Advancing timing on 99 Jeep XJ?

[thenag]

So after fixing my exhaust issues I got my Jeep dyno'ed again. (I will post up more info about that in my build thread soon)

Anyway Joe at Turbo Lab says that if there were a way to advance my timing 4 degrees the engine would run much better. (his exact words were "15 to 30 hp and lower exhaust temps")

I googled around and found that if you modify the crank position sensor bracket you can get up to 6 degrees of advance. This makes sense *if* the ignition timing is based solely on the crank position sensor. You move the sensor a few degrees toward TDC and the ignition fires earlier.

I thought that once the engine starts, timing was handled by Cam Position sensor. I was told this is why when you have a bad crank position sensor it runs fine once it starts.

My 99 XJ is the last year that has a distributor cap and rotor setup. The distributor is fixed but could easily be made non-fixed, but if the advance is controlled by other means it may not do what I want. If making the rotor so it would turn would adjust timing it could be done very easy, and it would be adjustable. modifying the crank position sensor wouldn't give me much adjustment, or be easy to adjust.


Does anybody have knowledge of the timing and advance workings of 99-ish Jeep?

Does anybody have experience advancing the timing on a 99-ish Jeep?

If anybody has a 4.6L stroker and wants to dyno their Jeep, PM me.


Oh and yes I am looking at moving the crank position sensor which is the single hardest part to get to on an XJ...

Thanks

Nathan
build thread;
https://www.rme4x4.com/showthread.php?83436-Nathan-and-Tanja-s-99-XJ-Build-up

 

[DaveB]

Moving the crank position sensor will do it but I think you can change the timing on your 99 by re-flashing your ECM. I have a 4.6 stroker that I would like to dyno but I have to get it to stop pinging at full throttle and finish break in.

 

[thenag]

Moving the crank position sensor will do it but I think you can change the timing on your 99 by re-flashing your ECM. I have a 4.6 stroker that I would like to dyno but I have to get it to stop pinging at full throttle and finish break in.

I believe that re-flashing the ECM is kind of expensive (not that I am afraid to spend money on this project) but it will cost me nothing but time to move the crank position sensor.

Is your stroker setup similar to mine, same ignition, EFI, etc. I am trying to find a similar setup I might be able to get a discounted dyno run for you.

Nathan

 

[DaveB]

My stroker is based on an OBD1 system from a 93 XJ. Yours with the OBD2 has a bit more flexibility in that you can re-flash your computer more easily. My stroker uses the longer 4.0 rods, 4.2 crank, and Kieth Black pistons. I have added an adjustable fuel pressure regulator and made an adjustable MAP sensor to help with pinging. I have an air fuel ratio meter that I need to add in so I can tune it. Once that is done a dyno run might be good.

 

[XJEEPER]

So after fixing my exhaust issues I got my Jeep dyno'ed again. (I will post up more info about that in my build thread soon)

Anyway Joe at Turbo Lab says that if there were a way to advance my timing 4 degrees the engine would run much better. (his exact words were "15 to 30 hp and lower exhaust temps")

I googled around and found that if you modify the crank position sensor bracket you can get up to 6 degrees of advance. This makes sense *if* the ignition timing is based solely on the crank position sensor. You move the sensor a few degrees toward TDC and the ignition fires earlier.

I thought that once the engine starts, timing was handled by Cam Position sensor. I was told this is why when you have a bad crank position sensor it runs fine once it starts.

My 99 XJ is the last year that has a distributor cap and rotor setup. The distributor is fixed but could easily be made non-fixed, but if the advance is controlled by other means it may not do what I want. If making the rotor so it would turn would adjust timing it could be done very easy, and it would be adjustable. modifying the crank position sensor wouldn't give me much adjustment, or be easy to adjust.


Does anybody have knowledge of the timing and advance workings of 99-ish Jeep?

Does anybody have experience advancing the timing on a 99-ish Jeep?

If anybody has a 4.6L stroker and wants to dyno their Jeep, PM me.


Oh and yes I am looking at moving the crank position sensor which is the single hardest part to get to on an XJ...

Thanks

Nathan
build thread;
https://www.rme4x4.com/showthread.php?83436-Nathan-and-Tanja-s-99-XJ-Build-up

Seems like modifying your CPS buy slotting the mounting holes is the adjustable CPS option. http://www.jeep4.0performance.4mg.com/electronic.html

 

[thenag]

Alright so after making it so I can rotate my distributor, I decided to see what the factory service manual says about the ignition system;



Big BOLD letters, do not modify the distributor so it can rotate, this will not advance timing.

So there is a thread on NAXJA on modifying a crank position sensor, so with his pictures I grabbed the new sensor that I carry as a spare. (yeah I am that guy that has a brand new Mopar Crank Position Sensor under the passenger seat for a spare...)





I drew an outline of the sensor on piece of metal with holes an OEM location, and figure (from NAXJA pictures) this is about what I want;



First thing make a hole closer to sensor;



I thought I took some pictures of the tab I made but here it is with bolt holes through it. The 1/4 bolt uses the OEM sensor hole, hopefully it won't interfere with the bell housing.



To space the tab out I got a big washer, tack welded it on and ground it down.





Here it is all bolted together. I did not want to weld on the sensor since it is a sensitive magnet and figured welding might screw that up. I was already nervous enough drilling and grinding that close to the sensor.




Nathan

 

[thenag]

On more picture;


The distance from the center of the sensor to the closest hole is pretty close to 3/4 of an inch. Since I made slots hopefully I have a little adjustment.

Now I get to do the hard part, installing it into an XJ. Hopefully I don't have to do many more modifications to it.

I will post up how it goes.

Nathan

 

[thenag]

I got my modified sensor installed. It wasn't too bad, tape on the universal joint socket to keep it stiff. Tape on the bolt so the bolt didn't drop into the bell housing. I omitted the plastic cover, I will probably modify the cover and install it when I re-build the transmission this winter. My hydraulic clutch line was more in the way than anything, although the driveshaft was blocking my view. I didn't feel the need to drop the cross member or anything.

My slots didn't work out, the sensor is as far as it can go in the hole in the transmission, and would not slide down.

My timing light showed 5 degrees advance from what it was. It did advanced the timing at idle.

I only did a short drive and I don't know that it felt much different.







Nathan

 

[TurboMinivan]

My timing light showed 5 degrees advance from what it was. It did advanced the timing at idle.

Now take it to the dyno so we can see the extra 30 HP this gave you. Please.

 

[thenag]

Now take it to the dyno so we can see the extra 30 HP this gave you. Please.

I will... I may wait until cool air temps though...

Nathan