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

Wildboating

Soo...  I am tired of throwing money at my boat while not fixing the problems.  My starboard motor since buying the boat does not build rpm like the port motor.  I have a rinda Scantool and all alarms are clear.  I typically drive with port throttle about half way and starboard full throttle to get the engines to 3500 rpm.  I recently replaced the long block on the starboard side as well and the problem persisted. I just installed vessel view and noticed that if I increase port motor it will build rpm, however the starboard motor will not exceed the port motor rpm without the port motor being increased as well.  Today I noticed on the vessel view if I increase the starboard motor without the port motor it will increase rpm for about a second then drop back to the port motor rpm.  I just can understand what I need to be looking at.  I rebuilt the top of both engines last year.  However port motor received new fuel injectors while starboard did not. Could this be a injector issue?  How are the engines linked? How come the starboard will not exceed the port motor like the port motor does the starboard?  The last half of starboard throttle does nothing without the port being increased, yet to run at 3500 I need the port half throttle and starboard pegged.  

I also switched to 22p 4x4 recently from 24p but find I still can not get over 3800 on starboard motor while port can break 4000. 

Sorry for the rambling amount of info, I'm hoping someone who KNOWS about these engines can point me in the right direction.  Thanks much!!!

Michael T

Need more data:  Can you run each engine safely to its proper WOT? Is each in the proper range and the same RPM? fly Do you have a DTS "fly by wire" throttle system or a Mercury "by traditional cable" system? Do the throttles move freely backward and forward? What positions are the handles of the fuel valves for the gas tanks in?  Is there any misfiring/lag/hesitation in acceleration or deceleration of either engine? Is the acceleration/deceleration steady and linear? Running only one engine at a time (in neutral) will each run up and down the rpm band smoothly? Running each engine in gear, (by itself) will each engine run up and down the rpm band smoothly? I predict there will be a simple explanation for this (fingers crossed).

Wildboating

@Michael T

i can not achieve full throttle, even with new props.

i have traditional mechanical cable throttles. 

Both th throttles move freely both directions. 

Both fuel valves are fully opened

There is no lag or hesitation other than described starboard issue

acceleration and deacceleration is smooth and as expected. 

Both engines both rev in neutral freely and without hesitation. 

Each engine, individually will rev up in gear however the starboard will not rev without the port motor. 

Wildboating

I wanted to share some photos also to help visually explain my situation.  The rpm's  were taken on a two hour long cruise today and both were running right at 3500 +- 50 rpm as they fluctuate.  Notice the starboard throttle is pegged and the port is about half 60% throttle.

Wildboating

Al, Fuel Pressure on both side shows 49 on the vessel view.  If i recall this is in line with what I measured last year on the fuel pressure gauge off the fuel rail.

Is there an easy test for the ignition system?  

Would it be advisable to swap port and starboard fuel injectors and retest?

aero3113

Looks like the cable needs to be re-rigged maybe?

99270fv

how about take the flame arrestor off of the trouble engine and with motor not running push throttle full open and look at the butterflies in the throttle body and ensure they are full open???

Wildboating

99270FV, I had not even considered that.  I will certainly do that next.

Wildboating

Here is a test at WOT last year when same problem existed.  This is Starboard.re 

Wildboating

Here is the Port motor last year.  Both engines are realizing near full throttle position in the ecu.  So being a butter fly or mechanical cable issue seems to me impossible.  Again, i am no seasoned mechanic.

Black_Diamond

That fuel flow rate at WOT is low to me.  I run 16-18 gph at 3800/4000 rpm (cruise). 350 MAG MPI 22P Bravo III

i had a similar issue, not quite as extreme as yours. I replaced both air temp/pressure sending units on mine (both in one unit) plus both PCV valves. Problem gone. The sending unit on mine is on the intake manifold behind the throttle body. I had oil on mine from the PCV valve being old/bad. 

Michael T

Am I a bit thick?

Are you saying that even in neutral (throttle only position) you can run each engine independently, by itself, from idle (+/- 700 rpm) right up to its maximum RPM (5000+/-rpm)?

Or are you saying that you can NEVER get the Starboard engine - whether in neutral OR in gear - to reach it's wot unless the Port throttle is also engaged?

My guesses:

1. Cable linkage adjustment - maybe even in the throttle housing itself. Something with the cables seems to be hung-up 2. Sensor malfunction - although with VV I would think it would indicate a code. 3. Exhaust flappers that have "caramelized" (as Al said) can easily limit rpms to the 2000+ range BUT I would think this should also increase your engine temperature - which from your data is okay.

.....and the fuel flow does seem to be off, particularly for almost 4000rpm!

Man, I'm going to love hearing the solution to this one!

Wildboating

@Black_Diamond, i am showing 17.5-18 gph at 4000 rpm which is what you state you show at the same rpm.  I cannot get the boat to wot so i have no idea what that rate would be like there.  I don't push the port throttle beyond what the starboard is able to keep up with to keep the motors synced.

Wildboating

@Michael T  I honestly have not tried to rev to full throttle while not under load.  I have blipped the throttle and seen it shoot over 4k so i assume it will run to 5k.

As for the motor rpm values being linked, i am stating that the first half of the starboard throttle seems to operate as expected.  The last half essentially does nothing, however i did notice on the vessel view the motor attempts for about a second to increase rpm then drops back to match the port motor rpm.  As far as the linkage is concerned, i do know that the TPS reads its values from neutral to wot as expected which says the cable linkage really is not the problem.

What fuel flow would you expect at 3500-4000rpm?

You and I both are going to be ecstatic once I figure it out.  I just hope to do so without throwing much more in.  The wife is not happy, I am about 15k in mechanical repairs in the first year of owning this boat.  The reality is I am not one of the boaters who knows something is not right but does not fix it.  I have repaired or replaced so much already.  The good news is I know exactly what I have now!

Wildboating

So i found this list on the internet, thought i would share in case someone else one day finds themselves troubleshooting the same issue.


Engine Won't Reach Operating RPM. Check List

1. Fuel condition. Type and Octane possibly old fuel--- Brand New Fuel, Full Tanks

2. Propeller pitch or diameter, damaged blades ---- Brand New 22p blades

3. Restricted fuel pickup tube or anti siphon valve Fuel System Test- Not sure where to check

4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse-- Just changed oil again, oil level is correct

5. Marine growth on hull and outdrive-- Bottom was freshly painted and cleaned, same issue

6. Wrong gear ratio in outdrive- Wouldn't explain why 1 engine runs correctly without the other, same drives

7. Restricted carburetor air intake (clogged flame arrestor) - Will check tomorrow

8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive-  Shutters are in tact and working properly.

9. Poor cylinder compression Compression Test-  Rebuild heads last year on both motors, problem persisted

10. Carburetor defective, or wrong type.--- N/A

11. Fuel pump pressure and vacuum--  Fuel pumps seem to have plenty of pressure, planning to do some vacuum test tomorrow.

12. Boat overloaded, improperly loaded, or improperly trimmed.-- Same issue with and without any load

13. Engine Overheating-- Temps are shown to be within specs

14. Engine timing and ignition system operation--- Diagnostics shows 24deg timing at wot on both motors


15. Remote control cables and linkage for proper travel to open throttle plates fully.-  TPS shows full sweep through range of throttle lever




I hope one of these few last unchecked items will be the answer, the exhaust port blocked sounded so good until you mentioned you would expect high engine temps.

Black_Diamond

When I was having this problem, my throttles would be near the extremes your pic shows, basically one engine seemed to do nothing with additional throttle above say 50%ish. That air temp/pressure sensor was the end issue for me. You could try swapping the sensors and see if the problem moves. 

Wildboating

@Black_Diamond. Can you tell me where that sensor is located?

Michael T

I would look at the sensors( #2 on my concern list posted above). You may remember, from an earlier post I made, my frustration with my new 502 Magnum at having my Port engine restricted to about 1000rpm by a faulty water pressure sensor. Everything was fine but that @#$%^& sensor kept using engine guardian to restrict my rpm. As @Black _Diamond said....swapping a sensor will eliminate that as a cause.

Wildboating

I am not getting guardian or any faults. However I will swap sensors as that is cheap diagnostics.

Michael T

My VV did not indicate a code for my "supposed" low water pressure. Guardian did however activate and restrict rpm. Swapping sensors would be an inexpensive way to check.

Black_Diamond

My bad sensor did not throw a code either.  On my 350MAG MPI, it is on the top of the intake, behind the throttle body.  One screw holds it in.  One wire connection.

Wildboating

Al, i done some searching online but have not seen any injector balance test while on the water.  Do you mind a quick explanation.

Wildboating

Going down to work on the boat this afternoon.  To verify exhaust is clear do i just need to inspect the flappers?  Is there a method of checking to see if exhaust port is clear or do i need to pull boat out of water to do this?

 

Black_Diamond

When you pull the elbows off the manifold to get to the flappers, if they are intact, probably no blockage in the y pipe. You can do all that in the water. 

Considering you are taking all that apart, you may consider replacing the flappers, rubber couplers and the clamps. Pretty straight forward job. 

212rowboat

i'm guessing the spark curve is 24* total, in addition to the base of either 8* or 10*, which puts it in right zone of total absolute advance of 32/34*.... that is right according to the charts I just pulled from a mercruiser issued service bulletin...  

i wish i knew more about strategies the pcm/ecu uses in certain conditions.  the only conflicting data is coming from the intake air temperature, right at 11*, but is that enough to trigger a guardian?  and if it was, is it not enough to set a trouble code?  I know some auto makers use simple strategies (if, then; "if a certain temperature is achieved then do this"), some use deltas (if reading from 'a' is X and reading from 'b' is x% from 'a' do this), and some are in a fluctuating stage that monitor individual sensors and place an 'if:then' on them as individuals, but also look at cumulative values and 'if:then' that, too... it can be confounding.  

the 11* delta between the same sensors on both engines kinda needs to be explained.  

I don't know much about these specific engines, but I do know a clever little trick that will tattle on whacky temperature sensors, that is really simple to do... simply key-on and wait for samples... in a non-running state, and if the sensors report to VV even prior to ignition- the readings should be absolutely the same... if they are not, there is an issue with one of the sensors, period.  

but back to timing:  again, I've limited experience with marine strategies, and a lot more with cars that utilize o2 monitors of the exhaust- and which use that data to reconcile the induction strategy to clean/optimize the combustion... spark is one of those things highly scrutinized, as 'when' a charge is ignited is of extreme importance for not only completing the burn (emissions) but for performance... this boat's power seems to be going right up to the top of the scale in it's curve (again, 24* is right, but is actually 24* of the curve plus whatever the base is) at near WOT... it wouldn't do (allow) that if there was an issue with one of the readings... which means the ten/eleven degrees from that IAT doesn't matter to the strategy...

what would limit it then, since all other available information between those two engines jives- it's likely with one of two other things NOT monitored- which is fuel pressure or air intake being obstructed.  The IAC's duty cycle on both is running near 100%, and though a gummed up one can likely offer as much as a 100~150rpm difference at a cruising speed- that passage is dang near negated when the fly's are fully open as rushing air negates it being there... which makes it a simple matter of cleaning both air filters/spark arrestors, or making sure there is nothing obstructing them (especially, obviously, the lower revving engine).... to me, this is what this situation is acting like....

but, it could be just as easily and just as likely a fuel issue... pumps can move volume and create pressure at lower engine demand, but when you stress them out (high RPM/load) they sometimes can't... the only way you'll be able to know for sure is to monitor them electronically if you can (i don't think they're monitored) or slap a gauge on each rail, and watch them while under load at higher RPM's... they should jump to proper pressure as soon as the key is turned, and that needle ought not move- it should maintain he same pressure throughout the range... if it drops, the pump, the filter, the hose, the tank pick-up, the vent, or obstructions in the rail are likely at fault... if the pressure is good- as it may very well be- then the injector(s) are an issue... either physically clogged baskets or an electrical issue with them... remember, injector harnesses as extremely sensitive to resistance- that's what motors their cycles... a bad connection or a slight ground can cause strange behavior from them.   I once saw a slightly bent spade on an ev6 injector wreak all grades of havoc, and that was found only by accident... once it was repaired/replaced, everything was in concert... 

Wildboating

Mechanic who just put the new motor in said all shutters were in tact and in good condition.  

Wildboating

Can anyone tell me what the lower drive ratio should be?  I know this pita boat had the drives replaced prior to me purchasing.  The lower drives state they are 2.2 on the sales sheet.  I do not know that for a fact but my mechanic is questioning if they really are or if one is different which is causing the issue with my starboard motor.  

Black_Diamond

2.2 should be correct. You would have to haul the boat and likely pull the drive to verify the ratio by turning the input shaft and counting revs to rotate the prop shaft 1 revolution

Did you swap the temp/pressure sensor yet to see if the problem moved?  Mine did almost the exact same thing, one engine just did 'nothing' between say 50% and 100% throttle. 

Wildboating

Heading down there in 30 minutes.  It is the first thing on my list BD.  

Wildboating

Haven't been able to swap sensors yet, needed did socket.

However, I just discovered the good motor at idle holds a steady 14 degree advance at idle.  The trouble motor however is jumping from 10 degrees to 14 very erratically.  Could this be related. 

Wildboating

Swapped the temp sensor however it did not help, thanks for the suggestion though.  Next up is to do balance test to verify each cylinder is firing.