Looking for a genuine Mercruiser Service Manual 1997 7.4 LX MPI plus idle stumble.

[OCMerrill]

I need to diagnose a rough idle or stumble at idle. Either in gear or out of gear. Its clearly missfire.
Had all the injectors rebuilt and installed them. Now I come to find out I'm under propped (straight past 5k) so that result was great.
Now if I could cure the rough idle stumble. Had it since I bought the boat 4 years ago now. Getting worse hence the rebuilding of the injectors. No change.
Its likely an electrical issue or the ECU thinks the engine is cold and needs to stay with a rich mixture?

Also when I took the upper plenum off there was some oil in there. Perhaps thats normal for 817 hrs. I know the intake arrester was filthy and thats now clean. Some of the tubes leading from the plenum were clogged with coaked oil and are now clean.

This is not something I want to just throw parts at although the Intake setup I purchased from @Maw has a mini parts wherehouse attached so I could swap stuff around.
I would rather look for codes or see if some enrichment table is being deployed.

I would like to own both however I am having a hard time figuring out the actual Merc Manual(s) as I see there is maybe a part one and two?
Best place to purchase and what manual number?
Also looking for a scan tool that will work with my year?


Engine serial number OK151969

All this is clean now, during re-assembly.

 

[LargeOrangeFont]

Not to just throw parts at it, but have you checked/ cleaned/ replaced the idle air control valve?

I bought a Japan made “car” IAC for my boat after mine failed, and it never idled better. It had an uneven idle for a few seasons before it finally died.

I’m assuming the PCV hose was routed to the air cleaner.. likely the source of the oil.

 

[Bowtiepower00]

I think this manual will work, I’ve been using it for my Mag MPI.

https://www.manualslib.com/manual/1813938/Mercury-Mercruiser-Mcm-454-Mag-Mpi.html

 

[OCMerrill]

Not to just throw parts at it, but have you checked/ cleaned/ replaced the idle air control valve?

I bought a Japan made “car” IAC for my boat after mine failed, and it never idled better. It had an uneven idle for a few seasons before it finally died.

I’m assuming the PCV hose was routed to the air cleaner.. likely the source of the oil.

I cleaned it when I cleaned the throttle body. It idles down to 650 or so in gear and holds there, just runs a bit rough and stumbles.

The throttle body was a oily mess to say the least.

 

[Shlbyntro]

Do a compression test and spark plug read and report back

 

[OCMerrill]

I think this manual will work, I’ve been using it for my Mag MPI.

https://www.manualslib.com/manual/1813938/Mercury-Mercruiser-Mcm-454-Mag-Mpi.html

Thank you.

 

[Fun Times]

Technically you’d need service manual number 16 as your serial number is 0K••••••, Manual number 23 wouldn’t really be the proper one especially depending on the specifications you’re testing such as fuel pressure, etc.

0K151969 shows the engine to be MERCRUISER MPI, W/PX, TWOPCEX, WORO, GEN-6 7.4LX MPI BRAVO.

Manual 23 covers: Gen. VI Engines MCM and L29/7.4L. With serial number higher than your 0K as 23 covers 0L and up numbers.
https://www.manualslib.com/manual/1813938/Mercury-Mercruiser-Mcm-454-Mag-Mpi.html?page=4#manual

MerCruiser Service Manual #16 - GM V-8 454 CID (7.4L) / 502 CID (8.2L)

This factory service manual provides detailed service information, step-by-step repair instruction, and maintenance specifications for your MerCruiser GM V-8 454 CID (7,4L) / 502 CID (8,2L) Marine Engines. This comprehensive overhaul and repair manual is designed as a "Service Guide" for...

www.emanualonline.com

Covers, 90-823224--2 796 iii V-8 Models Covered in This Manual Gen V Engines Model Serial Number Stern Drive Engines MCM 7.4L Bravo OD830779 to OF800699 MCM 7.4L Bravo Three OD838819 to OF800699 MCM 7.4LX MPI OF595275 to OF801999 MCM 454 Magnum (Carburetor) OD837587 to OF801999 MCM 454 Magnum EFI, EFI/MP and MPI OF111570 to OF802349 MCM 502 Magnum (Carburetor) OD831432 to OF114528 MCM 502 Magnum EFI, EFI/MP, MPI OD840650 to OF802599 Inboard Engines MIE 7.4L (Carburetor) OD840300 to OF820141 MIE 7.4L EFI/MP and MPI OF490697 to OF820103 MIE 8.2L (Carburetor) OD857200 to OF819619 Ski Engines MIE 454 Magnum EFI, EFI/MP and MPI Tournament Ski OF215800 to OF820099 Gen VI Engines Model Serial Number Stern Drive Engines MCM Bravo 7.4L (Carburetor) OF800700 and above MCM 7.4LX EFI OF820000 and above MCM 7.4LX MPI OF802000 and above MCM 454 Magnum (Carburetor) OF801700 and Above MCM 454 MPI OF802350 and above MCM 502 MPI OF802600 and above Inboard Engines MIE 7.4L (Carburetor) OF820142 and above MIE 7.4L EFI OF874815 and above MIE 7.4L MPI OF820104 and above MIE 8.2L MPI OF775694 and OF775695 MIE 8.2L MPI OF819620 and abov

Here’s your engine parts if needed, https://www.mercruiserparts.com/7-4lx-bravo-mpi-gen-vi-gm-454-v-8-19-1

Search eBay service manual number 16 and/or the manual part number for good prices.

 

[rrrr]

Plug wires.

I might have that manual. I'll wander out into the shop in a bit and check.

 

[Racey]

Plug wires.

I might have that manual. I'll wander out into the shop in a bit and check.

That was my first thought after reading as well. Cap/Rotor and WIRES

Wires are often overlooked, they will go bad after about 15 years or so even if kept in meticulous condition indoors etc.

 

[motormonkey]

Over 800 hours, might be time to check compression and a leak down. Heads might be getting tired.

 

[Runs2rch]

That was my first thought after reading as well. Cap/Rotor and WIRES

Wires are often overlooked, they will go bad after about 15 years or so even if kept in meticulous condition indoors etc.

The ignition module inside the distributor as well.

 

[Fun Times]

Plug wires.

I might have that manual. I'll wander out into the shop in a bit and check.

Hey rrrr: Maybe you could also check for Merc manual number 16…. I originally posted above you but had to hide it for a bit to double check something before reposting it.

Also adding an option to rent a scan tool for some Mercruiser models which will work for OCMerrill. https://www.ebay.com/itm/2852525116...BpWsqNwEQD/oK9VDwSWEJvaA==|tkp:Bk9SR-ymjMf4YQ

 

[OCMerrill]

Technically you’d need service manual number 16 as your serial number is 0K••••••, Manual number 23 wouldn’t really be the proper one especially depending on the specifications you’re testing such as fuel pressure, etc.

0K151969 shows the engine to be MERCRUISER MPI, W/PX, TWOPCEX, WORO, GEN-6 7.4LX MPI BRAVO.

Manual 23 covers: Gen. VI Engines MCM and L29/7.4L. With serial number higher than your 0K as 23 covers 0L and up numbers.
https://www.manualslib.com/manual/1813938/Mercury-Mercruiser-Mcm-454-Mag-Mpi.html?page=4#manual

MerCruiser Service Manual #16 - GM V-8 454 CID (7.4L) / 502 CID (8.2L)

This factory service manual provides detailed service information, step-by-step repair instruction, and maintenance specifications for your MerCruiser GM V-8 454 CID (7,4L) / 502 CID (8,2L) Marine Engines. This comprehensive overhaul and repair manual is designed as a "Service Guide" for...

www.emanualonline.com

Covers, 90-823224--2 796 iii V-8 Models Covered in This Manual Gen V Engines Model Serial Number Stern Drive Engines MCM 7.4L Bravo OD830779 to OF800699 MCM 7.4L Bravo Three OD838819 to OF800699 MCM 7.4LX MPI OF595275 to OF801999 MCM 454 Magnum (Carburetor) OD837587 to OF801999 MCM 454 Magnum EFI, EFI/MP and MPI OF111570 to OF802349 MCM 502 Magnum (Carburetor) OD831432 to OF114528 MCM 502 Magnum EFI, EFI/MP, MPI OD840650 to OF802599 Inboard Engines MIE 7.4L (Carburetor) OD840300 to OF820141 MIE 7.4L EFI/MP and MPI OF490697 to OF820103 MIE 8.2L (Carburetor) OD857200 to OF819619 Ski Engines MIE 454 Magnum EFI, EFI/MP and MPI Tournament Ski OF215800 to OF820099 Gen VI Engines Model Serial Number Stern Drive Engines MCM Bravo 7.4L (Carburetor) OF800700 and above MCM 7.4LX EFI OF820000 and above MCM 7.4LX MPI OF802000 and above MCM 454 Magnum (Carburetor) OF801700 and Above MCM 454 MPI OF802350 and above MCM 502 MPI OF802600 and above Inboard Engines MIE 7.4L (Carburetor) OF820142 and above MIE 7.4L EFI OF874815 and above MIE 7.4L MPI OF820104 and above MIE 8.2L MPI OF775694 and OF775695 MIE 8.2L MPI OF819620 and abov

Here’s your engine parts if needed, https://www.mercruiserparts.com/7-4lx-bravo-mpi-gen-vi-gm-454-v-8-19-1

Search eBay service manual number 16 and/or the manual part number for good prices.

Purchased and downloaded and yes thats my setup 100%. Bookmarked the parts link.

I apricate the effort / help here.

 

[OCMerrill]

That was my first thought after reading as well. Cap/Rotor and WIRES

Wires are often overlooked, they will go bad after about 15 years or so even if kept in meticulous condition indoors etc.

All was done before I purchased the boat 4 years ago. However...that said your right 100%.

I'll pull the plugs and do a cold compression test. I wont be able to do a warm test until it comes back out of my shop. It is no easy feat to maneuver that thing in there.

I used to build and tune engines...going way back but fuel injection needs to become my thing now.

 

[Racey]

All was done before I purchased the boat 4 years ago. However...that said your right 100%.

I'll pull the plugs and do a cold compression test. I wont be able to do a warm test until it comes back out of my shop. It is no easy feat to maneuver that thing in there.

I used to build and tune engines...going way back but fuel injection needs to become my thing now.

Have you put a scanner on it to monitor the basic tuning inputs? MAP, TPS, CTS, IAT, etc and the outputs like ignition timing and injector PW?
Especially during the conditions with the stumbke

 

[OCMerrill]

Have you put a scanner on it to monitor the basic tuning inputs? MAP, TPS, CTS, IAT, etc and the outputs like ignition timing and injector PW?
Especially during the conditions with the stumbke

I have not read the data however I will purchase one used here in a bit.

I'll check Ign timing and look for advance next time I run it on the trailer.

 

[rrrr]

Plug wires.

I might have that manual. I'll wander out into the shop in a bit and check.

I was wrong. It's a straight 7.4L manual and doesn't have any info about fuel injection.

 

[OCMerrill]

I was wrong. It's a straight 7.4L manual and doesn't have any info about fuel injection.

Thanks for checking.

 

[Runs2rch]

All was done before I purchased the boat 4 years ago. However...that said your right 100%.

I'll pull the plugs and do a cold compression test. I wont be able to do a warm test until it comes back out of my shop. It is no easy feat to maneuver that thing in there.

I used to build and tune engines...going way back but fuel injection needs to become my thing now.

Depending on what plugs you are using, switch to a projected tip. NGK BPR6FS. They will clean up the idle.

 

[Shlbyntro]

Depending on what plugs you are using, switch to a projected tip. NGK BPR6FS. They will clean up the idle.

I prefer the AC MR43T (or LTS for L29s). Cheap robust plugs that will burn oil better than a 2stroke

 

[Runs2rch]

I prefer the AC MR43T (or LTS for L29s). Cheap robust plugs that will burn oil better than a 2stroke

NGK makes AC plugs still I think.

 

[LargeOrangeFont]

Depending on what plugs you are using, switch to a projected tip. NGK BPR6FS. They will clean up the idle.

Good point. I run NGK TR55 myself.

 

[TPC]

If you have a Tachometer disconnect it.