mats

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.

mjb

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-

Dave_N

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

mjb

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

mats

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.

mats

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 No offense.

mjb

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.

txriverrat2001

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!!!