Distributor Indexing

Back in June I posted a thread about changing out my distributor in my '88 XJ. I noted that the mounting tab had been cut off. I thought this was odd but Cruiser54 pointed out there was a TSB (#18-53-88) regarding this due to an ignition crossover that might cause bucking or surging. While I never experienced this, I felt I needed to do this the proper way.

So I chopped up my old cap to cut a window.



Then set the engine to top dead center.



Verified the rotor pointed at #1



Then installed the "cutaway" cap. You can see the end of the rotor tip at the extreme left side of the window (Should've cut the window larger). I was about 5/16" away from the post.




So out came the distributor and made the mark to cut.



Used my dremel with a cutoff wheel to whack the tab off. Cleaned up the edges with some 220.



Reinstalled the distributor and clamp. Clamp tightened down to just snug but could still rotate. Turned the distributor until the rotor barely past the post. (The TSB says .020" but I eyeballed it). Sorry I guess I forgot to take this pic.

Tightened down the clamp, reinstalled the good cap, cranked the engine and GLORY, it started. Started it several times to make sure I still didn't find some way to mess this up.

Here's the "trophy" I have to mark the occasion.



So once again thanks to Cruiser54

Cruiser54's tip can be found here.
http://cruiser54.com/?p=68

Thank you for posting this, and documenting it with pictures. I want to try this with mine some day. I've read that these engines will run fine with the distributor completely disconnected, but I've not dared to try it. With the luck I've had with mine this past year it would probably burst into flames. Or cause a second pandemic!

tempest411 said:

Thank you for posting this, and documenting it with pictures. I want to try this with mine some day. I've read that these engines will run fine with the distributor completely disconnected, but I've not dared to try it. With the luck I've had with mine this past year it would probably burst into flames. Or cause a second pandemic!

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There is a reason they'll run fine with the connector disconnected. The wires go to a part in the distributor that has NOTHING to do with ignition!!

The indexing is to address another issue.

Here ya go.

HERE’S WHY DISTRIBUTOR INDEXING IS SO IMPORTANT:

Distributor indexing explained:

For clarification though, that’s not a cam sensor inside the Renix dizzy. It’s there to fire the injectors sequentially with the firing order. You’ll never notice if it went bad because the ECU will try to “guess” where it is and does a heck of a job at it.

As for the “timing”, it is controlled by the ECU. Ever notice how wide the tip of the rotor is? Try and wrap your head around this:

When the ECU yells “Fire” to the ignition control module, where is the rotor in relationship to the dizzy terminal? Not to the terminal yet? Past the terminal too far?

What happens to the spark/secondary ignition strength when it has to jump the Grand Canyon in comparison to shooting from a rotor tip? Poor ignition performance, bucking, jerking, longer crank times.

The factory was aware of this and issued a Technical Service Bulletin on it. This Tip, #13, is a condensed version of that factory TSB. You wouldn’t believe how many we found out of whack when I worked at the dealership. Yours is probably messed up also. RARELY did we find one set accurately.

http://www.angelfire.com/my/fan/dist_index.html

I have always referenced this.

The Renix Fuel Injection manual refers to the sensor in the distributor as the Sync Signal Generator. It says:

"SYNC SIGNAL GENERATOR
The sync signal generator, located in the distributor works with the speed sensor to provide the inputs the ECU needs to establish and maintain the proper fuel injector firing order. Proper firing order is maintained by locating pistons one and six. As the pulse ring rotates in the distributor it passes through a magnetic field (signal generator). When the pulse ring enters the signal generator, the magnetic field becomes weaker - indicating the position of piston number one. When the ring leaves the signal generator, the magnetic field becomes stronger - indicating the position of piston number six. The ECU receives this information and is able to determine the proper order of injection sequence."

The CPS (we all love so dearly) is referred to as the Engine Speed Sensor. It says:

"ENGINE SPEED SENSOR
The magnetic speed sensor is mounted on the transmission bell housing where it detects the passing of the toothed flywheel. The signal generated provides engine speed and crankshaft position information to the ECU. The ECU uses this information to determine proper fuel injection and ignition timing.

When a flywheel tooth nears the sensor's magnet, the magnet field begins to shift. The field then snaps back to its original position when the trigger notch is aligned with the sensor, inducing a voltage in the sensor's pickup coil. This voltage is sent to the ECU.

A voltage is generated each time one of the notches passes the sensor. These voltages allow the ECU to actually "count" the passing teeth. Because the ECU (knows that top dead center occurs 12 teeth after the trigger notch, it can adjust the ignition timing by counting these teeth. The ECU also uses Information from the speed sensor to determine when to energize the injectors for fuel delivery to the proper cylinders. The toothed flywheel rotating past the speed sensor, contains three notches 120 degrees apart. Each notch is separated by twenty teeth and is used to locate the position of two pistons. Pistons one and six approach TDC at the same time and use the same flywheel notch. Piston two Is matched with piston five while piston three is matched with piston four. From the speed sensor, the ECU knows two pistons are approaching TDC. The sync signal generator provides this information.

NOTE: The notches are located on the flywheel to relate precise piston position to the ECU. When one of the notches passes the speed sensor, the ECU is informed that the position of a particular set of pistons - such as 1 and 6-is 60 degrees before TDC. The twelfth tooth after the notch is top dead center."

blu3fan said:

http://www.angelfire.com/my/fan/dist_index.html

I have always referenced this.

Click to expand...

That's not for Renix systems or even all HO systems.