Crank sensor position? - Page 3 - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

LinkBack Thread Tools Display Modes
post #21 of (permalink) Old 04-28-2006, 10:59 PM Thread Starter
Way Outta Control
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
Re: Crank sensor position?

As in earlier systems that are adjustable by turning the distributor, setting the base initial timing off usually creates drivability problems. It assumes it's starting it's advance from a certain place. If it's starting from somewhere unkown -- it's lost.

If you "think" you are in New York but you are really in Dallas, you too are confused. Same thing. Ya gotta know where the beginning is.

Yes, at start-up it looks at the sensor as altitude. That in itself could offset the mixture. If you were actually at 2000 feet, but the new variable MAP voltage "tricked" it into thinking it was below sea level, it would end up rich. But richer didn't make much difference (as adding propane proved,) as it's already optimized.

The way the advance works is it's always trying to advance more and more, no matter where it started from. It keeps advancing till the knock sensor bumps it back down. That point is the optimum timing under that instantaneous speed, load, mixture, altitude, temp, throttle position etc.

Rockette products, and others, have an adjustable crank sensor, but it's for the earlier 4.0's.

BTW - I'm just shooting in the dark here - tried the richer idea, didn't seem to help. Already helped the external breathing with the exhaust and intake mods. Next thing was the crank sensor and initial timing - but that would take some machining - and the engine to be pulled out to do it.

RRich is offline  
Sponsored Links
post #22 of (permalink) Old 04-29-2006, 12:06 PM
Can't Get Enough
Join Date: Sep 1999
Location: Cotopaxi, Colorado
Posts: 1,036
Thanks: 0
Thanked 0 Times in 0 Posts
Re: Crank sensor position?

The spark timing dosn't quite work that way. True, if the CKP is offset to a different position, the PCM will be "fooled" in to thinking tdc is someplace else. This will allow for higher or lower total advance. If this is done, wou will also have to modify the CMP by 1/2 to correct "sync".

There is no "knock" sensor on your system, which retards timing at detination. But the amount of spark curve is determined by a software program which uses an equation to determine advance based on temp, rpm. load. throttle angle, etc. The amount of timing and various curves can be changed with flash files. High-altitude flash files have a lot more total advance than sea-level ones. I just checked, and there are no flash flies for the '03 4.0 to address spark knock or altituce changes. The stock spark curve is on the very high end anyway. So much that I can hear a small amount of knowk up here at 9,000'.

Another thing to think about is the enumerator factor. For OBD2 to determine cylinger mis-fire, it must learn the positions of the flywheel. The PCM will look at these positions going down hill with no throttle. It takes a pic of these positions and uses this info. to determine the relative speed of the flywheel acress the CKP to determine which cyld is mis-fireng. Any modifications to the position of the CKP will require a PCM clearing of learned enumerator, (disconnect the battery)
dorfs is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome