ECU and Timing Question

I've just adjusted the timing on my 95 Civic (SOHC 1.6L PGM-FI). I
warmed it up to operating temp, jumped the 2P connector and checked the
timing at 750 RPM. Then I made the necessary adjustment.

I've had no problems with setting the timing, but I noticed something.
I had supposed that the jumper was there to stop the ECU from "messing"
with the timing, but that it was not necessary for *reading* the
timing. Of course I checked and adjusted with the jumper on just to be
sure, but I found that when the jumper is not connected, timing at 750
RPM is retarded by a several degrees.

Is this normal behavior? Can anyone enlighten me as to why it does
that?

Thanks in advance.

 

are you sure it retarded, not advanced?

read this:
http://www.ecutek.com/tuning/ignition

very punny.

 

are you sure it retarded, not advanced?

read this:
http://www.ecutek.com/tuning/ignition

very punny.

 

It's necessary for BOTH.

Very simply, when you set the timing with the ECU locked out, you were
setting the "base timing". "Base timing" is the datum point for the ECU.
It's the point from which all other timing adjustments are measured.

Since the timing is affected by distributor position, the ECU has no
idea where the timing really is when it does its adjustments. The ECU
just has to assume you've set the datum to the right place.

Why did the ECU decide to retard the timing when you un-jumpered the
connector?
Couldn't tell you. But so long as the engine runs normally, I wouldn't
worry about it.

In cars without distributors, the ECU knows exactly where the timing is
at all times, so there's no need for the "base timing" adjustment.

 

It's necessary for BOTH.

Very simply, when you set the timing with the ECU locked out, you were
setting the "base timing". "Base timing" is the datum point for the ECU.
It's the point from which all other timing adjustments are measured.

Since the timing is affected by distributor position, the ECU has no
idea where the timing really is when it does its adjustments. The ECU
just has to assume you've set the datum to the right place.

Why did the ECU decide to retard the timing when you un-jumpered the
connector?
Couldn't tell you. But so long as the engine runs normally, I wouldn't
worry about it.

In cars without distributors, the ECU knows exactly where the timing is
at all times, so there's no need for the "base timing" adjustment.

 

Thanks, TeGGer. Spot-on as always.

Jim: Yes, I think you're right, it's advanced, not retarded. Thanks.

 

Thanks, TeGGer. Spot-on as always.

Jim: Yes, I think you're right, it's advanced, not retarded. Thanks.

 

Sorry about that. I just couldn't resist.

 

Sorry about that. I just couldn't resist.

 

Jim, I checked again, and at 750 RPM, it's definitely *retarded*.

 

Jim, I checked again, and at 750 RPM, it's definitely *retarded*.