Hi I am working with my 2000 Cherokee and I'm just wondering how to set ignition timing on the coil pack engines I've heard it needs to be done with a special computer is this true? Thank for any help

 

computer adjusts timing based off position of the crank and position of the camshaft, and reconciled off readings from manifold absolute pressure, engine temperature, and intake air temperature, and then graded by the o2 sensor for accuracy- which prompts changes to achieve the best burn which is going to be as close to stoichiometric as possible...

you can advance it using a computer/programmer..... but, out of curiosity, why? it's capable of nailing perfection and will curve advance something like 25* BTDC from the base advance of something like 10* or 12* BTDC... that would be a total of 25~37* advance.... any more than that is not only hurting performance, but dangerous to your engines health...

 

Drew nailed it. It's all in the ECU.

 

there are some things you can play with that will boost both performance and economy if you are so inclined, and have patience...

i like talking spark... it's like reminiscing... (diesel does it for me now)...

but anyway...

this is a nice trick, especially if you live at altitude... increase your spark temperature.. most are around 35k~45k volts... move it to the 55~60k range... when you do, widen your spark plug gaps to around .060~.065... you'll burst that little wad of air-fuel wider and more evenly, giving a harder push off after TDC, which pushes you up the TQ chart...

BUT WAIT!!!!

THERE'S MORE!!!!



there is this little thing with EFI called fuel sync- it works something like ignition timing, but with injectors instead of spark...

it uses the camshaft position sensor to time the spray of fuel...

now some people believe in the metal capacity of engineers... I am not one of those people... I believe, instead, in serendipity, aka dumb luck... engineers realized they needed to time the spray, but if it triggers at the same time spark is applied, there will be a really soggy burn and a really hot exhaust... well, y'all, that there ain't no good.

so.. they fire moments prior... this still ain't no good... the fuel is still droplets of liquid with the single hole injectors the gods of mud and tar issued with the mighty XJ...

before trying to crack that code, some smartarse engineer encountered this serendipity spoken of before... and just advanced the spray more than they had- and POOF!!! DUMB LUCK!!! instead of entering the chamber a liquid, it sprays on the back of a hot intake valve right before it opens... it atomizes... and the second it atomizes it's sucked into the chamber through the magic of vacuum of a downstroking piston and camshaft lobe driven opening of the valve... how 'bout that?

what's better, though, knowing that story- is the advancement of injectors over the past ten years- four hole sprayers instead of single... already misted fuel... no need for spraying the back of a hot valve...

back to hotter fatter spark... toss in the ingredient of what you now know about injectors and fuel sync...

pick up some ford motor sports four hole injectors... have someone like hemifever craft you up a script to SCT to your PCM to trim the fuel (you need about the same volume of spray, but you need it quicker- so, use heavier injectors with shorter duty cycle/duration).. you'll still want a lambda crossing zero on both STFT and LTFT, but you'll be doing it by dropping the same (slightly less) fuel in a shorter window of time, and AFTER the valve starts to open.....

what you get? quicker ignition and a more complete burn while using a little less fuel and chase that piston to the floor... quicker throttle response that your levi's will feel... the timing can actually retard a few degrees to protect the engine bearings and caps, with about the same benefits...

fun times, fellers... spark.... i'm gonna kick my kid out of that xj, like a dang pirate, and pilot it for myself for a while.... arrrrrrrrg....

 

I have a habit of emailing things I come across that I think might come in handy to know at some point in time. Not going to lie did not really understand any of it. Also not really sure if this applies to this question but...

http://www.jeepforum.com/forum/f11/h...think-2975897/

http://jeep.blackonyx.net/pdfs/jcss.pdf

 

wow thanks every one I've really just been interested in this. I am working on my 2000 and I have exhaust off and I've tried to start it and it doesn't want to stay running "running out exhaust manifold" I'm waiting for my exhaust to come in but I have been worried the spark timing is off. Could it be that the o2 sensors are not reading so the computer can't mix fuel and air mix right?

 

that's precisely your issue...

the o2 sensor is the jerk that validates everything the kids (previous mentioned sensors) do... w/o the o2 providing feedback, the engine (pcm/ecu) is going to think "dude, you're not running... here, you need more fuel..."... that doesn't end well.

 

"dude you're not running" lol thank you for the help Ill get back with you after I get my exhaust in thank u for the help.