computer?

[flippedXJ]

ok as you all know I got my XJ from a roll over accident and I am making it into a trail truck.

I have removed the plugs and blown all the oil out of the cyl so that with the plugs back in it turns over and sounds like it is ready to fire. But among further testing I am getting no spark or fuel, and after gettin my friend over here with wiring diagram.

We tested all the relays and fuses to find them ok. So we went on to pull the computer off the fender and check the wires going into and out of the computer and everything seems to be good which leaves me to think one thing :thumbdown: computer took a smack when it flipped (fender is bent right behind the computer) and now it isnt working.

I am open to opinions or if anyone has a comp for a 96 4.0HO auto please let me know

[BlueXJ]

Check the CPS before you blame the ECU. Computers rarely go bad. But it won't start with a bad signal from the CPS.

[4.3LXJ]

X2 If it doesn't know where the crank is, it won't do a thing.

[flippedXJ]

will it not even let the fuel pump turn on that way?

how do I test the cps?

[Mudderoy]

will it not even let the fuel pump turn on that way?

how do I test the cps?

Try this test.

:link: (http://www.jeepforum.com/forum/f11/cps-sensor-testing-861193/)

http://fototime.com/78EA763821BA137/standard.jpg

[BlueXJ]

Let us know what you find with the CPS and with no signal from it the computer will not add fuel pressure or turn on the mechanism to fire the injectors or the ignition.

[flippedXJ]

cool I will try that and let you guys know

[flippedXJ]

well the sensors are testing good but the comp is only puttin out 1.5 volts to them instead of 5 so i am headed to the junkyard sat to try and find another computer

[4.3LXJ]

well the sensors are testing good but the comp is only puttin out 1.5 volts to them instead of 5 so i am headed to the junkyard sat to try and find another computer

Have you got 12 volts to the computer and a good ground?

[flippedXJ]

ya the 12vlt wires were all reading properly and so were the grounds but the 5vlt out wires were only reading 1.5vlts. and they were only reading 1.5 at the sensors too.

[Mudderoy]

ya the 12vlt wires were all reading properly and so were the grounds but the 5vlt out wires were only reading 1.5vlts. and they were only reading 1.5 at the sensors too.

Has anyone mention to check the grounds?

[flippedXJ]

ya we went through and the grounds are grounded

[YellowSub2000]

Try opening the ECU. I did this to mine because I was having some problems, and noticed that a few circuits were burnt. Replaced the ECU, and it runs beautifully now.

[flippedXJ]

my buddy found me a new comp in the junkyard today so I will know shortly if it was the problem (crosses fingers)

[flippedXJ]

ok put in the new comp ( out of a 98 ) - now it will start and run (YAY) but only for 3 or 4 seconds then dies (BOO)
gonna figure it out tomorrow - any ideas?

[BlueXJ]

Still sounds like a CPS problem to me. Pinched wire somewhere between ECUand CPS. Or a bad plug at the pigtail leading from the CPS.