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Thread: 86 Century T Type 3.8 Engine Roughness on Acceleration

  1. #16
    Senior Member 85_Ciera_Rebuild's Avatar
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    Quote Originally Posted by turbokinetic View Post
    check is the ignition coils...Measure the resistance of each and see what you measure
    Interesting, with 2.8-V6 coils, I recall it being an open circuit on new/old coils when measuring from across spark tops, when coils were removed from ICM. Primary circuit showed an ohm reading of some 5 k ohms or so.

    When I change out spark wires, I'll take a second look at ohm reading for spark tops.



  2. #17
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    I have a new problem, possibly related to the first problem? I'm still having the engine getting rough on moderate to hard acceleration but I've never had a stalling problem till now. Today at a long train crossing I shifted to park and let the engine idle. After a few minutes it began to stumble and slow down, the CEL came on and it stalled. It started right up again and would not stall while idling in drive only in park. I checked for codes and got #44 lean exhaust. I checked the oxygen sensor wire and connections and it looks OK visually. Could a bad O2 sensor cause engine roughness on acceleration? Is there a way to test the O2 sensor with a multi-meter? If it is the O2 sensor is it very difficult to get it out?

  3. #18
    Senior Member turbokinetic's Avatar
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    Quote Originally Posted by T Type View Post
    I have a new problem, possibly related to the first problem? I'm still having the engine getting rough on moderate to hard acceleration but I've never had a stalling problem till now. Today at a long train crossing I shifted to park and let the engine idle. After a few minutes it began to stumble and slow down, the CEL came on and it stalled. It started right up again and would not stall while idling in drive only in park. I checked for codes and got #44 lean exhaust. I checked the oxygen sensor wire and connections and it looks OK visually. Could a bad O2 sensor cause engine roughness on acceleration? Is there a way to test the O2 sensor with a multi-meter? If it is the O2 sensor is it very difficult to get it out?
    It seems these old LG3 cars all want to run lean at idle. It seems that a combination of small vacuum leaks, an aging MAF sensor, and aging injectors work together to cause this problem. The problem is going to be worse with less load on the engine. That's because the less load the lower the airflow and that is the region where the MAF is least accurate.

    The 02 sensor is easy to change. It is simply screwed into the collector at the rear manifold. There is no way to test it with a meter. It is a chemical sensor and would require calibrated test-gas and special equipment to test it.

    The "lean exhaust" code means that the ECM was trying to add fuel and correct the lean condition, however it reached the maximum allowable fuel trim without correcting the problem.

    A dirty air filter or dust on the MAF element will both exacerbate this problem.

  4. #19
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    Now that it's cold -10 to -15 the 3.8 in my 86 Century runs much smoother than in the summer. Both idling and acceleration are smoother. Wouldn't a vacuum leak be worse in cold since rubber and gaskets would shrink? Can I assume that something is signaling the ECM to call for a richer mixture? I checked the resistance of coolant temperature sensor and the air intake temperature sensor and they were both within the specs on the tables. The check engine light is not on and there are no current codes.

  5. #20
    Senior Member 85_Ciera_Rebuild's Avatar
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    Quote Originally Posted by T Type View Post
    Now that it's cold -10 to -15 the 3.8 in my 86 Century runs much smoother than in the summer.
    Crank sensor - On semi-truck, the tachometer works excellent in cold weather, until things get warmed up...so either its sensor or tach itself fails (erattic readings, no reading, true reading, etc).

    On earlier GM/etc vehicles, I've heard of dead crank sensors, without setting a code.

    So heat apparently is related to your issue...maybe a coil, maybe a defective crank sensor (???maybe not), temp sensor, etc.

    A temp sensor should be tested in the kitchen, heated up......I think GM's temp sensors tend to increase fuel when going bad

    Footnote - When acquiring an used vehicle, I replace CPU's temp sensor, and oil pressure sending unit...no ifs, ands, butts.

  6. #21
    Senior Member Century7667's Avatar
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    IAC not moving freely?

    Ken T.

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