looking for help, possible efi issue
07-23-2013, 04:14 PM
#1
Registered
Thread Starter
Join Date: May 2012
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
looking for help, possible efi issue
well ive bean searching for weeks to find the cause of this problem. I think its time to get others involved. hope someone can help
1998 merc 7.4L (454) MPI mefi3 serial #L689184 25ft avantage citation
tops out at 47 MPH , 3900 rpm every so often kicks in for a few seconds and runs 56 mph at 4500. where it should be..only kicks in once in a blue moon. the problem is there 99% of the time
what ive done
tps ok
map ok
compression ok
injectors ok
fuel sep new
fuel pres 38 psi steady
no codes
next i will change the plugs and wires. when i check the timing in service mode it is at 8 btdc. when i check the timing advance (not in service mode) it raise till 28 btdc at 2700 rpm but stays there above that rpm. not sure if this means anything because this is on the trailer in neutral .any suggestions. no access to a scan tool.
1998 merc 7.4L (454) MPI mefi3 serial #L689184 25ft avantage citation
tops out at 47 MPH , 3900 rpm every so often kicks in for a few seconds and runs 56 mph at 4500. where it should be..only kicks in once in a blue moon. the problem is there 99% of the time
what ive done
tps ok
map ok
compression ok
injectors ok
fuel sep new
fuel pres 38 psi steady
no codes
next i will change the plugs and wires. when i check the timing in service mode it is at 8 btdc. when i check the timing advance (not in service mode) it raise till 28 btdc at 2700 rpm but stays there above that rpm. not sure if this means anything because this is on the trailer in neutral .any suggestions. no access to a scan tool.
07-23-2013, 05:40 PM
#2
I don't believe your timing is the issue. The timing you read on the trailer is an accurate number but not relative to when the boat is in the water and under load. While underway the MAP is significantly higher so the ECM is reading from a different cell in the table and this condition would be virtually impossible to duplicate on the trailer. It is highly unlikely the ECM timing table got corrupted.
When you say the injectors are ok do you mean they are all flow tested? They might be partially clogged.
Is the knock sensor pulling timing under load?
Check all the major ground wires for good connections and other connections for corrosion etc.
Does the ECM aural alarm actually work? The reason I'm asking is perhaps the drive oil level or temp sensor is throwing a code and limiting the engine but the aural alert is inop. I know that's probably a long shot......
When you say the injectors are ok do you mean they are all flow tested? They might be partially clogged.
Is the knock sensor pulling timing under load?
Check all the major ground wires for good connections and other connections for corrosion etc.
Does the ECM aural alarm actually work? The reason I'm asking is perhaps the drive oil level or temp sensor is throwing a code and limiting the engine but the aural alert is inop. I know that's probably a long shot......
07-23-2013, 06:06 PM
#3
Registered
Thread Starter
Join Date: May 2012
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
I took out the injectors and serviced myself using injector cleaner and compressed air .(found it on utube) forced cleaner backwards then forewards using 12 volts . they all opend and a nice stream. might not be the best but i figured it was worth a shot. they looked really good . i aslo checked the injector harness and found all wires good.
how can i check the knock sensor. can i unplug it when its in the water and see if the problem goes away?
alarm does work.
I need to check intake air sensor. does anyone know if i need resistance
values or volts sent to ecm...?
how can i check the knock sensor. can i unplug it when its in the water and see if the problem goes away?
alarm does work.
I need to check intake air sensor. does anyone know if i need resistance
values or volts sent to ecm...?
