chugging and backfiring intermittently. No codes - Page 3
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HT4100 4.1, 4.5, 4.9 Discussion, chugging and backfiring intermittently. No codes in Cadillac Engine Technical Discussion; Also check the vacumn line coming from the MAP sensor. When I bought my 91 it would not pass emissions, ...
  1. #31
    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Also check the vacumn line coming from the MAP sensor. When I bought my 91 it would not pass emissions, after replacing plugs, wires, and both O2 sensors the numbers got better but were still too high. My gas mileage was pretty bad and it ran rich; I eventually started getting a E034 code (MAP sensor out of range). At the advise of my buddy who is a smog tech I replaced the MAP sensor but the problem did'nt correct itself, another buddy that is a tech (I work for Nissan) asked if I had checked the vacumn line.

    When I did I found it faulty on the engine side, badly cracked and dried! It took all of two minutes to replace and I could immediately tell the difference! I drove the car over the weekend and the AVG MPG according to the DIC went from 10.8 to 18.2! I took it in the shop on Monday and asked the smog tech to put it on the machine to check the numbers and it passed effortlessly!! As a matter of fact I just had it put on the machine last week just to see and the numbers are still looking good! I know you have a different code regarding the MAP sensor, I am just suggesting you check the vacumn line while you are there... good luck and sorry for the novel LOL!

  2. #32
    steelybill is offline Cadillac Owners Enthusiast
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    Re: chugging and backfiring intermittently. No codes

    That was a good novel!! We sometimes look for complicated things when simple things are the problem.
    Most of the factory manuals I have call out a good visual inspection, (and mention vacuum lines) before getting in deep.

  3. #33
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    the map vacuum line was fine. The map sensor didn't fix the problem. It seems a little better though.. don't know how long that will last.

  4. #34
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    did it on the highway on my lunch break. chugged slightly, heard a slight little pop-pop-pop (not very loud), so I left off the gas for a few seconds; then it was fine the rest of the way home. maybe it is my ignition module. When I replaced it , i just got a cheap bwd.

  5. #35
    steelybill is offline Cadillac Owners Enthusiast
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    Re: chugging and backfiring intermittently. No codes

    A back fire can be caused by several things. A lean fuel mixture is one, and a plug firing when it shouldn't is another, like distributor problems.

  6. #36
    Sevillian273's Avatar
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    Re: chugging and backfiring intermittently. No codes

    See if you can ohm check the injectors when the car is hot. The stock ones were notorious for failing early. http://www.lindertech.com/dirty_dzn.htm <--- yours are #3 on the list. Easiest way to check is from the injector harness. 12-17 ohms is good.

  7. #37
    drewsdeville is offline Cadillac Owners Master
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by red_ghost View Post
    did it on the highway on my lunch break. chugged slightly, heard a slight little pop-pop-pop (not very loud), so I left off the gas for a few seconds; then it was fine the rest of the way home. maybe it is my ignition module. When I replaced it , i just got a cheap bwd.
    I agree with Steely on this one. Those pop-pop-pop misfires are a classic telltale sign of a lean misfire.

    A vacuum leak of some sort could explain that and your high idle symptom from your lunch break.

    Start probing all of the vacuum lines and the throttle body gasket with a can of ether. If you find a spot where your car runs better, you have a vacuum leak there.

  8. #38
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    I checked for vacuum leaks already. I did find a cracked line and replaced it; but that didnt fix anything. I haven't replaced the egr valve and solenoid yet though. Its still factory.

  9. #39
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by Sevillian273 View Post
    See if you can ohm check the injectors when the car is hot. The stock ones were notorious for failing early. http://www.lindertech.com/dirty_dzn.htm <--- yours are #3 on the list. Easiest way to check is from the injector harness. 12-17 ohms is good.
    I'll do that tonight. makes sense if its dirty that it would cause a lean fuel mixture. They are the original factory injectors.

    If thats what it turns out to be, should I get the bosch ones for this car, or the 5.0 mustang ones? I've heard mixed info on both. some people say the mustang ones make a big difference, others say they are not as good. I also saw some rebuilt and cleaned bosch injectors on ebay for around $170.

  10. #40
    drewsdeville is offline Cadillac Owners Master
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by red_ghost View Post
    I'll do that tonight. makes sense if its dirty that it would cause a lean fuel mixture. They are the original factory injectors.

    If thats what it turns out to be, should I get the bosch ones for this car, or the 5.0 mustang ones? I've heard mixed info on both. some people say the mustang ones make a big difference, others say they are not as good. I also saw some rebuilt and cleaned bosch injectors on ebay for around $170.
    While ohm'ing out the injectors will tell you if the coils are fucntioning, it won't tell you if the injectors are dirty or not otherwise operating properly. So you can't rule out injectors simply by checking their resistance..

    However, bad injectors won't cause your high idle symptom and injectors probably wouldn't give the intermittent (sometimes better/sometimes worse) symptoms you describe.

    Your symptoms say MAP sensor, your CEL tells you MAP sensor yet a new MAP sensor doesn't cure the problem...have you tested the wiring harness to the MAP sensor? You may have an intermittent short somewhere...Might be something as simple as some broken/wore insulation on a wire.

  11. #41
    Sevillian273's Avatar
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    Re: chugging and backfiring intermittently. No codes

    The injectors do weird things when the coils are failing. They go in and out of operation, sometimes hot, sometimes cold. When the resistance is low(shorting out) the ecm cant control the pulse width like normal. If they ohm out ok when hot then they are probably fine. If they are bad, its possible that they can damage the ecm. Our stock injectors are known as some of the worst in the business.

  12. #42
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by drewsdeville View Post
    While ohm'ing out the injectors will tell you if the coils are fucntioning, it won't tell you if the injectors are dirty or not otherwise operating properly. So you can't rule out injectors simply by checking their resistance..

    However, bad injectors won't cause your high idle symptom and injectors probably wouldn't give the intermittent (sometimes better/sometimes worse) symptoms you describe.

    Your symptoms say MAP sensor, your CEL tells you MAP sensor yet a new MAP sensor doesn't cure the problem...have you tested the wiring harness to the MAP sensor? You may have an intermittent short somewhere...Might be something as simple as some broken/wore insulation on a wire.
    the high idle is not constant. It actually only happened that once. The car idles fine normally. I'll have more time to find it now, as an o-ring just blew again on my rear suspension. 2nd time its happened this year. sending it back to the manufacturer.

  13. #43
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by Sevillian273 View Post
    The injectors do weird things when the coils are failing. They go in and out of operation, sometimes hot, sometimes cold. When the resistance is low(shorting out) the ecm cant control the pulse width like normal. If they ohm out ok when hot then they are probably fine. If they are bad, its possible that they can damage the ecm. Our stock injectors are known as some of the worst in the business.
    plus they set them up the stupidest position. hard to get at the harness.

  14. #44
    drewsdeville is offline Cadillac Owners Master
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by red_ghost View Post
    plus they set them up the stupidest position. hard to get at the harness.
    ???

    The harness connects at an easy point, near the oil filter if I remember correctly. You can check injector resistance in a matter of 2 minutes.

  15. #45
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Quote Originally Posted by drewsdeville View Post
    ???

    The harness connects at an easy point, near the oil filter if I remember correctly. You can check injector resistance in a matter of 2 minutes.
    crap, I was thinking the harness for each of the actual injectors. My bad. lol.

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