Where to start with distributor, after-market cam timing

[JeepFan]

I'm just about ready to put my new stroker in my 1990 Renix-equipped Cherokee and would like some advice on where to initially set the distributor.

I used a 1994 block and head, with my 1990 Renix F.I. and 1990 distributor, flexplate, and an after-market cam. I researched on how to install and index the cam and it said that I may have to remove the tabs on the distributor if the rotor does not line up near the #1 terminal when at TDC. It didn't. So I removed the tabs and can now rotate the distributor freely.

So... my first question is: Where should I set my distributor rotor in relation to the #1 terminal when at TDC?

I've also read that the timing is controlled by the computer and that the distributor controls the timing of the fuel injectors. True? If it is true, does that mean that a timing light will not allow me to set the ignition timing? Is a timing light used to adjust the F.I. timing or is a timing light not used at all?

I'm getting so confused...

[SilverXJ]

Stock location. See here: http://www.angelfire.com/my/fan/dist_index.html

[RenoF250]

Yeah, should be stock. Any advance or retard in the cam would be on the lobes and should not affect the distributor gear. I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

[Cheromaniac]

The ignition timing is programmed into the ECU and cannot be adjusted. The CPS reads the position of the flywheel and when it sees the notch, it knows when the no.1 piston is at TDC and the ignition timing is set by the ECU according to the signal that it receives from the CPS. When the CPS fails, there's no spark and the engine suddenly dies and refuses to start.
The signal from the cam position sensor in the distributor is used to synchronize the injector firing sequence with the timing of the spark.

[SilverXJ]

I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

At least on OBD II it uses the cam sensor the whole time to time injection.

[cruiser54]

Click on the link below and go to post # 13.

http://www.cherokeeforum.com/f51/cruise ... ps-153657/

[JeepFan]

Thanks all for the great info. I think I've got a good handle on it now. Can't wait to put the motor in - hopefully this weekend!

[jsawduste]

Yeah, should be stock. Any advance or retard in the cam would be on the lobes and should not affect the distributor gear. I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

Wrong again Reno.

[cruiser54]

Renix has an ECU, not a PCM.

The sync generator inside the dizzy on a Renix only advises the ECU when to fire injectors sequentially with the firing order.

If you read the post in my link, you can see why dizzy indexing id critical. It's to make sure that when the ECU tells the ICM to fire, the rotor is in the correct position in relationship to the dizzy terminal.

[RenoF250]

Yeah, should be stock. Any advance or retard in the cam would be on the lobes and should not affect the distributor gear. I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

Wrong again Reno.

I've got an idea, why don't you put me on your ignore list like you did on Pirate? You are so smart I thought you would have figured that out by now.

[jsawduste]

Yeah, should be stock. Any advance or retard in the cam would be on the lobes and should not affect the distributor gear. I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

Wrong again Reno.

I've got an idea, why don't you put me on your ignore list like you did on Pirate? You are so smart I thought you would have figured that out by now.

Review how to degree a cam. How the event of advancing or retarding a cam via the timing set effects the engagement of the dist. gear and how the cam timing event/injector phasing is effected by such means. How and why changing the lobe placement effects the valve timing event in respect to crank position. Keeping in mind the cut of the dist drive gear and it`s role in the big picture.

Do you now see that in some cases a cam may need to be degreed in order to meet spec or that the dist. be indexed differently in relation to piston position/cam phasing by removing the "ears" ? The ECM sees a crank signal and compares that to a cam signal and when the two fall within parameter the injection and timing event occurs. This is one of the key elements that folks like Ryan and Chris are able to modify to change the parameter with their tuning.

On one of my OBD1 SBEC engines the cam is advanced 4 degrees. Requiring an adjustment of the dist to compensate for the 4 degree advance. Taking things a step further the Crank Sensor is also repositioned. Thereby readjusting the timing event of the ignition AND the injectors as the ECM is looking for both inputs.

[RenoF250]

Yeah, should be stock. Any advance or retard in the cam would be on the lobes and should not affect the distributor gear. I have heard the PCM only uses the dist to know where the cam is from start-up and then times off of the flywheel/CPS.

Wrong again Reno.

I've got an idea, why don't you put me on your ignore list like you did on Pirate? You are so smart I thought you would have figured that out by now.

Review how to degree a cam. How the event of advancing or retarding a cam via the timing set effects the engagement of the dist. gear and how the cam timing event/injector phasing is effected by such means. How and why changing the lobe placement effects the valve timing event in respect to crank position. Keeping in mind the cut of the dist drive gear and it`s role in the big picture.

Do you now see that in some cases a cam may need to be degreed in order to meet spec or that the dist. be indexed differently in relation to piston position/cam phasing by removing the "ears" ? The ECM sees a crank signal and compares that to a cam signal and when the two fall within parameter the injection and timing event occurs. This is one of the key elements that folks like Ryan and Chris are able to modify to change the parameter with their tuning.

On one of my OBD1 SBEC engines the cam is advanced 4 degrees. Requiring an adjustment of the dist to compensate for the 4 degree advance. Taking things a step further the Crank Sensor is also repositioned. Thereby readjusting the timing event of the ignition AND the injectors as the ECM is looking for both inputs.

Yes, I understand that if you advance the cam you advance the distributor because you have turned the camshaft. I took his question differently, I thought he was asking if an aftermarket cam caused the dist timing to be different and it does only if you degree the cam to a different position.

I asked Crower about where I should put my cam and he said most are ground to be installed straight up, you can move them advanced or retarded but there are tradeoffs. Point being, aftermarket cam does not mean it will have to be advanced or retarded.

As far as the timing from the dist, I read that somewhere else and indicated that in my post, I did not know. I only posted so that those that did could comment and I would find out. I had suspected it was true to be honest since the wheel in the dist does not have a very precise edge, just a piece of stamped steel and only one edge. Crank seems better to time off of once you know where the cam is. With all of the timing issues I have read about it seems it would have been good for them to have a knock sensor like the old 4.2 did.

[the grey ghost]

Even if the advance or retard is ground in, and you install it straight up you have to degree the distributor, the lobe opening/closing is what matters, the injector timing is how our mpi engines make their power, injector timing is almost as important as spark. Otherwise we would just batch fire, it will run but like a tbi

[cruiser54]

Even if the advance or retard is ground in, and you install it straight up you have to degree the distributor, the lobe opening/closing is what matters, the injector timing is how our mpi engines make their power, injector timing is almost as important as spark. Otherwise we would just batch fire, it will run but like a tbi

Actually, not true.

You can unplug the sync generator harness on a Renix and notice little to no difference in running/drivability. Try it.

When I worked at the dealership when Renix came out, we never had a drivability problem solved by sync generator replacement.

Did we ever replace them? Yes. But only when we were reading live data through the factory tester and noticed it was dead.

[the grey ghost]

Oops