Knock sensors for 502 mag mpi
 

On 1999 502 mag mpi motors. These motors came used with knock sensors put on the blocks, but I looked in the actual mercruiser factory manual for that s/n motor and it says that external knock sensors are NOT used on this motor. It is controlled just buy the brain. Figured I could trust the manual but you never know. Any surefire knowledge of this. By the way there is a wire on the harness for the sensor but that means nothing as there are always extra wires for things. I have tapped on various places on the block with a hammer with no changes in timing.

service manual #23 , 90-861326-1, march 1999, page 5B22.

Manual 23 had 2 versions as you have the latest version of it as it was updated by merc in march of 1999. The older 454/502 service manual # 23 version was Sept 1997. There was no mentioned of this in the 1997 version hence a lot of updates were added in the 1999 your version service manual # 23 plus it should be a 2 manual set sections 1-4 and sections 5-9 so is this what you have ? Just want to be on the same page here.

next you are correct about the brain part but per Merc in the manual it should state not using knock sensors external hooked to a knock sensor module for MEFI 3 big blocks but before I go any further with this you need to post your engine serial serial # along with what ECM you have. MEFI 1 and 2 used the KNOCK sensor modules hooked to knock sensors.. Knock sensors used a dark blue wire connection here. Engine serial # will really tell the story for your app and what ECM was used. I can careless the year model of your hull that means nothing me to or anyone working on the engine professionally.

BUP - I have the book 1 of 2, sect 1-4. Don't have the other. what does it cover?
Engines: s/n OLO315551/565
ECM MEFI 3 square type, not the longer rectangular one.
I don't have the boat here at the moment to look at the wire color.
Can you recommend a shop that can do a top notch job on reflashing it for better fuel ratio and timing. This Sutphen runs a true 74 with two people and half gas with completely stock motors even before I just rebuilt one -
but the timing is 34 cruising but goes down to only 18 at mid range when hit throttle, then about 20 -22 at wot at 4700/4800 with no vac. Both motors identical and steady timing, just low timing at top end. Have checked all ignition and seems in good shape. Timing set properly at 8btdc with the shorting tool. THis low timing be a detonation OVER-precaution by mercruiser, but cant be making a lot of power at 19 degrees. I run nothing but premium. Seen too many detonate but probably from gas on motor not set up properly.
appreciate your time. nothing like experience.

8 and 22 = 30.

not getting the 22 except at midrange 3000rpm with 10-11 inches vac.
at wot 4800, zero vac, gets 8 plus 11 = 19
both motors identical.

Oh. Just going by what I read in red.

Hey I will look into your serial #'s when I get a chance tomorrow. Man I had a zillion questions and very long phone calls all freakin day so really mostly all boated out for the whole day. Recorrected post # 3, it was incomplete and not a very good post on my part so reread it. Anyways here is more and hopefully pin point some sort of problem with your engine(s)

In my best opinion I do not like reflashing the ECM's as here I am shipping it to you in mail / reflash it and send it back to me YOU ARE GOOD TO GO. Anyways I deal with one person and one person only who either does it on a dyno with that motor or he flys in and we go boating for the day with all of our diagnostic equipment and his retuning / reflashing skills.

Next - your manual in your hands then should say NUMBER 23 and at the bottom should say "BOOK 2 of 2" and below that should say "Sections 5 thru 9" is this correct ?

Next - book one for this set should say Book 1 of 2 and below that should say Sections 1 thru 4.
Sections 1 thru 4 in order
1. Important information -
2. Removal and Installation
3. Engine ----- IMO important to have if you are working on your app and have not torn into these many of times to go off your head
4. Electrical systems -------------- IMO can be important if you have work on this stuff only a very few times.

Next you bought the manual(s) how in the world are U missing the other half ? Just guessing here its missing

Next if you have a scan tool to hook and read MEFI 3 -whether its the DDT, Diacom or (whomever) OTC with Merc cartridges (MEFI). Scan the motor and see if CODE / FAULT CODE 43 or especially CODE 44 shows up or any other codes show up for a piece of mind and true diagnostics..

CODE 44 means NO KNOCK or CAN NOT DETECT KNOCK ACTIVITY - conditions this take place - after 513 TDC knock free events with RPMS greater than 3000 and MAP greater than 70 and filter noise less than 0.14 volts means any one of these or all -FAULTY KNOCK SENSOR or DISCONNECTED KNOCK SENSOR or OPEN or BROKEN CIRCUIT

CODE 43 means CONTINUOUS KNOCK - meaning not good for your engine. Conditions this takes place when you HAVE CONTINUOUS KNOCK RETARD FOR 30 SECONDS or MORE. means anyone of these, bad fuel - low octane fuel, INCORRECT TIMING, BAD or FAULTY IGNITION or FAULTY KNOCK SENSOR or KNOCK CURCUIT - Believe it or not I have seen very worn / lose / stretched timing chains set this as well.

OK post some jist of this for an FYI . will hit again tomorrow or after that. I tried to cap the words that are important.

Again FYI - knock sensor(s) used a dark blue wire connection. AND Lastly your knock sensor needs to be connected IMO is your problem retarding the timing. I went back over my post above as I think faster than I can type.

I recorrected it and read your 1st post thought your were stating knock sensor to no external knock module. My bad totally.. Its knock sensor to ECM is correct and should be connected..

If I recall correctly the big block L29 engines (MEFI) used 2 knock sensors, the rest of the big blocks use one knock sensors and MEFI 3 does not use a knock module 4 sure, MEFI 1 & 2 did use the knock module. Hope this clears all of this up. Sorry for my incomplete post above. It is corrected now. That's what I get trying to do to many things at once plus its hard to write these story books to make sense for everyone. I have a lot more info about this - later and will follow up.

Recorrected my posts to be a lot clearer in post # 3 and # 8 plus # 3 post was incomplete. It is all corrected now so maybe a reread for whomever.

Merc Manual - I do have the book #1 you state. A friend gave it to me that's why I don’t have book two.

It has never shown any fault codes on either motor. The knock sensor on both motors were replaced with no changes or codes on either one. I always run fresh Premium gas.
Maybe Merc has it cut back to 20 degrees (actual total not just the advance) at low vac for detonation reasons for the general public.

It is the MEFI 3. I have seen that come up on the computer.
It does have a knock sensor wire although im not there to check color. I have always run with it connected to the sensors on both motors.
QUESTION IS - SHOULD THIS WIRE BE CONNECTED ON THE MEFI3 ???

The timing is identical on both motors. Over 30 at cruising, drops to 18 instantly when hit the throttle and then slowly climbs up a couple degrees to about 20 when hit 4800 which is WOT. With more timing and thus HP, it should reach 5000 im sure.
DO YOU KNOW WHAT THE TIMING CURVE IS FOR THIS MOTOR. THAT WOULD BE A TREMENDOUS HELP.

Who do you use for a tuner BUP?

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

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.

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

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 !!

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.

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.

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.

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.

what???

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. .

I believe he knows and the "What ???" is more like "What the f*k answer is that ?"

I'm just more direct !

LOL.

BUP yes that is what I was trying to say, thank you. I was told that the ECM advances the timing until it detects knock to check the knock sensor and then retards timing a few degrees. If it does not detect knock it believes that the knock sensor is defective and retards timing to a safe amount. Because these are low compression engines, 93 octane fuel will not knock at the pre-programmed timing levels. If I have been misinformed, I apologize for suggesting that he try lower octane fuel to see if that resolved his problem. 87 octane has always worked for me and I do check with my Rinda Scan Tool.

Well I have heard that statement before about using premium will not let the knock sensor do its job, but I suspect that's not correct at all - doesn't even seem realistic.

I have used premium my whole life so I don't worry runnin it, and just for cheap insurance when things aren't exactly right. I know most people CAN run regular, but I also see many rebuilt motors from detonation damage and they sometimes wonder what happened. I've even seen it happen twice to one guy and finally he took my word for it to use premium as he didn't really look after his stuff. Anyway as long as you live and learn.

Ok one more question. The book says to install the knock sensor at 16 - 20ft lbs and with NO SEALER, nothing. I'm just not used to installing any threads on a boat without at least grease.

Do you know if this is really necessary to put nothing at all????

BUP I got a Mallory 9-33500 sensor for both motors. Mallory package says it replaces Merc 805544T. I did have the wrong BWD sensor though.

TRASH your probably right, it may be close to normal. I've always thought a v8 can run at least 30, or maybe 32 or so, even at WOT as long as tuned right and good gas. It may not be less than the factory 415hp rating, but WOULDN'T IT GAIN SUBSTANTIAL HP AT 30/32 ??

Thanks for all ya'lls information.

Well that's what I told you on the phone and to triple check it from post # 17. I believe you had the wrong knock sensor to begin with. The BWD book shows the wrong sensor to, but I would not have known until I seen the pic of it as you sent. Did you get my pics what the book listed from BWD ?

yes I got your pic. thanks. I got the merc 805544T which Palmer stocked as the Mallory 9-33500. Do you suggest installing it with the threads completely dry as the manual suggest? I sure like to grease or seal threads for corrosion.

Did you ever find the timing chart ?

Kurt I haven't even looked in the manual as of yet but I do not think its posted in there anyways, Also I can not believe I am drawing a black here about the timing table here.

I went back to read your posts - I am lost from your post # 4 and then your post # 6 you mention two different timing specs at 4800 / WOT ?

We talked about if it have Teflon tape on them installed ? You said at first but when you changed them out recently - you said you put something else on the threads. I would clean out the engine block threads with a stiff wire brush and or the correct tap with WD - 40.

Maybe a thin coat of dielectric grease on the threads. MERC says - not to use anything on the KS threads.

yea one post i said 19, the other posts I said 20/22. But both are close and that is at WOT, high map. They get around 20+/- one degree. as its hard to read when your running wot on the water. The both do run high timing - about 34 - cruising mid range at lower map. I sure would like a timing table for this 502 if you ever find it.

KS works off of a change in harmonic frequency, if something is used on the threads this can cause a dampening effect. Engine running WOT an the ever so slight ping may not be sensed right away if something is on the threads, like putting a cloth over a microphone.

Whats on these threads is all you need, like stated before dont put anything else on it

That was on a limited run of 502 early build motors (early 95 and older if memory serves me correctly). Tech bulletin came out about this way back( 94-12).