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Renix engine issues

Black1990jeep

NAXJA Forum User
Location
california
Hi .....I have a 1990 4.0 liter Renix and am having issues that are perplexing. I have a snap on MT2500 scan tool hooked up on the diagnositc port.

Sometimes the jeep lacks power, other times it is ok, sometimes the idle is rough, surging to maybe 1500 rpm then back down, this happens randomly, other times she idles fine, regardless of engine temperature.

I have a fairly recently installed O2 sensor that I used to pass smog last May.

Today I hooked up the scan tool. I Allowed the jeep to warm up, and this is what I get at idle...

800 rpm, Injector pulse width 6.3 msec, O2 volts is steady at 2.11 to 2.13 V. The system is indicated to be in "closed loop", and the scanner mixture cycles between "lean" and "rich" about once per second. HOWEVER WHY IS IT CYCLING BETWEEN LEAN AND RICH IF THE O2 VOLTAGE IS PRETTY MUCH CONSTANT?
the scanner also shows... ST (short term ) trim to be 201 to 206, LT (long term) Trim to be steady at 128, MAP sensor at 1.6 Volt, MAP Press is 12.1 Hg
Barometric pressure is 18.2 Hg, TPS is at 0.68 Volt, throttle is 14%. Throttle switch is "closed", Fuel sync signal cycles about once per second between + and -, Coolant is 168F, charge temp is 122F, spark is 14 degrees Before TDC, EGR commamd is off

Now when I rev to 2100 rpm and hold it there the O2 voltage goes to 2.42 volts, the mixture goes to lean, and it indicates open loop operation

I then drop back to idle (812 rpm) and now the O2 voltage is 2.44 with no cycling, system indicates it is now in closed loop and indicates "lean /rich" cycling once per second, the injector pulse width changed to 5.6 msec.

So what is happening?

Why is it in closed loop and cycling lean to rich when the O2 voltage is pretty much steady?

Also isnt the idle a bit high, If so how to adjust?

at anyrate, whatmis going on here?

Is it normal for throttle to be at 14% when at idle?

I am totally confused.

ps last week when I stuck the scan tool on the scanner read that the system stayed in open loop, and mixture remained "lean", so something is different now than then. during that time I replaced the water pump do to a leak.

Thanks
 
See my responses on Cherokee Forum.

Cruiser did a writeup on the proper routing for the O2/knock sensor/engine temp harness where it comes up the front of the motor. Many people, after a water pump swap, route the harness wrong and it cooks on the exhaust manifold. It is difficult to see where the harness is cooking, a quick glance may not see the trouble spot.
 
Cruiser did a writeup on the proper routing for the O2/knock sensor/engine temp harness where it comes up the front of the motor. Many people, after a water pump swap, route the harness wrong and it cooks on the exhaust manifold. It is difficult to see where the harness is cooking, a quick glance may not see the trouble spot.

I may have that photo somewhere. I can't post photos here though.
 
Cruiser did a writeup on the proper routing for the O2/knock sensor/engine temp harness where it comes up the front of the motor. Many people, after a water pump swap, route the harness wrong and it cooks on the exhaust manifold. It is difficult to see where the harness is cooking, a quick glance may not see the trouble spot.

I didnt need to touch the harness for the water pump swap other than disconnected the electric fan, and turning off the battery ground with the disconnect switch. I had running issues prior to the pump swap, I did the pump first cause the seal gave out makkng a river under the jeep, and I didnt want to lay in it nor have it drip on me when under the jeep while trying to troubleshoot the O2 sensor. so the problems electrically existed prior to the water pump swap.
 
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