Engine will not turn back on if hot
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500, 472, 425, 368 Discussion, Engine will not turn back on if hot in Cadillac Engine Technical Discussion; I have a 78 coupe, with the 425 EFI, it starts everytime easily, engine is good, but if engine gets ...
  1. #1
    gornati's Avatar
    gornati is offline Cadillac Owners Fanatic
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    Engine will not turn back on if hot

    I have a 78 coupe, with the 425 EFI, it starts everytime easily, engine is good, but if engine gets hot and i turn it on, i have to wait a long time, before i can start it again.

    Any advise on this?

    Thanks

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  3. #2
    gornati's Avatar
    gornati is offline Cadillac Owners Fanatic
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    Re: Engine will not turn back on if hot

    just adding, starter runs ok, but engine wont start if hot.
    And when it starts, starts failing a lot...

  4. #3
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Engine will not turn back on if hot

    You say it will not start when hot. When you turn the start circuit on does the starter turn the engine over, or does it seem to dead lock? Dead lock - the starter engages, but the engine will not turn over.

  5. #4
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by gornati View Post
    just adding, starter runs ok, but engine wont start if hot.
    And when it starts, starts failing a lot...

    This suggests that the engine turns over when hot. Does the engine turn over hesitatingly or freely spin?

  6. #5
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Engine will not turn back on if hot

    For openers, I would check the 2 EFI temp sensors. Then test the ECU to make sure its delivering the right amount of fuel under all conditions. The MAP sensor in those ECUs often fails. If consequently injector pulse width is reduced, the engine will start on cold enrichment but falter when hot. Swap a spare ECU if you have one. Otherwise, I'll check the ECU for postage. I have a new MAP replacement circuit (no originals available) if its needed. See stuff on Cad 70s EFI on my PHOTOBUCKET

    http://s93.photobucket.com/albums/l71/bcroe/

    (that is a lower case "L"71, not an upper case "i"71)

    click on an Album
    click on a picture to enlarge & description

    Bruce Roe CLC #14630

  7. #6
    gornati's Avatar
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by deVille33 View Post
    This suggests that the engine turns over when hot. Does the engine turn over hesitatingly or freely spin?
    Hesitates a little but turns over after that.

  8. #7
    gornati's Avatar
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by BRUCE ROE View Post
    For openers, I would check the 2 EFI temp sensors. Then test the ECU to make sure its delivering the right amount of fuel under all conditions. The MAP sensor in those ECUs often fails. If consequently injector pulse width is reduced, the engine will start on cold enrichment but falter when hot. Swap a spare ECU if you have one. Otherwise, I'll check the ECU for postage. I have a new MAP replacement circuit (no originals available) if its needed. See stuff on Cad 70s EFI on my PHOTOBUCKET

    http://s93.photobucket.com/albums/l71/bcroe/

    (that is a lower case "L"71, not an upper case "i"71)

    click on an Album
    click on a picture to enlarge & description

    Bruce Roe CLC #14630
    Can you tell me where the sensors are located?

    How much the new MAP replacement?

  9. #8
    gornati's Avatar
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by BRUCE ROE View Post
    For openers, I would check the 2 EFI temp sensors. Then test the ECU to make sure its delivering the right amount of fuel under all conditions. The MAP sensor in those ECUs often fails. If consequently injector pulse width is reduced, the engine will start on cold enrichment but falter when hot. Swap a spare ECU if you have one. Otherwise, I'll check the ECU for postage. I have a new MAP replacement circuit (no originals available) if its needed. See stuff on Cad 70s EFI on my PHOTOBUCKET

    http://s93.photobucket.com/albums/l71/bcroe/

    (that is a lower case "L"71, not an upper case "i"71)

    click on an Album
    click on a picture to enlarge & description

    Bruce Roe CLC #14630
    I see you have a lot of experience with those ECU's, i wish i had to know that, before my car were shipped to Brasil...

    Anyway, do you do that as a hobbie? or if i send you my ECU by mail are you willing to take a look? if yes PM with a pricing information...

    Are you the guy who sells those ECU's on EBAY?

    I could definetelly use some or a lot of help with my car, i want and will make run and look like when it came out of the factory.

    I have a lot of things to do in the car, including the brakes and some metal work, but so far the most important thing is the engine.

    Here you can find some pictures:

    http://picasaweb.google.com.br/cams1976/caddy

    http://picasaweb.google.com.br/cams1976/caddysp

    I already noticed that my ECU was "remanufacturated" so i cant tell exactly without knowing what to test if the ECU is 100%.

    What is the black hose on the ECU?

    Really appreciate all help from you and DEVILLE33 wich is responding to almost all of my posts.

    Regards,


    GORNATI

  10. #9
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Engine will not turn back on if hot

    Very nice appearing car. Some people don't like the '78s as much as the '79s. I find there is something about the '79s that don't appeal to me, although I have several of them. I really like the '78s. I have a '78 deElagance and a '78 Brougham. Both need a lot of TLC.

  11. #10
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Engine will not turn back on if hot

    Check your battery cables. Not that this will help your hot start problem, but will address your general engine starting. Remove and closely check your ground cable. Swelling along the insulation is an indication of corrosion. The original cables were made of aluminum cable, and over time they oxidize and corrode. Replace if neccessary. Make sure youe cable ends are clean and that your contact surface is clean also.
    There is also a ground strap at the starter, make sure it's connections are clean also.
    One of my cars has an additional strap to the engine block because of grounding problems.

  12. #11
    gornati's Avatar
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by deVille33 View Post
    Very nice appearing car. Some people don't like the '78s as much as the '79s. I find there is something about the '79s that don't appeal to me, although I have several of them. I really like the '78s. I have a '78 deElagance and a '78 Brougham. Both need a lot of TLC.
    78 it always had been my dream, had a 81 before...
    77 dont have the beautifull, IMO, vertical taillights, and the 79 have way too many holes in the front grille.

    this was what i could afford back in end of 2008, it is very expensive to bring those cars to Brasil, i paid originally $1700,00 for this car off ebay.

    I want to have some day a H&E Convertible... maybe a 78 or a 80-84.

    But first things first, let me put this one on the road first.

    I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

    How 77-79 devilles you have in total?

  13. #12
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    Re: Engine will not turn back on if hot

    what does CLC #14630 stands for?

  14. #13
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: Engine will not turn back on if hot

    I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

    How 77-79 devilles you have in total?[/quote]




    I know what you mean. I've got a couple cars I'd like to rip to the bones and start back up again. In fact I'm doing that with one of my coupes.

    I think I have 15. I had 2 others, but I let them go. Catch and release program. Several are parts cars and some need attention and evaluation. I'm looking at a nice '79 that is for sale at a local dealer, but not sure I want to add anymore cars to my collection at this time.

    I see someone bypassed the relay circuit board and installed a switch, eliminating the relay. Does the toggle switch regulate both high and low speed circuits?
    A lot of people do this because the heat generated at the relay burns out the relay board.

  15. #14
    gornati's Avatar
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    Re: Engine will not turn back on if hot

    Quote Originally Posted by deVille33 View Post
    I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

    How 77-79 devilles you have in total?



    I know what you mean. I've got a couple cars I'd like to rip to the bones and start back up again. In fact I'm doing that with one of my coupes.

    I think I have 15. I had 2 others, but I let them go. Catch and release program. Several are parts cars and some need attention and evaluation. I'm looking at a nice '79 that is for sale at a local dealer, but not sure I want to add anymore cars to my collection at this time.

    I see someone bypassed the relay circuit board and installed a switch, eliminating the relay. Does the toggle switch regulate both high and low speed circuits?
    A lot of people do this because the heat generated at the relay burns out the relay board.[/quote]

    Eliminate which relay? sorry if it seems a dumb question...

  16. #15
    BRUCE ROE is offline Cadillac Owners Fanatic
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    Re: Engine will not turn back on if hot

    GORNATI,

    The air temp sensor is in a runner from the carb to
    a cylinder. The water temp sensor in the coolant
    somewhere; I've seen them at the thermostat or in
    the back pipe to the heater. They are interchangeable,
    should measure around 1000 ohms at room temp. If
    only one is good, make sure it is in the water till you
    get another.

    I don't charge to check out your ECU. But postage &
    customs could be a problem here. Most ECUs need
    something; I usually recommend getting them checked
    so you can cross it off the problem list. If your
    pulse widths are OK, the MAP is probably OK too.
    Keeping a spare ECU can help, though people that
    far away sometimes just give up the fuel injection and
    put on a carb.

    I'm retired, advisor to the CLC (Cadillac LaSalle Club). I
    think their web site is under construction for a few days.
    I don't often sell ECUs, but if I had your model, it
    would be a small fraction of the $350 the Ebay guy
    wants. Don't know who that is, I wonder if he can
    test & repair them as well as I do?

    Lots of ECUs are marked "REMANUFACTURED". Not
    to worry, they are OK but renumbered. If you give me
    your email, I can send a list of ECUs and what they fit.
    And my EFI checklist. I'm bcroe@juno.com

    The usual problem with mixture, is a failing MAP
    sensor in the ECU. If it is putting out low voltage
    now, it will soon fail completely. Its on picture 10
    (SH 8) of ALBUM-78 K ECU SCHEMATIC. Notice
    that there is a test point VMAP where you can measure
    the MAP voltage, a 5 pin connector on the side. Or with
    ignition on but not running, no hose connected, you
    can remove the cover and and measure the MAP voltage
    at its pin, or wire jumper 13. It should be 9.5V input,
    7 to 7.5V output. The 7V will drop to 0-2V as vacuum
    is applied. The hose to the ECU connects to the MAP.
    If it is failing, I could install one of my replacements.

    Once the engine is hot, your ECU should put out a
    fuel injector pulse width around 4ms at idle, 8 ms at
    cruise, and near 12ms at Wide Open Throttle.

    deVille33 also gives good advice. Most cars that age
    should get a new timing chain; the original cam sprocket
    has plastic teeth which fall off, block oil flow, and let
    pistons hit valves. You can check it without taking the
    engine apart.

    good luck, Bruce Roe

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