JJobst

Hey Guys, so I have been doing some basic work on my 99 with a 4.0....The jeep has 230K orig miles on it and had been getting a little sluggish to respond. I did a basic tune up the other night and that helped but decided it would be good to go one step further and change out to new injectors since I was pretty sure they were disgusting. Last night I did the 4 hole injector swap, let the jeep idle for about 15-20 minutes and then took it for a test drive (about 5 miles). On the way back home i started feeling a bad miss and had to pull over because i was worried the car was about to die in the middle of the road. I got going but when I stopped at a light it almost went dead on me. I was able to make it home and pull into the garage and now had a terrible idle. I started thinking to myself that i may have screwed up and forgot to flash the computer and it was probably running off the flow of the old injectors. I disconnected the positive terminal, connected to the negative for 30-40sec, and then did the head light trick. I cranked it back up and the idle was good for a few minutes and then started to get rough, then rougher, then terrible. I started thinking that maybe a injector was bad so i put the old set back in, flashed the ecm, and let it idle. I now got the same results with the old injectors at this point. Called it a night and went to bed....

Tonight I put the new set back in, flashed, and let it idle. After about 10 minutes it went back to the same scenario. This time it threw a CEL. I went to the store and bought a new toy (obd2 scan tool). Only error code im pulling is a P0171 stating system to lean bank 1. I searched a few of the forums and it looks like fuel pressure, vac leak, upstream 02 sensor, or dirty sensor(s) related the TB could be the culprit. Ive rulled out the posibility of the injectors being clogged since both sets have the same results and I checked for vac leaks (everything checked is good so far). I cleaned the IAC which was pretty dirty but didnt make a change. The scan tool has live monitoring and the TPS is checking out correctly. The 02 sensor was getting low readings or high reading but wasnt quickly bouncing back and fourth like I read it was suppose to do but I am getting changes when monitoring so im going to say the wiring itself is good. I do not have a fuel pressure gauge here so i have not yet been able to confirm the system pressure.

Judging by the chain of events does it seem plausible that I fried out the 02 sensor due to putting the new injectors in, not flashing, and causing the system to run way to rich? The idle is fine until the vehicle starts to warm up and if i start pressing the gas I can get a smooth increase in rpms. I can clear the code and it will stay cleared until the idle starts to get bad again. If anyone else has had this code what did you do to solve it?

CCKen

What is your Short Term Fuel Trim?

If, when observing the upstream O2S activity on your scanner, the switching exceeds 2 seconds (or so) there's a possibility that the O2S heaters fuse is blown. Check it.

The O2S heaters fuse is in the PDC. A 15A mini fuse in the row closest to the firewall.

If the fuse is blown, examine the O2S wiring, especially the loom that crosses over the intake manifold. There have been cases where the intake has chafed through the loom to the wiring. Examine the downstream wring s well.

Here's a list of possible causes for P0171:

INTERMITTENT CONDITION
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SENSOR
O2 SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
O2 SENSOR HEATER OPERATION
TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED
TP SENSOR SWEEP
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM