F-2 Speedy

Both my gen 6 502's mefi 3's have knock sensor & wiring dark bl if I remember, and yes it should be connected into the wiring harness, and now my 502's are 540's and Im still running them

Cap'm Kurt

I guess that goes to show you, you cant always trust the manual. even though it shows for that particular motor. It says no knock sensors with the Mefi 3 as per the page # i listed below.

F-2 Speedy

How else is it going to retard timing incase of detonation, the ECM has to get its information from some where, that's interesting it said that, I don't know maybe my knock sensor is malfunctioning lol

Cap'm Kurt

My mistake 33 OUTLAW. It says the mefi3 has no knock sensor "module", which means no separate module from the ECM. Some models had a separate knock module along with the sensor and the ECM.
THe Mefi3 does however use one knock sensor on the block. Thanks to BUP for informing me of that one little word. yeah I was wandering how the ECM would monitor knock myself !!

Trash

I have not seen your particular timing table but I have studied several other Merc timing tables for MEFI controllers and the general theme is this:

Highest advance is in the mid-range cruise region.

Advance drops off drastically from mid-range rpm to high map mid-range rpm to WOT.

Snap idle decel has very high advance, as much as 40 degrees.

So from what your are observing it would appear to be not too far from norm.

All this isn't accounting for F1 ignition slope, other retard parameters or scalars etc. due to inputs or faults which can affect the total timing.

BUP

Sometimes Mercruiser manuals & Merc will have typos and wrong info posted in their manuals that is caught afterwards. Sometimes this happens for the first couple x amount of runs of manuals then they get fixed thru the printer afterwards and sometimes it might be a couple of years afterwards. Just saying and that's why I asked which manual was used and the dates of the manuals being used here. Plus the correct KS is important also. Its not one KS works for all apps here.

Kurt I sent you pics back in an email of the BWD listing the knock sensor in their own catalog as they have it wrong to. They do not list pics just part #'s. After your pic that's a knock sensor for a 496 / 8.1 and a 350 MPI for PCM & ECM 555. Like I said can't help what is printed. If you can not verify the correct KS let me know I can get them but not thru Merc as they list NLA.

BUP

I do not remember the timing curve for this engine and I'm almost 100 % it is not listed in the service repair manual. I have the manuals for this but not in front me to 100% verify that nor looked at it in a while but I am pretty sure it is not listed. If I get time, I will pull the service manual out to verify this.

Like I said MEFI 1 & 2 used EXTERNAL knock sensor MODULES and all Knock sensor(s) are external. On MEFI 3 NO EXTERNAL Knock Sensor MODULE was used as its bases / circuit is within the MEFI 3 ECM. Also like I said L29 Big blocks used 2 Knock sensors and had 2 dedicated connectors thru pin connector J1/30 and J1/14.- FYI J1/30 pin connector was for KS # 1 and if only one KS was used.

If you have a Knock Module you have MEFI 1 or 2 NOT MEFI 3. These ECMs MEFI 1 & 2 looks exactly the same but MEFI 3 looks totally different is more square and smaller dimensions.. His app is MEFI 3 - with one KS and NO Knock Module. I would triple check to make sure your BWD - KS is the correct one for the MEFI 3 / 502 app but heck you can not even go by the BWD catalog as it is listed wrong.

GMC271

Try running 87 Octane, if you run 93 the ECM does not hear any knock so it believes that the knock sensor is defective and it will retard the timing.

tunertech

what???

BUP

Tuner I think he met to say if it does detects knock it will retard timing but no sure either ? But will agree with you on the question marks.. just saying and sometimes I am not the greatest explaining / writing things either. .