XJ Mods VSB 14

[rainman]

Originally Posted by alexbrown64

Your right there Tony. Not much difference. The book is great at explaining tests and voltages etc. Should work well with your 96 XJ's.

When i bought my MT2500, it came in a briefcase with a bunch of books. One of the books explains all the readings.

This is a copy here on Ebay.. https://www.ebay.com.au/itm/SNAP-ON-...0AAOSwmetcdarm

Talks all about open/closed loop and when it happens and a bunch of values you should be seeing. On the OBD1, for fuel trim, the default setting is 128 to provide a perfect 14.7/1 air fuel ratio. Reading above or below 128 tell you if your Jeep is adding or subtracting fuel.

Also, injector pulse width should be 4-6ms. It explains how the map sensor works using barometric pressure and vacuum pressure to get manifold absolute pressure.

Overall, a great read.. helps put you to sleep at night..
I should of played with the MT2500 before, but been too busy with other stuff. Public holiday here in Perth tomorrow, so i wont get my Jeep back from its regear until Tue/Wed, but looking forward to having a crack at it..

Cheers,

mate my OBD1 fuel trim (adapttive fuel %) is 65 so what would that indicate?

also would you concider taking pics of the info regarding fuel trims and emailing them?

[alexbrown64]

I can do better than that Rainman. I can post the page about fuel trims here. This is fresh out of the Snap-On Scanner Jeep Reference Manual.

Obviously, you have two Fuel Trims.. You have your long term trim, which is the adaptive gain... this is what your XJ has learned over many cycles.. You also have your short term trim. Its what the Jeep is doing currently.

The ranges are from 0-255. 128 being the middle range and where your Jeep is running at the perfect 14.7/1 air/fuel ratio.

Anything below 128, and your fuel injection system is metering less fuel. Anything above 128 and your fuel system is metering more fuel.

All this only operates in closed loop, when your engine and O2 sensor are warm. In open loop, which is a cold engine, declaration and acceleration, the default setting is 128.

This explanation from: https://www.aa1car.com/library/what_is_fuel_trim.htm

"POSITIVE fuel trim values mean the engine computer is adding fuel (increasing the pulse width or on-time of the fuel injectors) to add more fuel to the engine. In other words, it is attempting to RICHEN the fuel mixture because it thinks the engine's air/fuel mixture is running too lean.

NEGATIVE (-) fuel trim values mean the engine computer is subtracting fuel (decreasing the pulse width or on-time of the fuel injectors) to reduce the amount of fuel injected into the engine. This is done to LEAN out the fuel mixture to compensate for what it perceives as a rich running condition".

So, Rainman, your system is trying to compensate for what it perceives is a rich running conditon, by trying to lean out the mixture.

According to the website, rich fuel mixtures generate negative fuel trim values and the problems can be:

Leaky fuel injector
Excessive fuel pressure due to bad fuel pressure regulator or restricted fuel return line
Extremely dirty air filter or restrictions in air intake system
Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler)
Bad O2 sensor (output shorted to voltage so it reads RICH all the time)



Its interesting putting all the pieces of the puzzle together. Obviously, Jeep didn't want us to know all this info back in the day. Thats why only they had the Jeep scanner. Now, its easy for us to figure out what is going on, using the right tools..

Cheers,

[rainman]

Thanks for that.
I have read up on obd2 fuel trims.
It’s just my scanner showS as parameters:
add fuel (us) - prety sure this is short term fuel trim in microseconds.
Adpt fuel (%) - long term as a percentage.

It’s at 65% which is way out of scale for fuel trim which is +-35%

[alexbrown64]

This is a pretty good vid that helps explain fuel trims too Rainman.
You 65% is getting me confused. There is a big difference between 65 and 65%, depending on what reader you are using for OBD1 systems.

On OBD1, we have 0-255, with 128 being perfect condition. With your 65, it would be adding a lot less fuel, and therefor trying to combat a rich condition.
If your reader is showing 65%, then that is a massive over fueling issue, which means your donk is combating a very lean condition.

What scanner are you using on your OBD1 96 XJ?

When i get my Snap-On running, it will show the 0-255 scale.

Sounds like you may have a bad O2 sensor, MAF sensor or big vacuum leak.
In reality, you should only be +- 10% of 128 or 0%.

Also, does your reader show pulse width. Normal is 4-6ms which is milliseconds. If your numbers are higher, then you will know your Jeep is over fueling to combat a rich condition.

Cheers,

You Tube

[alexbrown64]

OK, so i got a call from 4WD USA.

They found the problem with my vibes and noise from the front end. The 4.88 gears had never been installed properly. Also, there had been water in there at some time and it had pitted the ring and pinion. Also, the bearings were gone. Also, the uni joints in each wheel were suspect.

I remember years ago changing the oil and noticing it was milky. Ive never been through deep water, so not sure what happened there, but at least they found some problems and fixed them. I did change the axle uni's out for Moog a few years ago. Not sure whats going on there.. perhaps the vibes in the gears wore the axle unis.

New 4.56 gears installed, new bearings, front axle uni's etc..

The other problem is the left pull. They are still working on this. A few offset ball joints are being used, but they are also working on some bump steer. They are saying it has a drop pitman arm that could be causing it.

Strange, as i have never done a pitman arm swap, but the world is a strange place...

So hopefully tomorrow afternoon they will have it sorted, or at least on the right track and i will have my daily driver.

Might look at a RTC damper at some stage too. They are supposed to improve steering and ride and they are not a bad price.

Whoohooo..

[rainman]

thanks for the reply.
I use a actron 9690.



ADDed FUEL Adaptive Adjustment of Fuel Injector
ADPT FUEL (%) Adaptive Fuel Factor

it runs fine 12.6 AFR @WOT up a hill. just trying to figure out what the 2 paremeters mean. or more precisly what the scale for the adpt fuel is.

fuel presure is currently 42 psi @ WOT. might increse it it a bit and see what the numbers do.

[awg]

Originally Posted by alexbrown64

OK, so i got a call from 4WD USA.


The other problem is the left pull. They are still working on this. A few offset ball joints are being used, but they are also working on some bump steer. They are saying it has a drop pitman arm that could be causing it.

Strange, as i have never done a pitman arm swap, but the world is a strange place...

Might look at a RTC damper at some stage too. They are supposed to improve steering and ride and they are not a bad price.

Is your XJ lifted ?

If so, I find it strange they would say a "dropped" Pitman Arm would make bump steer worse

It was my understanding that is why one is fitted...this explains it better than me...I googled it lol..from NXAJA

" A drop pitman arm has nothing to do with death wobble. Lowering the mounting point of the draglink after installing a lift is done to keep the draglink parallel to the trackbar. If they are not parallel the rig will suffer from bump steer. A 1" drop (ZJ pitman arm) works very well to maintain the proper geometry. "