5.7 EFI stalls when warm and shifting into gear

[khe]

I took a look at the IAC valve again and the pictures show it as I just removed it. It is very clean.

I am hesitant to replace the IAC valve as I don't think it is the issue but do not know what is causing the stall condition.

Page 5E-81 of the service manual #17 has an idle air control functional test (2 of 2) states to start the engine, let it warm to operating temperature, record the engine RPM, then put it into base timing mode. A noticeable drop in RPM occurs so the chart then says to exit the base timing mode and the engine speed should return within 75 RPM of the recorded RPM. It does, briefly, then will die. It then states to verify a test light blinks at all four harness terminals (it does). The flow chart then points to a sticky or faulty IAC valve. I have experienced these type of flow charts leading to the wrong conclusion before.

With the scan tool plugged in, it the IAC position value starts off between 12 and 19 when the engine and gradually works its way to 0. Even when the engine stalls, the IAC position is 0 which doesn't seem right but it could be.

It would be nice if there were a method to definitely test the IAC valve so there was no question whether it was good or bad.

 

[alldodge]

Agree
You tested and it passed test, we don't have our hands on it so don't know if we can provide more info

 

[khe]

You tested and it passed test

This is because it briefly returned to within 75 RPM of the initial speed after exiting the set timing mode?

I am at a loss on who I can contact next. Most if not all places in my area won't work on anything older than 2000 model year and those that might have no experience with these engines. I called a place yesterday that works on Mercruisers and he told me he never bought any of the service information or diagnostic equipment for the TBI engines because they used them for such a short time. I believe they used them for longer than what he thought but that's the thing I am running into.

 

[alldodge]

IMO the Mechanic didn't buy it because he's not a "actual" Tech. TBI, MPI all used MEFI's and all use the same connector

 

[muc]

Hi, I haven't forgot you, but I've been very busy and don't have much time to devote to this.
I've been looking for reasons why your engine is commanding zero counts to the IAC, (other then a vacuum leak) and have some questions.
1996 1/2 had a few changes and I need to narrow down what you have.
What fuel system do you have? VST or cool fuel, follow the line that feeds the throttle body and tell me where it goes.
Need to know what ECM you have. Can you get me any numbers printed on it? Also measure the distance between the mounting bolts (center to center) on long side (from one set of wires to the other set of wires) I'm looking for 6 1/2" or 4 3/4".
Also pictures will help. Take the cover and flame arrestor off the throttle body and shoot some from different angles.

 

[khe]

Hi, I haven't forgot you, but I've been very busy and don't have much time to devote to this.
I've been looking for reasons why your engine is commanding zero counts to the IAC, (other then a vacuum leak) and have some questions.
1996 1/2 had a few changes and I need to narrow down what you have.
What fuel system do you have? VST or cool fuel, follow the line that feeds the throttle body and tell me where it goes.
Need to know what ECM you have. Can you get me any numbers printed on it? Also measure the distance between the mounting bolts (center to center) on long side (from one set of wires to the other set of wires) I'm looking for 6 1/2" or 4 3/4".
Also pictures will help. Take the cover and flame arrestor off the throttle body and shoot some from different angles.

I have the cool fuel system. The ECM is MEFI 1 in what looks like a MEFI 2 case.. The bolt to bolt dimension is 4-3/4". There is a label 9855 on the top edge of the ECM.

I checked a friends boat that has the 5.7 TBI engine and his IAC count was also 0 at idle. One thing I did notice is his manifold pressure is 11.1-12.9 in hg vs. mine is 9.4-9.5. I'm not sure if that indicates an issue.

Some have suggested the lower shift cable. I checked the freeplay and it was .432" which meets the 9/16" max. specification in the shop manual. I noticed on the lower shift cable is the dimension between the center of the barrel and the eye of the cable is less than 6" but there is not a way to adjust the cable as the brass barrel is staked to the cable. This is strange since the boat did not have a stalling issue prior to the engine failure.

 

[muc]

I have the cool fuel system. The ECM is MEFI 1 in what looks like a MEFI 2 case.. The bolt to bolt dimension is 4-3/4". There is a label 9855 on the top edge of the ECM.

I checked a friends boat that has the 5.7 TBI engine and his IAC count was also 0 at idle. One thing I did notice is his manifold pressure is 11.1-12.9 in hg vs. mine is 9.4-9.5. I'm not sure if that indicates an issue.

Some have suggested the lower shift cable. I checked the freeplay and it was .432" which meets the 9/16" max. specification in the shop manual. I noticed on the lower shift cable is the dimension between the center of the barrel and the eye of the cable is less than 6" but there is not a way to adjust the cable as the brass barrel is staked to the cable. This is strange since the boat did not have a stalling issue prior to the engine failure.

Yes, the bolt holes say MEFI 2 case. Are you sure it’s a MEFI 1 program in it? Do you need to manually advance the throttle when you put it in service mode?

The 0 IAC count kind of surprises me. But I’m one of those techs that didn’t work on many of the TBIs. When I did do diagnostic on them, a zero count usually would lead to finding someone had messed with the throttle stop or a clogged filter on the coolfuel 2 module causing high fuel pressure. Have you tried running this engine with the throttle cable disconnected from the throttle body? Sometimes too much pressure or not enough can cause issues.

The 9855 doesn’t show up in my class notes, the calibration numbers that I have all start with 120. I’m guessing that the ECM would have to be unbolted to see them.

With the engine running at 1500 RPM what happens when you manually trigger the shift Interrupt? MEFI 1 will kill the spark MEFI 2 will reduce IAC count and retard ignition timing.

I’m not sure if spraying carb cleaner into the crankcase is a valid test. I’ve never tried it because carb cleaner contaminants engine oil. Your engine shouldn’t have a PVC system so you should have a positive pressure at the breather hose going to the flame arrestor. You can hold a piece of thin plastic bag by it and make sure there isn’t any vacuum.

It is pretty common to have some issues after an engine replacement. Usually due to something during the replacement but sometimes it’s just a coincidence.

 

[khe]

Yes, the bolt holes say MEFI 2 case. Are you sure it’s a MEFI 1 program in it? Do you need to manually advance the throttle when you put it in service mode?

The 0 IAC count kind of surprises me. But I’m one of those techs that didn’t work on many of the TBIs. When I did do diagnostic on them, a zero count usually would lead to finding someone had messed with the throttle stop or a clogged filter on the coolfuel 2 module causing high fuel pressure. Have you tried running this engine with the throttle cable disconnected from the throttle body? Sometimes too much pressure or not enough can cause issues.

The 9855 doesn’t show up in my class notes, the calibration numbers that I have all start with 120. I’m guessing that the ECM would have to be unbolted to see them.

With the engine running at 1500 RPM what happens when you manually trigger the shift Interrupt? MEFI 1 will kill the spark MEFI 2 will reduce IAC count and retard ignition timing.

I’m not sure if spraying carb cleaner into the crankcase is a valid test. I’ve never tried it because carb cleaner contaminants engine oil. Your engine shouldn’t have a PVC system so you should have a positive pressure at the breather hose going to the flame arrestor. You can hold a piece of thin plastic bag by it and make sure there isn’t any vacuum.

It is pretty common to have some issues after an engine replacement. Usually due to something during the replacement but sometimes it’s just a coincidence.

When I plug in the scan tool, it displays MEFI 1 detected. I need to manually advance the throttle while in service mode to check the timing. Depressing the shift interrupt switch will kill the engine.

I will check the two hoses that connect to the flame arrester with a plastic bag per your suggestion. I recall running the engine with those hoses disconnected I could see oil vapor coming out of the hose. There is not a PCV system on this engine.

Is there a maximum force to extend/retract the lower shift cable with it disconnected? I could work it back and forth with my fingers but don't if that is enough to cause the issue.

 

[muc]

When I plug in the scan tool, it displays MEFI 1 detected. I need to manually advance the throttle while in service mode to check the timing. Depressing the shift interrupt switch will kill the engine.

I will check the two hoses that connect to the flame arrester with a plastic bag per your suggestion. I recall running the engine with those hoses disconnected I could see oil vapor coming out of the hose. There is not a PCV system on this engine.

Is there a maximum force to extend/retract the lower shift cable with it disconnected? I could work it back and forth with my fingers but don't if that is enough to cause the issue.

Ok, MEFI 1 software.

When you test those hoses, plug one and use the other for testing. Should be a constant flow of air. Plastic bag shouldn’t flutter.

No published numbers on inner transom cable that I’m aware of. It’s more of a “feel” thing. That you still have a staked brass barrel tells me that’s the original cable. Surprised you haven’t had to replace it yet, their life is usually 10-12 years tops. The fact that you no longer have the 6” tells me that it’s worn. If you want to rule out the shift interrupt, this is my recommendation. Boat MUST be in the water, tied 4 ways in a slip or strapped to the trailer. Because you shouldn’t be able to shift back to neutral with the engine running. Disconnect the shift interrupt switch and install the bravo bypass plug or jumper the two white wires. Now you can shift into forward and see if the problem goes away.

If you want to attempt adjusting the cable, it is possible to drill the stake. Instructions on how to do this are in the drive service manual. I’ve done it once and found it’s not worth it, ended up replacing the cable anyway.

 

[khe]

I replaced the lower shift cable and the engine is no longer stalling when coming out of gear. Once the engine is warmed up, when I am in just in gear at 600-625 RPM, the engine will randomly stall. I replaced the IAC motor a couple of weeks ago and that did not solve the issue.

What are the inputs to the ECM to tell it to increase the engine RPM? It seems like that is the next thing to look at.

I checked the hoses from the valve cover to the flame arrester yesterday while out on the water and there was no vacuum in those hoses. A piece of plastic bag held next to the end while plugging the opposite hose with my thumb would be pushed away from the open hose (no vacuum).

 

[alldodge]

Scanned back thru the thread and did not see where fuel pressure was tested, was it or did I miss it?

 

[khe]

I tested the fuel pressure - the spec. was 30 psi and it held steady at 32 psi even when the engine stalled.

 

[dubs283]

The ecm doesn't increase the rpm of the engine, that happens naturally

The ecm controls the amount of fuel the engine receives by adjusting the pulse width (amount of time the fuel injectors are open/passing fuel). The ecm uses the sensor parameters from the map, tps, ect, rpm (from the ignition sensor or the icm depending on ignition system type), iat, etc...to determine pulse width and timing advance

The ecm doesn't know the value of the fuel pressure, it just assumes it is within spec which according to you is correct. If the fuel pressure is correct and the engine mechanical is sound the engine should run well.

It is important the main harness ground, main battery ground and the ignition sensor ground (if equipped) are attached to the same ground stud at the flywheel cover, clean and tight

 

[khe]

The ecm doesn't increase the rpm of the engine, that happens naturally

The ecm controls the amount of fuel the engine receives by adjusting the pulse width (amount of time the fuel injectors are open/passing fuel). The ecm uses the sensor parameters from the map, tps, ect, rpm (from the ignition sensor or the icm depending on ignition system type), iat, etc...to determine pulse width and timing advance

The ecm doesn't know the value of the fuel pressure, it just assumes it is within spec which according to you is correct. If the fuel pressure is correct and the engine mechanical is sound the engine should run well.

It is important the main harness ground, main battery ground and the ignition sensor ground (if equipped) are attached to the same ground stud at the flywheel cover, clean and tight

I attached the ground wires in the same order they were removed when I pulled the old engine and I didn't notice any corrosion on the studs or terminals.

The engine runs fine most of the time. It seems like when it is just in gear and running around 600-625 RPM it will occasionally stall out. It seems that the IAC motor should retract to let more air around the throttle plate when the RPM drops below 600.

 

[khe]

It's been a long time but since I am the original poster, I wanted provide an update.

The IAC counts are in the 40s when the engine is first started up and they gradually decrement to zero as the engine warm up. With the engine in gear at idle, the RPMs will go below 600 and the system will attempt to increase the engine speed. Sometimes, it is successful but many times it isn't and that's when the engine stalls.

While on vacation, I checked a friends boat that has the same engine package and no stalling issue. His IAC counts were in the low 30s and gradually decremented to zero but then increased to maintain the idle speed.

Up until a couple of days ago, it wouldn't set any trouble codes but then I got a break. It set code 33 which is "MAP sensor fault". I checked the MAP system per the shop manual flowchart and it led me to "Replace MAP sensor". Knowing my luck, I figured I'd better do some additional testing to make sure I didn't replace a good $50.00 MAP sensor. My Cadillac Fleetwood has the same MAP sensor so I decided to install the Cadillac's sensor on the boat and see what happened. The Cadillac uses a vacuum hose to connect the sensor while the boat has a silicone adapter and the sensor presses into a bore near the throttle body. When I removed the boat's sensor, I discovered the silicone bushing was all torn up and the lower half was separated from the upper half. A 1/16" portion of the 3/8" length of the bushing was the only complete portion. the rest was separated or cracked.

I transferred the intact half of the bushing to the car's sensor, installed it and ran the boat on hose muffs. It did not stall once warmed up but it really needs to be in the water for an accurate test. There was a vacuum leak at the MAP sensor and I could get the engine to stumble if I sprayed brake cleaner on the underside. I could also hear the vacuum leak with a mechanic's stethoscope.

I can't say for sure if the vacuum leak was there prior to me swapping the sensor but considering the condition of the silicone bushing, it could have been. I have never messed with the MAP sensor but the previous owner of the boat may have. It is just strange that the problem occurred after the engine replacement.

I have to order the silicone bushing - what a pricey part for what it is... and see how the engine performs with the original MAP sensor. Since the car's sensor can be removed in about 30 seconds, I plan to take it with me the next time and if the engine gets a stalling fit, I'll swap out the sensor to see if the problem goes away. If it does, I'll buy a MAP sensor.

 

[khe]

The new adapter bushing arrived yesterday. I installed it and took the boat out to test it. I brought the MAP sensor from the Cadillac with me also.

The vacuum leak was gone but the stalling when warm persisted so I swapped in the sensor from the Cadillac. There was no improvement - the engine kept stalling in neutral when warmed up and the IAC counts were still 0 at idle.

The system attempts to maintain the idle speed but it seems that it doesn't react quickly enough before the engine stalls.

I am really lost since I was confident I found the issue when I discovered the damaged adapter bushing on the MAP sensor.

 

[alldodge]

Does the 5V circuit show exactly 5V (CKT 416)?
Has the MAP and TPS been tested per manual?

 

[dubs283]

Just read through the broad strokes on this thread and you've done a lot of proper troubleshooting and there's some really good info provided here (thanks, muc)

I get you're ready to hang it up but being a new/reman long block its wise to ensure the valves are adjusted properly and at this point a compression test on a warm engine is in order.

Can't recall seeing any WOT performance numbers posted here but I wouldn't rule out engine mechanical yet. I've had more than one reman block delivered that has not been properly set up for install.

If all checks out mechanically I'd try base timing at 10 btdc and verify the advance isn't higher than 32 total

The wonky iac behavior is concerning but the numbers you've posted show it is indeed operating, keep in mind the ecm tells it to behave accordingly based on inputs received from other sensors. A mechanically unsound engine will create sensor readings that while not necessarily out of spec but just enough to cause issues with no active faults.

 

[nola mike]

Does the Rinda allow you to see real time injector PWM? As the RPMs drop, ECM should be calling for more fuel as well as more air.

 

[khe]

Does the 5V circuit show exactly 5V (CKT 416)?
Has the MAP and TPS been tested per manual?

I tested the MAP sensor per the manual when I was investigating the code 33. I don't remember the exact voltage but it was very close to 5VDC.

I have not tested the TPS yet.