chugging and backfiring intermittently. No codes - Page 5
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HT4100 4.1, 4.5, 4.9 Discussion, chugging and backfiring intermittently. No codes in Cadillac Engine Technical Discussion; Its a 4.9L. Well, it started doing it this morning again. I've noticed it does it the most when teh ...
  1. #61
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Its a 4.9L. Well, it started doing it this morning again. I've noticed it does it the most when teh temperature is low. The temp was about 59F this morning. It also does it when battery voltage is low (the volume on my stereo is high). With the stereo 1/2 way up and the car running, my battery voltage was at 12.6v. This is obviously too low while the car is running. I ordered a 240 amp HO alternator kit. I also received a shock when I touched the #1 spark plug wire with the car running. The wires are only a year and a half old (accels). That's not normal... Any further help or suggestions would be appreciated.

    also, How do I check the BLM?

  2. #62
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    fuel pressure while idling is 35psi too

  3. #63
    the recluse is offline Cadillac Owners Connoisseur
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    Re: chugging and backfiring intermittently. No codes

    If you received a shock at the wire you're probably having a ground issue which may cause the chugging...

  4. #64
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    could be, just for the heck of it, i logged this:

    BLM:
    started teh engine and it was at 124. got on the gas and it went to 138, then as I wrote this, back down to 128. On the gas I got it up to 146 then 15 seconds later it went down to 126.

    at idle=

    throttle angle:
    between 1.7 and 2.1
    MAP:
    between 35 and 37 kpa
    BARO:
    99kpa
    coolant temp
    98C
    MAT
    104C
    Spark advancement (this sounds wrong)
    25

    was running at 630 rpm at idle.

  5. #65
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    Re: chugging and backfiring intermittently. No codes

    OK, now we are on to something here.

    The BLm values change while you are driving because there are multiple values that are stored in "cells". A cell is just a place to store a value for a particular load and RPM.

    Base value for the BLM is 128 and can range from 108 to 160. Any deviation from 128 means that the computer has to adjust, using O2 sensor data, for some unknown condition. Some deviation is ok. For example, my current high mileage 4.5 and 4.9 stay between 125 and 132 or so on all conditions. However, your numbers on acceleration are a concern. On that note, if I remember correctly this is where the car displays it's symptoms.

    A value of 146 on acceleration means that for some reason, the computer has to add 146/128 (or 14%) to the standard pulse width.

    There are two block learn values, one for each bank. I would start by looking to see if you have this problem on both banks or if it's isolated to one. Also view all load/rpm conditions that you can come up with. Idle, fast cruise, slow cruise, deceleration, acceleration, etc. Determining WHEN the fuel trim is out of whack can help.

  6. #66
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    If it makes a difference, the voltage was only 11.6 at this time. I had the stereo on (there is no off button on it). Is it possible the spark isn't strong enough? Also for this test it said I had 2 gallons of gas. My cadillac has hydraulics, and I had the front of the vehicle lowered 1/2 way (bumper about 6 inches from teh ground) and the rear bumper raised all the way (about 20 inches from the ground). That is how I drive it on the highway. I am also not using the stock air intake. I am using just a regular edlebrock air cleaner. How do I monitor each seperate bank for the BLM? I didn't see anything on that in FSM.

  7. #67
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    Re: chugging and backfiring intermittently. No codes

    It's a possiblity. If you are wondering if the stereo is making the difference, why don't you just pull the fuses on the system (it IS fused, right?) and see if anything changes?

    The multiple BLM values might be my bad. Now that I think about it, I don't think the 4.9 Deville got bank-to-bank fuel trim until '93 or so.

    That's unfortunate because now it's difficult to tell whats happening on each side (vacuum/air leaks from intake or exhaust manifold)) of the engine short of spark plug condition. Do the plugs on each side look different? A rich running cylinder will cover the spark plug in soot and a lean running cylinder will have a bright white or melted insulator. Pull the plugs and take a look, paying attention to the condition on one bank vs the other.

    BTW, which manifold is the O2 sensor in on those. I forget... the left one? Using the OBD, how many cross counts does it give?

  8. #68
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    Yes, the left one. It is in the exhaust manifold facing the rear.

  9. #69
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    I got my HO alternator kit. I ordered the CS144 (up to 1993 kit). Apperantly my alternator is a new style (past 1993) CS144 and the stuff wont work. Next day air'd the correct parts.

  10. #70
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    HO alternator made no difference. I took it to a stereo shop to see what they said. The ground wire for the alternator needed to be upgraded and that fixed teh problem. voltage now will not drop below 13 (unless i have the music really loud and am at a stoplight for over 5 mins). misfire seems to have gone away. Going to a car show this weekend thats about 2 hours away, so I'll be able to tell then.

  11. #71
    red_ghost is offline Cadillac Owners Fanatic
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    Re: chugging and backfiring intermittently. No codes

    The voltage regulator was bad. They did not put the HO voltage regulator in the alternator. Now its correct and much better!

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