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Thread: Sudden rough idle & Hesitations after parked overnight!

  1. #51
    Senior Member Beachdrifter's Avatar
    Join Date:  May 2011

    Location:  Space Coast, FL *USA*

    Posts:    180

    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

    Club(s):   (DCF)

    More pictures, show and tell...

    In an attempt to further eliminate any guess work on my part, I went ahead and finally after 17 yrs completed what is the rights of passage for any Delorean owner, I ventured into my Valley of Death. Figured why not, I'm so close to it, might as well finish taking that air intake off.

    I was surprised the valley looks pretty clean, I have a bit of oil in the crannies , likely from a clutch slave I replaced a few years ago. I will clean it up before patching everything together. My vacuum connections seems pretty good, and rubber hoses were not cracking or brittle. So that checks. I also will assume all those switches and sensors in the Y pipe are good to go too, as I heard their failure rates are low. But if anyone has some neat way of checking them with a multimeter, please let me know.

    4-24-22-VOD1.jpg

    What I was mostly concerned about, was the condition of my intake ports on the engine and valves. Lots of black deposits caked all over the place. The engine has 44K original miles. Is there anyway to clean this stuff up on the surface at least at this point? I intend to use regular Techron cleaner from now on to help. But what is the general diagnosis on this type of condition? Although I don't believe this is the reason for my car not performing one day to the next, it is obviously a concern to me.

    Here are pictures of my cylinder intakes:

    4-24-22-VOD2.jpg

    4-24-22-VOD3.jpg

    4-24-22-VOD4.jpg

    4-24-22-VOD5.jpg

    4-24-22-VOD6.jpg

    Finally, here is the inside of the air intake side, all black .

    4-24-22-VOD7.jpg
    Last edited by Beachdrifter; 04-24-2022 at 07:15 PM.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  2. #52
    Senior Member DMC-81's Avatar
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    Hi there,

    While you have the intake off, double check your vacuum hoses. Another member had similar symptoms and it turned out to be a vacuum hose that looked normal but was not tight. It caused a vacuum leak and made the car run very rough and rich. This was a sudden onset of symptoms as well
    Not sure if your problem is the same, but I would suggest changing all the vacuum hoses.

    Also Robert said that sometimes the green vacuum switch (with 3 lines) goes bad.

    Good luck
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  3. #53
    Senior Member Beachdrifter's Avatar
    Join Date:  May 2011

    Location:  Space Coast, FL *USA*

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    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

    Club(s):   (DCF)

    Quote Originally Posted by DMC-81 View Post
    Hi there,

    While you have the intake off, double check your vacuum hoses. Another member had similar symptoms and it turned out to be a vacuum hose that looked normal but was not tight. It caused a vacuum leak and made the car run very rough and rich. This was a sudden onset of symptoms as well
    Not sure if your problem is the same, but I would suggest changing all the vacuum hoses.

    Also Robert said that sometimes the green vacuum switch (with 3 lines) goes bad.

    Good luck
    Thanks Dana, good seeing you at Celebration. Car actually started acting up that Saturday morning and decided to tow it home that day rather than feel stranded on the road.

    Good advice, coincidentally I started reading up more on that green switch and symptoms seemed similar of a bad one. I'll went ahead and ordered a new one from DMC.
    Also got a coolant pressurizer to check for leaks before patching everything up.

    Also will throw in some new vacuum lines while I'm in my VOD anyways.

    This will likely take a few weeks, but will keep everyone posted. Thought about dressing up the engine too and maybe painting the air intake manifold. So making it a little project now.

    Thanks.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  4. #54
    Senior Member Beachdrifter's Avatar
    Join Date:  May 2011

    Location:  Space Coast, FL *USA*

    Posts:    180

    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

    Club(s):   (DCF)

    Well, today I replaced the cap and rotor. Fairly easy (once everything is accessible). Inside of the distributor it looked pretty clean.
    I also replaced the spark plugs, wires, and the thermal vacuum switch in the VOD. I heard those can go bad and since the plastic end seemed to rotate rather freely maybe I had a vacuum leak there . Worth replacing because the new one was firm, so maybe the old one was failing. Pressure tested coolant so seems good.

    Anyways, as I started to plug the wires on the distributor cap, I noticed something odd. Previously to taking the wires off, I had numbered them and taken a picture, just to be on the safe side. Although I see the cap is numbered and it should correspond to the cylinder numbers on the engine block as well. In addition, the wires from DMCH were numbered the same as well, so how could someone mess that up? Well, I noticed my wires were crossed/swapped by the previous owner --- cyl 2 was plugged in the "3" cap position, and cyl 3 was plugged in the "2" cap position. I have been running my car like this since I have owned it for 17 yrs apparently!!! The engine ran perfectly (at least to me all these years). Does swapping 1 set of cylinders /plug wires make much of a difference ? Needless to say, I stuck to the number convention on the cap/block this time and we'll see how she runs when its all said and done.

    I'm still working on it overall, decided to dress the engine up a bit with red silicone vacuum lines as well as do some painting.

    Thanks for any insight.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  5. #55
    Administrator Ron's Avatar
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    Quote Originally Posted by Beachdrifter View Post
    Well, I noticed my wires were crossed/swapped by the previous owner --- cyl 2 was plugged in the "3" cap position, and cyl 3 was plugged in the "2" cap position. I have been running my car like this since I have owned it for 17 yrs apparently!!! The engine ran perfectly (at least to me all these years). Does swapping 1 set of cylinders /plug wires make much of a difference ?
    That would kill the two cylinders and at least 1/3 of your power, probably more...should of ran like dodo.

  6. #56
    Senior Member
    Join Date:  Dec 2016

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    Quote Originally Posted by Ron View Post
    That would kill the two cylinders and at least 1/3 of your power, probably more...should of ran like dodo.
    Exactly! It's difficult to believe two plug wires could be reversed and not be noticed. I would think the motor would run terrible! But I've never seen it done so maybe not. I'm curious to hear what you find.

    Ron

    Distributor firing order.JPG

  7. #57
    Senior Member Rich's Avatar
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    Location:  San Francisco Bay Area, Calif.

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    My VIN:    0934

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    Quote Originally Posted by DMC-Ron View Post
    Exactly! It's difficult to believe two plug wires could be reversed and not be noticed. I would think the motor would run terrible! But I've never seen it done so maybe not. I'm curious to hear what you find.

    Ron

    Distributor firing order.JPG
    That's the very useful diagram out of the factory book. Good reference.
    New users: This diagram is "upside down" since the flywheel/clutch is at the bottom and the pulleys are at the top (engine isn't shown in the orientation seen from the rear of the car).
    March '81, 5-speed, black interior

  8. #58
    Senior Member Beachdrifter's Avatar
    Join Date:  May 2011

    Location:  Space Coast, FL *USA*

    Posts:    180

    My VIN:    * 5945 * Oct, 31, 1981. FranKenDeLorean

    Club(s):   (DCF)

    Quote Originally Posted by DMC-Ron View Post
    Exactly! It's difficult to believe two plug wires could be reversed and not be noticed. I would think the motor would run terrible! But I've never seen it done so maybe not. I'm curious to hear what you find.

    Ron

    Distributor firing order.JPG
    Yes, I was very surprised. But after referencing the firing order in the manual and seeing your diagram, if 3 and 2 were swapped, would it have made much of a difference? As long as it maintains the left to right alternating firing order maybe it would have not been noticed. Now I can understand more if wires were swapped to where the alternating firing order was broken up causing two cylinders to fire back to back on one side.

    But I'm no expert, all I can say was my car felt normal all these years and even took a trip to DMCFL a few years ago on unrelated work and they felt the car normal too.

    Oh well, interesting find. I'm patching everything back together and hoping after all this when I fire her back up, she will be running back to normal. Otherwise it will be back to the drawing board or a trip on a tow to DMCFL.
    We shall see in the next week or so and will let everyone know.


    Thanks.
    ** A wave is like an empty canvas, waiting for a masterpiece -- unknown **
    ** VIN 5945 - FranKenDeLorean Oct 31, 1981 ** SpaceCoast, FL, USA ** DMCTalk Member/DMCOwner Since 2005

  9. #59
    Administrator Ron's Avatar
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    Quote Originally Posted by Beachdrifter View Post
    Yes, I was very surprised. But after referencing the firing order in the manual and seeing your diagram, if 3 and 2 were swapped, would it have made much of a difference? As long as it maintains the left to right alternating firing order maybe it would have not been noticed. Now I can understand more if wires were swapped to where the alternating firing order was broken up causing two cylinders to fire back to back on on.
    If a plug wire is going to the wrong cylinder, that cylinder (and the cylinder the wire is supposed to go to) will fire at the wrong time, if at all.

  10. #60
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Ron View Post
    If a plug wire is going to the wrong cylinder, that cylinder (and the cylinder the wire is supposed to go to) will fire at the wrong time, if at all.
    The six plugs will all fire in sequence no matter where the plugs are. Now with two wires swapped, those plugs may fire at any of the four cycles of the stroke. I can't believe the engine would run without backfire or a blown exhaust with two wire swapped. Each cylinder still draws air and fuel on each intake cycle.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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