2001 MC 5.0 EFI Throttle Body-appear to be running rich. Trying to help a friend

[rothfm]

Hi All,

First, I'm on the OMC Boards alot here as I'm an outboard guy. I'm trying to help my frustrated friend with his MC issue. As always, Ive spent all week reading Posts of similar, and related topics.

Without getting too lengthy, I'll list symptoms and what has been done to date. Boat is NOT new to him. But I experienced this "bogging" symptom starting LAST season upon acceleration, and at that time if you easily or "feathered" the throttle, you could plane, and achieve full speed. It wast real bad last season, but this season, It cannot plane at all. It got progressively worse.

2001 5.0 EFI/Throttle body on 20' Tiara Persuit Alph1G2

Starts easily, and idles fine. On trailer, any hesitation/Bog is barely noticeable but still there. Water testing is where you really notice issue!

SYMPTOMS:

* Bogs upon any acceleration..can only get about 1500RPM out of it
* Smokes grey'ish to black out exhaust
* Exhaust water on land, shows sooty, black on the ground
* ALL spark plugs were black

THINGS HE HAD DONE/TRIED:

* Rebuilt upper TBI (replaced injectors, Fuel Regulator, TPS, IAC). Soaked the body, wired, and blew it all out clean.
* Replaced the coolant temp sensor
* Replaced Spark plugs
* New Fuel/water seperator
* Ran the engine on a SEPARATE FUEL SOURCE
* sprayed carb cleaner all around the intake, heads, hoses, and vacuum lines.
* This spring, new Manifolds and risers, Impeller (mantainance)


Just today (in water testing) I thought the TBI was flowing ALOT of fuel. I'm not really sure what the pattern should look like, But even at Idle, it appears heavy. IF he hits the throttle, I'm surprised how much fuel goes down...and there was several large "drips" just dropping off the injectors into the throats. AGAIN, no idea how this should appear, but it seems like he would be using a TON of fuel if this was normal.

I've been suggesting to do a couple basics (should have been done first) like Compression, and Spark checking.

My gut feeling is it is RICH, but not sure why. Almost like its always in "first start" mode with the ECM always telling the setup to feed extra fuel.

??? Appreciate any further insight... I like my outboards!-Just trying to help a pal out.

Thanks

 

[achris]

You need to know what the ECU is seeing, and to do that you need a computer with the diagnostics hooked up. It could be as simple as a broken wire between a sensor and the ECU making it think the engine needs a richer mixture.

It would help with a serial number and which ECU (MEFI 1, 2, or 3) it has on it.

Chris.........

 

[alldodge]

Just today (in water testing) I thought the TBI was flowing ALOT of fuel. I'm not really sure what the pattern should look like, But even at Idle, it appears heavy. IF he hits the throttle, I'm surprised how much fuel goes down...and there was several large "drips" just dropping off the injectors into the throats

New injectors and your not getting a spray pattern, also dripping. I'm thinking either the wrong injectors were installed or you have way to much pressure. Would like to know what the pressure is

 

[rothfm]

I will get the serial number and post with a pic of the ECM.

Ive suggested compression and fuel pressure. It doesnt jave a port so one will have to be plumbed somewhere.

Let me ask this.....those injectors were from a truck supply house he went to. They supposedly crossed ref'd and said they were same? Is this true?

Is this true for tps, iac etc? Im always leary of compatibility, but bieng an outboard guy-I dont know

When he rebuilt the pressure regulator on the throttle body, he noticed the new spring had a much different tension than the original, thus after testing, put original spring back in

Leads me to question if 5.0 TBI items are interchangeable to auto/truck items??

 

[achris]

Most of the EFI/MPI components are automotive anyway. It would be too expensive for Merc to make their own. The difference is the certification. To the used on a marine engine it needs to be SAE-J1171 certified.

I have successfully cross-referenced the IAC and quite a few other components, including relays, and wiring harness connectors. It wouldn't surprise me in the least to find that the injectors are the same as another application.

As for Fuel pressure, you are going to need to break into the line somewhere to get a read on it.

 

[rothfm]

Thank you...

Will get ECM pics, and work on Fuel pressure and convince him to do a compression test. Will report findings.

 

[alldodge]

You need one of these (91-806901) to attach at the TB to measure fuel pressure

 

[rothfm]

Thanks alldodge-will show him that adapter

The serial is M080534. I have pics of ECM but trouble uploading on my phone-I will from home in just a bit.

He located a map sensor today to try-same results.

Someone today told him there was a fuel preasure regulator sensor in the rear of the tbi, seperate from the the TBI itself

He took a pic of it, it just about the only thing in the related area not replaced. Will post a pic of it also.

Thanks for the help

 

[alldodge]

The fuel pressure sensor is item 16 in link below, and is located at the base of the TB
http://www.mercruiserparts.com/bam/subassembly/31846/4856/130

 

[rothfm]

Thanks again,

Attached are pics of the ECM, comparing against those in the thread above, not sure which one this is. Also attached a pic of this Fuel pressure sensor/switch. He is looking at one at a store but not sure of compatibility. Attempting to replace it as everything else has been done. I'm still pushing for a Fuel pressure test for sure.

It for sure is dumping a ton of fuel.

 

[achris]

That's a MEFI-3.

 

[rothfm]

Awsome. Good to know-Thank you!

I'm hoping he put on a port soon to properly pressure test. Time will tell.

 

[alldodge]

Just thought of something, the sensor is an 1/8 npt fitting/ Remove the sensor from the fitting and get a Tee fitting from the hardware store and connect the fuel gauge to the Tee

 

[rothfm]

Thanks Alldodge. Sent him that fitting. He is good and can make up an adapter-suggested he measures pressure asap.

Today he was sourcing the pressure regulator sensor to TRY. Everything done so far was to TRY.

He is frustrated and is going to give up and winterize it if the FUel press reg sensor is no help.

A baseline compression test and fuel press test is in order.

Just for chagrins-what would it take to make this a Carb motor?

 

[alldodge]

I don't see the issue as the fuel pressure sensor. I thing you either have the wrong parts or to much pressure

As for changing over, need a new harness, maybe distributer.

 

[achris]

... . Just for chagrins-what would it take to make this a Carb motor?

More trouble than its worth, and a serious backward step. He'd be better off spending the money on some diagnostic tools and getting the EFI working properly.

He'd be up for the carb, fuel pump, a new harness, distributor, ignition module and the whole pain of trying to get it set up. And maybe a new intake manifold too.

Chris. ...

 

[rothfm]

Thanks guys, he is really frustrated for sure

Bieng a longtime hands-on guy, ive become very regimented and methodical in my own troubleshooting

Ive expressed concern about intruducing a bad part or incompatible part, which can make one go down a worm-hole fast.

As such, he has put a couple things original back in with no change either way (injectors, & orig fuel pressure spring).

Agreed, already talked him out of the Carb idea after I read some about it.

Before tossing in the towel and winterizing it, he is gonna put a fitting in and get a pressure reading

By my eye, it looks to be dumping fuel. Any other things not already looked at that might contribute to this?

Also agreed, need good definitive scan readings!

Thank you

 

[alldodge]

Make a scan tool with a paper clip and a resistor LED

 

[rothfm]

Silly question about the paper clip & LED readout.....keep connector in place and jump into holes innplug, or remove and jumper, connected up or not?

We may try this.

Thank you

 

[alldodge]

Remove the cover connector, then jump into holes in the plug