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Stock Grand Cherokee Tech. All ZJ/WJ/WK Non-modified/stock questions go here!ZJ (93-98), WJ (99-04), WK (05+)
All ZJ/WJ/WK specific tech questions asked here!
I have an 02 grand cherokee 4.0 with 175k. Maybe it's just me but I feel like I'm burning more gas than usual. I have attached some pics from my obdII computer. Please check them out and see if they seem normal at idle. All with closed loop. Seems to run fine but looks to me like more fuel loss. Thank you.
Engine: 4.0, new lifters valve job with new springs and exhaust valves, preload set with shims
Get a scanner that has graphing and watch the pattern of your TPS. Then check for vacuum leaks or codes. Then take your IAT sensor out and clean it with brake cleaner. Change your air filter. Do not shoot seafoam down your tps sensor.
The primary purpose of the PCM is to reduce pollution, so as the PCM monitors the all of the sensors (including O2) and all the other inputs (their values) it will compute and control the fuel injectors, and other things such as the timing, etc. to produce the least amount of pollution, even if to do so requires more fuel.
175,000 miles isn't a huge amount of miles for a 4.0L which typically achieves at least 300,000 miles and capable of 300,000+ to over 400,000 miles. However as things wear out the PCM compensates for what it's able to monitor and receive input. Often the problem is the sensors themselves which many function on 5 volts, sending signals to the PCM, doesn't take much to through things off.
A good place to start and needs to be done on older vehicles is to renew the grounds and inspect plug-ins for sensors and other inputs for bent pins, corrosion and corrosion / damage to harnesses. Corrosion is one of the culprits with wiring systems, causing run-ability and other problems on older vehicles.
I tried to get my 98 XJ with 4.0L (changing o2 and other sensors, exhaust, etc.) to achieve better fuel mileage, closer to what it's rated for. It currently has 203,000 miles runs well but the fuel economy is under it's ratings, around ~13 to ~15 mpg depending on the driving conditions and payload.
My 95 ZJ with a 4.0L and 217,000 miles achieves noticeably better fuel mileage than the 98 XJ. I think one reason is the ZJ which I purchased used appears to have been garaged most of it's life, no rust issues, haven't yet found any corrosion problems. The uni-body and it's wiring are in very good shape.
There are other things to consider about fuel economy such as the condition of your exhaust system including the cat. Conditions of the fuel injectors. The CTS (coolant temp sensor). The PCM controls fuel injector output (amount of fuel) through coolant temperature readings (unless your vehicle has an engine temp sensor).
The PCM controls and computes fuel delivery through many different inputs and run-ability conditions which the PCM considers to be all related. O2 sensors are only one of the inputs monitored and used by the PCM to control and run the engine.
10-12-2018, 08:53 AM
O2 sensors and fuel ratio loss possible
