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Thread: 1991 lu4 code 44 super low o2 voltage high fuel trim extremly high idc

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    Carb and Points!
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    1991 lu4 code 44 super low o2 voltage high fuel trim extremly high idc

    Can anyone confirm that if the 02 is showing a voltage range.450-.025 on tuner pro it means its working and properly grounded all the way to ecm? Thanks (Im assuming it is working and showing LEAN.)

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    Changing voltage is a good thing but that seems odd it never goes about 0.45V. It takes very little AFR change for the O2voltage to swing from a low voltage to a high voltage which is why I'm thinking the swing stopping at 0.45V seems odd.

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    Thanks for the response. i believe its working as it should, seems normal at idle. its just that it stays in the lean range when driving. i know the injectors are dumping fuel. ie bad mileage, super high duty cycle(80-100% at idle and around 250-300+% while driving) and stinky exhaust. but o2 still low through out.???? ive been reading that unburnt fuel air will give a lean reading from a possible misfire? it seems to have a slight skip at idle. tunerpro says its at 7.4 AFR. i have touched every hose under the hood and sprayed all around TBI base and vacc ports, plugged aux vacc systems, checked exhaust for leaks... i dont think its unmetered air thats the problem... head scratchin. can anyone make sense of a tuner pro log if i can figure out how to post it? maybe the IAC? clogged CAT at this point? bad plugs? is there a injector control that can go bad? ive basically replaced all emission related parts and more in the past year...not lookin for performance just good operating numbers. any input will be much appreciated!!!

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    Carb and Points!
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    This is my latest tuner pro log. i think its attached. I have new injectors,fuel pump, fuel pressure reg, IAC,...vacuum slightly shaky at 20 on some ports, steady 20 on other ports. i know its pouring fuel, yet still really lean at o2 sensor and the blm is climbing way up. should knock the counter be registering more?

  5. #5
    Fuel Injected! jim_in_dorris's Avatar
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    You are not lean, you are stupid rich. Below 12.7 AFR is rich, above 12.7 is lean. I would also change your oil, it is probably full of gas with that much fuel.
    Square body stepsides forever!!!

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    Thanks Jim-will do on the oil change. i realize it is running rich, 7.4 is stupid rich, its just that o2 sensor is reading lean... The injector duty cycle is over 100 at idle...300+ driving around. could a fouled CAT from a past head gasket leak possibly be the culprit? its about the only thing i have not replaced yet?

  7. #7
    Fuel Injected! jim_in_dorris's Avatar
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    Duty cycle cannot exceed 100% That is static, full on, not pulsing. also does tunerpro show o2 cross counts occurring? I have to suspect a bad o2 sensor. I would pick one up at the JY, they usually don't charge for them because they can't guarantee they work. I would then swap it in to see if the symptoms change. because the o2 sensor is not swinging full range, the ecm is trying to compensate by adding fuel.
    Square body stepsides forever!!!

  8. #8
    Carb and Points!
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    So, a fresh, bosch 02 sensor didn't do it. The was able to test fuel pressure and had 17 at one point then settled down to about 14. brand new fuel pump two weeks ago with new injectors and also a fuel pressure regulator. there was a splice in the return line that had a slightly restrictive union, replaced it. will get to a tuner pro log tomorrow. one question. how accurate is AFR reading on tuner pro, and should i assume the IDC is accurate as well. thanks for any input.

  9. #9
    Fuel Injected! jim_in_dorris's Avatar
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    The O2 sensor is what is known as a narrow band O2 sensor, and is accurate only in a narrow band. The IDC may or may not be accurate depending on the XDF you are using. I am beginning to suspect that the problem is that your O2 sensor is not getting hot enough. Where is is located in the exhaust system right now? What ECM and mask are you using?
    Square body stepsides forever!!!

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    thanks Jim. i should clarify that the o2 will "occasionally" swing into the .600s, at idle only, then when cruising it begins to fall, ending in double digits, like around .015v?? it does show cross counts.

    the 02 is on top of the y pipe just after where they join. this vehicle is stock, no mods at all. xdf---- $42-1227747-v5.9.3.xdf adx-----$42-1227747-v5.2.adx

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    Heated O2 or 1-wire?

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    I think your ECM O2 ground is not 100%. Easy to measure with a good DVOM. But to do this correctly, the DVOM ground wire needs to be run to the Neg Battery terminal via a good jumper. The DVOM should be set to VOLTS and back probe the ECM O2 ground. Start the engine and hit the throttle. If you see 0.150 to 0.300mv the ground ring terminal or the wire or the crimp or head has resistance. (Using the DVOM on an OHM scale will not show this due to the low amperage.) Had many such as this. One more area is the actual O2 sensor itself. The connection to the manifold can be dirty. Use a die grinder with a wire brush or sand it to gain the ground. Anti-sieze the threads
    With the A/F this rich I take it you are using an seperate meter to measure this.

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    ok guys you had it right!! Hallalujah! the story starts when i replaced an o2 sensor about 2 yrs ago. just bought the vehicle new y pipe first off, followed by said 02 sensor. fast forward til rcently when the CEL showed an 044 code "lean o2 sensor". i assumed it was working fine since it was "recently". replaced. tuner pro was showing very low volt readings but again i assumed it was working as it should. two days ago i unplugged the 02 to see what happened. nothing just steady .442 to .474 volts back and forth, instead of plugging it back in i grabbed a new one (thanks to jim_in_dorris!!!) and threw it in, got tuner pro up while in the lot, then my laptop basically went on the fritz but from the glance at the idc i thought the new 02 didnt make a difference, and posted those results last night. then today with fresh charge on laptop i had great readings from the 02. .800-.100s back and forth. fuel trim up and down a little, back and forth just as it all should!!!! Anyway i couldnt be happier!! thanks so much. i just want my half-way decent milage back!!! thanks again Jim and Lionel and Billy. you guys were hovering it around the 02 sensor the whole time. case closed!!!

  14. #14
    Fuel Injected! jim_in_dorris's Avatar
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    glad to hear your problem is solved.
    Square body stepsides forever!!!

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