2005 320 5.7L with V - Missfire

ipxih

ipxih

New Member
Apr 9, 2020
22
Boat Info
2005 320
Engines
Mercruiser w/ V drives
Hello
just installed a port side new crate motor on my boat.

boat starts and idles 100% smooth.

during sea trial, As soon as i get the RPM to 1800+ it backfires and missfires ( only on port side *new motor*)

changed plugs, checked timing, checked coil, checked ground, checked all BRAND NEW injectors.

What can be the issue?

need advise please

my only option left is to change fuel module $$$$ ?

any other suggestions?
 
Why was the original motor replaced?

Did the new crate motor come with a new fuel module?

Can you get some fuel pressure readings, at idle and under load?
 
Thanks for your response.

the new crate motor came without it.

original motor still ran but needed much TLC , valve job and was milky inside. was cheaper and better long term to replace with new.
all new injectors were installed

in the last 3 days, i swapped;

ECU between motors to see if its computer related,
i rechecked timing,
i swapped distributor cap and module,
checked compression on new motor ( all 162-165 across the board )
installed a new crank sensor

i plugged a spare fuel tank and thought it was "bad fuel" issue

No codes come up when scanned during sea trial everytime.

the fuel pressure drops about 3-4PSI and reads around 36-40 under load (1500+ RPS)


both motors idle smooth as butter even under a load until i open throttle and get passed 1800 RPM, the starboard motor runs perfect and continues to accelerate without any hesitation, the port ( new ) motor begins to backfire / missfire and hesitates. as i open throttle it sounds worse between 1900-2700 rpm.

my only thought left now is the fuel module $$$$
could be not supplyin enough juice under a load


i took a video i can email as well

thank you
 
yes,
wires and plugs are new. i will swap them with another motor just in case and test
 
ipxih said:
Thanks for your response.

the new crate motor came without it.

original motor still ran but needed much TLC , valve job and was milky inside. was cheaper and better long term to replace with new.
all new injectors were installed

in the last 3 days, i swapped;

ECU between motors to see if its computer related,
i rechecked timing,
i swapped distributor cap and module,
checked compression on new motor ( all 162-165 across the board )
installed a new crank sensor

i plugged a spare fuel tank and thought it was "bad fuel" issue

No codes come up when scanned during sea trial everytime.

the fuel pressure drops about 3-4PSI and reads around 36-40 under load (1500+ RPS)


both motors idle smooth as butter even under a load until i open throttle and get passed 1800 RPM, the starboard motor runs perfect and continues to accelerate without any hesitation, the port ( new ) motor begins to backfire / missfire and hesitates. as i open throttle it sounds worse between 1900-2700 rpm.

my only thought left now is the fuel module $$$$
could be not supplyin enough juice under a load


i took a video i can email as well

thank you
Click to expand...
Can you swap the fuel module between motors? You’ll know for sure then
 
If that has the flat distributor cap with 4 wires sticking out each side, I think setting it up correctly is critical. Unless I’m wrong the spark timing and injector firing is controlled by the ECM based off of the crankshaft sensor. It’s critical that the distributor rotor be “aimed” at the correct lug in the distributor cap. If it’s not set up correctly as spark timing is increased the spark may be created when the rotor tip and cap lug are distant and the spark will jump where it’s not supposed to go. (Like the wrong cylinder)

It’s NOT set up with a timing light. I’m pretty sure that’s your issue.
 
Seapig said:
If that has the flat distributor cap with 4 wires sticking out each side, I think setting it up correctly is critical. Unless I’m wrong the spark timing and injector firing is controlled by the ECM based off of the crankshaft sensor.
Click to expand...

You are correct. The ECM controls the timing, spark advance on the 350 MAG MPI. Timing is listed as “non-adjustable” on the side of the plastic engine cover (I have the same engine, a few years newer).

It’s critical that the distributor rotor be “aimed” at the correct lug in the distributor cap. If it’s not set up correctly as spark timing is increased the spark may be created when the rotor tip and cap lug are distant and the spark will jump where it’s not supposed to go. (Like the wrong cylinder)
It’s NOT set up with a timing light. I’m pretty sure that’s your issue.
Click to expand...
When I changed the rotor in my distributor cap, it was keyed in such a way that it would only fit in one position. There was no ambiguity. I have read that this coarse timing is sufficient for the ECM to work from with its real-time adjustments.

I comment on this thread as I’m having very similar symptoms yet have very little left to replace, besides the fuel pumps. That thread is here: http://www.clubsearay.com/index.php...l-rail-injector-removal-and-inspection.97847/
 
I’m shooting from the hip here.......

in the automotive application with a similar engine control system we’d “park” the crank in a Very specific position And install the distributor with the rotor aimed at a mark on the base.

I’d review the Mercruiser distributor installation instructions and follow them to the letter.
 
Seapig said:
I’m shooting from the hip here.......

in the automotive application with a similar engine control system we’d “park” the crank in a Very specific position And install the distributor with the rotor aimed at a mark on the base.

I’d review the Mercruiser distributor installation instructions and follow them to the letter.
Click to expand...
Literally, in the last fifteen minutes, I have found similar suggestions/videos in order to address similar symptoms. I think you may be correct as it indicated the same general procedure (park the crank, verify distributor indexing).

It looks like I have additional investigation to do. Thanks for taking the time to chime in...
 
i think its the dist too - you can google vortec distributor installation - if you end up needing a complete new cf3 module, i may have one availale...
 
I have swapped both Fuel Modules earlier today and will do a sea trial in the morning to see if the issue transferred to the starboard side motor now.

Im hoping that it is just the module.

The shop that did all the engine work for me stated that he double checked the timing and distributor cap and module inside. he stated that there's only one way to insert and set it.
The plugs and wires are all new.

i can try to swap wires between motors as well .

wil know in the morning.

Thanks for all the brain work and suggestions !
 
Hello,

so took the boat out earlier. same issue.

swapping Complete Fuel module assembly didnt resolve the issue.

I do have to say that it began to run better and prior to swap the new " crate motor " would top out at 3500 rpm - other motor ( starboard side ) keeps climing way past 4500rpm without hesitation.

today sea trial shows that new crate motor "port side" ( after swapping fuel module ) ran better and misfire is very minimal now, and also i noticed that it ran past 4000RPM now, which it never did before.

could it be old bad fuel in the tank?

Boat did have a full tanks on both sides with fuel older then 2yrs old :(


my only thought now is to swap "new" plug wires between both motors

or

recheck timing and rotor cap again


Any other suggestions?
 
The distributor can be misinstalled if it’s the same as the automotive version.

simple to check:

review this http://www.gmtruckcentral.com/articles/distributor.html

then set your “good” motor to TDC and note the EXACT relationship of the rotor tip to the distributor body (it’ll be aimed at #1 or #6. One full crank revolution will rotate the rotor 1/2 turn)

Then compare it to your troubled engine.
 
Seapig said:
The distributor can be misinstalled if it’s the same as the automotive version.

simple to check:

review this http://www.gmtruckcentral.com/articles/distributor.html

then set your “good” motor to TDC and note the EXACT relationship of the rotor tip to the distributor body (it’ll be aimed at #1 or #6. One full crank revolution will rotate the rotor 1/2 turn)

Then compare it to your troubled engine.
Click to expand...

I think the Mercruiser "version" of this procedure is detailed in this video:


It appears that it might help address situations where everything else appears ok, but occasional misfires still occur due to the HVS not aligning properly under all timing conditions (e.g. under load). It seems to really be a fine tuning of the base timing in order to account for timing chain stretch and other mechanical wear factors in the engine.

I'm looking for the schematic for the camshaft sensor "tool" displayed but can't find anything. It's apparently detailed in Merc serv bulletin 2011-11r2...but I can't find it posted anywhere. It's a basic circuit to read the hall-effect cam shaft sensor but it'd be nice to know exactly how Merc says to construct it.

Camshaft sensor "tool" shown specifically at 5:12 in the video (forum software doesn't understand embedded time links to youtube content :mad:)
 
Last edited:
Yay !!!



this is the solution to my headache of 5+ days now


thank God !

Thank you everyone for your help. after watching this video i made the last and only attempt left.....

it did. boat runs like new and full throttle like a beast with 2xV8's

im so glad that someone could point me to the main issue. im thankful for the input and it has been a dificult 5+ days of swapping all components between motors until earlier today - bingo !

thank you thank you thank you

shes all perfect now and runs 100% !!!
im so happy
 
ipxih said:
Yay !!!

this is the solution to my headache of 5+ days now

thank God !

Thank you everyone for your help. after watching this video i made the last and only attempt left.....
Click to expand...

I’m happy to hear you’ve had success!

Can you elaborate on how far “off” your timing was? What did you use in place of the camshaft “position indicator tool”?
 
Timing was off by about a /16th
just a slight tap and it made all the diference.

shes running amazing
 
ipxih said:
Timing was off by about a /16th
just a slight tap and it made all the diference.

shes running amazing
Click to expand...
Ok, then it sounds like I need to give this a try before giving up entirely. Thank you and happy boating!
 
You must log in or register to reply here.

Forum statistics

Threads
113,170
Messages
1,427,755
Members
61,079
Latest member
capeharj
Back
Top