Gee oh Dee

This is gonna be a two part (or more) question. Probably many more once I start my mind working. If they seem like weird or pointless questions, I apologize in advance. Here we go...

How does the ECU see and read airflow into the motor? I know we don't have a MAS, so what exactly is used in the XJ? MAP? Other?

Question two, if the ECU sees more air than it expects, does the ECU cut fuel? Or more simply put, do our XJ's have a fuel cut function?

Last question, for now, is there any way of modifying the signal sent to the ECU? For example, some form of piggy back management? (SAFC I/II)

UserID6095

XJ uses a MAP system. http://en.wikipedia.org/wiki/MAP_sensor

For the second question are you talking in regards to a vacuum leak? If so then the system can only adjust fuel trim so much. With too much air and not enough fuel the system will run lean and that could create a huge issue (burned valves, piston tops, etc.).

You can modify the signal to the ECM from the MAP sensor with an adjustable MAP sensor. You could make one and/or buy one. A piggy back system would take over engine management and would require the end user to tune it. There are no direct fuel maps available for our beloved Cherokee's.

Gee oh Dee

Thought so.

I'm actually talking about adding air to the system, not leaking it. Boost.

Is it possible to modify the signal to accept...say...10 psi of boost?

I'm completely familiar with piggy back systems. I've had to use them on a few cars, and am very familiar with tuning. I'm almost ashamed to admit that, only because there are much better ways of tuning a motor. Like stand alone. Or some sort of chip and laptop link. I've just never seen or heard of using one on a XJ.

UserID6095

I must admit I am no turbo expert but I do know how a turbo system works.

You can use an adjustable MAP sensor but you would also need a way to control the A/F ratio while under and out of boost. Thats where custom tuning will have to come into play. Check NAXJA's street tech forum, they have a few threads on turbo installs. One gent' used the Megasquirt system where another used the AEM system to control the variables that come into play with a boosted engine.

Gee oh Dee

I'm pretty sure I got that covered with a set of larger injectors and one of these:

http://www.bellengineering.net/produ...&products_id=7