5.7 Mercruiser EFI, idle after warmup quits engine

[rossi45]

Hey everyone. This is my first post up on this forum. I thought I'd try to get some help. I have 5.7 merc EFI (serial # 0M033393) in my Bayliner 2455. Engine is about a year old with roughly 30 hours on it. It's winter here in Victoria, BC so the boat sits at the marina. I go out once a week or so to start it up and run to temperature just to give it a run while I'm not boating during the rainy months.

Issue I am having is, I have some engine quitting at idle problems. I give the engine a start from cold. It fires up nicely and I let it run until it gets to operating temperature. It does this very nicely as well. I like to throw it in neutral and run to 1500 rpms or so, but as soon as I bring it back down to idle the engine just quits. I go to start it up again, engine fires up for about 2-3 seconds and then quits. I thought it might be the Idle Air Control (IAC) valve, so I went and replaced it. This didn't fix the problem. I went through and tested the IAC plug for voltage and resistance. All turned out fine. I pulled the IAC and turned the ignition to the start (without starting the engine) and the pintal moves in and out, so I'm convinced the IAC is not causing the quitting issue. I'm not really sure what else it could be. Any suggestions?

Thanks,
Mike

 

[wrench 3]

Another possibility is the throttle position sensor. You can test the signal output with a multi meter. It should be a smooth progression across the full range of operation. If it's not getting a low enough reading from the TPS it doesn't know that it's supposed to idle.

 

[alldodge]

Howdy

When you first fire the motor up, is the throttle at idle position or do you have to give it some throttle to start?

 

[rossi45]

Hey thanks for the feedback. I'm going through the mercruiser manual.

Wrench 3: I'll look at the throttle position sensor and see what kind of readings I get.

AllDodge: When I start the boat when it is cold, it fires up perfectly without giving it any throttle (so at idle position). It's only when the engine has warmed up, and then I give it some throttle and then come back to idle, then the engine quits. It has no issue keeping the revs up when I give it some throttle.

 

[alldodge]

Since it starts and does fine until it warms up, I'm thinking either fuel pressure, primary injector or a vacuum leak.

Your throttle body has two injectors, one is used to enrich the fuel mixture when cold and at high rpm's under load. The other is used for idle and low to mid loading of the motor. When the motor warms up the Temp sensor tells the ECM and one injector is shut off. So the primary injector might be clogging up or fuel passages feeding the injector.

My next thought is fuel pressure (30 psi), if fuel pressure is low there will not be enough fuel delivered to keep the motor running. The injectors work the same as previously mentioned, just might not be enough pressure.

Have you checked/changed your filters lately?

There is a rubber hose which goes from the intake to the fuel pressure regulator. Check to see if you find fuel in this line, there should be none. If this hose is removed during idle the fuel pressure should increase. If the hose is removed and the motor will idle then it could vary well be fuel pressure issue. This same port can have a vacuum gauge placed on it to get a reading and should be between 15 to 21 in Hg

 

[wrench 3]

Since it starts and does fine until it warms up, I'm thinking either fuel pressure, primary injector or a vacuum leak.

Your throttle body has two injectors, one is used to enrich the fuel mixture when cold and at high rpm's under load. The other is used for idle and low to mid loading of the mhttp://forums.iboats.com/forum/engine-repair-and-maintenance/mercruiser-i-o-inboard-engines-outdrives/10116883-5-7-mercruiser-efi-idle-after-warmup-quits-engineotor. When the motor warms up the Temp sensor tells the ECM and one injector is shut off. So the primary injector might be clogging up or fuel passages feeding the injector.

My next thought is fuel pressure (30 psi), if fuel pressure is low there will not be enough fuel delivered to keep the motor running. The injectors work the same as previously mentioned, just might not be enough pressure.

Have you checked/changed your filters lately?

There is a rubber hose which goes from the intake to the fuel pressure regulator. Check to see if you find fuel in this line, there should be none. If this hose is removed during idle the fuel pressure should increase. If the hose is removed and the motor will idle then it could vary well be fuel pressure issue. This same port can have a vacuum gauge placed on it to get a reading and should be between 15 to 21 in Hg

I've only had experience on a couple of marine inboard fuel injection. But have had lots of experience on automotive systems (factory trained on GM).
Anyway, according to mercury parts catalog for that serial number, that is a multi-port system with one injector for each cylinder and no mention of a cold start injector.
Fuel pressure runs higher on multi-port system, 43 psi.

 

[thumpar]

Is it MEFI? If so what version version of MEFI do you have? I have the instructions to make a code reader for about $1 using an LED and paperclip and can post them. It only works on MEFI 1-4 though.

 

[Bondo]

Since it starts and does fine until it warms up, I'm thinking either fuel pressure, primary injector or a vacuum leak.

Ayuh,.... Welcome Aboard rossi45,.... Start simple, when was the fuel filter last changed,..??

Swap it out, 'n inspect the Contents of the take-off filter for water, 'n crud,.....

I use a quart freezer zip lock baggie, crack loose the filter, slip the baggie 'round it, spin it off, zip it up, flip it, 'n you can see the contents,....

 

[alldodge]

I've only had experience on a couple of marine inboard fuel injection. But have had lots of experience on automotive systems (factory trained on GM).
Anyway, according to mercury parts catalog for that serial number, that is a multi-port system with one injector for each cylinder and no mention of a cold start injector.
Fuel pressure runs higher on multi-port system, 43 psi.

Agree most MPI's fuel pressure is higher but according to manual 24 it shows 30 psi at 1800 rpm. Have been wrong before and maybe this is another time, but... on the Mercruiser website I find under serial number 0M033393 in the listing below and it shows the following listed below

 

[thumpar]

I also show it as EFI and not MPI. The computer comes up as a MEFI 3 or 4. You can read the codes, if any with these instructions. I have used it myself on my boat. I can't take credit for supplying the info only pasting it. Radio Shack carries the LED.

Some of you may know this trick, but I thought I would share it in hopes that it helps some folks. It is very easy to make a simple, but very useful, Marine EFI Code reading and clearing / Base Timing Tool. And you can make it for under $1.00!

Materials needed:

One 12volt resistor type LED light
One small paperclip cut in half

That?s it!

This home made code tool works every bit as well as the one I paid $50.00 for. It will work on most 1993 to 2000 marine EFI systems with the ten pin Data Link Connector. This includes Mercruiser, Volvo, Crusader, PCM, Indmar, and a few others.

How to hook it up:

1) Ignition key ?OFF?

2) Remove the cap from the Data Link Connector (DLC)

3) Slide the LED into the female terminals of position E and F on the DLC, making sure that the positive side goes into terminal F and the negative side into terminal E. No damage will occur if you get it backwards, it just won't work.

4) Turn the ignition key to the ?ON? position. The LED should come on steady.

5) Insert the half paperclip into terminals A and B ? This puts the engine in ?Service Mode? and codes will begin to flash on the LED. On 1996 and earlier engines you may hear the fuel pump come on. If not you should be able to hear the Idle Air Control (IAC) motor move. Use care in this step, do not insert in the wrong terminals or ECM damage could result! Look closely, the terminals are clearly marked.

6) Read codes by observing LED flashs. If the self diagnostic system is working it will flash code 12 ? one flash, pause, two flashes, long pause ? it will repeat three times. If other codes are present they will flash in order of lowest to highest. Continue to read codes until the code 12 sequence is repeated.

You can also be clear codes (by moving the throttle to 100% and back) and set base timing while in Service Mode.

Dave

 

[Fun Times]

Just to try and help clear up any confusion about the engine in question, this engine serial number is coming up as an MERCRUISER MEFI 3 with 3" exhaust risers 5.7L EFI BRAVO model number 4332077N1 that uses parts catalog part number 90-80950098 http://www.mercruiserparts.com/selec..._nbr=809500+98 which shows this engine to use the THROTTLE BODY design. ^ Guess I'm a little slow getting to the party.

rossi45, when was the last tune up performed such as distributor cap and rotor & spark plugs? What did/do the plugs look like? Carbon fouled at all?

When cold, what RPM does the engine idle at? Will it die if you bring the idle down slowly vs rapidly? If it can stay running at all when warm, what RPM is it idling at? Should be 600 RPM warm and right around 750 cold.

Be sure to try thoroughly cleaning the throttle body internals parts, walls & plates on all sides and the flame arrestor too.

Try disconnecting the throttle cable from the throttle body stud and see if it still dies when warm when you bring the idle down both slowly and rapidly to see if there's any differences.

The proper RPM to run the engine at while on the garden hose is 1300 RPM.

 

[rossi45]

Hey, thanks again everyone for the feedback.

One note about the engine. That is the serial number I posted for my engine. 5.7 Merc EFI with a Bravo III outdrive on a 2001 Bayliner Ciera 2455. I bought the boat last summer and the previous owner had a new engine put in in 2014 by a marine shop. I believe all the external parts are original (so throttle body, among others were taken from the old engine and put on the new). As I mentioned in my original post, the engine only has about 30 hours on it. The warranty on the new engine is over and this is why I haven't gone to the shop yet. Hoping this is a simple problem!

I'd like to respond to each question:

AllDodge: Thanks for the fuel pressure question. I've actually thought about this. I have a kicker motor on my boat that is hard wired straight to the fuel system. I had an issue with the primer hand pump (it had a crack in it) so I thought that there was some air being sucked back into the system through the crack, creating low pressure. I replaced the primer pump and the issue still persists. So, it may be a fuel pressure or a vaccum leak. I'm not sure how to check either. I guess this is where I admit that I am learning engine repairs by trial and I have a lot to learn, although I willing to do it.

Bondo: I replaced the fuel filter after I replaced the primer pump mentioned above. I checked the last fuel filter and there was no water present, nor any concerning particulates. I am going to replace the oil, oil filter and I'll do another fuel filter within the next couple weeks.

thumpar: Thanks for the tip! I do have a code reader already, and I am not getting any codes thrown on this issue.

Fun Times: Your specs on my engine are correct. So, to answer your questions:

1. when was the last tune up performed such as distributor cap and rotor & spark plugs? What did/do the plugs look like? Carbon fouled at all? Tuned up last summer. Had a new ignition coil put in at that point. Plugs and wires are all virtually brand new. I pulled the plugs last month and they're all still new looking.
2. When cold, what RPM does the engine idle at? Engine idles at 750 rpm's when cold on startup. It only drops slightly after warmup. Say around 700 rpm's
3. Will it die if you bring the idle down slowly vs rapidly? Yes, the engine dies regardless of how I bring it out of a higher rev. AFter it dies, I can turn over the engine, it starts, runs at about 1000 rpm's for a second or 2, then it wants to come down to regular idle and that's where it stalls again. Rinse and repeat. If I wait for 5-10 mins, the engine will start and stay on. I am assuming it cooled enough after 5-10 mins for it to start and stay on again.
4. If it can stay running at all when warm, what RPM is it idling at? Should be 600 RPM warm and right around 750 cold. As mentioned in your earlier question, around 700 rpm's.
5. By disconnecting the throttle cable, what's the purpose? Are you suggesting that I rev the engine by hand on the throttle body itself?

Thanks a lot for the feedback everyone!

 

[alldodge]

To check vacuum need to get a vacuum fuel pump tester, they cost about $20 or less. Harbor freight has one which is pretty cheap
http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

Find the small rubber hose which goes from the cool fuel module up to the intake/throttle body. Remove the hose and put the gauge on the port. The hose needs to fit snug so not to leak.

Testing fuel pressure is done but having a high pressure fuel pressure gauge (not the HF one) which can read at least 60 psi. Then you need an adapter 91-806901 to place in the fuel line. This is done by removing the fuel line at the throttle body and installing the adapter then reinstalling the fuel line.
http://www.cpperformance.com/p-62962-fuel-pressure-tee-91-806901.aspx

 

[rossi45]

This is a video of the engine after startup. I'm posting this to record the sound of how it is performed, so I had to put the phone down to rev the engine (this is why you just see the white seat).

What I did was, started then engine from cold and let it warm up to temperature at idle. At this point, the engine is running fine. Then, I put the gears into neutral and throttle the engine up to 1500 rpms and then I slowly bring the throttle back to idle position. That's where the video starts. What you are hearing is the engine nearly stalls before it catches itself and then surges up to about 2000 rpm's and then drops back and almost stalls again, and then back to high rpm's and does that a few times before stalling. At about the 1:05 minute mark, the engine completely dies. I restart the engine at this point and you can really here the near stall and surge.

Things I ahve done already:

• New Idle Air Control valve
• New gas + lots of seafoam
• New fuel filter
• Checked spark plugs and wires. All good.
• Thought it might be a shifter interupter switch, but this is a Bravo III setup, so I don't have one.

Things people have suggested:

• Possible vaccuum leak?
• Throttle body gaskets leaking?
• Fuel pressure low?

Aside from the great advice people have posted above, I'm just wondering if anyone else has some more feedback before I call the mechanic. Thanks!

 

[alldodge]

Has some kind of a whine in there, might just be how the mic picked up the sound. The hissing sounds like it is not getting fuel but this could be from a leak, low fuel pressure, incorrect control of IAC or other. Would sure like to know what the vacuum and fuel pressure readings are

 

[rossi45]

Hey Thanks AllDoge. There are 2 sounds. You can hear the fuel pump priming, so there is that. And then (my bad) in the first part of the video, before the engine quits halfway through, I had my blower on. I turned that off just before the engine quit, so the last half od the video doesn't have that sound. Also, the belts kinda make the raspy whining sound too.

 

[alldodge]

Pull some plugs and see what they look like, maybe white color or deposits

 

[rossi45]

As per the list I posted with the video, I checked the plugs and wires. All good. The current engine is new about a year and a half ago. Engine has ~30 hours on it. When I pulled the plugs, they still look brand new. Wires are all new too.

 

[alldodge]

Since they look new without any deposits then I'm back to the fuel pressure, fuel injector or a vacuum leak. There should be some color to them and not like new

 

[rossi45]

Thanks Dodge. I'm defintiely getting on the vaccuum leak idea. I'm going to get a mechanic down to give me a hand either this weekend or next. I'll make sure he has a gauge with him to test pressure.