stumbling LT1
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5.0 and 5.7 Discussion, stumbling LT1 in Cadillac Engine Technical Discussion; So this morning (35 F and damp) I was on my way to work when I noticed a low speed/idle ...
  1. #1
    kevinf is offline Cadillac Owners Member
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    stumbling LT1

    So this morning (35 F and damp) I was on my way to work when I noticed a low speed/idle stumble. It got significantly worse to the point where I thought the car would die waiting at a red light. While limping it back home it started to run smoother but still didn't completely go away. I've got my own theories as to the problem but wanted to see if any of you guys have any fresh ideas. Will further diagnose this evening. Has been running like a champ the previous 15k miles I've owned it.

    1996 FWB ~105k
    New plugs/wires
    3/4 tank fuel

    Thank you.

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  3. #2
    BCs71's Avatar
    BCs71 is offline Cadillac Owners Enthusiast
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    Re: stumbling LT1

    Quote Originally Posted by kevinf View Post
    So this morning (35 F and damp) I was on my way to work when I noticed a low speed/idle stumble. It got significantly worse to the point where I thought the car would die waiting at a red light. While limping it back home it started to run smoother but still didn't completely go away. I've got my own theories as to the problem but wanted to see if any of you guys have any fresh ideas. Will further diagnose this evening. Has been running like a champ the previous 15k miles I've owned it.

    1996 FWB ~105k
    New plugs/wires
    3/4 tank fuel

    Thank you.

    As a precaution I would throw in a new fuel filter and take a fuel PSI reading. PSI should be about 37 at idle.

    Otherwise sounds like symptoms of a bad EGR valve if problem only occurs when waiting at stoplight at idle, but seems fine while cruising and accelerating.

  4. #3
    kevinf is offline Cadillac Owners Member
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    Re: stumbling LT1

    Brian, thank you for the reply. I would like to PM you but I can't yet. I live over in Niles, I checked out all your rides at the B.A.D. site.

  5. #4
    BCs71's Avatar
    BCs71 is offline Cadillac Owners Enthusiast
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    Re: stumbling LT1

    Quote Originally Posted by kevinf View Post
    Brian, thank you for the reply. I would like to PM you but I can't yet. I live over in Niles, I checked out all your rides at the B.A.D. site.

    Feel free to join the message board at www.badbodies.com where you can email me or PM me.

    Or you can email me through the site's main email account: badbodies@gmail.com
    Although I don't check there very often.

    Hopefully you can make it out to the meeting Saturday (tomorrow, ST. Pats Day) in Hoffman Estates at McDonalds on Golf Rd (just east of Barrington Rd.) at 4pm. Meeting will run until 6 or 7pm.

  6. #5
    kevinf is offline Cadillac Owners Member
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    Re: stumbling LT1

    Well I didn't make the meeting, obviously, but thanks for the invite. I will check into badbodies. I'm familiar with that area, I work near Golf/Roselle.

    Drove fine again, threw a new fuel filter at it so we'll see if it ever pops up again. Couldn't find the right size fitting for the valve to check pressure, but sure did come flying out when I unclipped the old filter.

  7. #6
    BCs71's Avatar
    BCs71 is offline Cadillac Owners Enthusiast
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    Re: stumbling LT1

    Quote Originally Posted by kevinf View Post
    Well I didn't make the meeting, obviously, but thanks for the invite. I will check into badbodies. I'm familiar with that area, I work near Golf/Roselle.

    Drove fine again, threw a new fuel filter at it so we'll see if it ever pops up again. Couldn't find the right size fitting for the valve to check pressure, but sure did come flying out when I unclipped the old filter.

    Yeah, system is pressurized so there is a procedure to go through before removing old filter. Basically I like to unplug fuel pump harness behind fuel tank and start car. Will run out of gas ina few seconds and then it is basically de-pressurized and most fuel out of lines.

    Feel free to join the forum at badbodies.com and yap with us. There are three or so other FW members who live in the area and regularly post.
    That same McDonalds will be site to a weekly cruise-in on either Fri or Sat nights starting in a few weeks.

  8. #7
    kevinf is offline Cadillac Owners Member
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    Re: stumbling LT1

    Ok well it happened again Saturday, nice FOGGY cool humid morning. This is leaning heavily towards a damaged/cracked optispark. Also got the "check engine" light to come on, although it's currently off. Will a diagnostic machine be able to pull up what tripped it even though it's not coming on anymore?

  9. #8
    BCs71's Avatar
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    Re: stumbling LT1

    Quote Originally Posted by kevinf View Post
    Will a diagnostic machine be able to pull up what tripped it even though it's not coming on anymore?
    Yep. Even though CEL is off you can check for 'history codes' which remain until cleared through diagnostics or after a certain amount of drive cycles.

    I explained in detail on BaD Bodies board about manually looking for codes via on-board diagnostic check built into AC/heat panel in car.

  10. #9
    sj_sharx4 is offline Cadillac Owners Member
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    Re: stumbling LT1

    try having someone turn the ignition switch to the on position(not cranking) while your under the gas tank listening for the fuel pump to whine for 2 seconds and shut off. if you dont hear the whining noise cut on and off check to see if its getting power at the harness near the fill up area. if it is getting power, drop the tank down and check to see if all 4 of the wires to the sending unit are ok/and not touching the trunk floor, before you open up the tank or buy a fuel pump. This is a very common problem

  11. #10
    boatman is offline Cadillac Owners Member
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    Re: stumbling LT1

    give her a complete tune up, check fuel pressure and if that does not fix the problem, looks like the opti, the reason I got a LS1 powered car.

  12. #11
    kevinf is offline Cadillac Owners Member
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    Re: stumbling LT1

    123k miles now and the problem has gone away...but do have a new opti waiting for when current craps out. I'm sure I'll need it eventually.

    Thanks for your help.

  13. #12
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: stumbling LT1

    Keep us posted.

    I did a water pump on mine a year ago and pulled the cap/rotor and polished up and has run good ever since, but it did run poorly in really hot weather. Since I did that it no longer did. Might be simply just time for a cap/rotor. But being so involved to change cap rotor, a few $ more for the full Opti is probably worth it. Do a water pump at the same time too, replace ALL seals (dealer only on them). Wires too if you can. But it is pretty involved to get the pass side bank, but while you are at it, would be worth it.

  14. #13
    MadCaddie69's Avatar
    MadCaddie69 is offline Cadillac Owners Fanatic
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    Re: stumbling LT1

    I had that same problem in March 2007, due to the fact I forgot to check the oil. I had to tune it up completely and changed the oil. It ran fine afterwords. Keep sharp eyes on your fluids!

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