454 MPI advance timing issue
 

I have a 1999 baja outlaw 25 with a 7.4 MPI and I'm not getting advance timing... I have checked the base timing in service mode and it is at 8 deg. I took the boat out yesterday and had my friend drive the boat at 3000 rpm and I was only showing about 15 deg on the timing gun. I have tried a new ignition module and it does the same as the stock module. I am currently at 4100 rpm WOT running a 21p 3 blade prop. I just did a tune up and put new plugs, cap, wires, FPR, pulled and cleaned/serviced fuel injectors. I've never had the boat running right since I bought it and now it's close but I'm missing some timing up top. Any suggestions? Is it ok to clock the distributor to get more timing? Or is it critical to stay at the 8 deb base timing per the mercruiser recommendation? j

Could it be the knock sensors retarding the timing? I did put a new knock sensor on the port side, but didn't replace the starboard side.

All knock sensors are not created equal, are they the correct ones for your engine ? the timing needs to stay @ 8* and let the ecm do the rest, Id verify TDC on the balancer with #1 on compression stroke, dont rule out fuel pressure, where is it ?

Are you sure its out of BT mode

yes the knock sensor was specifically for my engine. Fuel pressure at the rail is about mid 40's. I'll have to check TDC again. It shouldn't be in BT mode since I jumped the A and B terminals with a paper clip. Once I pull the clip it should go back to regular mode right?

have no idea I use a scanner

Yes once you pull the clip it will return to regular timing mode.

I checked TDC on plug 1 and the line on the balancer matches the pointer and the piston is at the top when I pulled the plug and checked. I pulled the cap and checked the rotor and the plastic tab is pointing to where the plug 1 wire is (between 5 and 6 oclock). Is the plastic tab supposed to point to 1? Or is the opposite end with the metal contact supposed to point to 1? I would think it wouldn't even start and run if the rotor was 180 deg off (if the metal contact part is supposed to point to 1) . Here's a pic of the rotor at TDC
https://cimg9.ibsrv.net/gimg/www.off...daa888727a.jpg

where the metal contact is pointing now is to the wire for plug #6, which is 180deg from #1. Engine runs and idles great, just not getting advance timing so I am confused! lol

How do we know if the advance you saw isn’t correct for the throttle position/intake vacuum/coolant temp/ and rpm ?

Anyone know the tables ? Articfriends/sutphen30/others here that have programmed the ecu’s for these motors want to speak up ? :)

Looks like you're at TDC but on the exhaust stroke.
Turn the crankshaft 360 degs (in the normal direction) and check the rotor again. It will be pointing right at the #1 wire. The dist turns once for every 2 turns of the crankshaft.

It would be nice if you could get scanner connected while under way and see what the sensors are reporting.

You bring up a very valid point....but....I have not viewed the spark map for this particular motor but most Merc tables I have on hand would have more than 15 deg of timing at his stated rpm.

It is possible that knock retard is in affect but max retard is typically about 9 degrees, so he would still be shy in the timing department if it was pulling timing to the max.

ahhhh makes sense thanks for the clarification!!!!

https://cimg8.ibsrv.net/gimg/www.off...46aa955fc.jpeg
Here is the original coil... lol. I just got a new one since this one looks like it’s had much better days. Could this be one of my issues? Maybe under load it’s not working properly? It appears my base timing is set correctly with TDC and plug 1 with 8 deg on service mode

Coil won't have any effect on timing advance.
You should be seeing more than 30 degrees of timing advance by 3500 rpm.

ok thx. What else could it be? I tried a new ignition module and it didn’t make any difference. I thought that was supposed to control the advance ??

What do you mean by ignition module??? The pick up module in the distributor??
The timing advance is controlled by the ECM.

yes the module on the distributor with the two plugs

there has to be a bad looking coil award here

Not necessarily. The early mpi engines had a very lame timing curve. If you free rev them in nuetral , youll see the timing actually go way down, even negative timing. They did this to help prevent flare ups during shifting. The timing curve is based on map vs rpm. I dont think they ever see over 30* at wot in the factory tune

so if my base timing is at 8 deg, and i'm seeing about 15 deg at 3000 rpm, is that total of 23 deg? Does that sound right for that rpm?

The timing youre seeing with the gun, is the actual timing thats taking place. 15* sounds low, but i dont have the table handy to compare what it should be, vs what it really is.

What version of mefi is it ? Also, is this the 310hp or the 385hp version engine?

Okay, I did some digging. Found one of many of ArcticFriend's posts. Here is table on a 502MPIMAG 415hp:(should be quite similar to 454MAG MPI 385HP)
Note: do more diffing under his name and you'll surely find more :

https://www.offshoreonly.com/forums/...pi-timing.html

Now that you're on TDC :D also run the firing order on the plug wires from the cap to the plug may have 2 flipped.....

it’s a 1999 7.4 mpi 310hp version. The serial number has faded off of the plastic shroud on the top so i don’t have that unless it’s stamped on the block somewhere

i triple checked this when i put the new cap, rotor, plugs and wires but I’ll check again tonight!!!!

Being 310HP you have the L29 which has 2 knock sensors
Have you tried to remove or disconnected the sensors or knock module to see if timing increases?

I haven't but I will try that this weekend and check timing again. If it's the same, what else could be causing it not to advance?

That's what doesn't make sense. The L29 should have a MEFI 2 ECM. If the knock module is what is keeping it from advancing then there should be a code 43. Have not read where codes are found. Now if the ECM test on first throttle up the knock module to see if it can make it knock. If this doesn't happen (mine did that after repower) then there would be a code 44. So no codes but no advance. As said previous, the EST module and ECM is what controls the advance.

If there was a code 42 then it would be the module is not coming out of bypass

Again no codes so it doesn't make sense, so I'm spit balling

I scanned it and it pulled a code 44... no knock detected. What is the procedure to diagnose this code? thanks, I think we're getting closer!

also, I've been running premium ( i think its 93) octane fuel. From what I've read, these older engines were designed to run on 89 and that the higher octane fuel could cause code 44? Not sure what I take of that....?? Thoughts? I figured higher octane would be better

No you do not have that problem. The specific issue you are referring to was for a small batch of 454/502 Mag EFI/MP motors around 1994-1995. There was a Merc service bulletin put out at the time addressing the issue. Basically during engine start the ECM would advance timing until knock was detected which verified the knock sensor was working. If it didn't detect knock it would trigger a code and retard timing. This does not apply to your engine.

ok thanks!!! Any ideas what would cause what I’m experiencing?

I'm disagreeing
Since your getting the code the ECM is retarding timing, if the code was not ON the code would not show. It can be fixed easy if your ECM is no locked, most are not. Need MEFI Burn or other, down load the BIN file, turn the flag OFF, and reload it. I bought MEFI Burn to get rid of the same issue.

Running 93 is what causes the issue. Your motor is designed for 87, and running 93 means the ECM cannot advance the timing far enough to make it knock, so the code is thrown. My repower requires me to run high octane (89 or 90) so it would throw the code every now and then, and would really do it when running 93

would it still throw that code if i unplugged the knock sensors and did a test run ?

Yes, because it wants to test and is unable to get a knock signal back

Get a gas can and run the motor with some 87 octane to see how it works

will try 87 and see if it makes a difference... Just pulled the ECM and going to a shop to see if they have the MEFI burn or anything to turn off the flag. Will turning it off be bad in the long run? I just looked up my ECM and it's a MEFI 3 (16236999)

Merc Bulletin No. 94-12 is the bulletin I was referring too. Can't get it to upload right now.

Your MEFI 3 DOES NOT DO THE SPARK KNOCK TEST on startup. Your timing issue IS NOT FROM 93 octane gas.

I've run anything from 87 octane to VP110 in my MEFI 1 and it will not flag the knock sensor BECAUSE it is not one of the affected ECMs as stated in the Merc bulletin.

any thoughts on what could cause my timing issue then?

I just did a continuity test on both wires from each knock sensor to the ECM and they are both good

Disagree again,
My repower by a well known OSO member is a MEFI 3 and had the code 44 show up. Don't know how certain you can be that it is not from high octane. I also cannot say its from the gas, BUT (the big but) you can not get a code that is not programmed into the ECM. If it is turned OFF then it will not show up

It is showing up, so it IS programmed

will it hurt to run it if I get it turned off?