HoratioTheJeep
NAXJA Forum User
- Location
- Texas
Important stuff is in bold.
1996 (note: OBDII) 2WD 4.0L Auto
intake manifold heat shield
cool air intake
62mm throttlebody
Problem: O2 sensors throwing CEL & codes ("voltage too high" for both the upstream & downstream, and for the sensor heating circuit). Have been driving 8 months w/this problem, running a little rich, but now emissions inspections are due for my Jeep & I need to get this fixed once & for all.
This began when I installed a new upstream Denso brand sensor 8 months ago. I did not have a CEL on before installing the new sensor, but I wanted better gas mileage than 16mpg (city), & the original sensor had 100 000 miles on it. I should have left it alone. But I installed the Denso & I reset the computer by disconnecting the battery & turning the ignition to "on" (not "Start," but one step before). Everything was fine for a while; the CEL came on after about 130 miles of driving. I thought to myself, "I must've bought the wrong brand sensor." Since the CEL had not come on with the original sensor, I put the original sensor back in in place of the Denso. I cleared the computer memory again.
30-35 miles down the road, the CEL comes back on again. Jeep developed a bit of hesistation (on acceleration) after both cold & hot startups. It seemed like the computer was restricting fuel flow to the injectors, presumably b/c of the O2 sensor readings. The hesitation on accel only lasts a few minutes, then goes away, I presume because the computer relapses into default mode at that point. Unplugging the sensors made the hesitation problem go away.
I tested the sensors, the sensors seemed fine, & read within normal operating ranges. I bought a downstream Denso sensor, & reinstalled both Denso sensors, upstream & downstream. Cleared the codes/computer memory, & drove it. 30 -35 miles later, CEL came back on!
Took it to a mechanic. Mechanic said maybe there was just dirt in my intake/exhaust or I got a tank of bad gas. Mechanic cleared the codes & reset the computer. Used some fuel injector cleaner. Cleaned the TB for the second time in 4 months. 30-35 miles later, the CEL came back on anyway. And it was giving me that hesitation again, on acceleration.
Unplugged both sensors from the wiring harness. Hesitation on acceleration goes away, Jeep runs perfectly, though rich (judging by the deposits left on my spark plugs. Gas mileage drops to 15mpg. Drove this way for 6 months.
I tested the output voltage from the wiring harness & compared it to a 1994 XJ Cherokee Factory Service Manual (FSM) which I had access to. The voltage coming from the harness seemed to read 1.5-2 volts higher than it should, but then the '94 Cherokees were OBDI & the '96 Cherokees are OBDII, so maybe that accounts for the difference in voltage?
Took it to another (different) mechanic. They tested the sensors & ran a diagnostic, decided I needed a new catalytic converter. I disagreed, but, I let them do it. 40 miles down the road, the CEL comes back on. I take it back to the mechanic, & they run a different test (that they didn't do before, the little jerks) & tell me that by grounding the wires at such & such, & doing such & such, they decided that the Jeep just doesn't like Denso sensors, & I should buy OEM sensors from the dealership.
Fine. I buy $220.00 worth of OEM sensors (both upstream & downstream) from the dealership, & install them myself, & clear the codes by the method of disconnecting the battery & turning the ignition key to "on." CEL stays off for nearly 90 miles, then comes back on again! Hesitation on acceleration reappears again, too.
That's where I'm at. I can try one more time to go to a mechanic, except now I'm virtually out of money.
Possible causes not yet investigated: two people (one of them rebuilds CJs for a hobby) have suggested to me (1) that the voltage regulator might be the culprit--I haven't played with it yet--but it seems to me that I would have other symptoms (besides the O2 sensors) if the voltage was out of spec--am I right or wrong here?--& (2) there might be a short somewhere in the wiring--I favor this possibility. I followed the wires as far back (from the sensors) to where they are taped together with the fuel injector wires. I chose not to unwrap (untape) the injector wires b/c I figured it wouldn't be worth all the work (that was several months ago, but now I'm thinking I might be willing to take all the wiring apart even if it takes me a week to get it back together).
Sorry for the long post. Any suggestions/ideas/comments/questions/complaints?
1996 (note: OBDII) 2WD 4.0L Auto
intake manifold heat shield
cool air intake
62mm throttlebody
Problem: O2 sensors throwing CEL & codes ("voltage too high" for both the upstream & downstream, and for the sensor heating circuit). Have been driving 8 months w/this problem, running a little rich, but now emissions inspections are due for my Jeep & I need to get this fixed once & for all.
This began when I installed a new upstream Denso brand sensor 8 months ago. I did not have a CEL on before installing the new sensor, but I wanted better gas mileage than 16mpg (city), & the original sensor had 100 000 miles on it. I should have left it alone. But I installed the Denso & I reset the computer by disconnecting the battery & turning the ignition to "on" (not "Start," but one step before). Everything was fine for a while; the CEL came on after about 130 miles of driving. I thought to myself, "I must've bought the wrong brand sensor." Since the CEL had not come on with the original sensor, I put the original sensor back in in place of the Denso. I cleared the computer memory again.
30-35 miles down the road, the CEL comes back on again. Jeep developed a bit of hesistation (on acceleration) after both cold & hot startups. It seemed like the computer was restricting fuel flow to the injectors, presumably b/c of the O2 sensor readings. The hesitation on accel only lasts a few minutes, then goes away, I presume because the computer relapses into default mode at that point. Unplugging the sensors made the hesitation problem go away.
I tested the sensors, the sensors seemed fine, & read within normal operating ranges. I bought a downstream Denso sensor, & reinstalled both Denso sensors, upstream & downstream. Cleared the codes/computer memory, & drove it. 30 -35 miles later, CEL came back on!
Took it to a mechanic. Mechanic said maybe there was just dirt in my intake/exhaust or I got a tank of bad gas. Mechanic cleared the codes & reset the computer. Used some fuel injector cleaner. Cleaned the TB for the second time in 4 months. 30-35 miles later, the CEL came back on anyway. And it was giving me that hesitation again, on acceleration.
Unplugged both sensors from the wiring harness. Hesitation on acceleration goes away, Jeep runs perfectly, though rich (judging by the deposits left on my spark plugs. Gas mileage drops to 15mpg. Drove this way for 6 months.
I tested the output voltage from the wiring harness & compared it to a 1994 XJ Cherokee Factory Service Manual (FSM) which I had access to. The voltage coming from the harness seemed to read 1.5-2 volts higher than it should, but then the '94 Cherokees were OBDI & the '96 Cherokees are OBDII, so maybe that accounts for the difference in voltage?
Took it to another (different) mechanic. They tested the sensors & ran a diagnostic, decided I needed a new catalytic converter. I disagreed, but, I let them do it. 40 miles down the road, the CEL comes back on. I take it back to the mechanic, & they run a different test (that they didn't do before, the little jerks) & tell me that by grounding the wires at such & such, & doing such & such, they decided that the Jeep just doesn't like Denso sensors, & I should buy OEM sensors from the dealership.
Fine. I buy $220.00 worth of OEM sensors (both upstream & downstream) from the dealership, & install them myself, & clear the codes by the method of disconnecting the battery & turning the ignition key to "on." CEL stays off for nearly 90 miles, then comes back on again! Hesitation on acceleration reappears again, too.
That's where I'm at. I can try one more time to go to a mechanic, except now I'm virtually out of money.
Possible causes not yet investigated: two people (one of them rebuilds CJs for a hobby) have suggested to me (1) that the voltage regulator might be the culprit--I haven't played with it yet--but it seems to me that I would have other symptoms (besides the O2 sensors) if the voltage was out of spec--am I right or wrong here?--& (2) there might be a short somewhere in the wiring--I favor this possibility. I followed the wires as far back (from the sensors) to where they are taped together with the fuel injector wires. I chose not to unwrap (untape) the injector wires b/c I figured it wouldn't be worth all the work (that was several months ago, but now I'm thinking I might be willing to take all the wiring apart even if it takes me a week to get it back together).
Sorry for the long post. Any suggestions/ideas/comments/questions/complaints?