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

Wildboating

I have looked everywhere.  I am dedicating all day sunday to ether the motor over again.   The vaccum leak will be on the intake side of the motor correct?

212rowboat

the MAP at WOT should be buried- straight atmospheric pressure (14.7 most often @ sea level - restrictions) and yours is 14.03/weak engine and 14.09 strong engine... you've got unmetered air... either at manifold, a port off the manifold (including TB) or a port off the TB- OR, a bad valve seat.  

Wildboating

@212rowboat


I know you cant cuss on here but son of a #&@*$.  I have not seen that after pouring over these files for ever.  I went back and slowed the file down to real time and you are right!!!, the starboard motor is around 66% iac at wot.    Where should I be looking?   Should i just start spaying ether all over the motor?  Sounds scary, fire & boats never mix well.

Wildboating

I noticed while at WOT the IAC does creep up from 66% to 99%.  If there was a leak it wouldnt change would it?  Is this more condusive of a bad IAC?  That was replaced from day one when I bought the boat.  We had trouble with the engine staying running, members here suggested replacing the IAC.  Ultimately we found tuliped valves was causing the running issue.

212rowboat

yes- has to be on the intake side... an exhaust obstruction could also 'back up' the process, but after looking those numbers over it doesn't make sense as the temperature of an obstructed engine would be higher. 

Wildboating

Is this a good explanation on how to do the valves?   https://www.youtube.com/watch?v=CEV3Yz0kpDY

212rowboat

start with a new IAC, and pay careful attention to the plunger DON'T PUSH IT OR PULL IT... let it be- let the computer exercise it mapping voltage to position... 

ether is your friend finding vacuum leaks, but be **** careful.... a bit of silly putty or that goop stuff made to clean stuff out of window's controls/crevices will also work, and though a PITA its better to isolate with... don't forget about PCV valves and the hoses.  

212rowboat

yup.. video nails it- for a flat tappet... for hydraulic roller, same except 1/8th past silent.  

Wildboating

Thanks so much Drew!!   I will report back after Sunday.

Wildboating

Drew,  @212rowboat

I ran new test yesterday after swapping map sensors, IAC between motors.    Map sensors appeared wet, maybe even oily.  I am going to check the PCV's today.

Based on your knowledge of how the MAP works with the IAT and fuel tables would a 5-8* variance on IAT's cause much issue?   I see the IAC is 10% closed at WOT and still can not find a vaccum leak anywhere.   I am so close to buying a smoker to find it.....


The starboard IAT shows 5-8* cooler at the same coolant temp after warming up both engines then doing 2 comparable runs.  Cruise at 20% throttle, 40% throttle then WOT.

Wildboating

Also, without balancing the motors.   My port motor caps out at around 4k rpm.  I wonder if something is up with it or if it just cant get higher rpms due to the other motor lagging behind.

Wildboating

Would the starboard be running much fatter since it thinks the intake air is denser?

212rowboat

yeah, port could be carrying the drag starboard is making, causing it excess load.  

the reason the IAT is metering less than full duty cycle is because one of two things- either there is unmetered air or the linkage is jacked up and not allowing 100% full throttle (which is the condition of the throttle position/sensor, too).... 

davidbrooks

Watched a video yesterday of a guy looking for a vacuum leak with a cigar and a length of tubing attached to the air intake. Blow cigar air in and look for it to come out somewhere.  $4 vs $1000.

Wildboating

Well..... I took a rubber glove and blocked off the intake.  Grabbed a couple cigarettes and fire extinguisher, I blew through the pcv valve end of the rubber tubing going into the top of the intake.  The other end of the hose I blew through at the top of the intake manifold was leaking once I built up some pressure and inflated the glove.  Once I get a test run I will report back.    The rockers on the starboard motor are definitely chattering compared to the port motor.  With the risers and fuel injection rails over the valve covers I don't see how to safely adjust the valves.  I guess tear top down, remove covers, reassemble then try setting but as far as getting towel in there to set against I'm not sure it's possible. 

Wildboating

What about the lower MAT temp?  

212rowboat

i wouldn't worry too much about that right now.... it could be caused by an advanced spark on the warmer engine (due to base timing?), it could be caused by slightly obstructed exhaust (due to bad valve event timing or lash or a tight flapper?) or it could simply be carbon on the sensor.  it's not enough to warrant concern in my opinion. 

Black_Diamond

Any updates on your situation?  What prop pitch did you end up chsnging to?

Wildboating

We put the Hill Marine 22p 4x4 on at the begining of this thread.   It didnt help.   I have another mechanic looking at it.  Guy seems very knowledgeable but rarely available to look.   

Found vaccum leak, didnt help any thing though.
He ordered new plug wires and new distributors.   He thinks this is a spark issue.   He is coming back soon to disconnect the motor harness and plug into and auxillary system that isolates the boats electrical system to test.  The saga continues.  

Wildboating

So, Distributor was pulled, checked the gear on it and verified correct alignment.  Also, just to throw some more money away we replaced plug wires again.   I took boat out and not a change as been made.  With that being said, I understand the new mechanic not wanting his hands tied behind his back and he felt the wires had reached their age.   I show they were replaced 3 years ago on my maintenance spreadsheet, but he felt they were older than that.



SOO...  I found a schematic of our ignition system, also my new mechanic mentinoed this to me the other day.   What is the chances i have a bad knock sensor or spark control module?   He seems to think this is a ignition related issue.  Im not sure as I show full timing being reached on both engines.   

212rowboat

the timing chain being one tooth off- either advancing or retarding- could be causing your issue too... the crank position sensor (ckps) and camshaft position sensor (cps) are only as good as how they're aligned.  slop in the chain could certainly cause it, but it would likely be (really close to) okay until the engine is loaded-  if the valve events don't align to the spark and injection events (sync), then...... issues.... if the valves are closing even a hair later than they're supposed to (retarding valve timing) that engine will lose (dynamic) compression- and power- though through its monitoring system 'all will be well'.  

Wildboating

@Alswagg

At this point if this is not figured out by time to put the boat away I think i will be pulling both and bringing them to you.  

As far as the timing light, Im told this motor ECM 555 does not have a adjustable timing.  The ECM controls it.   Also, there are no timing marks on the bottom of the motor.   2003 350 mag mpi

Black_Diamond

Still a very vexing problem and quite interested in the end cause. 

Wildboating

According to this the Iat and map sensor are 2 separate devices.  I was under the impression the were both in the same sensor.  Which is correct?  

Black_Diamond

#16 is the combined tmap sensor. At least on my '03 350 MAG MPI. 

Wildboating

Thanks BD, that is what i thought but i seen this exploded view for a 350 mag MPI that showed different.  Thanks again.

Black_Diamond

Later models had them separate I think. Took me awhile to get it figured out too. 

Black_Diamond

Old link, but has the part number.

http://www.ebay.com/itm/OEM-REPLACEMENT-Mercury-MAP-Temperature-Pressure-TMAP-Sensor-885165-mercruiser-/282068462856

Wildboating

So after multiple mechanics telling me there is no cool fuel on my boat i scored a manual and found that yes indeed there is.  It is underneath the motor on the port side.   Could i have a messed up fuel regulator??  I read a lot about these things being foobarred.  

Handymans342

Yup