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4.3 MPI EFI Stalls on idle/when shifting out of gear

E

eelstone

New member
I need help with my MerCruiser 2003 4.3 MPI CCS with an Alpha One Gen 2 drive that is driving me crazy.

Since buying the boat 3 years ago it has occasionally stalled when going from forward to neutral or neutral to reverse. It doesn’t feel like it is the drive that cause the stall rater that the rpm dips very low when going out of gear which leads to a stall. It also stalls on idle but less common. In the beginning it stalled just a few times every season but it has gotten progressively worse with stalls every single trip this season. On any higher rpms than idle the engine runs perfectly fine and it also starts right up after a stall.

I have changed and replaced:

IAC-valve
IAC muffler
Fuel filter
Fuel pump
Fuel regulator
Spark plugs

All of this has resulted in it running really well once in gear but the stalling when maneuvering at low speed persists, which is when you least need a stall:)

Any ideas on what could be wrong or where to go from here?
 
Your lower shift cable is most likely binding causing the shift interuptor to retard the timing when it shouldn't.
 
Before you jump to a cable issue

Deacribe in very careful detail how you shift.

when shifting a mercruiser alpha, you shift firmly and quickly both in and out of gear. If you shift out of gear to slowly you can stall the engine.

If you understand and are shifting correctly then you can review shift cable adjustment or short cable failure/replacement.
 
kghost said:
Before you jump to a cable issue

Deacribe in very careful detail how you shift.

when shifting a mercruiser alpha, you shift firmly and quickly both in and out of gear. If you shift out of gear to slowly you can stall the engine.

If you understand and are shifting correctly then you can review shift cable adjustment or short cable failure/replacement.
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I have been driving boats my whole life and some experience working on engines but I am new to MerCruiser.

I shift firmly in and out to not let the gears slip, as you say if you do shift too slowly it will let you know by making noises. I perceive the shift lever to have a lot of play before going in and out of gear and most people driving the boat comment how much force you need to put on the shift lever.

My technique to maneuver in the marina is to go into gear and up in throttle quickly to avoid stalling but you need to go so high to avoid stalling that maneuvering becomes near impossible.
 
eelstone said:
Ahh could it be that easy? The shift lever has always been a bit sketchy. What’s the easiest way to resolve the binding?
Click to expand...

If it is the lower cable, the only cure is replacement & then complete proper adjustment.

The system is supposed to actuate when shifting out of gear only. It depresses the interuptor switch which causes the timing to go retarded to base timing, thus slowing the idle. (Early models literally turned the ignition off, causing a misfire). This reduces the force on the shift clutch & it slips out of gear. Tension is relieved, switch returns to neutral position & idle recovers. If cable binds, switch remains actuated too long or even continuosly.

If/when the cable binds it causes the same situation except while going into gear also.

Now I'm not telling you to rip your drive off & tear the cable out. Troubleshoot 1st.
 
Droid said:
If it is the lower cable, the only cure is replacement & then complete proper adjustment.

The system is supposed to actuate when shifting out of gear only. It depresses the interuptor switch which causes the timing to go retarded to base timing, thus slowing the idle. (Early models literally turned the ignition off, causing a misfire). This reduces the force on the shift clutch & it slips out of gear. Tension is relieved, switch returns to neutral position & idle recovers. If cable binds, switch remains actuated too long or even continuosly.

If/when the cable binds it causes the same situation except while going into gear also.

Now I'm not telling you to rip your drive off & tear the cable out. Troubleshoot 1st.
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Thanks! The drive is coming off either way this winter for maintenance. Any trick to troubleshooting? Read somewhere to disconnect the upper cable and try to shift by hand?
 
The drive doesn't need to come off to T/S. T/S is easy if you're familiar with the system. Explaining it in writing is a bit more difficult.
 
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Droid said:
The drive doesn't need to come off to T/S. T/S is easy if you're familiar with the system. Explaining it in writing is a bit more difficult.
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I was down to the boat today to try to figure out a good way to diagnose if it really is the lower cable binding without any luck. The plunger type switch engages when shifting but really difficult to tell if it is touched when the engine dies.

Anyone able to give a hint to what I should be looking for?
 
OM631XXX

I have analogue gauges which are a little hard to read, it idles strong at something like 750-ish rpm. I’m currently unable to get it to idle in gear, the lowest I can go in gear without stall is 1100. A few weeks ago it would idle fine in gear once you’ve shifted but it has gradually gotten worse.
 
Motor
HVS ignition

Need a scanner but without that, measure voltage on gray wire at either TPS, MAP or water pressure sensor. Looking for 5V reference to be at 5V

Measure voltage on IAC and TPS with motor idling, not the gray wire reference but the sensor output voltage

Fuel pressure should be 43 psi with vacuum line removed

Remove IAC and look inside, when key is turned ON does valve move in and out?

My motor serial numbers are
3B384246 and 3B268335
 
AllDodge said:
Motor
HVS ignition

Need a scanner but without that, measure voltage on gray wire at either TPS, MAP or water pressure sensor. Looking for 5V reference to be at 5V

Measure voltage on IAC and TPS with motor idling, not the gray wire reference but the sensor output voltage

Fuel pressure should be 43 psi with vacuum line removed

Remove IAC and look inside, when key is turned ON does valve move in and out?

My motor serial numbers are
3B384246 and 3B268335
Click to expand...
Awesome, thank you for taking the time!

I can borrow/rent a TechMate pro scanner, it will take me like a week or two to fix that though. I get that the scanner would indicate faulty sensors, but would it help rule out a sticky shift cable as well?
 
eelstone said:
Awesome, thank you for taking the time!

I can borrow/rent a TechMate pro scanner, it will take me like a week or two to fix that though. I get that the scanner would indicate faulty sensors, but would it help rule out a sticky shift cable as well?
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Your first post was leaning me to think it's a mis-adjusted shift interruptor, but your comment

I’m currently unable to get it to idle in gear, the lowest I can go in gear without stall is 1100
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Has me thinking it's not the cable or the interrupter. Thinking it's a low reference voltage or a sensor. The issue gets multiplied by replacing things that were most likely not bad, and therefore can induce other problems now. Always best to test first before replacing anything

The scanner will provide most all the info needed except fuel pressure

Were all the parts replaced OEM or after market?
 
AllDodge said:
Your first post was leaning me to think it's a mis-adjusted shift interruptor, but your comment


Has me thinking it's not the cable or the interrupter. Thinking it's a low reference voltage or a sensor. The issue gets multiplied by replacing things that were most likely not bad, and therefore can induce other problems now. Always best to test first before replacing anything

The scanner will provide most all the info needed except fuel pressure

Were all the parts replaced OEM or after market?
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You live and you learn…

Yeah that is why I initially was skeptical to a drive issue as well. I just recently learnt I can get a hold of scanner, had I known that from the beginning I might have started in that end.

The progressive nature of these issue over several seasons seem unaffected by the work I have done so far this season.

IAC, got a cheap Chinese one, switched it out without effect but is now back on the original OEM one. Spark plugs OEM. Old fuel regulator was corroded, got a Recmar one which I think is ok quality. Fuel pump, got a cheap one now switched back to the original. All work done according to Merc Service Manual #32.

I’ll get the scanner and go from there, really grateful for all help so far - thank you!
 
Oh since you have the HVS distributor I would suggest replacing that with rotor. There are hundreds of threads were the cap looks great but goes bad. If it isn't the problem, keep old one in the boat because they can go out without warning
 
An update after I have run the diagnostics.

I get the following errors if I run the engine without stalling it i.e. just idle:

94 Pitot pressure low
75 Fuel level 1 circuit high
119 Steering Circuit low
104 Lake/sea Temp circuit high
130 Trim sensor Circuit high

I think these are unrelated to my issue.

However when I run the engine, in gear at idle, leading to a stall I also get:

193 Shift anticipate fault

Note I get it to stall when I reduce throttle in gear close to idle, not necessarily when shifting into gear.
When I disconnect the lower shift cable I am able to move it pretty easily by grabbing it between thumb and index finger pulling it back and forth without much resistans. Any tips to isolate the issue to the switch itself?

In the freeze frame memory I also get a recent TPS error but I wasn’t able to replicate that during my test drive.

Any other tests i should run while I still have the scanner?
 
The 193 error is saying the shift interrupter is engaging when it should not. Most likely you need a new shift interrupter switch

Test, disconnect wires from switch. Put meter on ohms and connect to switch. Move the switch contact and see if it changes states (zero ohms to high ohms) real easy, maybe with slight pressure.
 
I don't remember if that switch is open or closed when not depressed & obviously, visa versa.
Regardless, usually the switch contacts begin to fail as in engine vibration causes them to intermittently make contact. So, the engine thinks you are in the process of shifting when you are not. It retards the timing & slows the idle when it shouldn't & you get stalling.

Testing the switch as AllDodge says may not show a defect because it's not vibrating.

If unsure of test results, verify if switch when NOT depressed is open (high/infinite resistance) or closed (zero resistance). This would be the switch position in normal (not during shifting operation) conditions. At this point you can unplug the switch and leave unplugged or jumper the engine harness end as required to simulate the above findings to create an in gear condition for the ECM. See then how it runs but understand shifting to neutral will be difficult. So don't do this in tight or crowded conditions.
 
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Droid said:
I don't remember if that switch is open or closed when not depressed & obviously, visa versa.
Regardless, usually the switch contacts begin to fail as in engine vibration causes them to intermittently make contact. So, the engine thinks you are in the process of shifting when you are not. It retards the timing & slows the idle when it shouldn't & you get stalling.
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I will order a new switch thanks guys!

I can’t reliably tell if it is broken or not by measuring it with the multimeter, it does close and open when I press it manually but seem to be more sensitive than it should be.
 
eelstone said:
I will order a new switch thanks guys!

I can’t reliably tell if it is broken or not by measuring it with the multimeter, it does close and open when I press it manually but seem to be more sensitive than it should be.
Click to expand...
I was editing my post. I added more after you posted. Go back & read the updated version.
 
Droid said:
I was editing my post. I added more after you posted. Go back & read the updated version.
Click to expand...
Gotcha, I believe it is open when depressed.

I should then be able to jump the end of the harness contact, fire up the engine, go into gear and see if it will run better at idle. I’m guessing going into gear will be more rough when the switch is disconnected and isn’t killing the engine as it should?
 
Switch only functions while shifting out of gear. And even then it is only monentary. When gear releases everything returns to normal.
 
I think this confirms it!

I ran the boat with the switch bypassed, jumper cable between pin 1 and 3 on the connector according to a Service Bulletin I saw one of you link to in another thread. This allowed me to run it in gear all the way down to hot idle at 630-650 RPM without any stall tendencies. After fiddling around with the switch and reconnecting, it ran better but I still got the 193 error and it sputters when close to idle.

I will order a new switch and install it according to the manual.

Massiv thank you @AllDodge @Droid for all help and guidance.

Next time I work on an unfamiliar engine with a ECM/PCM I will for sure make every possible effort to get access to a scanner as the first step, that would have saved me a ton of time and effort:)
 
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