98 MPI Timing

[IamMe]

I have been a lurker around here for years. Normally what I need can be found in the archives. This time I need a specific answer that I can't find in the archives. It doesn't mean it isn't there, just explains why my wifes my job is to keep track of my keys, my wallet and my cellphone. I can not find a decent timing spec for my mercruisrr 7.4 MPI. At one point a few years ago I found a thread that told how to put it into base timing mode and it worked great. Now I can't find that thread. Seloc manual says three different setting 1ATDC OTDC and 1BTDC the rebuild just doesn't seem right and sounds out of time. Any suggestions?

 

[Fun Times]

Hi, were you thinking of this one? https://www.perfprotech.com/blog/art...-engine-timing

If so, your how to guide should be toward the bottom of the link.

http://www.offshoreonly.com/forums/...e-marine-efi-code-tool-less-than-$1-00-a.html

 

[IamMe]

The bottom link is the base timing guide thank you. Now I just need to find out exactly where the film in is supposed to be set. I can't find that spec solidly anywhere. I trust my last spec either as it appears the motor was replaced due to detonation I am guessing. It have been a faulty piston but I had only the top of a piston left with the wrist pin knocking holes in the cylinder wall so I want to be sure. I did replace the knock sensors as well just in case.

 

[Fun Times]

The bottom link is the base timing guide thank you. Now I just need to find out exactly where the film in is supposed to be set. I can't find that spec solidly anywhere. I trust my last spec either as it appears the motor was replaced due to detonation I am guessing. It have been a faulty piston but I had only the top of a piston left with the wrist pin knocking holes in the cylinder wall so I want to be sure. I did replace the knock sensors as well just in case.

Are you wanting to confirm the timing specifications for your engine? It's either 8 or 10 degrees before top dead center as those are the two common numbers. Yours looks to be 8*. But first, if you look at all the stickers on top of your engine and if they are still legible then you should notice some basic engine specifications for your engine model which usually includes the timing numbers.

https://www.perfprotech.com/blog/tech-specs/mercruiser-74lbigv8-marine-engines-specifications

 

[IamMe]

No stickers. Ok, I wonder why Seloc says 1 0 -1

 

[IamMe]

First I would like to thank you for all your help. I promise I'm not as much of an idiot as I seem on this thread. So I was looking at my engine. The balancer has only one line on it. My timing cover has only a single index on it as well no degree marks. More of just a single index like on some vortec auto engines. So I am trying to figure out how to set this now. I've never been through this much of a pita to time an engine.

 

[Bt Doctur]

just set it to the notch with #1 at TDC. the computer takes care of the timing

 

[IamMe]

See this is the problem I have 2 different books giving me different info. I'm set to the mar but sounds out of time.

 

[Pete104]

Why does it sound out? They never really sound good in "service mode". You sure you are getting it out?

 

[Bt Doctur]

You have a MPI that is run by the ECM, you should also have a crank position sensor in the timing cover, check the firing order , clockwise on the cap 1,8,4,3,6,5,7,2

 

[Fun Times]

You have a MPI that is run by the ECM, you should also have a crank position sensor in the timing cover, check the firing order , clockwise on the cap 1,8,4,3,6,5,7,2

He has an L29 MPI that uses the MEFI 3 which is the old system so he needs base timing to be 100% exact by way of using a dial adjustable timing light to line up 8 degrees in service mode. No crank sensor is used on this engine. http://www.mercruiserparts.com/7-4l-bravo-mpi-gen-vi-gm-454-v-8-199-1

 

[Bt Doctur]

The ECM controls the primary current going to the ignition coil. It sends a voltage signal to
the IC module that sends a voltage signal to the ignition coil. This signal will trigger the coil
creating secondary spark to be produced. The secondary spark is sent to the distributor and
then to the correct cylinder by high tension leads.
The Ignition Control (IC) module maintains the base ignition timing. It also has a 27-degree
spark advance built into it in case there is a Code for an IC operation failure detected while
the engine is running. The engine will continue to run but at reduced performance.

 

[Bt Doctur]

High Energy Ignition with Ignition Control (IC)
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.
In order for the ECM to properly calculate spark advance, it must always know at what speed
the engine is running. The engine speed signal is accomplished by a circuit within the distributor
module which converts the pickup coil voltage to a square wave reference signal that
can be used by the ECM. This square wave engine speed reference signal is known as REF
HI. The ECM must also have something to compare the REF HI value against. Therefore,
an additional line is provided between the ECM and the distributor module that is known as
REF LO. These two lines, between the ECM and the distributor, provide a precise indication
of engine speed.
The two other lines between the ECM and distributor which control the Ignition Control (IC)
operation are known as the bypass and IC circuits.
Modes Of Operation
There are two modes of ignition system operation:
DISTRIBUTOR MODULE MODE
The ignition system operates independent of the ECM. The distributor module module in
the distributor maintains a base ignition timing and is able to advance timing to a total of 27
degrees. This mode is in control when a Code 42 is detected while engine is running and
will have a noticeable effect on engine operation.
ECM CONTROL MODE
The ECM control mode controls the ignition timing. The ECM calculates the desired ignition
timing based on information it gets from input sensors.

 

[Bt Doctur]

Base Ignition Timing
In order to check or change base timing on a HEI system the ECM has to be entered into
the service mode by using a scan tool or code tool. The IC module will go to base timing.
The ECM will stabilize timing to allow timing adjustment. The ECM incorporates a spark control
override, which allows timing to be lowered if spark knock (detonation) is encountered
during normal operation. At this time, the timing can be adjusted by turning the distributor.

 

[Pete104]

You mean that the engine has to be put in to "service mode"?!

I have the old school "rinda" code reader with the switch just for this purpose. Best thing ever.

 

[achris]

If you have the later style timing cover (with just a notch on it), you are going to need an 'advance' timing light. Something like THIS.
The 'special timing tool' is just a shorting clip, I remember seeing details of how to make your own for about 16c on iboats somewhere. I'll search for it and if I find it, I'll edit this post.

Hope this helps,

Chris...........

EDIT: Have a look HERE

 

[IamMe]

I can put it into base timing mode. Thats not a problem. I need to find me a dial type timing light I guess. I am currently set to 0. It is low on power and runs like it is out of time slightly. I will see if I can locate a dial light and reset to 8? btdc and try that.

 

[achris]

The other option of you don't have an advance timing light is to use timing tape on the pulley. http://m.summitracing.com/search/product-line/summit-racing-timing-tape

Chris.

 

[IamMe]

I found an advance timing light and have since times the engine. Thank you all for the help.