which advance reading on RINDA scan tool ???
 

I'm having a timing issue on one of my 502 MEFI 1's. Maybe some efi guru's can help with this question.
At cruising speed(3500 RPM)I understand that the ECM selects the baseline timing advance from a look up table based on RPM and MAP reading. The ecm will reduce that baseline advance if the knock sensor is activated. Then the ecm sends this final advance reading thru the IC wire to the distributor.

QUESTION: when you hook up a scan tool(RINDA/MERCRUISER) and read the timing advance(at 3500 rpm's cruising- not at idle), is the advance shown on the screen the baseline timing from the lookup table before any knock reduction or is the final adjusted reading that is being sent to the distributor??

The RINDA tech and several mechanics don't know and I can't pinpoint my problem until this question is answered. Hopefully someone on this board is sharp enough to know.
THANKS-

Re: which advance reading on RINDA scan tool ???
 

Base Timing (ECM assumes it is set to factory spec) + ECM supplied advance - Knock Retard = displayed Spark Advance.

In other words, the Spark Advance shown on the Diacom display is the actual timing advance from TDC, and includes the Knock Retard if any. You should read the same advance on the Diacom screen that is shown on your timing light.

Dave

Re: which advance reading on RINDA scan tool ???
 

Dave- you were just one of the ones I was hoping to hear from....My timing light(new MSD non advance) at 3500 RPM is showing about 4-6 degrees less advance than my scan tool on my starboard engine only. The engine is clearly less powerful than the port engine. My knock retard is showing 0* at 3500. All sensors seem good- no fault codes.
ASM remapped by boxes and Jim told me to bump my initial timing to 10*. He says he remapped the ecm to account for the extra 2* advance. I switched ecm's between engines and the problem stayed with the starboard engine so I don't think the ecm's are the problem.
I wanted to check to see if maybe I was actually running on the distributor "limp home" curve instead of the ecm curve so I cut the white ic wire with the engine running. The engine died...telling me that I was running on the ecm curve, not the dist. curve.
So now it seems as though the distributor(new MSD) is doing something different than the ecm is telling it to do. I'm thinking that it may be a defective distributor or dist. module??? any more thoughts from anyone on what would cause this.
THANKS-

Re: which advance reading on RINDA scan tool ???
 

I hope my posting is not keeping anyone else from jumping in. Please do.

I may have suggested some of these things before, but I would;

1) swap distributors - to identify the distributor as the problem or not

2) check timing advance with the MSD box disconnected and running stock type inductive ignition - to confirm advance is the same with or without MSD

3) Check proper function of Knock Retard system. It may be coincidental, but the amount of retard you are showing (about 5 degrees) is the exact amount of maximum Knock Retard, like when a code 44 is set. I think I would force a code 44 by disconnecting the Knock Sensor and then checking the advance to see if it has retarded an additional 5 degrees, or if it stays the same.

Dave

Re: which advance reading on RINDA scan tool ???
 

Thanks Dave- I'll try your suggestions this weekend and repost my results.

Re: which advance reading on RINDA scan tool ???
 

Dave- Could you please clarify your comment #3 pertaining to the knock sensor.
In a properly running engine, is a code 44 set anytime the knock sensor is working and pulls out timing... or is it set only if your knock sensor has malfuntioned?

When you disconnect the wire to the knock sensor in a properly running engine will that prevent the sensor from working(ie...prevent it from pulling out timing) or will it do just the opposite and make the ecm think that there is a major knock thereby pulling out the maximum(5*??) timing?

Thanks-

Re: which advance reading on RINDA scan tool ???
 

Isn't this just a case of the timing of the distributor position is out of sync with the ECM. In other words, rotate the distributor when at 3500 until the timing light matches the scan tool. Now the engines actual timing is matching what the ECM is asking for.

Yes, this will change the base timing but that isn't as important as accuracy of timing at 3000 and up.

Rick

Re: which advance reading on RINDA scan tool ???
 

This may not be related - but I ran into a 502MPI that would not adjust timing - the module was defective. It would still run - but not advance.

Just my 2 cents!

Re: which advance reading on RINDA scan tool ???
 

If I understand you correctly the timing light shows an advance that is 4-6 degrees lower than the scan tool at 3500 rpm. Have you confirmed that you have 10 degrees initial advance (in service mode) on the starboard engine?

Re: which advance reading on RINDA scan tool ???
 

Sorry if I was unclear. I also forgot your setup is MEFI1. Which means you would not get a code 44, you would actually get a code 43 if the ECM detected a problem in the knock control system.

I know MEFI2-up systems go to full Knock Retard (4.94 degrees) when a Code 44 is set, but i'm not 100% sure if the MEFI1's do the same thing when a Code 43 is set.

The MEFI 1's use a seperate Knock Module that supplies an 8 to 10 volt signal to the ECM when NO knock is detected, and remove that voltage when there is knock, and the ECM retards the timing. Might be a good thing to check to make sure you have that 8-10 volt signal at the ECM, and check to see if it goes to full retard (like it should) when you disconnect the Knock Module. Then check to see if the voltage is removed (and the ECM retards the timing) when tapping on the side of the engine block.

Go over the entire knock system, including the ECM's ability to detect a problem in the system and set a code.

Dave

Re: which advance reading on RINDA scan tool ???
 

Just thinking out loud; What can create this discrepancy in timing between what you read on the crank and what the ECM tells you?
1. Initial timing.(checked?)
2. Faulty ECM (checked by swapping ECMs)
3. Something funny going on in the knock circuit (to be checked)
4. The ignition control module having control over the timing. (checked)

Another stupid question(please forgive me); On number 4, when you cut the Ignition Control circuit, did you disconnect the whole 4 wire harness? What I am thinking is that cutting the other circuits (ignition controll bypass, ref low, ref high) would stop the engine.

Re: which advance reading on RINDA scan tool ???
 

Dave- thanks for the info...there is only a single wire going to my knock sensor. With only one wire, how could the knock sensor SEND a voltage signal to the emc? Where would the voltage come from? I would think that the wire supplies a reference voltage to the "normally closed" sensor and the sensor opens when knocking thereby grounding the reference voltage and signaling the ecm that there is a problem???

Matts- yes, initial timing was set in sevice mode to 10*, checked and rechecked. when I cut the IC wire, I only cut that wire(white). Because the engine stopped right away I am pretty sure that means that the engine is using the advance signal from the ecm. If it did not stop, then I would assume that the engine was running on the distributor module. So an advance signal is leaving the ecm and I have to assume that the value of that advance signal is what I am reading on my scan tool. Something is corrupting that signal after it leaves the ecm???

As Dave suggested, I did bypass my MSD box and go back to stock ignition but the problem remains....so I guess I can rule out an MSD box problem. I still need to check the knock sensor and switch distributors. I think it will be easier to swith distributor modules than the whole distributor??

So the saga continues. I appreciate the help and I will post again after more testing. In the mean time I welcome any more input.
Thanks-

Re: which advance reading on RINDA scan tool ???
 

On a MEFI1 system, the Knock Sensor does not connect directly to the ECM. The Knock Sensor is connected to the Knock Module, which is connected to the ECM. The Knock Module is hiding out in the electrical box (where the ECM and relays are) and is supplied with 12 volts, and then sends the 8-10 volt signal to the ECM when no knock is detected.

The trouble shooting chart I attached in my last post is supposed to be used when a Code 43 is set, but it is a pretty good procedure to test the knock control system. I attached a similar troubleshooting procedure that uses a scan tool on this post.

As far as swapping modules vs swapping distributors, I know swapping the distributors will take a little longer, but thats what I would do.

Dave

Re: which advance reading on RINDA scan tool ???
 

Thanks Dave- I'll post a follow up when I have done some more homework.

Re: which advance reading on RINDA scan tool ???
 

I can only chime in on the the tests Dave have proposed, swapping distributors and checking the knock circuit. There is basically nothing else left to check apart from maybe the coil.

Some loose thoughts; A "reduced" advance translates to a delay. And that delay is introduced either in the ECM or in the circuitry somewhere between the ECM and the plugs. The only absolute time reference is when setting the base timing in service mode. What is different in terms of involved circuitry when in service mode as opposed to being in normal mode? In Service Mode; pickup coil, ignition module, coil, distributor, plugwires, plugs. In normal mode; pickup coil, ignition module, ECM, back to some other circuitry in the ignition module, coil, distributor, plugwires, plugs. The ECM must get its timing reference through the ref high/ ref low wires from the ignition module. The ignition module is definitely a suspect.......

Good luck.

Re: which advance reading on RINDA scan tool ???
 

A quick correction. Looked in my dictionary and realized that "chime in" maybe was a bad wording for expressing full support of something. Sorry about that Dave:D No offense.

Re: which advance reading on RINDA scan tool ???
 

I was able to do a little testing this weekend. It turned out to be a bad distributor module on my new MSD distributor. I replaced the module with the old one from my original mercruiser distributors and it fixed the timing problem. Now I think I should go ahead and replace the module in the other engine before that one goes bad.

So now I have had to replace a brand new MSD coil and a new MSD distributor module. I have read all the stories on this board about MSD problems. Now I know what it feels like. How does such a reputable company get away with selling so much junk????

Thanks for the help Dave and Mats.

Re: which advance reading on RINDA scan tool ???
 

I'm not sure why everyone is so hyped up over MSD vs. factory Mercruiser ignitions...... We run blower motors with Merc stuff (using a 6 cyl module though) and never have any problems. I've seen numerous boats with MSD stuff just quit or misfire and cause more damage.

Glad to hear you got yours running!!!