Page 2 of 4 FirstFirst 1 2 3 4 LastLast
Results 11 to 20 of 36

Thread: Engine Hunts at Start and Then Rough Idle When Warm

  1. #11
    Delorean Guru
    Join Date:  May 2011

    Location:  Northern NJ

    Posts:    6,097

    My VIN:    10757

    Club(s):   (DMA)

    If he is getting dwell readings the Lambda ECU is getting power and it is working, it just isn't in closed loop. There are tests you can do (grounding the O2 lead or putting 1.5 DC volts on it) to make sure the Lambda ECU is working. Once you prove out the ECU then the O2 sensor is probably bad or the mixture screw is WAY out of adjustment. Refer to D:04:15 for the specific tests. Also read the system notes on the previous page.
    David Teitelbaum

  2. #12
    Senior Member
    Join Date:  May 2011

    Location:  Houston

    Posts:    593

    My VIN:    16113

    Club(s):   (SCDC) (DCUK)

    This has me puzzled. I replaced the fuel injectors and the engine is running better. When I start the engine, it hunts fr about three minutes and then it settles down and idles fairly decently. Occasionally it will suddenly start hunting again briefly and settle down. After it warmed up and the fans came on and off several times, I put a dwell meter on it to check it. It consistently stays between 10-11. The other day it seemed to be fluctuating in the 30-50 range so I don't know what has happened.
    https://youtu.be/8Ca4UV654cE

    What's going on? Bad O2 sensor?
    Shannon

  3. #13
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    6,583

    My VIN:    03572

    Did you readjust the mixture when you installed the new injectors?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #14
    Senior Member
    Join Date:  May 2011

    Location:  Houston

    Posts:    593

    My VIN:    16113

    Club(s):   (SCDC) (DCUK)

    Quote Originally Posted by Bitsyncmaster View Post
    Did you readjust the mixture when you installed the new injectors?
    Yes, I've tried to but I've had to do it by ear since I can't seem to get the reading off the meter.

    I actually drove the car yesterday down to the street and back. It actually drove well. But I know that the tune is not dialed in. I plan to start the car this morning o see if it still hunts when cold but my bet is that it still does.
    Shannon

  5. #15
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    6,583

    My VIN:    03572

    Quote Originally Posted by lazabby View Post
    Yes, I've tried to but I've had to do it by ear since I can't seem to get the reading off the meter.

    I actually drove the car yesterday down to the street and back. It actually drove well. But I know that the tune is not dialed in. I plan to start the car this morning o see if it still hunts when cold but my bet is that it still does.
    If you make adjustments to the mixture for best idle (by ear) it will cause other more important problems.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #16
    Senior Member
    Join Date:  May 2011

    Location:  Houston

    Posts:    593

    My VIN:    16113

    Club(s):   (SCDC) (DCUK)

    Quote Originally Posted by Bitsyncmaster View Post
    If you make adjustments to the mixture for best idle (by ear) it will cause other more important problems.
    Yes, I've adjusted it so that it doesn't hunt when warm. Did yo use my video? I'm trying to figure out why the meter reading is between and not in the 30-50 range.
    Shannon

  7. #17
    Not a DeLorean Guru
    Join Date:  May 2011

    Location:  Rochester, NY

    Posts:    1,845

    My VIN:    01049

    Quote Originally Posted by lazabby View Post
    Yes, I've adjusted it so that it doesn't hunt when warm. Did yo use my video? I'm trying to figure out why the meter reading is between and not in the 30-50 range.
    Is it set to 4 cylinder mode?
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  8. #18
    Senior Member Jonathan's Avatar
    Join Date:  Jun 2011

    Location:  Ontario, Canada

    Posts:    3,912

    My VIN:    3937

    Quote Originally Posted by lazabby View Post
    This has me puzzled. I replaced the fuel injectors and the engine is running better. When I start the engine, it hunts fr about three minutes and then it settles down and idles fairly decently. Occasionally it will suddenly start hunting again briefly and settle down. After it warmed up and the fans came on and off several times, I put a dwell meter on it to check it. It consistently stays between 10-11. The other day it seemed to be fluctuating in the 30-50 range so I don't know what has happened.
    https://youtu.be/8Ca4UV654cE

    What's going on? Bad O2 sensor?
    Hey Shannon, when I was doing some dwell meter/mixture setting troubleshooting and fine tuning, it did the same thing where it stayed at one reading instead of fluctuating and also tended to settle in after running for a few minutes. In my case, it turned out to be a bad O2 sensor.

    I didn't manage to get my own O2 sensor out and replaced, so I took it to a shop I've used in the past and he got it out, replaced it and then set the dwell properly. Idle and fuel mileage has been good ever since.

    I'm sure there is a more technical or scientific explanation as to what happens with that circuit when the O2 sensor fails to cause it to stay steady or not fluctuate or whatever. I don't have that explanation, but also figured I didn't need it after a new O2 sensor in my car fixed it all up anyway.

    I couldn't get your youtube video to play by the way. It was marked as private.
    One damn minute Admiral...


  9. #19
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    6,583

    My VIN:    03572

    If the mixture is to far off, the dwell will read solid low about 10 deg. or high about 85 deg.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #20
    Senior Member Chris 16409's Avatar
    Join Date:  May 2011

    Location:  Fresno, CA.

    Posts:    1,086

    My VIN:    16409

    When my oxygen sensor went bad I had a pronounced hunting. Oscillation of the dwell meter needle is normal. Remember the lambda computer tries to maintain the correct dwell. If the mixture is set mecanically too lean, the computer attempts to richen the mixture and vice versa. If the mechanical adjustment is too far out of whack, the computer defaults to like a 40 to 50 percent duty cycle.
    Chris Miles

    For Better or Worse I own a DeLorean!
    1983 Grey Manual, VIN #16409, Fresno, California

Page 2 of 4 FirstFirst 1 2 3 4 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •