5.7 EFI stalls when warm and shifting into gear

[khe]

Engine serial no. 0K007751 350 TBI engine. I recently replaced the engine due to zero compression in cylinders 3 & 5 due to fire-slotting of the block and head.

I have the base timing set at 8° per the service manual. When I leave the dock, it is all fine. The problem occurs when the engine is warm and coming into the dock. When I shift into neutral and then back into gear, the engine stalls.

When the issue occurs, I notice the IAC parameters on the scan tool are:
IAC position: 19, 29
Base IAC Position: 19, 29
IAC follower: 0, 0

This was two data points. Shouldn't the IAC follower reading be close to the IAC position reading? Is the IAC position what is commanded by the ECM and the follower is the feedback parameter to let the ECM know the IAC motor moved to the position commanded by the ECM?

When the engine is cold and or just gets up to operating temperature, I noticed the IAC follower tracks the IAC position closely.

I didn't have this issue before the engine replacement so to me it seems like a coincidence that it occurred now. Do the scan tool readings indicate a flaky IAC motor? If not, what should I check next?

 

[khe]

I double checked that the timing was 8° in base timing mode this evening and once I took it out of the set timing mode, after the idle stabilized, the engine died but would restart with a slight amount of throttle in neutral. This was while running on the trailer with hose muffs.

I restarted the engine and then unplugged the IAC motor. Testing each of the four terminals on the harness, the test light blinked while on each of the four terminals.

The IAC Functional test in the shop manual states the engine should gradually return to within 75 RPM of the speed before entering service mode. It does briefly, then dies. This might be interpreted as a faulty or sticky IAC motor but it seems strange that I did not have this issue before the engine replacement.

 

[dubs283]

Is the reference line/hose seated properly on the map sensor and intake?

 

[khe]

Is the reference line/hose seated properly on the map sensor and intake?

The MAP sensor plugs into a port on the throttle body - there's no hose/tube that I know of. I can also see the MAP sensor readings change with throttle position/RPM.

 

[alldodge]

I'm thinking a vacuum leak, IAC should be closer to 40

 

[khe]

I'm thinking a vacuum leak, IAC should be closer to 40

The only hose that resembles a vacuum hose is the one that is from the cool fuel module to the flame arrester and I don't think that is a vacuum hose.

I did remove the oil fill cap and spray a shot of carb. cleaner inside the valve cover and there was no change in engine RPM.

The shop manual states the IAC values at 600-700 RPM (idle, engine warmed to operating temperature) should be 0-40 and at idle, all three parameters are at 0 (IAC position, Base IAC position and IAC follower).

One thing I did notice is the injector pulse width should be 2-3 milliseconds per the manual and my reading was 1.4 - 1.5 milliseconds. The fuel consumption at idle should be 1-2 gallons per hour and my reading was 0.73-0.74 gallons per hour. I tend to think this isn't an issue as the boat runs fine at cruising speed and above 600 RPM. I would think if it were a fuel delivery issue, it would run lousy at all speeds.

 

[alldodge]

I understand the manual, I'm thinking intake leak
Could be the IAC is just not responding quick enough, but most times I'll see the counts higher. With it down in the lower numbers, it's almost closed. IAC can go to 100

 

[khe]

I understand the manual, I'm thinking intake leak
Could be the IAC is just not responding quick enough, but most times I'll see the counts higher. With it down in the lower numbers, it's almost closed. IAC can go to 100

Where would I check for a vacuum leak? Where the intake mates with the cylinder heads?

The three IAC parameters on the Rinda Techmate Pro are IAC position, IAC Base Position and IAC Follower. Are those defined as: IAC commanded position from ECM, IAC Minimum count, and actual IAC position respectively?

 

[alldodge]

Yes, spray intake and base of TB

Numbers track each other pretty close to each other.

I'm no expert just what I'm use to seeing, as before might try cleaning IAC but not chemicals

 

[khe]

Yes, spray intake and base of TB

Numbers track each other pretty close to each other.

I'm no expert just what I'm use to seeing, as before might try cleaning IAC but not chemicals

I'll take a look this evening if it is not raining. I had the IAC out last night and the plunger head that contacts the port in the throttle body was spotless - no buildup whatsoever. I'm not sure on the plunger shaft though.

When the engine is at idle, all three IAC parameters on the scan tool are 0 which does not make sense to me. I am wondering what other sensor would provide input to the ECM for it to request a certain IAC valve position? The throttle position sensor? MAP sensor? Water temperature sensor? The water temp sensor reading on the scan tool correlates with the temperature gage on the dash. The MAP reading is 1.15 - 1.17 volts at idle which is within specification according to the service manual. The throttle position sensor voltage is 0.49V at idle and the spec. is 0.4-0.8 volts. The corresponding throttle angle is 0.3 and the spec is 0-100.

 

[alldodge]

Maybe @muc has an idea

 

[khe]

There are no vacuum leaks - I sprayed carb cleaner along the cylinder to intake manifold interfaces on both sides along with the throttle body base and there was no change in idle.

I decided to take a gamble and purchase and install the IAC that Advance Auto Parts had in stock but it was different enough that the screws would not line up with the tapped holes.

 

[khe]

One thing I noticed is when I rev it up in neutral and then put the shift lever in neutral, the IAC Follower parameter decrements at twice the rate of the IAC Position parameter on the scan tool until both reach zero.

I assume the zero count is the plunger is seated against the throttle body. Is there another passage to provide minimum air to the mix or is it strictly through the IAC port?

 

[alldodge]

The TB butterfly are factory set and if there is a gap or not I'm don't know. The IAC is what gives motor air otherwise

 

[muc]

Something to keep in mind with this system, there is a lot that the ECM doesn’t know. Fuel pressure is the biggest. With symptoms like you’re having with this engine, one of the first things to check is fuel pressure. Fuel pressure can and will only affect just at certain RPMs.

Next is IAC position, The ECM only knows what it has commanded it has no idea what it actually is.

A quick explanation of the 3 scan tool #s you see.

IAC position—this is what the ECM is commanding based on the feedback it’s getting from RPMs, MAP, TPS and temp. The ECM has tables in its program that it uses to calculate this #.

IAC base—this is a learned # that has been stored in RAM and is lost at every key off.

IAC follower—this is only used during deceleration mode. It provides additional air when the throttle is rapidly closed to the idle position to prevent the engine from dying. So stop looking at IAC follower, it doesn’t have any bearing on your symptoms.



Agree with @alldodge, looks like you might have extra air getting into the engine that the ECM doesn’t know about.



Here is what I see with the limited information you have posted.

First and foremost--- “I recently replaced the engine due to zero compression in cylinders 3 & 5 due to fire-slotting of the block and head”. If this is still the 24’ Sea Ray with a 1.62:1 Alpha drive? I don’t see anything you have identified that cased this failure. This is a rare failure that is almost always caused by operator abuse. You have a V8 engine with a V6 drive; this usually means Sea Ray knew this boat was underpowered from the factory. Or was meant to be sold to a customer at higher elevation. Guessing under powered. So it follows that this probably wasn’t propped right for how the boat is used, maybe pulling a tube? And that the operator continued to run the boat with a blown head gasket. So once you get past this current issue ---- check that the boat is propped correctly for how you use the boat and quit using it when it isn’t running right. This is a very dumb ECM and can’t correct for this type of abuse.



Things I would look at;

Fuel pressure

Idle screw – This throttle body will have a screw that if you don’t know better you would think it’s for adjusting the idle (it isn’t) luckily Merc usually sprays a bunch of paint on this screw so you will be able to see if someone moved it. Check it because this maybe the air leak.

Look at both the scan tool and the shift interrupt switch when you’re shifting into gear (in the water like when your problem happens) and make sure it isn’t hanging up and causing the engine to die.

Watch the fuel spray out of your injectors both when the engine is running normal and when the problem happens. Hint: connect your timing light and shine it at the fuel spray, it will help see what’s going on.



My advice to remember: With this ECM the scan tool will mostly tell what’s right, not so much what’s wrong. Take those ECM tables in the manual with a grain of salt. They are kind of an average, not gospel. They can be different for different engines. In the end, this is really closer to a carb motor then EFI. ------ spark at the right time, enough compression, and the right amount of fuel. ----- still need these 3 things and a scan tool only helps a little.

 

[khe]

Something to keep in mind with this system, there is a lot that the ECM doesn’t know. Fuel pressure is the biggest. With symptoms like you’re having with this engine, one of the first things to check is fuel pressure. Fuel pressure can and will only affect just at certain RPMs.

Next is IAC position, The ECM only knows what it has commanded it has no idea what it actually is.

A quick explanation of the 3 scan tool #s you see.

IAC position—this is what the ECM is commanding based on the feedback it’s getting from RPMs, MAP, TPS and temp. The ECM has tables in its program that it uses to calculate this #.

IAC base—this is a learned # that has been stored in RAM and is lost at every key off.

IAC follower—this is only used during deceleration mode. It provides additional air when the throttle is rapidly closed to the idle position to prevent the engine from dying. So stop looking at IAC follower, it doesn’t have any bearing on your symptoms.



Agree with @alldodge, looks like you might have extra air getting into the engine that the ECM doesn’t know about.



Here is what I see with the limited information you have posted.

First and foremost--- “I recently replaced the engine due to zero compression in cylinders 3 & 5 due to fire-slotting of the block and head”. If this is still the 24’ Sea Ray with a 1.62:1 Alpha drive? I don’t see anything you have identified that cased this failure. This is a rare failure that is almost always caused by operator abuse. You have a V8 engine with a V6 drive; this usually means Sea Ray knew this boat was underpowered from the factory. Or was meant to be sold to a customer at higher elevation. Guessing under powered. So it follows that this probably wasn’t propped right for how the boat is used, maybe pulling a tube? And that the operator continued to run the boat with a blown head gasket. So once you get past this current issue ---- check that the boat is propped correctly for how you use the boat and quit using it when it isn’t running right. This is a very dumb ECM and can’t correct for this type of abuse.



Things I would look at;

Fuel pressure

Idle screw – This throttle body will have a screw that if you don’t know better you would think it’s for adjusting the idle (it isn’t) luckily Merc usually sprays a bunch of paint on this screw so you will be able to see if someone moved it. Check it because this maybe the air leak.

Look at both the scan tool and the shift interrupt switch when you’re shifting into gear (in the water like when your problem happens) and make sure it isn’t hanging up and causing the engine to die.

Watch the fuel spray out of your injectors both when the engine is running normal and when the problem happens. Hint: connect your timing light and shine it at the fuel spray, it will help see what’s going on.



My advice to remember: With this ECM the scan tool will mostly tell what’s right, not so much what’s wrong. Take those ECM tables in the manual with a grain of salt. They are kind of an average, not gospel. They can be different for different engines. In the end, this is really closer to a carb motor then EFI. ------ spark at the right time, enough compression, and the right amount of fuel. ----- still need these 3 things and a scan tool only helps a little.

Thank you for the explanation of the IAC parameters.

This is the same 24' Sea Ray and I have not been able to identify the cause of the failure which really bothers me. When I thought it was just a bad head gasket, I was going to have a machine shop resurface the valves, etc. They were recommended by a local marina that sends all their engine rebuilds to. When I spoke to them, they said they see this on small block Chevy marine engines due to the exhaust ports on #3 and #5 and #4 and #6 being next to each other.

Once I saw the block and head were fire slotted, I started shopping for a remanufactured long block.

I have owned this boat for nine years and the previous two owners were within 30 miles of my location which rules out the boat was made for a different elevation. I don't know what the drive ratio is. The base timing is set to 8° BTDC.

In the years I've owned it, I haven't abused it - I cruse between 3200 and 3400 RPM which is between 23 and 27 MPH. Occasional wide open throttle but not very often. I believe the RPMs max out around 4400 RPM. I'm not sure what type of abuse may have caused the failure.

I did not have the stalling issue with the original engine (before the failure). It only appeared once I transferred the necessary components to the remanufactured long block and installed it in the boat. When running the engine on hose muffs in neutral, it will begin its stalling routine as soon as the temperature gets around 160-170°. If I recall from last evening, the IAC position was 0 when the problem occurred. The IAC is clean - no carbon buildup and there is no buildup in the TBI housing. The throttle plates and bores are clean also.

There is not a port on the fuel supply line to hook up my fuel pressure tester gage - Autozone has a fuel pressure tester kit that has a GM TBI adapter in their loan a tool program so I'll pick that up so I can test the fuel pressure. I looked at the "idle stop screw" last night - no one has touched that as there is a plug installed to prevent someone from messing with it and there are no marks or signs of tampering on the plug.

I have sprayed carb cleaner along the interfaces between the cylinder heads and the throttle body base and there is no change in engine speed. I have also given it a shot of carb. cleaner in the oil fill hole in the valve cover and the engine did not change speed. The only line that resembles a vacuum line is the line that runs from the cool fuel module to the flame arrestor but because it is open and not connected to the throttle body or intake manifold it can't be a vacuum hose. Where else would I look for a possible vacuum leak?

I can watch the injector spray pattern with the timing light and see what they do when the engine dies.

I wonder if it is a flakey IAC valve but again, I did not have the stalling issue on the original engine.

 

[khe]

Autozone's "GM TBI adapter" in their fuel pressure tester will not work with the Mercruiser lines. The end that threads into the throttle body has the wrong type of fitting. I would up using a different adapter from their kit, a length of 3/8" hose, a couple of short pieces of 3/8" brake line and a brake line coupler to patch in a schrader valve.

I verified the fuel pressure holds 32 psi which meets the 30 psi minimum spec. in the shop manual. When it stalled, the pressure held at 32 psi. The injectors kept spraying even when the RPMs started to drop and when the engine died, the injectors turned off. It was not a case where the injectors stopped first and then the engine died.

Since I had the timing light hooked up, I checked the base timing and it was slightly greater than 8° so I adjusted it to put it right at 8° and started the engine. I couldn't get it to stall in neutral after that.

I think the next step is to get it out on the water and see how it performs. That's when it will probably resume its stalling routine when I come into the dock...

 

[Scott06]

Thank you for the explanation of the IAC parameters.

This is the same 24' Sea Ray and I have not been able to identify the cause of the failure which really bothers me. When I thought it was just a bad head gasket, I was going to have a machine shop resurface the valves, etc. They were recommended by a local marina that sends all their engine rebuilds to. When I spoke to them, they said they see this on small block Chevy marine engines due to the exhaust ports on #3 and #5 and #4 and #6 being next to each other.

Once I saw the block and head were fire slotted, I started shopping for a remanufactured long block.

I have owned this boat for nine years and the previous two owners were within 30 miles of my location which rules out the boat was made for a different elevation. I don't know what the drive ratio is. The base timing is set to 8° BTDC.

In the years I've owned it, I haven't abused it - I cruse between 3200 and 3400 RPM which is between 23 and 27 MPH. Occasional wide open throttle but not very often. I believe the RPMs max out around 4400 RPM. I'm not sure what type of abuse may have caused the failure.

I did not have the stalling issue with the original engine (before the failure). It only appeared once I transferred the necessary components to the remanufactured long block and installed it in the boat. When running the engine on hose muffs in neutral, it will begin its stalling routine as soon as the temperature gets around 160-170°. If I recall from last evening, the IAC position was 0 when the problem occurred. The IAC is clean - no carbon buildup and there is no buildup in the TBI housing. The throttle plates and bores are clean also.

There is not a port on the fuel supply line to hook up my fuel pressure tester gage - Autozone has a fuel pressure tester kit that has a GM TBI adapter in their loan a tool program so I'll pick that up so I can test the fuel pressure. I looked at the "idle stop screw" last night - no one has touched that as there is a plug installed to prevent someone from messing with it and there are no marks or signs of tampering on the plug.

I have sprayed carb cleaner along the interfaces between the cylinder heads and the throttle body base and there is no change in engine speed. I have also given it a shot of carb. cleaner in the oil fill hole in the valve cover and the engine did not change speed. The only line that resembles a vacuum line is the line that runs from the cool fuel module to the flame arrestor but because it is open and not connected to the throttle body or intake manifold it can't be a vacuum hose. Where else would I look for a possible vacuum leak?

I can watch the injector spray pattern with the timing light and see what they do when the engine dies.

I wonder if it is a flakey IAC valve but again, I did not have the stalling issue on the original engine.

I think what he was getting at - If it maxed out at 4400 rpm just means that this set up was over propped a little and would have been at some points lugging the engine which can lead to detonation and higher exhaust gas temps being under max load a lot due to over pitch.

Would suggest going down in pitch 2” to get rpm up around 4800 or so. Not that u have to run it at 4800 just the pitch, drive ratio, engine and hull combo has enough grunt to allow it.

People think having a lower max rpm is easier on an engine but in a boat that is under load at all times this is infact harder on the engine

 

[alldodge]

You can either get a Merc adapter (91-806901) or can remove item 3 (plug) and attach gauge there

https://www.mercruiserparts.com/bam/subassembly/31880/2338/130

 

[khe]

It stalled when I left the dock this afternoon - when I shifted from reverse to neutral prior to shifting to forward. It's never done that before - it usually waits until it is warmed up...

Once it warmed up to temperature, I couldn't get it to stall for quite some time, then it started to stall when I shifted into forward from neutral. Several times, I noticed the tach dropping below 500 RPM - sometimes it would recover, other times it would stall.

I am starting to think the IAC valve is "lazy" and not able to keep up with the position request from the ECM. Sometimes, it keeps up but other times, a lag can be seen on the tach and that's usually when it stalls.