Rotor phasing question

**blue68deville** · 04-10-2014

Is anyone using an MSD distributor to trigger their EST module, and if so did you have a problem getting the timing set up? I'm pretty sure my rotor phasing isn't jiving with my magnetic pickup.

I have a Caddy 472 motor, 7747 TBI from a 7.4L and a MSD distributor with the advance locked out. I have the EST module wired with the polarity correct per the Megasquirt site info. Caddy distributor spins clockwise.

I originally set the timing with the motor at TDC#1, rotor terminal pointing at #1. It would not start, backfired, etc...

Put my timing light on it, cranking the starter with the fuel pump fuse removed, and it was way off. Like 90deg clockwise on the crank kind of off.

Using the starter only, I set it to 0deg. Added fuel and it fired and ran ok. Timing light showed ECU running the timing, fluctuating around 20ish degrees.

When I tried to set the timing with the EST feedback wire unplugged, it ran but my timing light showed way off again. Weird for sure, like it's a full cylinder off in the firing order??

I have the old chevy distributor, it looks like the rotor is slightly ahead (cw) of the tower terminal when the reluctor points are lined up. I'm guessing the ECU sees the signal and then calculates timing for the next spark event.

I found out MSD makes an adjustable rotor so I ordered one. I got the adjustable rotor in today, it can go 20deg either way. I messed with it a little bit, 5deg clockwise and it seems to have a more stable idle, but the timing still does the 90ish degree jump with the EST wire unplugged. Called it a night at that point.

I can keep screwing with it, but if someone else has already dealt with this it would save me some headache. I did a search, but didn't come up with anything helpful...

**delcowizzid** · 04-10-2014

what style of est module are you using.polarity the wrong way does weird things to advance.is the tune setup for the correct base timing most dizzy modules are 10 degrees base timing if the tunes set on 60 for dis ignition weird shit will happen

**mmigacz** · 04-10-2014

I had rotor phasing problem that I uncovered this past weekend.

Here were my symptoms:

When warmed up and idling, the engine ran ok. It did miss once in a while and the data log showed weird timing spikes. When I would start the engine, it would start fast. However, after a second or two it would run like complete crap (when start-up advanced was added). Most of the time it would stall. If it didn't stall it would go up and down in RPM, missing and backfiring through the exhaust. After about 15 seconds (as startup advance decayed to zero) the issue would start to go away.

I cut a window in the distributor cap like the one shown below:

rotor window.jpg
This is what I found when I put a timing light on it. The engine was fully warmed up and idling, the EST was commanding 19 degrees of advance. I checked the timing at the harmonic balance and the actual timing agreed with 19 degrees. The rotor was pointing about 20 degrees from the pole attached to the timing light.

rotor phasing2.jpg
When I would start the engine, start-up advance was added (30 degrees total), and the rotor would index even further, approximately 25 degrees from the pole. This is bad, because now the spark is jumping to the wrong pole. I ended up modifying the rotor so it was about 5 degrees from the pole when the EST was commanding 19 degrees of advance.

The result was no missing, back firing, timing spikes (when datalogging) and no startup issues. I'm not saying this is your issue, but it wouldn't hurt to check your rotor phasing. At least you would know for sure that it is right and not the issue. The only part that sucks is you need to buy another cap after cutting the window.

**blue68deville** · 04-10-2014

Im using the 8 pin module, delco pn 19179578. I'll try reversing the polarity but I think I'll be cutting a hole in my cap to look at the phasing.
I didn't realize the ecu changes timing for cranking, makes sense given my symptoms.

**mmigacz** · 04-10-2014

I don't think the ECU changes the timing during cranking. Once the engine starts, ECU adds additional advance.

**blue68deville** · 04-11-2014

Thanks for the help, I cut my old cap and adjusted it. Nice that the MSD dist uses the same cap as the old points dist.

It was pretty far out, almost firing on the next cyl. It was making a pretty big arc back to the #1 terminal, I could hear it ticking loudly.

15 deg counter cw got it centered on the #1 tower terminal pretty well.

With the EST feedback unplugged its firing a little cw of dead center, with the EST advancing timing it tends to be dead on.