6.2 mpi timing issue mercruiser om670840

[henry1357]

Hi everyone

i have just rebuilt my mercruiser 6.2 mpi and all was well until i took it out on the lake
boat running rough sounds like its missing and won't rev fully
tried turning the distributor to adjust the timing but no different

i believe it it is a timing issue and have read that this can only be set with marine software, is this the case or is there another way of setting timing

thanks in advance

henry

 

[MikDee]

I'm guessing you had the distributor out, and now it is back in at the wrong spot. You can't just turn the distributor for a fix. If you have a Thunderbolt IV, or Tbolt 5, there is a special procedure you need to do to set the timing. What distributor do you have?

 

[henry1357]

No Title

hi thanks for reply

i have tried turning the distributor but it makes no difference

boat seems to run well and rev up fine on muffs just wouldn't run properly under load

i have attached a pic of the type of dizzy obviously mine is v8

regards
henry

 

[henry1357]

if it helps its a merc om670840

 

[Bondo]

hi thanks for reply

i have tried turning the distributor but it makes no difference

boat seems to run well and rev up fine on muffs just wouldn't run properly under load

i have attached a pic of the type of dizzy obviously mine is v8

regards
henry

Ayuh,.... My guess is the timin' is bein' set by the 'puter all right,...

It's starvin' for Fuel,... A Lean condition skip,....

 

[henry1357]

hi bondo
thanks for reply
i will check that its not starving for fuel tomorrow.

regarding setting the timing i have read that i need to set engine in base timing mode either with a scan tool or by jumping 2 pins on dcl and the set timing at 8 deg btdc

is this correct for my engine

regards
henry

 

[Bondo]

hi bondo
thanks for reply
i will check that its not starving for fuel tomorrow.

regarding setting the timing i have read that i need to set engine in base timing mode either with a scan tool or by jumping 2 pins on dcl and the set timing at 8 deg btdc

is this correct for my engine

regards
henry

Donno ain't got one,.... I've Heard, ya stab the distributor good, 'n close, then the 'puter handles it from there,....

Also Heard the distributor caps can give ya issues like yer seein',.....


What caused the need for the recent rebuild,..??

 

[henry1357]

when i bought the boat the engine was out as needed a new coupler which had spun, so was sold as a non runner

exhaust manifolds were off as well so i decided to take engine apart and check it for ware before reinstalling.

there was surface rust around dizzy so i removed dizzy and cleaned the rust up.

put it all back together with new gaskets and new coupler aligned engine and it fired up instantly, runs and revs well on muffs.

dropped in the water and engine won't rev over 2500-3000 and has no power, won't get on plane.
sounded like it was miss firing so i assumed it was timing issue

 

[achris]

Bondo is completely correct in that the ECU handles the timing based on engine speed, manifold pressure, air and engine coolant temperature and another handful of parameters. The only way to 'check the timing' is with the computer software and the plug-in adapter for the engine. There is no way to adjust the timing, it's done in the ECU... What you do need is the 'distributor' to be in the right place. If you have moved it too far away, then when the ECU advances the timing the rotor may not be lining up with the post for that spark plug lead properly. There is a set up procedure in the manual for the distributor....

Chris.....

 

[alldodge]

Hi everyone

i have just rebuilt my mercruiser 6.2 mpi and all was well until i took it out on the lake
boat running rough sounds like its missing and won't rev fully
tried turning the distributor to adjust the timing but no different

i believe it it is a timing issue and have read that this can only be set with marine software, is this the case or is there another way of setting timing

thanks in advance

henry

Are you sure it's missing or does it just lack power to get full running RPM

 

[henry1357]

hi everyone after all your advise and reading on the forum i went and changed the fuel, fuel filter/seperator and ht leads. (holding back on dizzy until after test)

the engine sounds much better on muffs than before and i will take it to lake next week to see.

hopefully it will be ok, do you guys think it could be that simple

regards

henry

 

[henry1357]

Just one more thing guys
i have put a timing light on my engine just to check, and the timing mark on balancer is a little bit erratic, what I'm asking is should it be dead stable on the mark or is is normal to move back and forth a little

 

[MikDee]

Just one more thing guys
i have put a timing light on my engine just to check, and the timing mark on balancer is a little bit erratic, what I'm asking is should it be dead stable on the mark or is is normal to move back and forth a little

It will probably bounce a little

 

[henry1357]

hi mikdee

thanks for quick reply, you have put my mind at rest a little, will know for sure if all is well once i get back to lake.

the timing doesn't go past the mark on engine but moves about 1/4 inch back from mark

 

[achris]

Just one more thing guys
i have put a timing light on my engine just to check, and the timing mark on balancer is a little bit erratic, what I'm asking is should it be dead stable on the mark or is is normal to move back and forth a little

Completely normal for MPI....

 

[henry1357]

thanks Achris

will post results once I've done lake test

 

[henry1357]

Also guys please listen to my engine on muffs and let me know what you think

thanks again
everyone has been a great help

 

[achris]

That sounds like it's missing on one or some cylinders. Using a pair of properly insulated pliers pull a plug lead at a time off and see if the sound changes.

 

[henry1357]

hi achris
pulling leads off one at a time nearly stops engine on all leads except 3 and 7, sound doesn't seem to change.

have had new plugs and leads, what could it be

distributor ?

thanks henry

 

[MikDee]

That don't sound good not running on all cylinders! Check out your plug wiring, firing order! 1-8-4-3-6-5-7-2 clockwise, Port side 1-3-5-7, Stbd side 2-4-6-8, Next check your valve adjustment, loosen till they clatter slightly, then snug up till quiet then 1/2 turn down slowly, do them all, and your done!