code 27 has me stumped!

[8Mud]

I've had the same thing happen numerous times for different reasons. Until the engine heats up a bit it runs on preset program fuel, after it heats up it switches over to O2 sensor fuel metering.

I'm guessing the O2 sensor switch over isn't working right, either the O2 sensor or the wiring. Happened to me, it eventually threw a O2 code after the O2 sensor was dead, dead,dead, not while it was failing and I was getting intermittent issues.

Second, possibility is the CPS is getting low input voltage. Happened to me, the CPS tested good it wasn't.

Third, something fuel pump related, either low voltage or a bearing that starts to seize when it warms up. Happened to me, I had a connector slowly cooking and it acted like a resistor and cut my fuel pump voltage/amperage way down.

Fourth, Coil heats up and craps out, fairly common. It may not fail completely every time, but can make such a weak spark the motor barley runs.

If you figure out if it is fuel or spark this can really help narrow down the probable causes. If it is both it can also narrow it down.

 

[ceasar]

i am walking away from this thing for a day or two....:skull2: the o2 sensor was replaced by a local shop as i ripped out the harness and wiring on a run and it had to be replaced with a universal....crap how do i test its installed right?

 

[90xj06]

unplug one injector at a time and see if it starts. could be an injector is bad and shorting out. or the harness is chaffed or damaged. also check if the injectors are getting a constant 12v feed when it wont start. could be a bad relay acting up.

 

[Runnin'OnEmpty]

i am walking away from this thing for a day or two....:skull2: the o2 sensor was replaced by a local shop as i ripped out the harness and wiring on a run and it had to be replaced with a universal....crap how do i test its installed right?

Ah Ha. :idea: If the O2 sensor isn't wired right, when the ECU goes into closed loop it loses the O2 signal to the injectors (which the code 27 indicates)....?

I don't have wiring diagrams handy now, maybe someone can help with O2 wiring, or I'll hunt mine up tomorrow.

 

[ceasar]

please do runninon empty i am starting to lose my mind!!:wierd:

 

[Runnin'OnEmpty]

This is for a Grand Cherokee but maybe it'll be of some help.

http://troubleshootmyvehicle.com/jeep/4.0L/oxygen-sensor-wiring-diagram

 

[ceasar]

so....looks like the wiring diagram you posted is the right one.however the shop that put in o2 sensor used a universal one wiite and black wires.so i am thing i should buy one with a harness and the correct colored wires and just cut off the harness and splice?

 

[Runnin'OnEmpty]

So if the shop replaced your 4-wire O2 sensor with a 2-wire, I'm at a loss as to how it should be connected. The 2-wire sensor has a ground wire and signal wire, and the 4-wire sensor also has ground and power wires for the heater circuit. Maybe someone will chime in with suggestions...?

 

[90xj06]

2 wire sensor may not have a heater in it. best bet would be to get the correct o2 sensor.

 

[ceasar]

geez...i need to proof read my posts before posting them as part of it got cut out. anyways the XJ has 4 wires...one is green with a white stripe. the other three wires are black with tan,green and blue stripe.the universal o2 sensor has one grey,one black and two white wires.i went to two local parts stores and their harness wired o2 sensors are not color coded to match the jeep so i am out of luck there...

 

[Runnin'OnEmpty]

Deleted

 

[Runnin'OnEmpty]

https://mechanics.stackexchange.com/questions/15387/do-i-have-to-rely-on-wire-color-to-correctly-wire-up-an-o2-sensor

 

[ceasar]

crap the color of wires dont match mine but maybe the test might get me somewhere....

 

[Runnin'OnEmpty]

Ceasar, did the trouble (and the code 27) start right after the
O2 sensor was changed, or did it run OK for a while?

What brand is the aftermarket sensor; Bosch, Standard, etc.?

I can't find a wiring color code anywhere. I'll try to get under my 96
tomorrow and see if the sensor colors match with yours.

 

[ceasar]

it ran ok for maybe 50 miles of regular driving.took it on a short but hard mudhill run and it overheated.thats when it started with code 27.its just a standard o2 sensor.

 

[90xj06]

how muddy? did the engine bay get wet and mucky?

 

[ceasar]

no...

 

[ceasar]

runninon empty....any chance the wires matched?i ran all the tests on the link and i" think"i got it right??still dont want to run after warm up though...!!!1

 

[Runnin'OnEmpty]

it ran ok for maybe 50 miles of regular driving.took it on a short but hard mudhill run and it overheated.thats when it started with code 27.its just a standard o2 sensor.

If it ran OK for 50 miles, that indicates the O2 sensor was
wired correctly. It still might be a loose or bad connection
since the aftermarket sensor had to be spliced in. Or the
overheating could have ruined the new sensor.

The Jeep code 27 is listed as "Fuel injector control circuit".
There's a Chrysler code 27 that references #2 injector as
having no signal (broken or shorted wire). I don't know why
only #2 injector signal would be affected by this code...

 

[ceasar]

well i rewired the o2 sensor and checked for any bad connections.i didnt think the o2 sensor could go faulty from an overheat??i have no problem buying a new one

that is weird it references #2 injector....i will go over that injector with a fine tooth comb and even maybe replace it....