Mercruiser 4.3 MPI 262 CID s#1A34694Z NOT IDLING CORRECTLY SOMETIMES

[carterme1968]

i have a 2010 tahoe Q5i with a 4.3 MPI 262 CID V6 fuel injection..First issue I had was engine idling but when giving throttle boat wouldn't go. Took it to shop and they replaced spark plugs. Now boat will idle good and run good in water but if I stop it then like 10 minutes later try to crank it, it will idle rough around 500 rpm's then a few seconds later cuts off. If I give it gas before it cuts off it will just cut off sooner..Then waiting in water for 5 to 15minutes(trying to crank several times during this time which it cranks, idles then cuts off) it will idle fine and I'm good until I cut it off again. This doesn't happen each time. Normally if I cut off for more than 5 minutes it happens more times than not. Like to get some ideas before taking back to shop. Thanks.

 

[carterme1968]

i have a 2010 tahoe Q5i with a 4.3 MPI 262 CID V6 fuel injection..First issue I had was engine idling but when giving throttle boat wouldn't go. Took it to shop and they replaced spark plugs. Now boat will idle good and run good in water but if I stop it then like 10 minutes later try to crank it, it will idle rough around 500 rpm's then a few seconds later cuts off. If I give it gas before it cuts off it will just cut off sooner..Then waiting in water for 5 to 15minutes(trying to crank several times during this time which it cranks, idles then cuts off) it will idle fine and I'm good until I cut it off again. This doesn't happen each time. Normally if I cut off for more than 5 minutes it happens more times than not. Like to get some ideas before taking back to shop. Thanks.

 

[alldodge]

Need a serial number
Check the fuel pressure at the rail

 

[carterme1968]

Engine S# 1A34694Z...

 

[alldodge]

Thanks
Your motor
https://www.mercruiserparts.com/4-3l-mpi-alpha-bravo-0w658583-thru-0w6

The fuel rail fitting item 13, pressure should be 43 psi
https://www.mercruiserparts.com/bam/subassembly/31503/13808/90

 

[carterme1968]

Thanks
Your motor
https://www.mercruiserparts.com/4-3l-mpi-alpha-bravo-0w658583-thru-0w6

The fuel rail fitting item 13, pressure should be 43 psi
https://www.mercruiserparts.com/bam/subassembly/31503/13808/90

Put fuel pressure guage on with pressue relief. 38 to 40 psi and boat run fine. tested in yard 20 to 30 times. Worked good. Put in water run good 20 more starts ok..Then fill up with gas and put in water. Started several times than we stopped for about 20 minutes wouldn't start. 10 psi on guage. You can hear fuel pump start.Tied several times, same and then after 5 mintues of waiting it started,40 psi. Run fine for 30 minutes and stopped again for 20 minutes or so. Tried 10 psi. Tried several times same. Put hose on pressure relief and got pressure off then tried again 40 psi.. I have already replaced filter, gas sigoen vale(straight piped it in for now), hoses look good. I'm assuming next step is to replace fuel pump. Suggestions? Thanks for the help in advance.

 

[dubs283]

Would guess piece of debris in fuel tank occasionally blocking pickup tube

 

[alldodge]

Agree could be something is clogging up the pickup tube

See if you can remove the tube and have a look

 

[QBhoy]

Sure sounds like you’re picking up crap at the pick up pipe. I’d take the hose off the filter housing or from the pick up…then dip it into a can of fresh fuel. Rule things out.
Listen to the sound of the pump when key turned too. You can hear if it’s primed with fuel or if it’s struggling, aerated or otherwise. Any air from the shrader valve on the rail ?
Although technically speaking and heard many mention it. If you have had air in the fuel supply side or filter…apparently it should self prime on the mpi…I’ve never had the patience to wait that long or think it clever to keep keying on and off a million times.
It takes an age to prime that way and without intervention. Any occurrences of such a thing on boats I’ve worked on…I’ve just held the shrader open whilst keying on a few times to expel air. Filter primed first too, obviously.

 

[muc]

Vapor lock? You didn't post a valid serial number so I can't be sure exactly what engine you have. But it wouldn't hurt to look at the MCM 99-7 service bulletin Don S posted.

Under certain conditions, engines may experience a `vapor lock' condition. The three most common complaints that vapor locking cause are:
1.The engine starts. When the throttle is advanced, the engine quits running and will not restart.

5.0 MPI vapor lock question

I have all the symptoms of vapor lock on my 2008 5.0 MPI runs like a champ till you stop for a few minutes and then no start. Let it sit for a hour or two and it runs like a champ. If I open the engine compartment when I stop it never misses a beat. I have tried idling and running blowers that...

forums.iboats.com

 

[muc]

Sure sounds like you’re picking up crap at the pick up pipe. I’d take the hose off the filter housing or from the pick up…then dip it into a can of fresh fuel. Rule things out.
Listen to the sound of the pump when key turned too. You can hear if it’s primed with fuel or if it’s struggling, aerated or otherwise. Any air from the shrader valve on the rail ?
Although technically speaking and heard many mention it. If you have had air in the fuel supply side or filter…apparently it should self prime on the mpi…I’ve never had the patience to wait that long or think it clever to keep keying on and off a million times.
It takes an age to prime that way and without intervention. Any occurrences of such a thing on boats I’ve worked on…I’ve just held the shrader open whilst keying on a few times to expel air. Filter primed first too, obviously.

One of the problems with the coolfuel two is the only place air can get out of the system is through the injectors so once air starts getting in (thru a air leak or vapor lock) it’s hard to get it out without using the fuel pressure tester.

 

[alldodge]

Good point on VL
Did not think about it because of no mention of it happening after a run.

Does this happen after the motors been running for a bit or is it when its cold and not yet warmed up?

 

[muc]

Good point on VL
Did not think about it because of no mention of it happening after a run.

Does this happen after the motors been running for a bit or is it when its cold and not yet warmed up?

I would have thought this engine would have a boost pump on it, but I don’t see any mention of one in the parts link you posted. Maybe got something stuck in the cooling system check valve?

Maybe a distributor cap starting to fail, O.P. Mentioned spark plug replacement helped but didn’t say anything about the crab cap?

 

[alldodge]

I would have thought this engine would have a boost pump on it, but I don’t see any mention of one in the parts link you posted. Maybe got something stuck in the cooling system check valve?

Maybe a distributor cap starting to fail, O.P. Mentioned spark plug replacement helped but didn’t say anything about the crab cap?

OP posted 1A34694Z and I replaced the Z with a 5 and it does have the carb cap

 

[carterme1968]

Good point on VL
Did not think about it because of no mention of it happening after a run.

Does this happen after the motors been running for a bit or is it when its cold and not yet warmed up?

It happens in water when running for a bit..30 mintues or so..then sitting for 10 mintues or so in water and then it might happen. 10 psi on fuel rail..I can wait about 10 mintues or so and it will be 40 psi and I'm good. It happen the last time I hit pressure relief on gauge I put on fuel rail. tried and went to 40psi and ran fine. Haven't got it to do it in yard testing yet.
It does seem like a vapor lock issue.

 

[muc]

It happen the last time I hit pressure relief on gauge I put on fuel rail. tried and went to 40psi and ran fine.

yes, vapor lock or air entering the system.
Suggest you follow the S.B. I linked step by step as written. It’s an old one but hasn’t been updated because it’s still completely valid. Only difference with your engine is the cooling system check valve. You should already have one, question is if it’s working.

 

[alldodge]

I'm easing away from VL because it happens so fast and pressure being at 10 psi.

Most VL happens when its a hot day, stop for a hour or 2. Go to restart and it goes but soon as throttle up it dies and then it won't start but will cough every now and then, happened to me a few times before issue was fixed

40 psi fuel pressure or air pressure should still be 40 and not 10.