How Sophisticated is the 2.5 TBI?

[Joe Jeep]

I was just wondering how well the 2.5 ECU and TBI are at adapting to changning conditions. I was poking around the engine this weekend and noticed that a few of the vacuum lines are in need of replacing. They are not broken, but cracked.

When I start the truck, it runs a bit rough for the first ~15-30 seconds and then settles out. It has 235000 miles so it isn't new (though the PO had the topend done at ~115000 miles).

I am sure the O2 sensor is original as well as many of the hoses which I am thinking about replacing. This is my first vehicle with TBI injection so just wondering more about how it works.

Thanks.

[mjeff87]

It's a fairly simple system, injector pulse length is controlled by a handful of sensors: O2, coolant temp, MAP, MAT, and TPS feed info to the ECU, which in turn controls the injector. Make sure the vac line to the MAP (sensor bolted to the firewall with a little cover over it) is intact, replace the O2 sensor, and don't get the TPS wet and you'll be good.

 

Jeff

[tjbliley]

Pretty simple. If you want to try and make it a little more reliable you can throw some money at it by replacing the sensors and vacuum lines, including the O2 sensor, MAP, AIC, and TPS sensor as well as the EGR vave. As always if you are replacing stuff you need to replace the CPS on the bell housing cause they will just die cause. Doing all this as well as adding a spacer to the throttle body, and freeing up the air flow before and after the motor with cold air intake and free flowing exhaust will make it run pretty good, for a pretty long time. I have to add there may be quite a few people here that will tell you the best way to improve the 2.5 TBI is by adding 2 more cylinders and a few more injecters by swapping to a 4.0 MPFI. If you want to keep it just do the basic stuff and it should serve you well as long as you take care of it.

[feerocknok]

02 sensors are suggested to be replaced every 100,000 miles.

The 2.5s have alot of sensors, but are not a complex design compared to newer MPI motors.

[Joe Jeep]

What's the $ for a new O2 sensor?

[Eagle]

02 sensors are suggested to be replaced every 100,000 miles.

The 2.5s have alot of sensors, but are not a complex design compared to newer MPI motors.

It's supposed to be 80,000, per the factory. That's what the count-down timers were calibrated for.

[feerocknok]

http://www.partsamerica.com/ProductDeta ... 91&PTSet=A

Either way, 200+ is probably time to change it.

[jtdesigns]

It's supposed to be 80,000, per the factory. That's what the count-down timers were calibrated for.

 

How the he!! do you know all this stuff,,,,, did you work for amc in a past life????

[feerocknok]

He's a freaking genius.

[Oizarod115]

we (i) refer to Eagle as god of the MJ/XJ platform (and many other things to boot I'm sure)

 

:bowdown: :bowdown:

 

somebody mail that man a case of bud select! :cheers:

[Joe Jeep]

So, does what does the O2 sensor do exactly and if it is not functioning what happens to the MJ?

Is it a part that wears out or is there a way to test if it is functioning?

On the 2.5, this sensor is located on the exhaust manifold, right?

[87manche]

So, does what does the O2 sensor do exactly and if it is not functioning what happens to the MJ?

Is it a part that wears out or is there a way to test if it is functioning?

On the 2.5, this sensor is located on the exhaust manifold, right?

it counts how much oxygen is in the exhaust flow. It converts that into an electrical impulse that the ECU uses to determine the mixture.

You can test it with a multimeter, but at 200K it's shot. With an O2 sensor that doesn't register properly the ECU will not get the mixture right. Classis symptoms are a lack of power, poor gas mileage and the fouling of the cat from a rich mixture.