Mercruiser 350 low WOT error code 42 w/video

Got a ‘94 ski boat with 5.7 350 EFI last fall. Had sat for 10 years but seller got it running and would idle and go up to 2500 rpm no problem. When I got it I Cleaned out the vst tank and got the rpm up to wot no problem in the driveway. Never got up to temperature and found that the thermostat was installed improperly and was getting water all the time. Straightened that out and now gets to temperature. Did a compression check and was getting good consistent numbers for all cylinders except #8 which was at 45. Was advised by mechanic to rev engine and see if it was a stuck ring. Ended up freeing that up and now have 150ish accross the board. Took it on the lake for a run and would get to about 3500 rpms and that’s it. I replaced the fuel/water filter already no change. Start of the year I filled the tank with fresh gas after winter. Maybe less then 5 gallons were in it previously. Ran through a lot of that and then cleaned vst and new filter again. Boat honestly seemed to run better when the thermostat was installed improperly and was getting cold water all the time. Had the E

Serial 0F230168

Sent the ECM out to OBD diagnostics and it checked out fine. He was able to pull the engine hours 724 and logged codes which he cleared. M43 ESC M42 EST M33MAP M21 TPS M14 Coolant. Said it was good on harness with injectors and all sensors and relays and IAc was good. He did mention a lot of dirt in J1 and J2.

I borrowed a scan tool and was getting error code 42 even after ECM was cleared. I also took the below video so you can see the timing jumping around as well as some of the other readings.

https://www.youtube.com/watch?v=nqMt...ature=youtu.be

Any help or suggestions would be great. Thank you

There is always the possibility that the engine is over propped. Often folks want more speed and go up a couple of inches in pitch, which often results in the engine not revving up to where it used to.. Also... did not see where you changed cap, rotor, wires....etc. or verified correct firing order, i.e. correct connections to plugs.

Sorry forgot to mention that I did check the prop. It is factory pitch. Does have a slight burr but was advised that it wouldn't affect it as much as the issues I'm experiencing. Also forgot to mention that I did replace cap and rotor as well as wires originally. Unfortunately didn't solve my problems.

This EFI system is fuel only. The ECU doesn't control spark. The noisy timing signal might be a faulty ignition amplifier module.

o2batsea said:

This EFI system is fuel only. The ECU doesn't control spark. The noisy timing signal might be a faulty ignition amplifier module.

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This is 100% wrong. Here are some direct quotes from MerCruiser manuals.

The Electronic Fuel Injection is controlled by an Engine Control Module (ECM). This module
is the nerve/decision center of the system. It uses all the information it gathers to manage
ignition spark, delivering increased fuel economy and maximum engine performance.
The system uses inputs from sensors to make decisions on the amount of spark advance
or retard allowed.
The system has been designed to control ignition advance and retard electronically by the
ECM.

CIRCUIT DESCRIPTION:
When the system is running on the ignition module,
that is, no voltage on the bypass line, the ignition
module grounds the IC signal. The ECM expects to
detect a low voltage on the IC line during this condition.
If it detects a voltage, it sets Code 42 and will not
go into the IC mode.
When the RPM for IC is reached (about 300 RPM),
and bypass voltage applied, the IC should no longer
be grounded in the ignition module, so the IC voltage
should be varying.
If the bypass line is open or grounded, the ignition
module will not switch to IC mode so the IC voltage
will be low and Code 42 will be set.
If the IC line is grounded, the ignition module will
switch to IC but, because the line is grounded, there
will be no IC signal. A Code 42 will be set

The timing jumping around on the scan tool is completely normal.

MerCruiser manual MCM#17 p/n 90-823225--1 will lead you through the steps to correct the code 42. Once that is corrected, the low WOT might be corrected or if not you can move on to more troubleshooting. But first the code 42 needs to be addressed.

Hm this would be a pretty advanced EFI for 1994. Had no idea. Thanks.

muc said:

This is 100% wrong. Here are some direct quotes from MerCruiser manuals.

The Electronic Fuel Injection is controlled by an Engine Control Module (ECM). This module
is the nerve/decision center of the system. It uses all the information it gathers to manage
ignition spark, delivering increased fuel economy and maximum engine performance.
The system uses inputs from sensors to make decisions on the amount of spark advance
or retard allowed.
The system has been designed to control ignition advance and retard electronically by the
ECM.

CIRCUIT DESCRIPTION:
When the system is running on the ignition module,
that is, no voltage on the bypass line, the ignition
module grounds the IC signal. The ECM expects to
detect a low voltage on the IC line during this condition.
If it detects a voltage, it sets Code 42 and will not
go into the IC mode.
When the RPM for IC is reached (about 300 RPM),
and bypass voltage applied, the IC should no longer
be grounded in the ignition module, so the IC voltage
should be varying.
If the bypass line is open or grounded, the ignition
module will not switch to IC mode so the IC voltage
will be low and Code 42 will be set.
If the IC line is grounded, the ignition module will
switch to IC but, because the line is grounded, there
will be no IC signal. A Code 42 will be set

The timing jumping around on the scan tool is completely normal.

MerCruiser manual MCM#17 p/n 90-823225--1 will lead you through the steps to correct the code 42. Once that is corrected, the low WOT might be corrected or if not you can move on to more troubleshooting. But first the code 42 needs to be addressed.

Click to expand...

Ok I have a 1996 MerCruiser 454 EFI Mag with the same problem. Code 42. The engine is running very rich and it pops through the exhaust when revving it up. I replaced all the normal plugs,wires and cap rotor.
I also replaced the pick up coil in the distributor along with the module. I bought them both from a Merc dealer. They are Quick Silver parts. It will not start with the new module. I put the old one back on and it runs poorly as before. I swapped the module again and no start! I put the old one back on and it runs. The dealer is getting me a new module. I hope this is the problem.
MUC, you said you would walk us through the steps to diagnose this issue of code 42?
Please do so. Thank you in advance!

If the Delphi ECM was used, it definitely can control timing advance. The timing light jumping around and as muc posted, the bypass needs to be used to stop what is called 'Spark Stabilization' by the trainers at the Mastercraft/Indmar sessions I attended and in order to correctly set base timing, the engine speed needs to be increased to 1000 RPM. Spark Stabilization can also be defeated by connecting a diagnostic tool to the ALDL (Assembly Line Diagnostic Link) on the harness at the rear of the engine. The little metal tool that makes the check engine flash can be used in pins A and B, or this can be accomplished with a bent paper clip. The light on the dash should flash a code denoting the number 12 three times (one flash, pause, two flashes) at the beginning of the code sequence and at the end. Any flashes between these sets of three are the codes and it takes a little time, so don't blink when it flashes- flashes can be missed. You can also connect

a test light to terminals E & F- that would be parallel to the dash light.

Since this boat has a Mercruiser, I'll assume it's a Tige or Malibu since Mastercraft didn't usually come with Merc- MC, Malibu, Supra/Moomba came with Indmar engines, Nautique used PCM with Ford engines at that time.

If the fuel pump is on the engine and it looks like the one in the photo, it has a screen at the bottom, after the fuel supply line- check that for debris because the fuel tank may have collected it during manufacture.

Look inside of the tank through the opening where the fuel sender plate is mounted- I worked on ski boats for several years and was always amazed by the amount of leaves, seeds and other garbage I saw in fuel tanks. People would leave the filler cap off when the boats were under trees and I assume this was during Fall, when leaves and other stuff was dropping.

The boat may have a fuel shut off valve at the fitting for the line that feeds the fuel pump- make sure the lever is aligned with the hose. Also, it may have fuel filter at the tank- on the Mastercraft boats, it was an AC GF-626. If it does, change it.

Make sure the fuel tank vent hose isn't clogged- spiders like to spin webs over these and if the screen is missing, they might build nests.

The fact that this engine has problems in the 3000+ RPM range tells me that the cause is somewhere between the tank and engine, including the pump.

In addition, I would like to know if the boat was on the trailer during troubleshooting after the first run on the water- that doesn't work for this problem because it needs to be run in gear, for the MAP sensor to read the real load.

The early injected Mercruisers used a combination of Motorola and Delphi ECMS (Indmar was first injected engines in ski boats, IIRC, and they used Delphi MEFI-1 at first, then MEFI-2). If the relays for Ignition and Fuel System have a thin wire that shows continuity to the block when the relay is controlled by the ECM, it's MEFI-2, MEFI-1 sent 12VDC to the relays.

The ECT (Coolant Temperature Sensor) was working correctly, in light of the thermostat being installed backward. The ECT senses low temperature and that's indicated by high resistance in the sender. You can measure the resistance at various temperatures to verify proper operation of the sender by using the chart below-

Hi @Cobalt Scott
I think you misread what I posted.

MerCruiser manual MCM#17 p/n 90-823225--1 (As in this is the part number for the manual) will lead you through the steps to correct the code 42. Once that is corrected, the low WOT might be corrected or if not you can move on to more troubleshooting. But first the code 42 needs to be addressed.

Please note that this was for the O.P.s engine. You have a different engine, so you will need a different manual. You can find the correct manual here.


Please search using your engine serial number so you get the correct manual. If the serial number search isn't available, I suggest you call Mercury.

After you read the section on fuel injection and the tests that will need to be run for code 42. I will try to answer any questions you might have.

Ok I’ll check into that repair manual. Thank you.

As much as I prefer the Factory service manuals, for this issue, you can find the procedure in one of the many, readily available, Delphi MEFI-1 manuals from the www...

Cobalt Scott said:

Ok I’ll check into that repair manual. Thank you.

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Does that scanner allow taking a snapshot of all data? If so, I would recommend doing that at KEOE (Key On, Engine Off) and at idle. Look for the differences.

As I posted, you can (and should) disable Spark Stabilization, so your timing won't vary. If Mercruiser used similar programs, and there's no reason to 'reinvent the wheel', the base timing should be 10°BTDC or whatever the Merc manual shows. You will need to raise the engine speed because defeating Spark Stabilization will also drop the idle to about 400RPM- we were told to raise it to 1000RPM.

I really doubt that the timing is the problem, but it's not a bad idea to verify is at this point in time. If you can use the service tool, do that but if you can't, use the paper clip method I described above.

Since this boat doesn't have the in-tank fuel pump, can you run it using a tank for an outboard motor? If so, do that. Connect it as close to the engine as possible, so you can bypass the tank, fuel shutoff valve (it should have one), anti-siphon device (it MIGHT have one), rear fuel filter (if it has one) and the fuel line.

The original fuel line for this boat is from the same range of years as the boats I worked on at the Mastercraft dealers and I remember a service bulletin for a delamination problem, caused by the fuel additives like MTBE and Ethanol.

How many fuel filters are in this boat, just the fuel/water separator at the engine?

In this thread, I have seen absolutely nothing about the fuel pressure. That's ALWAYS the first thing that should be checked when a performance issue begins and Indmar used to include that recommendation in their on hold phone message.

The recommended tests were:

KEOE (Key On, Engine Off
Idle
2000RPM
WOT.

I would bet that it will be normal for the first three tests but will fall around 3200-3500RPM and as I posted, the screen in the fuel pump I showed was the cause of most WOT problems I repaired and there were a lot of them. This MUST be done on the water and under load- testing on the trailer won't cause this problem to occur unless the fuel flow is severely restricted.

Have you tested the fuel pressure regulator? If the fuel line is clear of obstructions, that will be necessary.

Blizzmet061 said:

Sorry forgot to mention that I did check the prop. It is factory pitch. Does have a slight burr but was advised that it wouldn't affect it as much as the issues I'm experiencing. Also forgot to mention that I did replace cap and rotor as well as wires originally. Unfortunately didn't solve my problems.

Click to expand...

In this thread, I have seen absolutely nothing about the fuel pressure. That's ALWAYS the first thing that should be checked when a performance issue begins and Indmar used to include that recommendation in their on hold phone message.

The serial number is shown, but nothing about the manufacturer. Using a Mercruiser diagnostic tool doesn't tell me that it's Mercruiser because I used a Tech 1 with the marine module for Indmar prepped engines and that OF number isn't a Mercriuser 5.7L serial number. You indicated that the engine was replaced- can you show it, so we can be more specific to its build? Ideally, the fuel pump will be seen.

The recommended tests were:

KEOE (Key On, Engine Off
Idle
2000RPM
WOT.

Fuel pumps weren't in the tank at the time of manufacturer of this engine, although a couple of boat brands used a 'helper' pump. The normal pressure was usually in the 30-35psi area across the RPM range I showed.

I would bet that it will be normal for the first three tests but will fall around 3200-3500RPM and as I posted, the screen in the fuel pump photo I posted was the cause of most WOT problems I repaired and there were a lot of them. This MUST be done on the water and under load- testing on the trailer won't cause this problem to occur unless the fuel flow is severely restricted.

Have you tested the fuel pressure regulator? If the fuel line is clear of obstructions, that will be necessary.