 
My 2001 Chris craft launch 25 with 5.7 mercruiser runs great until I keep a consistent speed and RPM for 2-3 min then goes into “LIMP MODE”, I have to bring it to neutral and let sit for 20-30 sec then will run great again, until I do the same (run at constant rpm). The boat will run great when running low rpm’s… I’ve replaced t-stat and have had the yacht club (mechanic) try to figure out the problem…. Anyone else have this issue?
 
Gcowan27 said:
My 2001 Chris craft launch 25 with 5.7 mercruiser runs great until I keep a consistent speed and RPM for 2-3 min then goes into “LIMP MODE”, I have to bring it to neutral and let sit for 20-30 sec then will run great again, until I do the same (run at constant rpm). The boat will run great when running low rpm’s… I’ve replaced t-stat and have had the yacht club (mechanic) try to figure out the problem…. Anyone else have this issue?
Click to expand...
You might want to specify which engine is in the boat. There aren't many problems that will cuase teh RPM to be limited- overheat is one of them, but that cam be caused by a bad raw water pump/impeller, clogged water inlet or if it has one, a filter for fresh water or the ECT (Engine Coolant Temperature) sensor.
 
Gcowan27 said:
My 2001 Chris craft launch 25 with 5.7 mercruiser runs great until I keep a consistent speed and RPM for 2-3 min then goes into “LIMP MODE”, I have to bring it to neutral and let sit for 20-30 sec then will run great again, until I do the same (run at constant rpm). The boat will run great when running low rpm’s… I’ve replaced t-stat and have had the yacht club (mechanic) try to figure out the problem…. Anyone else have this issue?
Click to expand...
Sorry it’s a volva penta 5.7 L GI
 
jimn said:
You might want to specify which engine is in the boat. There aren't many problems that will cuase teh RPM to be limited- overheat is one of them, but that cam be caused by a bad raw water pump/impeller, clogged water inlet or if it has one, a filter for fresh water or the ECT (Engine Coolant Temperature) sensor.
Click to expand...
We sent the ECM to get reprogrammed, new exhaust manifolds, new impeller. Problem got worse after we just replaced the oil pan (makes no sense to me). It’s now smoking, burning oil….
 
Gcowan27 said:
We sent the ECM to get reprogrammed, new exhaust manifolds, new impeller. Problem got worse after we just replaced the oil pan (makes no sense to me). It’s now smoking, burning oil….
Click to expand...
Who decided that the ECM needs to be reprogrammed?

Were the manifolds leaking? Why did you replace the oil pan?

What is the service and use history for this engine? I can't imagine many situations that would require a new oil pan and ECM reprogramming.

Have the compression, fuel pressure been tested and ECT/TPS/MAP been monitored WHILE at typical speeds on the water, or is it being tested on the trailer? If the latter, those tests aren't valid- the engine needs to be under load.
 
1. This is a Mercruiser forum. Maybe you should seek the Volvo Penta forum sponsered by this web site
 
Back
Top