vadergator

i have a 97 jeep ( grand cherokee laredo ZJ 4.0 L ) that had been giving me problems with stalling while warming up. after alot of helpful suggestions from mechanics ( pro & backyard variety ) i did some upkeep repairs. i have some questions at the end of this post so, please don't think i am just posting what i did to the vehicle. it helps to know what i did so that hopefully you can help me narrow down my problem. i changed my valve cover gasket. replaced both of my positive crankcase ventilation 90 degree elbow hose connectors on the valve cover. one was cracked and the other got tore up during the attempt to take off the valve cover gasket. i had been having erratic play in some of the gauges on the dashboard due to bad grounds. i installed a # 4 gauge ground from the fuel rail bolt to the firewall ( there was no ground on any dipstick stud or the cylinder head to the firewall ) . i also installed another # 4 gauge ground from my negative batterry post bolt/ nut to one of my radiator support bolt/ nuts. grounding problems are now resolved. i removed my throttle body and it's 3 sensors ( IAC / MAP / TPS ) and thoroughly cleaned my throttle body with a toothbrush. nice and shiny everywhere inside and out. sprayed electronic cleaner inside all sensors, electrical connectors, and in the slots of the power distribution center where the relays and fuses go. used emory cloth / fine sandpaper to clean the prongs / legs of all relays and fuses. every connector i could find. PCM, coil, purge solenoid, crankshaft position sensor, cam position sensor / pick-up, lights, mini-coils to the fuel injectors, A / C , O2 sensors, tranny sensors, the works.. applied dielectric grease to every connector and connection on every sensor. even a little dab on each leg / prong of each fuse and relay. replaced my throttle body gasket as well. i changed my coolant temp sensor as well. needless to say, it fired right up and ran like a charm. perfect timing , idle, smooth as can be. no gauges moving on their own. just beautiful. drove for about 10 miles and noticed the motor was loping ( sounding like a muscle body car engine ) and idling rough with a misfire. for the first time in 5 months, the vehicle finally threw a check engine light. my vehicle never stalled though. hoo-ray. shut it down for 2 hours, it fired right back up. about a minute into the warmup, the loping and misfirng started again. drove her home without any stalling but, noticed the gas was being used up quicker on the fuel gauge. i let it sit overnight and checked the OBD-2 codes this morning. a PO171. i looked at possible causes of this code. there are 8 of them listed. to knock some off the list, fuel pressure and fuel system check out great with a 49 load reading ( 44 - 54 ) is where the pressure should fall between. O2 sensors worked great before i worked on jeep. their 4 months old and worked great still after firing up the motor for the first time. cannot be them BOTH going bad at the same minute of the day. my jeep does not have a MAF ( Mass Airflow Sensor ) on it. there has not been any vacuum leaks. no bad fuel injectors. no exhaust leaks. i thought it was a bad EGR sensor or valve but, their only on V8's. like i said, this code just started. other than stalling during the motor warming up, this beast ran great. now, the idle's rough. the fuel is too lean. and worse yet, it stalls at every turn or about every 5 blocks. this is insane. before i pull a Thelma & Louise off a cliff with the jeep, can anyone think of what would cause the PO171? again, it's a 97 GCL ZJ 4.0 L in-line 6. i would appreciate some input. thanks

dave1123

My only thought is maybe the dielectric grease is a problem for the very low voltage signals from the 02 sensor. Only the front one controls mixture settings. Clean off the plugs for the 02 sensor and see if that fixes your mixture problems.

alg

I too have a 171 code, which I never had b4. I had gone through some strange issues that ended up changing the pcm, some injectors, plug on coils. (which were unrelated to the original problem, I broke 2 of them trying to take them off) I had to replace a couple of connectors to the fuel injectors due to the clip braking off. But I dont think that would cause the lean problem. I replace 2 o2 sensors up and down. waiting on the other 2 to arrive to change them also. But again I did not have a 171 prior to replacement of the pcm. could this be the cause and not the o2. although they should be changed since the engine has 140k on it. Could you lend a hand in solving this thanks