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Indexing distributor 88 4.0


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Hi everyone,

 

I've had my 1988 Comanche long bed, 4.0, five speed stick, since it was new in spring of 1988. About 130,000 miles, over all has run well for close to 30 years. Rust is the main issue currently.

 

This site is full of great information, and  looks like fantastic group of users!

 

Cruiser's list of Renix tips should be mandatory for every Comanche. The information about cleaning ground connections looks like it's essential. I'm going to try to do them, little by little.

 

I have some questions on indexing the distributor. I understand what should be done, but I'm not sure of the reason for it. Does this actually affect ignition timing? Or does it just align  the rotor more properly with the distributor cap terminal, so the spark has a shorter distance to jump inside the cap?

 

Thanks so much.

 

Gene

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Not all of them are off...  If you are in need of a tune up, you can easily cut your old distributor cap and see where you stand, or how far off it is...  When I checked mine it was spot on based on the write ups where it should be, so I cannot speak to how the adjustment helps because I didn't have to make it.

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Indexing the HO 4.0 distributor is the alignment procedure performed to install a distributor correctly as I understand it. This involves rotating the engine to TDC on the #1 cylinder on the compression stroke, turning the oil pump shaft slot to accept the aligned distributor shaft, and making sure the rotor is pointing to the correct position relative to the distributor housing. Lots of write-ups are available online detailing this procedure. I've done it many times, it's a straightforward procedure, and I can't remember getting it right the first time - I'm always one tooth off retarded or advanced. So perhaps I'm retarded.  :doh:

 

The timing is fixed and not adjustable on the stock distributors without machine work. But it's very important to get the indexing right so the ECU can dial in the timing based on the engine setup. One tooth off is unsat. I run a mild grind Hesco cam on the stroker, and whenever I make distributor changes like a newer distributor or even a new sync sensor, cap or rotor, I throw a timing light on it and check the timing at the marks on the timing chain cover and harmonic balancer to make sure it's in the ballpark. It's always a bit retarded less than the 14-16 degree BTDC ideal at first, then after driving it a few miles the ECU corrects it up to about 16-18 degrees BTDC because of the cam.

 

Distributor "indexing" IMO is a term carried over from the old mechanical points distributor systems when the timing was set by rotating the distributor housing to advance or retard the point's dwell setting.

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Thanks guys,

 

What you said above is pretty much what I had believed.

 

Cruiser's writeup (and he seems to know Jeeps inside and out) implies that there is a benefit to getting rotor position EXACTLY right. 

 

Any thoughts/experience with this?

 

Thanks

 

Gene

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Yes, there's a benefit.

 

Here's why:

 

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? 
 
Tip 13 gets the thing right. Use Tip 12 first to guarantee you're on #1 TDC.
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Hi Hornbrod,

 

Yeah, I know that I'm being a nusiance, especially for a newbie on this forum.

 

I'm trying to get a feel for the "why" not just the "how" for this. 

 

I'm old enough to remember points and timing lights, and carbs and jet sizes and floats. Waaaayyyyyy back then I understood how a car ran.

 

The Renix control system is something of a mystery to me.  Cruiser's comment on controlling injector timing is an eye opener, I would like to know more about that.

 

Thanks!

 

Gene

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Hi Cruiser,

 

Actually, somewhere on this site (I'm not quite sure where I found this link) is this list of service manual downloads.

 


 

It looks like the fuel injection manual gives lots and lots and lots of details on the computer control system. That provides everything I was looking for.

 

Once more, great site and great bunch of members!

 

Thanks

 

Gene

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