Smarty pants, I really could use your help! 350 Mag trouble SOLVED?? MAJOR UPDATE

Wildboating

Can anyone answer these questions.......   

WHY IS MY FUEL CONSUMPTION AT WOT LOW??    How can i build more rpm if i am not using the adequate amount of fuel.

I believe my problem is in the lack of fuel being burned.


Starboard Motor WOT: 16.5GPH - 3600 RPM


Port Motor WOT:  18.3GPH - 4000 RPM


I read on the site linked below that my fuel flow at WOT and 5000 rpm / 300hp should be 23GPH.    

So how do I get more fuel into the combustion chamber?  In my mind, if we add more fuel we get a bigger bang.  The bigger bang drives the piston down harder and faster ultimately creating more rpms.

SO WHY IS MY FUEL CONSUMPTION SO LOW???   I can not seem to answer this.  Fuel pressure stays at or above 43.


http://www.boat-fuel-economy.com/mercury-mercruiser-350-magnum-5.7-fuel-consumption-us-gallons

Black_Diamond

It's  fixable. Swapping the coil and new tMap will be interesting. 

Wildboating

Black_Diamond said:

It's  fixable. Swapping tbe coil and new tMap will be interesting. 

Tomorrow both of these will happen.   Cant belive nobody on this site other than me has a Rinda Diacom.   I really wish i had a known good 350 mag mpi to compare data too.

Black_Diamond

Must be someone on here close to you with that engine to compare too.  

Black_Diamond

Just tossing this out there:

try running the boat with the engine hatch open a tad to see if intake air is being restricted. I mean out on the water, not at slip.  

Wildboating

I have ran it open.  I have also cleaned and visually inspected the flame resistor.  At this point earlier today i decided to do a test run with it completley off.    We will see

Dude_Himself

The Mercruiser is one big feedback loop, with the exception to Acceleration, Deceleration, and WOT. (I believe, this is from reading countless Mercruiser documents. They don't publish all their secrets). When you're moving the throttle it's following a preprogrammed fuel/ignition curve, but it won't throw 23GPH at an engine that's not developing 3k RPM - there's checks in place for that. Chasing fuel burn could be chasing your tail. If you back off until they're even RPM - is the fuel burn near identical?

I still think ignition - either spark delivery or timing. I've had a bad timing module that didn't advance the ignition curve past a certain point. I've also had a bad coil that weakened past a certain point. I just read the whole thread - sounds like you've replaced the spark plug cables and distributor a few times. Did you ever swap the spark timing module though? You were going to, but I didn't read where that happened.

Funny story - in college I was rebuilding an old Jeep. I bored and stroked it from a 4.0 to a 4.6L. My dad came down, neither of us had ever done something like this before, and helped me finish the long block and drop it into the chassis. She started right up, and after a little coolant escaped the freeze plugs didn't lose a drop of fluid. She'd start, run, but never developed full power. Sounds familiar? We spent 3 days tearing it back out, stripping it down, double checking all the tolerances, etc. Mechanically I had done good. Know what it was? The distributor was 180° out of sync. She idled great, and ran all the way to the mechanic, just slower than expected.

I'd start back at the beginning - fuel, spark, compression. We know compression is definitely good. Fuel appears to be correct (or the plugs would show it). What about the spark?

Wildboating

We have not replaced the spark control module. I have been trying to get more info on this device.  Either way, we are seeing 24* timing st WOT.   I will swap between motors and retest. 


Al, I did not have a barbed fitting, it was just the cut end of the hose.   This is interesting and worth trying again.  

Wildboating

@Dude_Himself. 

If i back the rpms down on the port motor to match engine speed  the fuel burn is the same. 

Black_Diamond

Well, I tried with the air restriction idea. lol. 

Have you pulled the pick up unit from
the tank?  Maybe partially clogged or a stuck anti-siphon valve?  

Wildboating

I have not BD, I am achieving and maintaining fuel pressure psi from idle to WOT. If a filter was clogged, line collapsed or stuck ASV I would not be able to maintain pressure. 

Black_Diamond

This is killin me!  Are your electrical connections to the injectors all clean/good?  Dielectric grease on them?  An erratic connection might be cutting off one/some injectors at higher rpm.  

212rowboat

Black_Diamond said:

This is killin me!  Are your electrical connections to the injectors all clean/good?  Dielectric grease on them?  An erratic connection might be cutting off one/some injectors at higher rpm.  

i've seen spades on a ev6 connection not sit flush in the union and cause all grades of discontent... it misfired inconsistently.. that spades footprint in the connector has a pretty stout impact on resistance... was caught by absolute accident. 
but.... 
what's the chances the flexplate is magnetizing?

CaptianDan

This does sound like an air/fuel mix issue to me.  Sounds like you have done all the right things too with troubleshooting fuel delivery up to the rail and it's unlikely to be tank/pickup/filter issues if you have had an external tank.  
Personally I would spend some time on the injectors.  I know you have replaced these but it's certainly not uncommon for Marelli IWP069's to have issues even when new, at this point I would send to be tested to ensure you are getting the correct spray pattern (should be fine direct pulse) and also checking the volume of fuel delivery is synchronised across all 8 injectors.  Out of interest where did you purchase the new ones from?  If these are not genuine Marelli IWP069's then the coils are VERY likely to be suspect and would give you this condition.  There are a huge amount of Chinese remakes flooding the market being sold as Marelli's.
I would definitely also swap the coil plus wires from a known good engine or new.

dalek

What color are the Sparkplugs from the other engine? The only time I have seen plugs that color is when someone puts a small amount of diesel in a petrol tank by accident.

Carsnmorellc

Good luck today and my fingers are crossed that its the coil.  Keep us updated

Black_Diamond

As I keep pondering on this, and thinking simple: have you tried running (again under load) with the fuel caps off?  This would eliminate a venting issue that could be a vent line plugged/pinched. 

Wildboating

Some interesting new information, and our first ever actual visual and audible information.


Keying on the ignition seems to run the fuel pump for 3 seconds.  This was my graduated cylinder test to determine fuel flow on each motor.

Starboard side pumps 230/224/210 ML per seconds on each test   -  This equals  72.91gph, on the high number


Port motor:  160/169/176  ML per seconds on each test this equals -55.79 GPH
The port motor is aereating (sp) while pump on.   It is definetly spitting air which may be the reason for the lower number.

Wildboating

Sooooo....  for the first time ever, we now have a visual and audible clue.  

I was sent the fuel pressure test today and the mechanic who recorded it noticed something earlier today.  The fuel pressure starts bliping around the rpm when the engine cuts out.  You can see and hear it audibly in the motor.  I will post the video asap.   First run is smooth, keep watching through second run .   Gauge shows 2psi with key off. 

Wildboating

Watch all the way through, 2nd time we throttle up.   
https://www.youtube.com/watch?v=mWNu8drY5LA&feature=youtu.be

Wildboating

Blank

Wildboating

+++++++  We found a failure!!!!    The lift pump runs electrically but does not pump anything!

randy56

When you say lift pump do you mean fuel pump? I got to tell you we have all been rooting for ya, even though some of us has not commented.  As most do not have skilled advice for ya. 

davidbrooks

Agree @randy56 I feel like i have been taking a masters class in engine diagnostics.

Handymans342

I was right again

Black_Diamond

Lift pump meaning the pump on the fuel/water separator side?

Would make sense under high load it is running the filter out of gas I bet.  

Wildboating

BD is correct, the pump that is mounted next to water/fuel separator outputs nothing.  It runs, but it is supposed to supply the cool fuel pump with 8 psi and it had 0, furthermore no fuel flows through it.  The cool fuel pump is not designed to draw fuel, it needs this lift pump to draw and supply.  

Black_Diamond

Awesome news!  Will be interesting to see the performance with a new pump. 

rasbury

So how did you have such good fuel pressure with no fuel? I don't have cool fuel on my 05 mpi 350...i do have a silver cylinder which I assume is the fuel pump...have not had problems there...yet..

rasbury

Ps- glad and hope you found the problem..is their an easier sequence of checking to get where you got?